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Look up into the sky and you’ll see the stars twinkling in different colors. Some are dull and red, while others are white and others look bright blue. So how do you get so many different star colors?
The color of a star depends on its surface temperature. Our Sun’s surface temperature is about 6,000 Kelvin. Although it looks yellow from here on Earth, the light of the Sun would actually look very white from space. This white light coming off of the Sun is because its temperature is 6,000 Kelvin. If the Sun were cooler, it would give off light more on the red end of the spectrum, and if the Sun were hotter, it would look more blue.
And that’s just what we see with other stars. The coolest stars in the Universe are the red dwarf stars. These are stars with just a fraction of the mass of our Sun (as low as 7.5% the mass of the Sun). They don’t burn as hot in their cores, and their surface temperature is about 3,500 Kelvin. The light released from their surface looks mostly red to our eyes (although there are different colors mixed up in there too, red is the majority).
This is also the color you see with red giant stars; solar-mass stars that ran out of hydrogen fuel and bloated up many times their original size. The luminosity of the star is spread out over the much larger surface area of the red giant and so they’re cooler,
On the opposite side of the spectrum are blue stars. These are stars with many times the mass of the Sun and so their surface temperatures are much hotter. Blue stars start out above 10,000 Kelvin but they can reach 40,000 Kelvin with the largest hypergiant stars.
We have written many articles about stars on Universe Today. Here’s an article about the biggest stars in the Universe.
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The core of a star is located inside the star in a region where the temperature and pressures are sufficient to ignite nuclear fusion, converting atoms of hydrogen into helium, and releasing a tremendous amount of heat.
The size of the core depends on the mass of the star. For example, our Sun measures 1,391,000 km across and is a fairly normal star. The core of the Sun makes up about 20% of the solar radius; about 278,000 km across. It’s within this region that temperatures reach 15,000,000 Kelvin and nuclear fusion can take place. Fusion doesn’t take place in any other part of the Sun.
As you know, stars can be larger or smaller than the Sun. Larger stars will have larger, hotter cores. The largest stars have cores of 18 million Kelvin, and inside this region hydrogen is fused into helium using a different process called the CNO cycle.
The least massive star capable of sustaining fusion in its core is about 7.5% the mass of the Sun. Below this size, temperatures are too low and you end up with a brown dwarf.
Much like any living being, stars go through a natural cycle. This begins with birth, extends through a lifespan characterized by change and growth, and ends in death. Of course, we’re talking about stars here, and the way they’re born, live and die is completely different from any life form we are familiar with.
For one, the timescales are entirely different, lasting on the order of billions of years. Also, the changes they go through during their lifespan are entirely different too. And when they die, the consequences are, shall we say, much more visible? Let’s take a look at the life cycle of stars.
Molecular Clouds:
Stars start out as vast clouds of cold molecular gas. The gas cloud could be floating in a galaxy for millions of years, but then some event causes it to begin collapsing down under its own gravity. For example when galaxies collide, regions of cold gas are given the kick they need to start collapsing. It can also happen when the shockwave of a nearby supernova passes through a region.
As it collapses, the interstellar cloud breaks up into smaller and smaller pieces, and each one of these collapses inward on itself. Each of these pieces will become a star. As the cloud collapses, the gravitational energy causes it to heat up, and the conservation of momentum from all the individual particles causes it to spin.
Protostar:
As the stellar material pulls tighter and tighter together, it heats up pushing against further gravitational collapse. At this point, the object is known as a protostar. Surrounding the protostar is a circumstellar disk of additional material. Some of this continues to spiral inward, layering additional mass onto the star. The rest will remain in place and eventually form a planetary system.
Depending on the stars mass, the protostar phase of stellar evolution will be short compared to its overall life span. For those that have one Solar Mass (i.e the same mass as our Sun), it lasts about 1000,000 years.
T Tauri Star:
A T Tauri star begins when material stops falling onto the protostar, and it’s releasing a tremendous amount of energy. They are so-named because of the prototype star used to research this phase of solar evolution – T Tauri, a variable star located in the direction of the Hyades cluster, about 600 light years from Earth.
A T Tauri star may be bright, but this all comes its gravitational energy from the collapsing material. The central temperature of a T Tauri star isn’t enough to support fusion at its core. Even so, T Tauri stars can appear as bright as main sequence stars. The T Tauri phase lasts for about 100 million years, after which the star will enter the longest phase of its development – the Main Sequence phase.
