Posted on by Tammy Plotner

Messier 42 – The Orion Nebula

The stunning, shaped clouds of gas in the Orion Nebula make it beautiful, but also make it difficult to see inside of. This image of the Orion Nebula was captured by the Hubble Telescope. Image: NASA, ESA, M. Robberto (STScI/ESA) and The Hubble Space Telescope Orion Treasury Project Team
The stunning, shaped clouds of gas in the Orion Nebula make it beautiful, but also make it difficult to see inside of. This image of the Orion Nebula was captured by the Hubble Telescope. Image: NASA, ESA, M. Robberto (STScI/ESA) and The Hubble Space Telescope Orion Treasury Project Team

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at that Great and most brightest of nebulae – the Orion Nebula!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is the Orion Nebula, a diffuse nebula situated just south of Orion’s Belt in the Orion constellation. Located between 1,324 and 1,364 light years distant, it is the closest massive star forming region to Earth. Little wonder then why it  is the brightest nebula in the night sky and can be seen on a clear evening with the naked eye.

Description:

Known as “The Great Orion Nebula,” let’s learn what makes it glow. M42 is a great cloud of gas spanning more than 20,000 times the size of our own solar system and its light is mainly florescent. For most observers, it appears to have a slight greenish color – caused by oxygen being stripped of electrons by radiation from nearby stars.

A pair of binoculars will make the “Curlicue” pop in Orion’s Belt. Although the stars aren’t related, they form a delightfully curvy line-of-sight pattern. Credit: Bob King

At the heart of this immense region is an area known as the “Trapezium” – its four brightest stars form perhaps the most celebrated multiple star system in the night sky. The Trapezium itself belongs to a faint cluster of stars now approaching main sequence and resides in an area of the nebula known as the “Huygenian Region” (named after 17th century astronomer and optician Christian Huygens who first observed it in detail).

Buried amidst the bright ribbons and curls of this cloud of predominately hydrogen gas are many star forming regions. Appearing like “knots,” these Herbig-Haro objects are thought to be stars in the earliest stages of condensation. Associated with these objects are a great number of faint red stars and erratically luminous variables – young stars, possibly of the T Tauri type.

There are also “flare stars,” whose rapid variations in brightness mean an ever changing view. “Orion may seem very peaceful on a cold winter night, but in reality it holds very massive, luminous stars that are destroying the dusty gas cloud from which they formed,” said Tom Megeath, an astronomer at the Harvard-Smithsonian Center for Astrophysics.

While studying M42, you’ll note the apparent turbulence of the area – and with good reason. The “Great Nebula’s” many different regions move at varying speeds. The rate of expansion at the outer edges may be caused by radiation from the very youngest stars present. Said Massimo Roberto, an astronomer at the Space Science Telescope Institute in Baltimore:

“In this bowl of stars we see the entire formation history of Orion printed into the features of the nebula: arcs, blobs, pillars and rings of dust that resemble cigar smoke. Each one tells a story of stellar winds from young stars that impact the environment and the material ejected from other stars.”

The star Alnitak and Flame Nebula in Orion. Credit and copyright: César Cantú.

Although M42 may have been luminous for as long as 23,000 years, it is possible that new stars are still forming, while others were ejected by gravitation – known as “runaway” stars. A tremendous X-ray source (2U0525-06) is quite near the Trapezium and hints at the possibility of a black hole present within M42. The Trapezium’s stellar winds also are responsible for the formation of stars inside the nebula – their shock waves compressing the medium and igniting starbirth.

“When you look closely, you see that the nebula is filled with hundreds of visible shock waves,” said Bob O’Dell, an astronomer from Vanderbilt University. O’Dell was fortunate enough to use Hubble to map Orion’s stellar winds and create a map of two of Orion’s three star-forming regions… Regions where the winds have been blowing continuously for nearly 1,500 years!

What else have we learned about the Great Orion nebula in recent years? Try the discovery of 13 drifting gas planets. These rare, “free-floating” objects were confirmed by Patrick Roche of the University of Oxford and Philip Lucas of the University of Hertfordshire just before the turn of the century. They were found with the Hubble Space Telescope while looking for faint stars and brown dwarfs. As he explained:

“The objects are likely to be large gas planets similar in size to Jupiter and consisting primarily of hydrogen and helium. From the measured brightness and the known distance to the Orion nebula, we knew they did not have enough material for any nuclear processing in their interiors.”

Orion's Horsehead Nebula Credit & Copyright Ryan Steinberg & Family, Adam Block, NOAO, AURA, NSF
Orion’s Horsehead Nebula Credit & Copyright Ryan Steinberg & Family, Adam Block, NOAO, AURA, NSF

Chances are very good these planets may be failed stars – much like our own Jupiter. But these planets don’t orbit a star the same way our solar system’s planets orbit the Sun… they simply roam around. Dr. Roche said that the 13 objects “probably formed in a different way from the planets in our solar system” in that they were not made “out of the residue of material left over from the birth of the sun.”

Instead, they formed “like stars via the collapse of a cloud of cold gas,” explained Lucas. “But they possess most of the physical properties and structure of gas giant planets,” added Lucas.

History of Observation:

Messier 42 was possibly discovered 1610 by Nicholas-Claude Fabri de Peiresc and was recorded by by Johann Baptist Cysatus, Jesuit astronomer, in 1611. For fans of the great Galileo, he was the first to mention the Trapezium cluster in 1617, but did not see the nebula. (However, do not despair! For it is my belief that he was simply using too much magnification and therefore could not see the extent of what he was looking at.)

The first known drawing of the Orion nebula was created by Giovanni Batista Hodierna, and after all of these documents were lost, the Orion nebula was once again credited to Christian Huygens 1656, documented by Edmund Halley in 1716. It then went on to Jean-Jacques d’Ortous de Mairan in his nebulae descriptions, to be added by Philippe Loys de Chéseaux to his list, expounded by Guillaume Legentil in his review.

Horsehead Nebula at the Orion Credit & Copyright Adam Block, Mt. Lemmon SkyCenter, U. Arizona
Horsehead Nebula at the Orion. Credit & Copyright Adam Block, Mt. Lemmon SkyCenter, U. Arizona

At last, Charles Messier added the nebula to his catalog on March 4, 1769. As he wrote of the stunning objectL

“The drawing of the nebula in Orion, which I present at the Academy, has been traced with the greatest care which is possible for me. The nebula is represented there as I have seen it several times with an excellent achromatic refractor of three and a half feet focal length, with a triple lens, of 40 lignes [3.5 inches] aperture, and which magnifies 68 times. This telescope made in London by Dollond, belongs to M. President de Saron. I have examined that nebula with the greatest attention, in an entirely serene sky, as follows: February 25 & 26, 1773. Orion in the Meridian. March 19, between 8 & 9 o’clock in the evening. [March] 23, between 7 & 8 o’clock. The 25th & 26th of the same month, at the same time. These combined observations and the drawings brought together, have enabled me to represent with care and precision its shape and its appearances.

“This drawing will serve to recognize, in following times, if this nebula is subject to any changes. There may be already cause to presume this; for, if one compares this drawing with those given by MM. Huygens, Picard, Mairan and by le Gentil, one finds there such a change that one would have difficulty to figure out that this was the same. I will make these observations in the following with the same telescope and the same magnification. In the figure which I give, the circle represents the field of the telescope in its true aperture; it contains the Nebula and thirty Stars of different magnitudes. The figure is inverted, as it is shown in the instrument; one recognizes there also the extension and the limits of this nebula, the sensible difference between its clearest or most apparent light with that which merges gradually with the background of the sky. The jet of light, directed from the star no. 8 to the star no. 9, passing by a small star of the 10th magnitude, which is extremely rare, as well as the light directed to the star no. 10, and that which is opposite, where there are the eight stars contained in the nebula; among these stars, there is one of the eighth magnitude, six of the tenth, and the eighth of the eleventh magnitude. M. de Mairan, in his Traite de l’Aurore Boreale, speaks of the star no. 7. I report it in my drawing below such as it is at present, and as I have seen; so to speak surrounded by a thin nebulosity. In the night of October 14 to 15, 1764, in a serene sky, I determined with regard to Theta in the nebula, the positions of the more apparent stars in right ascension and declination, by the means of a micrometer adapted to a Newtonian telescope of 4 1/2 feet length. These stars are numbered up to ten; I have reported them in the drawing containing the field of the telescope; and an eleventh of them is beyond the circle. The positions of the stars which are not marked with numbers have been fixed by estimating their relative alignments. One will know easily also the magnitude of the Stars by the model which I have reported on the figure. Those of the tenth and the eleventh magnitude are absolutely telescopic and very difficult to find.”

However, it would be Sir William Herschel who would devote much love, time, and attention to the Great Orion Nebula – even though his findings would never be made public. As a true master observer, he had quite a talent for sensing what truly might lay beyond the boundary:

“In 1783, I reexamined the nebulous star, and found it to be faintly surrounded with a circular glory of whitish nebulosity, faintly joined to the great nebula. About the latter end of the same year I remarked that it was not equally surrounded, but most nebulous toward the south. In 1784 I began to entertain an opinion that the star was not connected with the nebulosity of the great nebula in Orion, but was one of those which are scattered over that part of the heavens. In 1801, 1806, and 1810 this opinion was fully confirmed, by the gradual change which happened in the great nebula, to which the nebulosity surrounding this star belongs. For the intensity of the light about the nebulous star had by this time been considerably reduced, by attenuation or dissipation of nebulous matter; and it seemed now to be pretty evident that the star is far behind the nebulous matter, and that consequently its light in passing through it is scattered and deflected, so as to produce the appearance of a nebulous star. A similar phenomenon may be seen whenever a planet or a star of the 1st or 2nd magnitude happens to be involved in haziness; for a diffused circular light will then be seen, to which, but in a much inferior degree, that which surrounds this nebulous star bears a great resemblance.”

But of course, the great Sir William Herschel also had nights from his many notes on M42 where he simply said: “The nebula in Orion which I saw by the front-view was so glaring and beautiful that I could not think of taking any place of its extent.”

Locating Messier 42:

Finding Messier 42 is very easy from a dark sky location by centering on the glowing region in the center of Orion’s “sword”. However, from urban locations, these stars might not be visible, so aim your binoculars or telescope about a fist width south of the three prominent stars that make the asterism known as Orion’s Belt. It’s a very bright and large object well suited to all sky conditions and instruments!

This chart shows the location of Messier 78 in the famous constellation of Orion (The Hunter). Credit: ESO, IAU and Sky & Telescope

Remember to use low power to get the full majesty of M42 and to increase magnification to study various regions. And trust us when we tell you, you are in for some pretty awesome viewing!

And of course, here are the quick facts on Messier 42 to help you get started:

Object Name: Messier 42
Alternative Designations: M42, NGC 1976, The Great Orion Nebula, Home of the Trapezium
Object Type: Emission and Reflection Nebula with Open Galactic Star Cluster
Constellation: Orion
Right Ascension: 05 : 35.4 (h:m)
Declination: -05 : 27 (deg:m)
Distance: 1.3 (kly)
Visual Brightness: 4.0 (mag)
Apparent Dimension: 85×60 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Posted on by Tammy Plotner

Messier 41 – the NGC 2287 Open Star Cluster

Image of the open star cluster Messier 41, highlighting its combination of red dwarf, white dwarf and K3-type class stars. Credit: Wikisky

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the double star known as Messier 41. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is the open star cluster known as Messier 41 (aka. M41, NGC 2287). Located in the Canis Major constellation – approximately 4,300 light years from Earth – this cluster lies just four degrees south of Sirius, the brightest star in the night sky. Like most open clusters, it is relatively young – 190 million years old – and contains over 100 stars in a region measuring 25 to 26 light years in diameter.

Description:

Running away from us at a speed of about 34 kilometers per second, this field of about 100 stars measures about 25 light years across. Born about 240 million years ago, it resides in space approximately 2300 light years away from our solar system. Larger aperture telescopes will reveal the presence of many red (or orange) giant stars and the hottest star in this group is a spectral type A.

View of the night sky in North Carolina, showing the constellations of Orion, Hyades, Canis Major and Canis Minor. Credit: NASA

As G.L.H. Harris (et al) explained in a 1993 study:

“We have obtained photoelectric UBV photometry for 100 stars, uvbyb photometry for 39 stars and MK spectral types for 80 stars in the field of NGC 2287. After combination with data from other sources, several interesting cluster properties are apparent. Both the UBV and uvbyb photometry point to a small but nonzero reddening, while our spectral types confirm previous results indicating a high binary frequency for the cluster. Based on our spectral and photometric data for the cluster members, we find a minimum binary frequency of 40% and discuss the possibility that the results may imply a binary frequency closer to 80%. The cluster age is found to be based on both the main-sequence turnoff and the red giant distribution; the width of the turn up region can probably be explained by a combination of duplicity and a range in stellar rotation.”

But there’s more than just red giant stars and various spectral types to be found hiding in Messier 41. There’s at least two white dwarf stars, too. As P.D Dobbie explained in a 2009 study:

“[W]e use our estimates of their cooling times together with the cluster ages to constrain the lifetimes and masses of their progenitor stars. We examine the location of these objects in initial mass-final mass space and find that they now provide no evidence for substantial scatter in initial mass-final mass relation (IFMR) as suggested by previous investigations. This form is generally consistent with the predictions of stellar evolutionary models and can aid population synthesis models in reproducing the relatively sharp drop observed at the high mass end of the main peak in the mass distribution of white dwarfs.”

Messier 41 and Collinder 121. Image: Wikisky

As you view Messier 41, you’ll be impressed with its wide open appearance… and knowing it’s simply what happens to star clusters as they get passed around our galaxy. As Giles Bergond (et al.) stated in their 2001 study:

“Taking into account observational biases, namely the galaxy clustering and differential extinction in the Galaxy, we have associated these stellar overdensities with real open cluster structures stretched by the galactic gravitational field. As predicted by theory and simulations, and despite observational limitations, we detected a general elongated (prolate) shape in a direction parallel to the galactic Plane, combined with tidal tails extended perpendicularly to it. This geometry is due both to the static galactic tidal field and the heating up of the stellar system when crossing the Disk. The time varying tidal field will deeply affect the cluster dynamical evolution, and we emphasize the importance of adiabatic heating during the Disk-shocking. During the 10-20 Z-oscillations experienced by a cluster before its dissolution in the Galaxy, crossings through the galactic Disk contribute to at least 15% of the total mass loss. Using recent age estimations published for open clusters, we find a destruction time-scale of about 600 million years for clusters in the solar neighborhood.”

That means we’ve only got another 360 million years to observe it before it’s completely gone (though some estimates place it at about 500 million). Either way, this star cluster is destined to disappear, perhaps before we are!

History of Observation:

Messier 41 was “possibly” recorded by Aristotle about 325 B.C. as a patch in the Milky Way… quite understandable since it is very much within unaided eye visibility from a dark sky location. Said Aristotle:

“.. some of the fixed stars have tails. And for this we need not rely only on the evidence of the Egyptians who say they have observed it; we have observed it also ourselves. For one of the stars in the thigh of the Dog had a tail, though a dim one: if you looked hard at it the light used to become dim, but to less intent glance it was brighter.”

Messier 41 and Sirius. Image: Wikisky

However, Giovanni Batista Hodierna was the first to catalog it in 1654, and the star cluster became a bit more astronomically known when John Flamsteed independently found it again on February 16, 1702. Doing his duty, Charles Messier also logged it:

“In the night of January 16 to 17, 1765, I have observed below Sirius and near the star Rho of Canis Major a star cluster; when examining it with a night refractor, this cluster appeared nebulous; instead, there is nothing but a cluster of small stars. I have compared the middle with the nearest known star; and I found its right ascension of 98d 58′ 12″, and its declination 20d 33′ 50″ north.”

Following suit, other historical astronomers also observed M41 – including Sir John Herschel to include it in the NGC catalog. While none found it particularly thrilling… their notes range from a “coarse collection of stars” to “very large, bright, little compressed”, perhaps you will feel much differently about this easy, bright target!

Locating Messier 41:

Finding Messier 41 isn’t very difficult for binoculars and small telescopes – all you have to know is the brightest star in the northern hemisphere, Sirius, and south! Simply aim your optics at Sirius and move due south approximately four degrees. That’s about one standard field of view for binoculars, about one field of view for the average telescope finderscope and about 6 fields of view for the average wide field, low power eyepiece.

The location of Messier 41 in the Canis Major constellation. Credit: IAU and Sky & Telescope magazine/Roger Sinnott & Rick Fienberg

Because Messier 41 is a large star cluster, remember to use lowest magnification to get the best effect. Higher magnification can always be used once the star cluster is identified to study individual members. M41 is quite bright and easily resolved and makes a wonderful target for urban skies and moonlit nights!

Because you understand what’s there…

Object Name: Messier 41
Alternative Designations: M41, NGC 2287
Object Type: Open Galactic Star Cluster
Constellation: Canis Major
Right Ascension: 06 : 46.0 (h:m)
Declination: -20 : 44 (deg:m)
Distance: 2.3 (kly)
Visual Brightness: 4.5 (mag)
Apparent Dimension: 38.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Posted on by Tammy Plotner

Messier 40 – the Winnecke 4 Double Star

The double star Messier 40 (Winnecke 4), along with PGC 39934, NGC 4290 and NGC 4284. Credit: Wikisky

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the double star known as Messier 40. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is Messier 40, this double star is now known to be an optical double star (i.e. two independent stars at different distances that appear aligned based on our perspective). It is also included in the Winnecke Catalogue of Double Stars as number 4, and is located in the constellation of Ursa Major (aka. the Big Dipper).

Description:

At roughly 500 light years away from us, no one is quite sure if this pair of stars is truly a binary system or an optical double star. According to Richard Nugent’s 2002 data, “The observed relative proper motion, as measured in separation and position angle, is consistent with a straight, independent motion of the two stars, one crossing between us and the other.”

The double star Messier 40 (Winnecke 4), along with PGC 39934, NGC 4290 and NGC 4284. Credit: Wikisky

The two stars are nearly the same brightness as each other, with the primary star being magnitude 9 and the secondary being magnitude 9.3 and they are separated by about 49 arc seconds – a wide gap. At one time, the angular separation of the pair was measured at 49.2″, but has gradually changed to about 52.8″ in more recent years.