Main Sequence:
Eventually, the core temperature of a star will reach the point that fusion its core can begin. This is the process that all stars go through as they convert protons of hydrogen, through several stages, into atoms of helium. This reaction is exothermic; it gives off more heat than it requires, and so the core of a main sequence star releases a tremendous amount of energy.
This energy starts out as gamma rays in the core of the star, but as it takes a long slow journey out of the star, it drops down in wavelength. All of this light pushes outward on the star, and counteracts the gravitational force pulling it inward. A star at this stage of life is held in balance – as long as its supplies of hydrogen fuel lasts.
The life cycle of a Sun-like star, from its birth on the left side of the frame to its evolution into a red giant on the right after billions of years. Credit: ESO/M. Kornmesser
And how long does it last? It depends on the mass of the star. The least massive stars, like red dwarfs with half the mass of the Sun, can sip away at their fuel for hundreds of billions and even trillions of years. Larger stars, like our Sun will typically sit in the main sequence phase for 10-15 billion years. The largest stars have the shortest lives, and can last a few billion, and even just a few million years.
Red Giant:
Over the course of its life, a star is converting hydrogen into helium at its core. This helium builds up and the hydrogen fuel runs out. When a star exhausts its fuel of hydrogen at its core, its internal nuclear reactions stop. Without this light pressure, the star begins to contract inward through gravity.
This process heats up a shell of hydrogen around the core which then ignites in fusion and causes the star to brighten up again, by a factor of 1,000-10,000. This causes the outer layers of the star to expand outward, increasing the size of the star many times. Our own Sun is expected to bloat out to a sphere that reaches all the way out to the orbit of the Earth.
The temperature and pressure at the core of the star will eventually reach the point that helium can be fused into carbon. Once a star reaches this point, it contracts down and is no longer a red giant. Stars much more massive than our Sun can continue on in this process, moving up the table of elements creating heavier and heavier atoms.
White Dwarf:
A star with the mass of our Sun doesn’t have the gravitational pressure to fuse carbon, so once it runs out of helium at its core, it’s effectively dead. The star will eject its outer layers into space, and then contract down, eventually becoming a white dwarf. This stellar remnant might start out hot, but it has no fusion reactions taking place inside it any more. It will cool down over hundreds of billions of years, eventually becoming the background temperature of the Universe.
Eta Carinae Credit: Gemini Observatory artwork by Lynette Cook
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Stars can range in temperature, from the relatively cool red dwarfs to superhot blue stars. So what is the hottest star in the Universe?
First, let’s talk a bit about temperature. The color of a star is a function of its temperature. If a star looks red, that means its surface temperature is approximately 2,500 Kelvin. Just for comparison, our Sun, which actually looks white from space, measures about 6,000 Kelvin. The hotter the star, the further up the spectrum you go. The hottest stars are the blue stars. A star appears blue once its surface temperature gets above 10,000 Kelvin, or so, a star will appear blue to our eyes.
So the hottest stars in the Universe are going to be a blue star, and we know they’re going to be massive. So the question is, how massive can stars get? One example is the star Rigel, in the constellation Orion. Rigel is thought to have 17 times the mass of the Sun, and puts out 40,000 times the luminosity of the Sun. It’s surface temperature is a mere 11,000 Kelvin. Another star in Orion, Bellatrix, has a temperature of 21,500 Kelvin. That’s even hotter.
But the hottest known stars in the Universe are the blue hypergiant stars. These are stars with more than 100 times the mass of the Sun. One of the best known examples is Eta Carinae, located about 7,500 light-years from the Sun. Eta Carinae could be as large as 180 times the radius of the Sun, and its surface temperature is 36,000-40,000 Kelvin.
Just for comparison, 40,000 Kelvin is about 72,000 degrees F.
So it’s the blue hypergiants, like Eta Carinae, which are probably the hottest stars in the Universe.
We have written many articles about stars on Universe Today. Here’s an article about how Eta Carinae is almost ready to explode as a supernova. And here’s a link to a nice photo of the nebula around Eta Carinae.
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The color of a star is defined by its temperature. The coolest stars are red, while the hottest stars are blue. And the temperature of a star is defined by its mass. The most massive stars in the Universe are the blue supergiant stars; then can have more than 20 times the mass of the Sun. Blue giant stars are very hot, with surface temperatures of 20,000-50,000 Kelvin. Just for comparison, our own Sun is only 6,000 Kelvin.