History of Observation:

Messier 40 was discovered by Charles Messier in 1764 while he was searching for a nebula that had been reported in the area by Johann Hevelius. As he wrote at the time:

“The same night on October 24-25, [1764], I searched for the nebula above the tail of the Great Bear [Ursa Major], which is indicated in the book Figure of the Stars, second edition: it should have, in 1660, the right ascension 183d 32′ 41″, and the northern declination 60d 20′ 33″. I have found, by means of this position, two stars very near to each other and of equal brightness, about the 9th magnitude, placed at the beginning of the tail of Ursa Major: one has difficulty to distinguish them with an ordinary refractor of 6 feet. Here are their position: right ascension, 182 deg 45′ 30″, and 59 deg 23′ 50″ northern declination. There is reason to presume that Hevelius mistook these two stars for a nebula.”

History often credits Messier for being a little bit crazy for cataloging a double star, but upon having read Messier’s report, I feel like he was an astronomer doing his job. If Hevelius reported a nebula here – then he was bound to look and write down what he saw. He didn’t just stumble on a double star and catalog it for no reason!

Close-up of the double star Messier 40. Credit: Wikisky

Later astronomers would also search for M40 and report a double star, and it was cataloged by such as by Friedrich August Theodor Winnecke at Pulkovo Observatory in 1863 as WNC 4. However, to give the good Hevelius credit, John Mallas reports, “the Hevelius object is the 5th-magnitude star 74 Ursae Majoris, more than one degree away, as reference to his star catalogue will show.”

In 1991, the separation between the stars was measured at 52.8 arcseconds, which represented an increase since 1966, when it was measured at 51.7. In 2001 and 2002, studies conducted by Brian Skiff and Richard L. Nugent suggested that the stars comprising the double star (HD 238107 and HD 238108) were in fact an optical double star, rather than a double star system.

In 2016, by using parallax measurements from the Gaia satellite, this theory was proven for the first time. Distance estimates were also produced, indicating that the two components are 350±30 and 140±5 parsecs (~1141±98 and 456±16 light years).

Locating Messier 40:

Finding Messier 40 isn’t very difficult for fairly large binoculars and small telescopes – but you need to remember that it’s a double star. First locate the easily recognized constellation of Ursa Major and focus on the ‘Big Dipper’ and look for the two stars that form the edge that connect to the handle – Gamma and Delta.

The location of Messier 40 in Ursa Major, above and to the left of MegrezCredit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

Aim your telescope’s finderscope at Delta – the point where the ‘handle’ would connect. In the finder, you will see a fainter star to the northeast. Hop there. Now, using a low power eyepiece, scan slightly further northeast and you will locate M40. Once located, you may go to higher magnification to more closely examine this Messier catalog curiosity.

While this pair of stars will show easily in binoculars, you must remember that binoculars give such a wide field that it will be difficult to distinguish them from surrounding stars. However, this is a great object for light-polluted skies and moonlit nights!

Enjoy the controversy… and this pair! And here are the quick facts on M40 to help you get started:

Object Name: Messier 40
Alternative Designations: M40, WNC 4
Object Type: Double Star
Constellation: Ursa Major
Right Ascension: 12 : 22.4 (h:m)
Declination: +58 : 05 (deg:m)
Distance: 0.51 (kly)
Visual Brightness: 8.4 (mag)
Apparent Dimension: 0.8 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Posted on by Tammy Plotner

Messier 39 – The NGC 7092 Open Star Cluster

The open star cluster Messier 39. Credit: Wikisky

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the open galactic star cluster known as Messier 39. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is known as Messier 39, an open star cluster located in the direction of the Cygnus constellation. Because of its proximity to Deneb and its size – it is actually larger in the night sky than a full Moon – it is easily observed using binoculars and small, low magnification telescopes.

Description:

Positioned only about 800 light years away from our solar system, this 300 million year old group of about 30 stars may look like they are spread fairly far apart in the sky. But as clusters go, they are close, really close! This group is gathered in space in only a 7 light year neighborhood! All of its stars are main sequence and the very brightest of them are just about to evolve into the red giant star phase.

In a study done by Jean Claude Mermilliod (et al), they conducted a long-term monitoring of solar-type dwarfs with CORAVEL – a study which took 19 years. While most individual radial velocities were never published – apart from a small number of spectroscopic binaries – the stars themselves and their properties were well documented in the works of B. Uyaniker and T. L. Landecker of the National Research Council, Herzberg Institute of Astrophysics.

Low-magnification image of Messier 39. Credit: Christian van Endern

As Uyaniker and Landecker claimed in their 2002 study, “A Highly Ordered Faraday-Rotation Structure in the Interstellar Medium“:

“We describe a Faraday rotation structure in the interstellar medium detected through polarimetric imaging at 1420 MHz from the Canadian Galactic Plane Survey (CGPS). The structure, at l = 918,b = -25, has an extent of ~2°, within which polarization angle varies smoothly over a range of ~100°. Polarized intensity also varies smoothly, showing a central peak within an outer shell. This region is in sharp contrast to its surroundings, where low-level chaotic polarization structure occurs on arcminute scales. The Faraday rotation structure has no counterpart in radio total intensity and is unrelated to known objects along the line of sight, which include a Lynds Bright Nebula, LBN 416, and the star cluster M39 (NGC 7092). It is interpreted as a smooth enhancement of electron density. The absence of a counterpart, in either optical emission or total intensity, establishes a lower limit to its distance. An upper limit is determined by the strong beam depolarization in this direction. At a probable distance of 350 ± 50 pc, the size of the object is 10 pc, the enhancement of electron density is 1.7 cm-3, and the mass of ionized gas is 23 M. It has a very smooth internal magnetic field of strength 3 UG, slightly enhanced above the ambient field. G91.8-2.5 is the second such object to be discovered in the CGPS, and it seems likely that such structures are common in the magneto-ionic medium.”

So where do these gases come from? Perhaps they are there all along. As Yu N. Efremov and T.G. Sitnik wrote in their 1988 study:

“It is found that about 90% of young clusters o-b2 and OB-associations situated within 3 kpc from the Sun are united into complexes with diameters from 150 to 700 pc. Almost all complexes contain giant molecular clouds with masses. A number of complexes (mostly large ones)-are connected with giant H I clouds; a few of small complexes are situated in the H I-caverns. Older (>b2) cluster avoid the regions occupied by young star groups. Complexes often have an hierarchic structure; some neighbouring complexes may be united into supercomplexes with diameters about 1.5 kpc.”

Does this mean it’s possible that M39 could be more than one cluster combined? As H. Schneider wrote in his 1987 study:

“Early-type stars up to 12.0 mag and spectral type F2 in two young northern clusters were investigated by means of Stromgren and H-beta photometry. The distance and reddening of the clusters were estimated, and the membership of the stars discussed. In the case of NGC 7039 a distance of 675 pc and a color excess of E(b-y) = 0.056 were found; the respective values for NGC 7063 were 635 pc and E(b-y) = 0.062. The reality of NGC 7039 is somewhat puzzling: it seems that there exists a loose star aggregate called NGC 7039, containing about six to nine stars, and in the background another cluster at a distance of about 1500 pc. Besides this, variable reddening across the cluster area is probable.”

Atlas Image mosaic of Messier 39, obtained as part of the Two Micron All Sky Survey (2MASS). Credit: NASA/NSF/IPAC/Caltech/Univ. of Mass.

History of Observation:

While it is possible this bright star cluster was remarked upon by Aristotle as a cometary appearing object about 325 BC, and it is also possible that it may have been discovered by Le Gentil in 1750, the fact remains M39 is most frequently attributed to be an original discovery of Charles Messier. As he recorded in his notes:

“In the night of October 24 to 25, 1764, I observed a cluster of stars near the tail of Cygnus: One distinguishes them with an ordinary (nonachromatic) refractor of 3 and a half feet; they don’t contain any nebulosity; its extension can occupy a degree of arc. I have compared it with the star Alpha Cygni, and I have found its position in right ascension of 320d 57′ 10″, and its declination of 47d 25′ 0″ north.”

Because Sir William Herschel did not publish his findings on Messier’s works, very few have read his observations of the object -“Consists of such large and straggling stars that I could not tell where it began nor where it ended. It cannot be called a cluster.” However, it would later go on to receive a New General Catalog (NGC) designation by Sir John Herschel who would describe it as “A star of 7th mag [position taken], one of a large loose cluster of stars of 7th to 10th magnitude; very coarsely scattered, and filling many fields.”

Even as accomplished as historic observers were, they sometimes didn’t always do the right thing. In the case of Messier 39, it is so close to us that it appears large dimensionally in the sky – and therefore needs less magnification instead of more to be properly studied as a whole. However, don’t always put away the magnfication, because as Admiral Smyth reports:

“A loose cluster, or rather splashy galaxy field of stars, in a very rich visinity between the Swan’s tail and the Lizard, due south of Beta Cephei, and east-north-east of Deneb [Alpha Cygni]. This was picked up by Messier in 1764, with his 3 1/2 foot telescope, and registered as being a degree in diameter. Among them there are several pairs, of which a couple were slightly estimated; the first being the brightest star (7m) and its comes, and the second a pretty pair of 10th-magnitudes.”

The location of Messier 39 in the Cygnus constellation. Credit: IAU/Sky & Telescope magazine/Roger Sinnott & Rick Fienberg)

Locating Messier 39:

This coarse open star cluster is easily found in small optics. Start first by identifying the very large constellation of Cygnus and pinpointing its brightest, northernmost star. Aim you binoculars there. You’ll find M39 about 9 degrees east and a bit north of Deneb (Alpha Cygni). If at first you don’t succeed, try looking at Deneb from a dark sky location and see if you can spot a small, hazy patch about a fist width away to the east. There’s your star cluster!

It will also show easily in the telescope finderscope as a hazy patch and even begin resolution with larger aperture finders. M39 is very well suited to light polluted skies and moonlit observing and will even hold up well to less than ideal sky conditions. Small instruments will easily see a bright handful of stars while larger telescopes will resolve many more faint members and pairs. Because of its large apparent size, you’ll enjoy viewing M39 far more if you use the least amount of magnification possible.

Enjoy this star-studded cluster and the great Milky Way field that frames it!

And here are the quick facts on this Messier Object to help get you started:

Object Name: Messier 39
Alternative Designations: M39, NGC 7092
Object Type: Galactic Open Star Cluster
Constellation: Cygnus
Right Ascension: 21 : 32.2 (h:m)
Declination: +48 : 26 (deg:m)
Distance: 0.825 (kly)
Visual Brightness: 4.6 (mag)
Apparent Dimension: 32.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Posted on by Tammy Plotner

Messier 38 – The Starfish Cluster

The open star cluster Messier 38, in proximity to Messier 36 and Messier 37. Credit: Wikisky

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the Starfish Cluster, otherwise known as Messier 38. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects it the Starfish Cluster, also known as Messier 38 (or M38). This open star cluster is located in the direction of the northern Auriga constellation, along with the open star clusters M36 and M37. While not the brightest of the three, the location of the Starfish within the polygon formed by the brightest stars of Auriga makes it very easy to find.

Description:

Cruising around our Milky Way some 4200 light years from our solar system, this 220 million year old group of stars spreads itself across about 25 light years of space. If you’re using a telescope, you may have noticed its not alone… Messier 38 might very well be a binary star cluster! As Anil K. Pandey (et al) explained in a 2006 study:

“We present CCD photometry in a wide field around two open clusters, NGC 1912 and NGC 1907. The stellar surface density profiles indicate that the radii of the clusters NGC 1912 and NGC 1907 are 14′ and 6′ respectively. The core of the cluster NGC 1907 is found to be 1′.6±0′.3, whereas the core of the cluster NGC 1912 could not be defined due to its significant variation with the limiting magnitude. The clusters are situated at distances of 1400±100 pc (NGC 1912) and 1760±100 pc (NGC 1907), indicating that in spite of their close locations on the sky they may be formed in different parts of the Galaxy.”

The Starfish Cluster also known as Messier 38. Credit: Wikisky

So what’s happening here? Chances are, when you’re looking at M38, you’re looking at a star cluster that’s currently undergoing a real close encounter! Said M.R. de Oliveira (et al) said in their 2002 study:

“The possible physical relation between the closely projected open clusters NGC 1912 (M 38) and NGC 1907 is investigated. Previous studies suggested a physical pair based on similar distances, and the present study explores in more detail the possible interaction. Spatial velocities are derived from available radial velocities and proper motions, and the past orbital motions of the clusters are retrieved in a Galactic potential model. Detailed N-body simulations of their approach suggest that the clusters were born in different regions of the Galaxy and presently experience a fly-by.”

However, it was Sang Hyun Lee and See-Woo Lee who gave us the estimates of M38’s distance and age. As they wrote in their 1996 study, “UBV CCD Photometry of Open Cluster NGC 1907 and NGC 1912“: “The distance difference of the two clusters is 300pc and the age difference is 150 Myr. These results imply that the two clusters are not physically connected.”

So, how do we know they are two clusters passing in the night? The credit for that goes to de Oliveira and colleagues, who also asserted in their 2002 study:

“These simulations also shows that the faster the clusters approach the weaker the tidal debris in the bridge region, which explain why there is, apparently, no evidence of a material link between the clusters and why it should not be expected. It would be necessary to analyse deep wide field CCD photometry for a more conclusive result about the apparent absence of tidal link between the clusters.”

Atlas image mosaic of the Starfish Cluster (Messier 38), obtained as part of the Two Micron All Sky Survey (2MASS). Credit: NASA/NSF/Caltech/UofMass/IPAC

History of Observation:

This wonderful star cluster was originally discovered by Giovanni Batista Hodierna before 1654 and independently rediscovered by Le Gentil in 1749. However, it was Charles Messier’s catalog which brought it to attention:

“In the night of September 25 to 26, 1764, I have discovered a cluster of small stars in Auriga, near the star Sigma of that constellation, little distant from the two preceding clusters: this one is of square shape, and doesn’t contain any nebulosity, if one examines it with a good instrument: its extension may be 15 minutes of arc. I have determined its position: its right ascension was 78d 10′ 12″, and its declination 36d 11′ 51″ north.”

By correcting cataloging its position, M38 could later be studied by other astronomers who would also add their own notes. Caroline, then William Herschel would observe it, where the good Sir William would add to his private notes: “A cluster of scattered, pretty large [bright] stars of various magnitudes, of an irregular figure. It is in the Milky Way.”

Messier Object 38 would then later be added to the New General Catalog by John Herschel, who wasn’t particularly descriptive, either. However, there was an historic astronomer who was determined to examine this star cluster and it was Admiral Symth:

“A rich cluster of minute stars, on the Waggoner’s left thigh, of which a remarkable pair in the following are here estimated. A [mag] 7, yellow; and B 9, pale yellow; having a little companion about 25″ off in the sf [south following, SE] quarter. Messier discovered this in 1764, and described it as ‘a mass of stars of a square form without any nebulosity, extending to about 15′ of a degree;’ but it is singular that the palpable cruciform shape of the most clustering part did not attract his notice. It is an oblique cross, with a pair of large [bright] stars in each arm, and a conspicuous single one at the centre; the whole followed by a bright individual of the 7th magnitude. The very unusual shape of this cluster, recalls the sagacity of Sir William Herschel’s speculations upon the subject, and very much favours the idea of an attractive power lodged in the brightest part. For although the form be not globular, it is plainly to be seen that there is a tendency toward sphericity, by the swell of the dimensions as they draw near the most luminous place, denoting, as it were, a stream, or tide, of stars, setting toward the centre. As the stars in the same nebula must be very merely all at the same relative distance from us, and they appear to be about the same size [brightness], Sir William infers that their real magnitudes must be nearly equal. Granting, therefore, that these nebulae and clusters of stars are formed by their mutual attraction, he concludes that we may judge of their relative age, by the disposition of their component parts, those being the oldest which are the most compressed.”

Open Cluster M38, photographed on Feb 19, 2015. Credit: Wikipedia Commons/Miguel Garcia

Perhaps by taking his time and really observing, Smyth gained some insight into the true nature of M38! Observe it yourself, and see if you can also locate NGC 1907. It’s quite a pair!

Locating Messier 38:

Locating Messier 38 is relatively easy once you understand the constellation of Auriga. Looking roughly like a pentagon in shape, start by identifying the brightest of these stars – Capella. Due south of it is the second brightest star which shares its border with Beta Tauri, El Nath. By aiming binoculars at El Nath, go north about 1/3 the distance between the two and enjoy all the stars!

You will note two very conspicuous clusters of stars in this area, and so did Le Gentil in 1749. Binoculars will reveal the pair in the same field, as will telescopes using lowest power. The dimmest of these is the M38, and will appear vaguely cruciform in shape. At roughly 4200 light years away, larger aperture will be needed to resolve the 100 or so fainter members. About 2 1/2 degrees to the southeast (about a finger width) you will see the much brighter M36.

More easily resolved in binoculars and small scopes, this “jewel box” galactic cluster is quite young and about 100 light years closer. If you continue roughly on the same trajectory about another 4 degrees southeast you will find open cluster M37. This galactic cluster will appear almost nebula-like to binoculars and very small telescopes – but comes to perfect resolution with larger instruments.

The location of Messier 38 open star cluster in the Auriga constellation. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

While all three open star clusters make fine choices for moonlit or light polluted skies, remember that high sky light means less faint stars which can be resolved – robbing each cluster of some of its beauty. Messier 38 is faintest and northernmost of the trio and located almost in the center of the Auriga pentagon. Binoculars and small telescopes will easily spot its cross-shaped pattern.

And here are the quick facts on the Starfish Nebula to help you get started:

Object Name: Messier 38
Alternative Designations: M38, NGC 1912
Object Type: Galactic Open Star Cluster
Constellation: Auriga
Right Ascension: 05 : 28.4 (h:m)
Declination: +35 : 50 (deg:m)
Distance: 4.2 (kly)
Visual Brightness: 7.4 (mag)
Apparent Dimension: 21.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Posted on by Tammy Plotner

Messier 37 – the NGC 2099 Open Star Cluster

The open star cluster Messier 38, in proximity to Messier 36 and Messier 37. Credit: Wikisky

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the open star cluster known as Messier 37. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is the open star cluster known as Messier 37 (aka M37 and NGC 2099). Located in the direction of the Auriga constellation, Messier 37 is one of three open star clusters (including Messier 36 and Messier 38) in this portion of the night sky – and also the brightest.