Blue supergiant star have extremely high masses, sometimes with dozens of times the mass of the Sun. They form in the largest, most active star forming regions where large amounts of mass can come together to form the biggest stars: star clusters, the arms of spiral galaxies and in irregular galaxies.
Perhaps the best known example of a blue supergiant star is Rigel, located in the constellation Orion. It has about 20 times the mass of the Sun, and puts out 60,000 times as much energy.
Blue supergiants can turn into red supergiants and vice versa. When the star is smaller and more compact, its luminosity is contained over a smaller surface area and so its temperature is much hotter; this is the blue supergiant phase. These stars can then puff up expanding to a much larger size, spreading their luminosity over a much larger area. Then they become red supergiant stars, and appear the cooler red color. Astronomers think supergiants can fluctuate back and forth between red and blue supergiant, puffing off an outer layer of material with each contraction.
Eventually a supergiant runs out of material to continue supporting fusion in its core, and will detonate as a supernova – one of the brightest explosions in the Universe.
We have written many articles about stars on Universe Today. Here’s an article that talks about the constellation Orion, including the star Rigel, and here’s a nice picture of Rigel passing behind Saturn.
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Stars come in many shapes and sizes and they come in many colors. Some of the hottest stars in the Universe are blue giant stars. You see, the color of a star is defined by its temperature; the coolest stars are red, while the hottest ones appear blue. And the temperature of a star comes from its mass. The more massive a star, the hotter it’s going to be. Stars don’t get more more massive or hot than blue giant stars.
Blue giants blaze with a surface temperature of 20,000 Kelvin or more, and are extremely luminous. Just for comparison, a star like our Sun only has a surface temperature of about 6,000 Kelvin. A blue giant star can put out 10,000 times as much energy as the Sun. Astronomers categorize blue giants as type O or B stars, belonging to the luminosity class III. The can reach an absolute magnitude of -5 or -6.
The true monsters of the Universe are blue supergiant stars, like Rigel. These can be a blue star with surface temperatures of 20,000 – 50,000 Kelvin and can be 25 times larger than the Sun. Because they’re so large, and burn so hot, they use up their fuel very quickly. A middle-sized star like our Sun might last for 12 billion years, while a blue supergiant will detonate with a few hundred million years. The smaller stars will leave neutron stars or black holes behind, while the largest will just vaporize themselves completely.
We have written many articles about stars on Universe Today. Here’s an article that looks for the biggest star in the Universe.
The constellation of Vulpecula is unusual, because it did not belong originally to those created by Ptolemy – but to the works of Johannes Hevelius. Vulpecula was included in Firmamentum Sobiescianum, a 56 page atlas created by Hevelius, which outlined seven new constellations which survived time – and many which did not. Positioned north of the ecliptic plane, it spans 268 square degrees of sky, ranking 55th in constellation size. It has 5 main stars in its asterism and 33 Bayer Flamsteed designated stars within its confines. Vulpecula is bordered by the constellations of Cygnus, Lyra, Hercules, Sagitta, Delphinus and Pegasus. It is best seen at culmination during the month of September.
Since Vulpecula is considered a “modern” constellation, there is no mythology associated with it – although the stellar pattern was very visible to the ancient Greeks and Romans. Late in 17th century, astronomer Johannes Hevelius created the constellation of Vulpecula when he was preparing his own set of star charts known as Firmamentum Sobiescianum At the time, he named it “Vulpecula Cum Ansere” which literally translated to the little fox with the goose – and he illustrated it as a fox with a goose caught in its jaws. At the time, Hevelius did not consider it to be two separate constellations – yet it was later divided into two halves – Vulpecula and Anser “The Goose”. When star charts were once again consolidated, the constellations merged again to be known under to modern named assigned to it by the International Astronomical Union as Vulpecula, yet the primary star retains a reminder be being properly named Anser.
Let’s begin our binocular tour of Vulpecula with a look at the Alpha (“a”) star – Anser. Its name literally translates to “goose”, but this class M giant star is anything but flighty. Residing 297 light years from Earth, Anser puts out 390 times more light energy than our Sun from a size about 45 times larger. It may have a dead helium core about to begin hydrogen fusion – and it may have a dead carbon-oxygen core awaiting a second brightening before turning K class. If you’ve notice another nearby star – good for you! Although it’s only a line of sight companion, 8 Vulpeculae makes checking out Anser a real treat!
Now head on to Collinder 399. This wonderful asterism is often called “Brocchi’s Cluster” or the “Coathanger” and it’s a splendid object in binoculars or a rich field telescope. This unique collection of stars was known as far back as 964 AD when astronomer Al Sufi recorded it, and it was independently rediscovered by Giovanni Hodierna in the seventeenth century. In the 1920s, D. F. Brocchi, an amateur astronomer and chart maker for the American Association of Variable Star Observers, created a map of this object for use in calibrating photometers. Thanks to its expansive size of more than 60 arc minutes, it escaped the catalogues of both Messier and Herschel. Only around a half dozen stars share the same proper motion, which may make it a cluster much like the Pleiades, but studies suggest it is merely an asterism…but one with two binary stars at its heart.
Our next target is the magnificent Messier 27 (RA 19 : 59.6 Dec +22 : 43). This incredible planetary nebula appears like a pale green apple core and is unquestionably the brightest study of its kind. Easily located around a finger-width north of Gamma Sagittae, it’s not the largest of all planetaries but is the largest of its kind on the Messier list. M27’s expanse and luminosity suggest that it is quite close to our own system. Some think it difficult to find, but there is a very simple trick. Look for the primary stars of Sagitta just to the west of bright Albireo. Make note of the distance between the two brightest and look exactly that distance north of the “tip of the arrow” and you’ll find M27.
Discovered in 1764 by Messier in a 3.5 foot focal length telescope, I discovered this 48,000 year old planetary nebula for the first time in a 4″ telescope. I was hooked immediately. Here before my eager eyes was a glowing green “apple core” which had a quality about it that I did not understand. It somehow moved… It pulsated. It appeared “living.” For many years I quested to understand the 850 light-year distant M27, but no one could answer my questions. I researched and learned it was made up of doubly ionized oxygen. I had hoped that perhaps there was a spectral reason to what I viewed year after year – but still no answer. Like all amateurs, I became the victim of “aperture fever” and I continued to study M27 with a 12″ telescope, never realizing the answer was right there – I just hadn’t powered up enough.
Several years later while studying at the Observatory, I was viewing through a friend’s identical 12″ telescope and, as chance would have it, he was using about twice the magnification that I normally used on the “Dumbbell.” Imagine my total astonishment as I realized for the very first time that the faint central star had an even fainter companion that made it seem to wink! At smaller apertures or low power, this was not revealed. Still, the eye could “see” a movement within the nebula – the central, radiating star and its companion. Do not sell the Dumbbell short. It can be seen as a small, unresolved area in common binoculars, easily picked out with larger binoculars as an irregular planetary nebula, and turns astounding with even the smallest of telescopes. In the words of Burnham, “The observer who spends a few moments in quiet contemplation of this nebula will be made aware of direct contact with cosmic things; even the radiation reaching us from the celestial depths is of a type unknown on Earth…”
Ready for a galactic star cluster for both binoculars and a small telescope? The return to Alpha and begin about two fingerwidths southeast and right on the galactic equator you’ll find NGC 6823 (RA 19 : 43.1 Dec +23 : 18). The first thing you will note is a fairly large, somewhat concentrated magnitude 7 open cluster. Resolved in larger telescopes, the viewer may note these stars are the hot, blue/white variety. For good reason. NGC 6823 only formed about 2 billion years ago. Although it is some 6000 light-years away and occupies around 50 light-years of space, it’s sharing the field with something more – a very large emission/reflection nebula, NGC 6820. In the outer reaches of the star cluster, new stars are being formed in masses of gas and dust as hot radiation is shed from the brightest of the stellar members of this pair. Fueled by emission, NGC 6820 isn’t always an easy visual object – it is faint and covers almost four times as much area as the cluster. But trace the edges very carefully, since the borders are much more illuminated than the region of the central cluster. Take the time to really observe this one! Its processes are very much like those of the “Trapezium” area in the Orion nebula. Be sure to mark your observing notes. NGC 6823 is Herschel VII.18 and NGC 6820 is also known as Marth 401!