Description:

Of the trio of Messier star clusters in this area, M37 is by far the most stellar populated. It contains at least 150 stars that are around magnitude 12 and easily resolved by even small telescopes – and science is still counting actual members! At around 347 – 550 million years old, you’ll find at least a dozen red giants living here about 4,500 light years away from Earth… and they do it in a neighborhood that spans anywhere from 20 to 25 light years across!

The open star cluster Messier 37. Credit: Wikisky

Just how many stars might be inside this intermediate-aged cluster? As R. Sagar and Nilakshi of the Indian Institute for Astrophysics said in their 2002 study:

“The CCD observations of the rich open star cluster NGC 2099 and its surrounding field region have been carried out up to a limiting magnitude of V ~ 22 mag in B, V and I passbands for the first time. A total of ~ 12 000 stars have been observed in the area of about 24 arcmin x 34 arcmin in the cluster region, as well as ~ 2180 stars in the ~ 12arcmin x 12arcmin area of the field region located ~ 45arcmin away from the cluster center.”

Out of this huge number of stars, astronomers have been able to observe white dwarfs, too. This helps us to understand how they develop and what affects their helium or hydrogen content. Jasonjot Singh Kalirai et al. had the following to say in a 2004 study:

“Spectra have been obtained of 21 white dwarfs (WDs) in the direction of the young, rich open star cluster NGC 2099. This represents an appreciable fraction (>30%) of the cluster’s total WD population. The mean derived mass of the sample is 0.8 M—about 0.2 M larger than the mean seen among field WDs. A surprising result is that all of the NGC 2099 WDs have hydrogen-rich atmospheres (DAs); none exhibit helium-rich ones (DBs) or any other spectral class. We explore possible reasons for the lack of DBs in these clusters and conclude that the most promising scenario for the DA/DB number ratio discrepancy in young clusters is that hot, high-mass WDs do not develop large enough helium convection zones to allow helium to be brought to the surface and turn a hydrogen-rich WD into a helium-rich one.”

So, we’re setting the stage with number of stars and types. We have white dwarfs – but what about variables? Y.B. Kang (et al), put it this way in a 2007 study:

“Time-series CCD photometric observations of the intermediate-age open cluster NGC 2099 were performed to search for variable stars. We also carried out BV photometry to study physical properties of variables in the cluster. Using V-band time-series data, we carefully examined light variations of about 12,000 stars in the range of 10 < V < 22 mag. A total of 24 variable stars have been identified; seven stars are previously known variables and 17 stars are newly identified. On the basis of observational properties such as light curve shape, period, and amplitude, we classified the new variable stars as nine delta Scuti-type pulsating stars, seven eclipsing binaries, and one peculiar variable star. Judging from the position of delta Scuti-type stars in the color-magnitude diagram, only two stars are likely to have the cluster membership. One new variable KV10 shows peculiar light variations with a delta Scuti-type short period of about 0.044 day as well as a long period of 0.417 day.”

M37 (NGC 2099) open cluster. Credit: Wikipedia Commons

So what does knowing about these two types of stars help with our understanding of stellar evolution? That’s one of the goals of the RACE-OC project. As S. Messina (et al) said in 2008:

“Rotation and solar-type magnetic activity are closely related to each other in main-sequence stars of G or later spectral types. The presence and level of magnetic activity depend on star’s rotation, and rotation itself is strongly influenced by strength and topology of the magnetic fields. Open clusters represent especially useful targets to investigate the connection between rotation and activity. The open cluster NGC 2099 has been studied as a part of the RACE-OC project (Rotation and ACtivity Evolution in Open Clusters), which is aimed at exploring the evolution of rotation and magnetic activity in the late-type members of open clusters of different ages. We collected time series CCD photometric observations of this cluster in January 2004, and we determined the presence of periodicities in the flux variation related to the stellar rotation by Fourier analysis. We investigate the relations between activity manifestations, such as the light curve amplitude, and global stellar parameters. Results: We have discovered 135 periodic variables, 122 of which are candidate cluster members. Determination of rotation periods of G- and K-type stars has allowed us to better explore the evolution of angular momentum at an age of about 500 Myr. In our analysis, we have also identified 3 new detached eclipsing binary candidates among cluster members. A comparison with the older Hyades cluster (~625 Myr) shows that the newly-determined distribution of rotation periods is consistent with the scenario of rotational braking of main-sequence spotted stars as they age. However, a comparison with the younger M 34 cluster (~200 Myr) shows that the G8-K5 members of these clusters have the same rotation period distribution. That is, G8-K5 members in NGC 2099 seem to have experienced no significant braking in the age range from ~200 to ~500 Myr. Finally, NGC 2099 members have a smaller level of photospheric magnetic activity, as measured by light curve amplitude, than in younger stars of the same mass and rotation, suggesting that the activity level also depends on some other age-dependent parameters.”

History of Observation:

Although this great star cluster was originally recorded Giovanni Batista Hodierna before 1654, it would be 230 years before his records would be uncovered, so when Charles Messier first logged as Messier 37, it was believed to be an independent discovery.

“In the same night [September 2 to 3, 1764], I have observed a second cluster of small stars which were not very distant from the preceding, near the right leg of Auriga and on the parallel of the star Chi of that constellaiton: the stars there are smaller than that of the preceding cluster: they are also closer to each other, and contain a nebulosity. With an ordinary refractor of 3 feet and a half, one has difficulty to see these stars; but one distinguishes them with an instrument of greater effectivity. I have determined the position fo this cluster, which may have an extension of 8 to 9 minutes of arc: its right ascension was 84d 15′ 12″, and its declination 32d 11′ 51″ north.”

While William Herschel would return in later years to study Messier’s object, he did not publish his notes – but gives some great observing advice:

“A useful, coarse step; it will serve to learn to see nebulae, because it contains many small stars mixed with others in various magnitudes, many of which are not to be seen without great and long attention.” Messier 37 would be later given its NGC catalog designation by John Herschel who was the first to make a guess at its true stellar population: “Very fine large cluster, all resolved into stars of 10th to 13th magnitude. It fills 1 1/2 field, but the straggling stars extend very far. There may be 500 stars.”

As always, Admiral Smyth was the most poetical about his observing, and of M37 he writes:

“A magnificent object, the whole field being strewed as it were with sparkling gold-dust; and the group is resolvable into about 500 stars, from the 10th to the 14th magnitudes, besides the outliers. It was found and fixed by Messier in 1764, who described it as “a mass of small stars, much enveloped in nebulous matter.” This nebulous matter, however, yields to my telescope, and resolves into infinitely minute points of lucid light, among the distinct little individuals.”

The location of Messier 37 in the constellation Auriga. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

Locating Messier 37:

Locating Messier 37 is relatively easy once you understand the constellation of Auriga. Looking roughly like a pentagon in shape, start by identifying the brightest of these stars – Capella. Due south of it is the second brightest star which shares its border with Beta Tauri, El Nath. By aiming binoculars at El Nath, go north about 1/3 the distance between the two and enjoy all the stars! You will note two very conspicuous clusters of stars in this area, and so did Le Gentil in 1749.

Binoculars will reveal the pair in the same field, as will telescopes using lowest power. The dimmest of these is the M38, and will appear vaguely cruciform in shape. At roughly 4200 light years away, larger aperture will be needed to resolve the 100 or so fainter members. About 2 1/2 degrees to the southeast (about a finger width) you will see the much brighter M36.

More easily resolved in binoculars and small scopes, this “jewel box” galactic cluster is quite young and about 100 light years closer. If you continue roughly on the same trajectory about another 4 degrees southeast you will find open cluster M37. This galactic cluster will appear almost nebula-like to binoculars and very small telescopes – but comes to perfect resolution with larger instruments.

While all three open star clusters make fine choices for moonlit or light polluted skies, remember that high sky light means less faint stars which can be resolved – robbing each cluster of some of its beauty. Messier 37 is the brightest and easternmost of the trio and you’ll very much notice its density.

When you view this cluster with binoculars, you’ll be seeing it much as Messier did… But use the power of a telescope if you can. Because this cloud of stars is quite worth your time and attention!

Object Name: Messier 37
Alternative Designations: M37, NGC 2099
Object Type: Galactic Open Star Cluster
Constellation: Auriga
Right Ascension: 05 : 52.4 (h:m)
Declination: +32 : 33 (deg:m)
Distance: 4.4 (kly)
Visual Brightness: 6.2 (mag)
Apparent Dimension: 24.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Posted on by Tammy Plotner

Messier 36 – The Pinwheel Cluster

The open star cluster Messier 38, in proximity to Messier 36 and Messier 37. Credit: Wikisky

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the Pinweel Cluster, otherwise known as Messier 36. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

Included in this list is the open star cluster Messier 36, also known as the Pinwheel Cluster. This cluster is so-named because of its association with the Auriga constellation (aka. “the Charioteer”). Though similar in size and make-up to the Pleiades Cluster (Messier 45), the Pinwheel Cluster is actually ten times farther away from Earth – and one of the most distant of any clusters catalogued by Messier.