If you’d like to try something new, return to M27 and head 2 degrees west-northwest to find NGC 6830 (RA 19 : 51.0 Dec +23 : 04). This rich 7.9 magnitude, cross-shaped open cluster is a real treat. Continue another 2 degrees in the same direction to pick up 7.1 magnitude cluster NGC 6823. Those with large telescopes should look for a faint sheen of nebulosity associated with this youthful open cluster!
Now let’s work on a pair of open star clusters for both binoculars and small telescopes, starting with NGC 6885 (RA 20 : 12.0 Dec +26 : 29). This little 6th magnitude sparkle of stars includes that bright O class star you can see visually and is also known as Caldwell 37. In binoculars you’ll see another compression nearby listed as NGC 6882 (RA 20 : 11.7 Dec +26 : 33). While it doesn’t contain a bright and splashy star like its neighbor, NGC 6882 is a nice ring shaped collection!
Our last official target in Vulpecula is superb galactic star cluster NGC 6940 (RA 20 : 34.6 Dec +28 : 18). This 6th magnitude, 31 arc minute cloud of stars is sure to please anyone with any size binoculars or telescope. The more aperture you have – the more stars you resolve! Discovered by Sir William Herschel in 1784 and logged as H VIII.23, this intermediate-aged galactic cluster will blow your mind in large aperture. Although visible in binoculars, as aperture increases the field explodes into about 100 stars in a highly compressed, rich cloud. Although not visited often, NGC 6940 is on many observing challenge lists. Use low power to get the full effect of this stunning starfield!
While NGC 6834 (RA 19 : 52.2 Dec +29 : 25) is officially listed as Cygnus, why not visit anyway? You’re in the neighborhood! It’s a very rich and compact small star cluster that’s a worthy challenge to pick out of the Milky Way star field in a telescope!
The southern circumpolar constellation of Volans was first introduced in 1589 by Petrus Plancius on a celestial globe which was later added to Johann Bayer’s atlas – Uranometria – in 1603. Volans spans 141 square degrees of sky, ranking 76th in size. It has 6 mains stars in its asterism and 12 Bayer Flamsteed designated stars within its confines. Volans is bordered by the constellation of Carina, Pictor, Dorado, Mensa and Chamaeleon and is best seen at culmination during the month of March.
Since Volans is considered a “new” constellation, it has no mythology associated with it – only what the constellation is meant to represent. The constellation of Volans was originally created by Petrus Plancius from the stellar observations of Dutch sea navigators Pieter Dirkszoon Keyser and Frederick de Houtman when exploring the southern hemisphere. Volans’ stellar patterns became known when it appeared on a celestial globe in 1597 and was considered a constellation when it was added to Johann Bayer’s Uranometria catalog in 1603 and it was then called Piscis Volans – the “Flying Fish”. When it was later adopted as a permanent constellation by the International Astronomical Union, the name was simplified and shortened to just Volans.
Let’s begin our binocular tour of Volans with its Alpha star – the “a” symbol on our chart. Alpha Volantis is located approximately 124 light years from Earth and it is a white class A (A2.5) subgiant star. While it is not anything particularly special, it is about twice the size of our Sun and shines about 30 times brighter. Somehow it got the Alpha designation, even though Beta (the “B” symbol) is physically brighter and 16 light years closer! Want a real trip? Then have a look at Delta – the “8” symbol. Even though it appears almost as bright as the rest of the stars, Delta is an F-type bright giant star that’s 660 light years from our solar system!
Now, get out your telescope for Epsilon Volantis – the backwards “3”. Epsilon is a triple star system! Located approximately 642 light years from Earth, the primary component, Epsilon Volantis A, is a spectroscopic binary star all of its own. It’s a blue-white B-type subgiant star with a companion that orbits so close we can only see it spectroscopically and know that it causes changes about every two weeks. But take a close look and you’ll discover a third, 8th magnitude star there, too. Epsilon Volantis B is 6.05 arcseconds away and an easy capture for a small telescope and large binoculars.
How about Gamma Volantis? It’s the “Y” symbol. This wide double star was just meant for binoculars! The two members are brighter, western Gamma-1 Volantis (magnitude 5.67) and dimmer, eastern Gamma-2 (magnitude 3.78). Set apart by 14.1 seconds of arc, you won’t have any trouble cutting these two stars apart and their color contrast make them a real winner in a telescope. Gamma-2 is a standard orange class K (K0) giant star and Gamma-1 is a a white class F (F2) dwarf star. While you might think this is an optical double star, it isn’t. The pair is physically bound to each other and both stars are about 142 light years away.
For those wishing a challenge, take on about the only deep sky study to be found in Volans – NGC 2442 (RA 7 : 36.4 Dec -69 : 32). At 11th magnitude and 6 arc minutes in size, this low surface brightness barred spiral galaxy is a nice study for a large telescope. Located about 50 million light years away from our Milky Way Galaxy, NGC 2442 was first was discovered by Sir John Herschel and contains a very unusual dark cloud of gas – one devoid of any stars. How did this come to be? Astronomers believe the cloud was torn loose from NGC 2442 by a companion during a galaxy interaction. Why not? After all, NGC is surrounded! If you have large aperture, you’ll see PGC 21457, PGC 21406, NGC 2434, PGC 21212, PGC 21323, PGC 21369 and PGC 21426 are nearby, too. Several of these satellite galaxies are physically related to NGC 2442. Be sure to look for two spiral arms extending from a pronounced central bar, giving the whole galaxy a hook-shaped appearance.
You asked for more? You got it. This time our dimensional visualization is going to take us 9500 light years away from where you’re sitting now and deep into the Perseus spiral arm of the Milky Way Galaxy. Buckle your seat belt and relax your eyes, because we’re heading into two versions of a 132 light year expanse known as NGC 281 and the central core called IC 1590…
Just like last time, this dual image requires a little bit of a challenge on your part to create a 3D effect. Thanks to the wizardry of Jukka Metsavainio, we’ve gone even one better. There’s two! The first version you see on this page are for those of you who have success relaxing your eyes and being a certain distance from the screen to get the images to merge. The one below is for those of you who have better luck crossing your eyes and catching dimension in the center image. Are you ready for your journey? Then have a look and let’s learn…
NGC281/IC1590 Hubble Heritage Cross Vision - Jukka Metsavainio
The whole gigantic region of nebulosity is known as NGC 281 and most commonly referred to as the “Pac Man Nebula”. Visible to small telescopes and located in the constellation of Cassiopeia (RA 00:42:59.35 Dec +56:37.18.8), this cloud of high density hydrogen gas is being ionized by an incredible output of ultraviolet radiation from the hot, neophyte stars which coalesced there. Deep in the center of this HII region is a open area called IC 1590 – home to a young galactic star cluster – and several dark patches known as “Bok Globules”.
If that sounds like something you might expel when you have a cold, you’re right. They are cold… Cold pockets of dense dust, molecular hydrogen and gas. Bok globules are the brain child of astronomer Dr. Bart Jan Bok – who, among other things, loved to study the paranormal. When Bok proposed their existence in the 1940’s, he knew what was going on. These dark regions were acting like interstellar cocoons – protecting their inner stars from being stripped by the radioactive stellar winds of nearby companions and blocking visible light. When stellar metamorphosis had occurred, the new star then begins to send out its own winds and radiation to evaporate the globule – but this isn’t always the case. Sometimes the cocoon gets destroyed before the life inside ignites.
In our image you will see bright blue stars, members of the young open cluster IC 1590, near the globules. Meanwhile, the cluster’s partially revealed core in the upper right hand corner is filled with a tight grouping of extremely hot, massive stars emitting visible and ultraviolet light, causing those incredible pink clouds. When these star forming dust clouds were first imaged by Hubble, we thought we knew a lot about them. But what have we learned since?
According to research done by T.H. Henning (et al): “The exciting star HD 5005 of the optical nebulosity is a Trapezium system… and emission shows that the molecular cloud NGC 281 A consists of two cloud fragments. The western fragment is more compact and massive than the eastern fragment and contains an NH3 core. This core is associated with the IRAS source 00494+5617, an H2O maser, and 1.3 millimeter dust continuum radiation. Both cloud fragments contain altogether 22 IRAS point sources which mostly share the properties of young stellar objects. The maxima of the 60 and 100 micrometers HIRES maps correspond to the maxima of the (12)CO (3 to 2) emission. The NGC 281 A region shares many properties with the Orion Trapezium-BN/KL region the main differences being a larger separation between the cluster centroid and the new site of star formation as well as a lower mass and luminosity of the molecular cloud and the infrared cluster.”