What You Are Looking At:

Located a little more than 4000 light years from our solar system, this group of about 60 stars spans across about 14 light years of space. As you are studying it, you’ll notice one star which seems brighter than the rest… With good reason! Its a spectral type B2 and about 360 more luminous than our Sun. Many of the cluster members here are also B-type stars and rapid rotators.

Close-up of the central region of Messier 36. Credit: Wikisky

This means that 25 million year old Messier 36 shares a lot in common with another nearby star cluster, the Pleiades. By taking a deep look at young clusters with stars of varying ages, astronomers are able to how long circumstellar disks may last – giving us a clue as to whether or not planet-forming stars may lay within them.

As Karl E. Haisch, Jr. (et al), wrote in a 2001 study “Disk Frequencies and Lifetimes in Young Clusters“:

“We have completed the first systematic and homogeneous survey for circumstellar disks in a sample of young clusters that both span a significant range in age and contain statistically significant numbers of stars whose masses span nearly the entire stellar mass spectrum. Analysis of the combined survey indicates that the cluster disk fraction is initially very high and rapidly decreases with increasing cluster age, such that one-half the stars within the clusters lose their disks in 3 million years. Moreover, these observations yield an overall disk lifetime of ~6 million years in the surveyed cluster sample. This is the timescale for essentially all the stars in a cluster to lose their disks. This should set a meaningful constraint for the planet-building timescale in stellar clusters.”

ut, can M36 hold surprises? You betcha’. As Bo Reipurth stated in a 2008 study titled “Star Formation and Molecular Clouds towards the Galactic Anti-Center“:

“The open cluster M36 (NGC 1960), which apparently forms the center of the Aur OB1 association, has been the subject of numerous analyses, and of these the earliest studies are today of historical interest only. NGC 1960 has recently attracted attention as the most likely origin of a massive OB star that exploded about 40,000 yr ago, creating the supernova remnant Simeis 147, an old supernova remnant listed in the catalog compiled at Simeiz by Gaze & Shajn (1952). A pulsar, PSR J0538+2817, has been found near the center of Simeis 147.”

2MASS Atlas Image Mosaic of the open star cluster Messier 36. Credit: NASA/IPAC/Caltech/University of Massachusetts

And the search for planet-building stars within M36 hasn’t stopped yet. The Spitzer Space telescope will also be investigating it, thanks to a proposal made by George Rieke:

“We propose a deep IRAC/MIPS survey of NGC 1960, a ~20 Myr-old massive cluster unexplored in the mid infrared. This cluster is at a key stage in terrestrial planet formation. Our survey will likely detect infrared excess emission from debris disks and transition disks from ~ 100 intermediate-mass (1-3 solar mass) stars. Together with ground-based photometry/spectroscopy of this cluster, proposed observations of 10 Myr-old NGC 6871, scheduled cycle 4 observations of the massive 13 Myr old clusters h and chi Persei, and existing data on NGC 2547 at 30 Myr, this survey will yield robust constraints on the frequency of debris/transition disks as a function of spectral type, age, and cluster environment at a critical age range for planet formation. This survey will provide a benchmark study of the observable signatures of terrestrial planet formation that will inform James Webb Space Telescope observations of planet-forming disks a decade from now.”

History of Observation:

The presence of this awesome star cluster was first recorded by Giovanni Batista Hodierna before 1654 and re-discovered by Le Gentil in 1749. However, it was Charles Messier who took the time to carefully record its position for future generations:

“In the night of September 2 to 3, 1764, I have determined the position of a star cluster in Auriga, near the star Phi of that constellation. With an ordinary refractor of 3 feet and a half, one has difficulty to distinguish these small stars; but when employing a stronger instrument, one sees them very well; they don’t contain between them any nebulosity: their extension is about 9 minutes of arc. I have compared the middle of this cluster with the star Phi Aurigae, and I have determined its position; its right ascension was 80d 11′ 42″, and its declination 34d 8′ 6″ north.”

M36 Open Cluster. Credit: NOAO/AURA/NSF

It would be observed again by Caroline, William and John Herschel who would be the first to note the double star in M36’s center. Although none of their notes are particularly glowing on this awesome star cluster, Admiral Symth does come to the historic rescue!

“A neat double star in a splendid cluster, on the robe below the Waggoner’s left thigh, and near the centre of the Galaxy stream. A [mag] 8 and B 9, both white; in a rich though open splash of stars from the 8th to the 14th magnitudes, with numerous outliers, like the device of a star whose rays are formed by very small stars. This object was registered by M. [Messier] in 1764; and the double star, as H. [John Herschel] remarks, is admirably placed, for future astronomers to ascertain whether there be internal motion in clusters. A line carried from the central star in Orion’s belt, through Zeta Tauri, and continued about 13deg beyond, will reach the cluster, following Phi Aurigae by about two degrees.”

Locating Messier 36:

Locating Messier 36 is relatively easy once you understand the constellation of Auriga. Looking roughly like a pentagon in shape, start by identifying the brightest of these stars – Capella. Due south of it is the second brightest star which shares its border with Beta Tauri, El Nath. By aiming binoculars at El Nath, go north about 1/3 the distance between the two and enjoy all the stars!

You will note two very conspicuous clusters of stars in this area, and so did Le Gentil in 1749. Binoculars will reveal the pair in the same field, as will telescopes using lowest power. The dimmest of these is the M38, and will appear vaguely cruciform in shape. At roughly 4200 light years away, larger aperture will be needed to resolve the 100 or so fainter members. About 2 1/2 degrees to the southeast (about a finger width) you will see the much brighter M36.

The location of M36 in the Auriga constellation. Credit: IAU and Sky and Telescope Magazine (Roger Sinnott & Rick Fienberg)

More easily resolved in binoculars and small scopes, this “jewel box” galactic cluster is quite young and about 100 light years closer. If you continue roughly on the same trajectory about another 4 degrees southeast you will find open cluster M37. This galactic cluster will appear almost nebula-like to binoculars and very small telescopes – but comes to perfect resolution with larger instruments.

While all three open star clusters make fine choices for moonlit or light polluted skies, remember that high sky light means less faint stars which can be resolved – robbing each cluster of some of its beauty. Messier 36 is intermediate brightness of the trio and you’ll quite enjoy its “X” shape and many pairings of stars!

Has the central double changed with time? Why not observe for yourself and see!

Object Name: Messier 36
Alternative Designations: M36, NGC 1960, Pinwheel Cluster
Object Type: Galactic Open Star Cluster
Constellation: Auriga
Right Ascension: 05 : 36.1 (h:m)
Declination: +34 : 08 (deg:m)
Distance: 4.1 (kly)
Visual Brightness: 6.3 (mag)
Apparent Dimension: 12.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Posted on by Tammy Plotner

Messier 35 – the NGC 2168 Open Star Cluster

The open star cluster Messier 35, with NGC 2158 and IC 2157 shown nearby. Credit: Wikisky

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the open star cluster known as Messier 35. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is known as Messier 35, a large open star cluster located in the northern constellation Gemini. M35 is the only Messier Object located in Gemini, and lies near the border with the adjacent constellations of  Taurus, Auriga and Orion. It consists several hundred stars that are scattered over an area that is about the same size as a Full Moon.

What You Are Looking At:

Messier 35 is 2,800 light years away from Earth and is relatively young as star clusters go, having formed only about 100 million years ago. The cluster occupies a region of space that is roughly 24 light years in diameter, and an area of 28 arc minutes on the sky – which is roughly equal to the size of the full Moon.

Image of Messier 35 obtained by the Two Micron All Sky Survey (2MASS). Credit: NASA/2MASS

M35 has a central mass that spans 11.4 light years (3.75 parsecs), with an estimated mass of 1600 to 3200 solar masses. While most of the molecule cloud from which it formed has been blown away, some of the material resides in the immediate vicinity of its stars. This can be seen in the way that light from its particularly bright blue stars is scattered to create a diffuse glow.

These are the hottest main sequence stars in the cluster, which correspond to a spectral classification of B3. M35 also contains more evolved stars, including several orange and yellow giants, which have longer lifespans than the more-massive blue stars (only a few tense of millions of years).

As a result, these stars will likely die out in the near future while the smaller stars continue to evolve, drastically affecting the cluster’s luminosity and appearance. In short, it will become redder and dimmer over time.

History of Observation:

This wonderful star cluster was discovered by Philippe Loys de Chéseaux 1745-46 and recovered again by John Bevis before 1750. However, we know and love it best as Messier Object 35, when it was penned into being by Charles Messier. As he wrote of the cluster upon observing it for the first time:

“In the night of August 30 to 31, 1764, I have observed a cluster of very small stars, near the left foot of Castor, little distant from the stars Mu and Eta of that constellation [Gemini]. When examining this star cluster with an ordinary refractor of 3 feet, it seemed to contain nebulosity; but having examined it with a good Gregorian telescope which magnified 104 times, I have noticed that it is nothing but a cluster of small stars, among which there are some which are of more light; its extension may be 20 minutes of arc. I have compared the middle of this cluster with the star Eta of Castor; its right ascension has been concluded at 88d 40′ 9″, and its declination at 24d 33′ 30″ north.”