Great! It’s confirmed! It’s a star forming region, very much like what we can observe when we see M42. But, maybe… Maybe there’s just a little bit more to it than that? Hubble observations shows the jagged structure of the dust clouds as if they are being stripped apart from the outside. What could have caused that? Only the radiation from the nearby stars? Hmmm…. Not everyone seems to think so.
A 2007 study done by Mayumi Sato (et al) states: “Our new results provide the most direct evidence that the gas in the NGC 281 region was blown out from the Galactic plane, most likely in a superbubble driven by multiple or sequential supernova explosions in the Galactic plane.” Supernova? Yeah, you bet. And someone else thinks so, too…
Says S.T. Megeath (et al): “We suggest that the ring has formed in a superbubble blowout driven by OB stars in the plane of the Galaxy. Within the cloud complex, combined optical, NIR, mm and cm data detailing the interaction of a young O star with neighboring molecular cores, provide evidence of triggered star formation inside the cloud complex on a few parsec scale. These data suggest that two modes of triggered star formation are operating in the NGC 281 complex – the initial supernovae triggered formation of the entire complex and, after the first generation of O stars formed, the subsequent triggering of star formation by photoevaporation-driven molecular core compression.”
You’ve got it. This type of research suggests the cores were created within the molecular cloud. When they were exposed to direct UV radiation, the low density gas was stripped. This increase in pressure then caused a rippling shockwave which triggered star formation – first in the compressed regions and then in the HII areas. Says Megeath, “The total kinetic energy of the ring requires the energy of multiple supernovae. Both the high Galactic latitude and large expansion velocity may be explained if the NGC 281 complex originated in the blowout of an expanding superbubble. The loop of HI seen extending from the Galactic plane may trace the edge of a superbubble powered by supernovae near the Galactic plane. The expansion of a superbubble into the increasingly rarefied Galactic atmosphere can lead to a runaway expansion of the shell and the blowout of the bubble into the Galactic atmosphere. NGC 281 could have formed in the gas swept up and compressed in a blowout. Hence, NGC 281 maybe an example of the supernovae-driven formation of molecular clouds (and consequently, supernovae-triggered star formation).”
What incredible region! Hope you enjoyed your journey… And be sure to tip your hat to Bart Jan Bok who told the IAU (when they named Asteroid Bok for him in 1983) “Thanks for a little plot of land that I can retire to and live on.”
Our many, many thanks to Jukka Metsavainio of Northern Galactic for creating this unique image for Universe Today Readers! We look forward to more…
For those of you who like observing curiosities, it’s time to take a look at R Coronae Borealis. As you may have guessed from the single letter designation, R is a variable star, but it’s not just any old variable – it’s the prototype of its class. What exactly is an R CorBor star, what does it do and why is taking the time to check it out now so important? Then step inside and find out…
R Coronae Borealis stars (RCB) type stars are one of the oldest known classes of variable star. In just a period of a few weeks, they can drop in brightness by factors of thousands and what they do is totally unpredictable. Within months, they recover again to their maximum brightness… But why? While astronomers don’t fully understand the evolutionary origin and the physical mechanism behind what drives R CorBor types, they do know the stars pulsate – generating a sort of sooty dust cloud just above the surface. Like an old-fashioned oil lamp with its wick turned up too high, when R Cororonae Borealis stars burn their fuel, they smoke up their exterior – just like the lamp smokes its glass chimney and dims the light. What remains on the glass? That’s right. Carbon. And the surfaces of RCB stars are unusually poor in hydrogen, and rich in carbon and nitrogen. Chances are very good that R CorBor stars are actually the remnants of more fully evolved stars.
“R Coronae Borealis, the prototype of the R CrB class, is apparently at or near historic minimum; a number of observers have put this star below m(vis)=14.0 since early November 2008, and both visual and instrumental measures are now indicating R CrB is near or below V=14.5. R CrB began its current fading episode around JD 2454288 (2007 July 6 +/- 1 day), and faded from m(vis) ~ 6.0 to below m(vis) ~ 12.0 by JD 2454325 (2007 August 12). The star has continued to fade for the past 17 months. Current visual observations by a number of AAVSO visual observers estimate the star to be around m(vis) 14.3-14.5, and V-band CCD observations suggest the star may be at or near V=15.0. BAAVSS observer J. Toone also visually estimated the star is at m(vis) ~ 14.9 (via baavss-alert). Both visual estimates and instrumental photometry of R CrB are strongly encouraged