Close-up of the Messier 35 open star cluster, showing its blue stars. Credit: Wikisky

How long would it be before the companion cluster was observed as well? My guess is Sir William Herschel’s time. Although Herschel would not publish his notes on Messier objects, they do state while observing M35 that “There is no central condensation to denote a globular form.”

And what of Admiral Smyth? He observed the cluster in September of 1836, though he appeared to have missed its companion cluster. As he recorded of M35 at the time:

“A cluster, near Castor’s right foot, in the Galaxy, discovered and registered by Messier in 1764. It presents a gorgeous field of stars from the 9th to the 16th magnitudes, but with the center of mass less rich than the rest. From the small stars being inclined to form curves of three, four, and often with a large [bright] one at the root of the curve, it somewhat reminds one of the bursting of a sky-rocket.”

A nice description, but if you see the companion cluster, you’ll know it!

Locating Messier 35:

Locating M35 in binoculars is fairly easy once you recognize the constellation of Gemini. You’ll find it just a little more than the average field of view north of Eta – the center most of the three “foot” stars on the northernmost twin. In the finderscope of a telescope, begin with Eta and starhop north until you spot a faint fuzzy in the finderscope.

The location of Messier 35 in the norther n Gemini constellation. Credit: IAU/Sky & Telescope magazine/Roger Sinnott & Rick Fienberg

Because Messier 35 is large, you’ll need low magnification to appreciate the size of this cluster in a telecope. It stands up well to moonlight and light polluted skies – as well as less than perfect sky conditions, but you will need around a 10″ or larger telescope to really begin to notice its companion cluster, NGC 2158. In smaller telescopes with good conditions, it will appear as a faint nebulous patch.

And as always, here are the quick facts on M35 to get you started!

Object Name: Messier 35
Alternative Designations: M35, NGC 2168
Object Type: Galactic Open Star Cluster
Constellation: Gemini
Right Ascension: 06 : 08.9 (h:m)
Declination: +24 : 20 (deg:m)
Distance: 2.8 (kly)
Visual Brightness: 5.3 (mag)
Apparent Dimension: 28.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Posted on by Tammy Plotner

Messier 34 – the NGC 1039 Open Star Cluster

The location of Messier 34 in the northern skies. Credit: Wikisky

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the Triangulum Galaxy, also known as Messier 33. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is known as Messier 34, an open star cluster located in the northern Perseus constellation. Located at a distance of about 1,500 light years from Earth, it is one of the closest Messier objects to Earth, and is home to an estimated 400 stars. It is also bright enough to be seen with the naked eye or binoculars, where light conditions permit.

What You Are Looking At:

This cluster of stars started its journey off together through our galaxy some 180 million years ago as part of the “Local Association”… groups of stars like the Pleiades, Alpha Persei Cluster and the Delta Lyrae Cluster that share a common origin, but have become gravitationally unbound and are still moving together through space. We know the stars are related by their common movement and ages, but what else do we know about them?

The core region of the Messier 34 open star cluster. Credit: Wikisky

Well, one thing we do know is that out of the 354 stars in the region survey, 89 of them are actual cluster members and that all six of the visual binaries and three of the four known Ap stars are members of the cluster. There’s even a giant among them! But like almost all stars out there, we know they usually aren’t singles and actually have companions. As Theodore Simon wrote in his 2000 study regarding NGC 1039 and NGC 3532:

“Roughly half the sources detected in both images have likely optical counterparts from earlier ground-based surveys. The remainder are either prospective cluster members or foreground/background stars, which can be decided only through additional photometry, spectroscopy, and proper-motion studies. There is some indication (at the 98% confidence level) that solar-type stars may lack the extreme rotation and activity levels shown by those in the much younger Pleiades and alpha Persei clusters, but a detailed assessment of the coronal X-ray properties of these clusters must await more sensitive observations in the future. If confirmed, this finding could help to rule out the possibility that stellar dynamo activity and rotational braking are controlled by a rapidly spinning central core as stars pass through this phase of evolution from the Pleiades stage to that represented by the Hyades.”

If there’s companion stars to be discovered, what else might be in the field that we just can quite “see”? Try white dwarfs. As Kate Rubin (et al.) published in the May 2008 issue of the Astronomical Journal:

“We present the first detailed photometric and spectroscopic study of the white dwarfs (WDs) in the field of the ~225 Myr old (log ?cl = 8.35) open cluster NGC 1039 (M34) as part of the ongoing Lick-Arizona White Dwarf Survey. Using wide-field UBV imaging, we photometrically select 44 WD candidates in this field. We spectroscopically identify 19 of these objects as WDs; 17 are hydrogen-atmosphere DA WDs, one is a helium-atmosphere DB WD, and one is a cool DC WD that exhibits no detectable absorption lines. Of the 17 DAs, five are at the approximate distance modulus of the cluster. Another WD with a distance modulus 0.45 mag brighter than that of the cluster could be a double-degenerate binary cluster member, but is more likely to be a field WD. We place the five single cluster member WDs in the empirical initial-final mass relation and find that three of them lie very close to the previously derived linear relation; two have WD masses significantly below the relation. These outliers may have experienced some sort of enhanced mass loss or binary evolution; however, it is quite possible that these WDs are simply interlopers from the field WD population.”

Close-up image of M34 showing its white dwarf population, taken by the Sloan Digital Sky Survey. Credit: SDSS

While it sounds a little confusing, it’s all about how star clusters evolve. As David Soderblom wrote in a 2001 study:

“We analyze Keck Hires observations of rotation in F, G, and K dwarf members of the open cluster M34 (NGC 1039), which is 250 Myr old, and we compare them to the Pleiades, Hyades, and NGC 6475. The upper bound to rotation seen in M34 is about a factor of two lower than for the 100 Myr-old Pleiades, but most M34 stars are well below this upper bound, and it is the overall convergence in rotation rates that is most striking. A few K dwarfs in M34 are still rapid rotators, suggesting that they have undergone core-envelope decoupling, followed by replenishment of surface angular momentum from an internal reservoir. Our comparison of rotation in these clusters indicates that the time scale for the coupling of the envelope to the core must be close to 100 Myr if decoupling does, in fact, occur.”

History of Observation:

M34 was probably first found by Giovanni Batista Hodierna before 1654, and independently rediscovered by Charles Messier in on August 25, 1764. As he described it in his notes:

“I have determined the position of a cluster of small stars between the head of the Medusa and the left foot of Andromeda almost on the parallel of the star Gamma of that letter constellation. With an ordinary refractor of 3 feet, one distinguishes these stars; the cluster may have 15 minutes in extension. I have determined its position with regard to the star Beta in the head of the Medusa; its right ascension has been concluded at 36d 51′ 37″, and its declination as 41d 39′ 32″ north.”

Image of Messier 34 taken by the Two Micron All-Sky Survey (2MASS) of Messier 34 (also known as M34 or NGC 1039). Credit: 2MASS/UMass/IPAC-Caltech/NASA/NSF

Over the years, a great many historic observers would turn a telescope its way to examine it – also looking for more. Said Sir William Herschel: “A cluster of stars; with 120, I think it is accompanied with mottled light, like stars at a distance.” Yet very little more can be seen except for the fact that most of the stars seem to be arranged in pairs – the most notable being optical double in the center – h 1123 – which was cataloged by Sir John Herschel on December 23rd, 1831.

Charles Messier discovered it independently on August 25th, 1764, and included it in the Messier Catalog. As he wrote in the first edition of the catalog:

“In the same night of [August] 25 to 26, I have determined the position of a cluster of small stars between the head of the Medusa [Algol] & the left foot of Andromeda almost on the parallel of the star Gamma of that letter constellation. With an ordinary [non-achromatic] refractor of 3 feet [FL], one distinguishes these stars; the cluster may have 15 minutes in extension. I have determined its position with regard to the star Beta in the head of the Medusa; its right ascension has been concluded at 36d 51? 37?, & its declination as 41d 39? 32? north.”

But as always, it was Admiral William Henry Smyth who described the object with the most florid prose. As he wrote in his notes when observing the cluster in October 1837, he noted the following:

“A double star in a cluster, between the right foot of Andromeda and the head of Medusa; where a line from Polaris between Epsilon Cassiopeiae and Alpha Persei to within 2deg of the parallel of Algol, will meet it. A and B, 8th magnitudes, and both white. It is in a scattered but elegant group of stars from the 8th to the 13th degree of brightness, on a dark ground, and several of them form into coarse pairs. This was first seen and registered by Messier, in 1764, as a “mass of small stars;” and in 1783 was resolved by Sir W. Herschel with a seven-foot reflector: with the 20-foot he made it “a coarse cluster of large stars of different sizes.” By the method he applied to fathom the galaxy, he concluded the profundity of this object not to exceed the 144th order.”

The location of Messier 34 in the northern Perseus constellation. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)

Locating Messier 34:

M34 is easily found in binoculars about two fields of view northwest of Algol(Beta Persei). You will know when you have found this distinctive star cluster because “X” marks the spot! In a telescope finderscope, it will appear as a faint, hazy spot and will fully resolve to most average telescopes. Messier 34 makes an excellent target for moonlit nights or light polluted areas and will stand up well to less than perfect sky conditions.

It can even be seen unaided from ideal locations! Enjoy your observations!

And as always, we’ve included the quick facts on this Messier Object to help you get started:

Object Name: Messier 34
Alternative Designations: M34, NGC 1039
Object Type: Galactic Open Star Cluster
Constellation: Perseus
Right Ascension: 02 : 42.0 (h:m)
Declination: +42 : 47 (deg:m)
Distance: 1.4 (kly)
Visual Brightness: 5.5 (mag)
Apparent Dimension: 35.0 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources:

Posted on by Tammy Plotner

Messier 32 – the “Le Gentil” Dwarf Elliptical Galaxy

Color view of M31 (The Andromeda Galaxy), with M32 (a satellite galaxy) shown to the lower left. Credit and copyright: Terry Hancock.

Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at dwarf elliptical galaxy known as Messier 32. Enjoy!

During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.

One of these objects is the dwarf elliptical galaxy known as Messier 32 (aka. NGC 221). Located about 2.65 million light-years from Earth, in the direction of the Andromeda constellation, this dwarf is actually a satellite galaxy of the massive Andromeda Galaxy (M31). Along with Andromeda, the Milky Way and the Triangulum Galaxy (M33) is a member of the Local Group.

Description:

M32 is an elliptical dwarf galaxy which contains about 3 billion solar masses. While it looks small compared to its massive neighbor, this little guy actually stretches across space some 8,000 light years in diameter. Once you pick it up, you’ll notice it’s really quite bright on its own – and with very good reason – its nucleus is almost identical to M31. Both contain about 100 million solar masses in rapid motion around a central supermassive object!

The dwarf elliptical galaxy Messier 32 (Le Gentil). Credit: Wikisky

As Alister W. Graham wrote in his 2002 study – titled “Evidence for an outer disk in the Prototype `Compact Elliptical’ Galaxy M32“:

“M32 is the prototype for the relatively rare class of galaxies referred to as compact ellipticals. It has been suggested that M32 may be a tidally disturbed r1/4 elliptical galaxy or the remnant bulge of a disk-stripped early-type spiral galaxy reveals that the surface bightness profile, the velocity dispersion measurements, and the estimated supermassive black hole mass in M32 are inconsistent with the galaxy having, and probably ever having had, an r1/4 light profile. Instead, the radial surface brightness distribution of M32 resembles an almost perfect (bulge+exponential disk) profile; this is accompanied by a marked increase in the ellipticity profile and an associated change in the position angle profile where the “disk” starts to dominate. Compelling evidence that this bulge/disk interpretation is accurate comes from the best-fitting r1/n bulge model, which has a Sersic index of n=1.5, in agreement with the recently discovered relation between a bulge’s Sersic index and the mass of a bulge’s supermassive black hole.”

By probing deeply into Messier 32, we’ve learned this little galaxy is home to mainly mature red and yellow stars. And they’re good housekeepers, too… because there’s practically no dust or gas to be found. While this seems neat and tidy, it also means there isn’t any new star formation going on either, but there are signs of some lively doings in the not too distant past.

Because M32 has shared “space” with neighboring massive M31, the strong tidal field of the larger galaxy may have ripped away what once could have been spiral arms – leaving only its central bulge and triggering starburst in the core. As Kenji Bekki (et al) wrote in their 2001 study:

“The origin of M32, the closest compact elliptical galaxy (cE), is a long-standing puzzle of galaxy formation in the Local Group. Our N-body/smoothed particle hydrodynamics simulations suggest a new scenario in which the strong tidal field of M31 can transform a spiral galaxy into a compact elliptical galaxy. As a low-luminosity spiral galaxy plunges into the central region of M31, most of the outer stellar and gaseous components of its disk are dramatically stripped as a result of M31’s tidal field. The central bulge component on the other hand, is just weakly influenced by the tidal field, owing to its compact configuration, and retains its morphology. M31’s strong tidal field also induces rapid gas transfer to the central region, triggers a nuclear starburst, and consequently forms the central high-density and more metal-rich stellar populations with relatively young ages. Thus, in this scenario, M32 was previously the bulge of a spiral galaxy tidally interacting with M31 several gigayears ago. Furthermore, we suggest that cE’s like M32 are rare, the result of both the rather narrow parameter space for tidal interactions that morphologically transform spiral galaxies into cE’s and the very short timescale (less than a few times 109 yr) for cE’s to be swallowed by their giant host galaxies (via dynamical friction) after their formation.”

Messier 31 (the Andromeda Galaxy), along with Messier 32 and Messier 110. Credit: Wikisky

History of Observation:

M32 was discovered by Guillaume Le Gentil on October 29th, 1749 and became the first elliptical galaxy ever observed. Although it wasn’t cataloged by Charles Messier until August 3rd, 1764, he had also seen it some seven years earlier while studying at the Paris Observatory, but his notes had been suppressed. But no matter, for he made sure to include it in his notes with a drawing! As he wrote of the object:

“I have examined in the same night [August 3 to 4, 1764], and with the same instruments, the small nebula which is below and at some [arc] minutes from that in the girdle of Andromeda. M. le Gentil discovered it on October 29, 1749. I saw it for the first time in 1757. When I examined the former, I did not know previously of the discovery which had been made by M. Le Gentil, although he had published it in the second volume of the Memoires de Savans erangers, page 137. Here is what I found written in my journal of 1764. That small nebula is round and may have a diameter of 2 minutes of arc: between that small nebula and that in the girdle of Andromeda one sees two small telescopic stars. In 1757, I made a drawing of that nebula, together with the old one, and I have not found and change at each time I have reviewed it: One sees with difficulty that nebula with an ordinary refractor of three feet and a half; its light is fainter than that of the old one, and it doesn’t contain any star. At the passage of that new nebula through the Meridian, comparing it with the star Gamma Andromedae, I have determined its position in right ascension as 7d 27′ 32″, and its declination as 38d 45′ 34″ north.”

Later, Messier 32 would be examined again, this time by Admiral Symth who said:

“An overpowering nebula, with a companion about 25′ in the south vertical M32 … The companion of M31 was discovered in November, 1749, by Le Gentil, and was described by him as being about an eighth of the size of the principal one. The light is certainly more feeble than here assigned. Messier – whose No. 32 it is – observed it closely in 1764, and remarked, that no change had taken place since the time of its being first recorded. In form it is nearly circular. The powerful telescope of Lord Rosse is a reflector of three feet in diameter, of performance hitherto unequalled. It was executed by the Earl of Rosse, under a rare union of skill, assiduity, perseverance, and muniference. The years of application required to accomplish this, have not worn his Lordship’s zeal and spirit; like a giant refreshed, he has returned to his task, and is now occupied upon a metallic disc of no less than six feet in diameter. Should the figure of this prove as perfect as the present one, we may soon over-lap what many absurdly look upon as the boundaries of the creation.”

The location of Messier 32 location in the Andromeda constellation. Credit: Roberto Mura

Locating Messier 32:

Locating M32 is as easy as locating the Andromeda Galaxy, but it will require large binoculars or at least a small telescope to see. Even under moderately light polluted skies the Great Andromeda Galaxy can be easily be found with the unaided eye – if you know where to look. Seasoned amateur astronomers can literally point to the sky and show you the location of M31, but perhaps you have never tried to find it.

Believe it or not, this is an easy galaxy to spot even under the moonlight. Simply identify the large diamond-shaped pattern of stars that is the Great Square of Pegasus. The northernmost star is Alpha, and it is here we will begin our hop. Stay with the northern chain of stars and look four finger widths away from Alpha for an easily seen star.

The next along the chain is about three more finger widths away… And we’re almost there. Two more finger widths to the north and you will see a dimmer star that looks like it has something smudgy nearby. Point your binoculars there, because that’s no cloud – it’s the Andromeda Galaxy!

Now aim your binoculars or telescope its way… Perhaps one of the most outstanding of all galaxies to the novice observer, M31 spans so much sky that it takes up several fields of view in a larger telescope, and even contains its own clusters and nebulae with New General Catalog designations. If you have larger binoculars or a telescope, you will be able to pick up M31’s two companions – M32 and M110. Messier 32 is the elliptical galaxy to the south.

Why not stretch your own boundaries? Go observing! Halton Arp included Messier 32 as No. 168 in his Catalogue of Peculiar Galaxies. It’s bright, easy and fun! And here are the quick facts on this Messier Object to help you get started:

Object Name: Messier 32
Alternative Designations: M32, NGC 221
Object Type: Type E2, Elliptical Galaxy
Constellation: Andromeda
Right Ascension: 00 : 42.7 (h:m)
Declination: +40 : 52 (deg:m)
Distance: 2900 (kly)
Visual Brightness: 8.1 (mag)
Apparent Dimension: 8×6 (arc min)

We have written many interesting articles about Messier Objects here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, , M1 – The Crab Nebula, M8 – The Lagoon Nebula, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.

Be to sure to check out our complete Messier Catalog. And for more information, check out the SEDS Messier Database.

Sources: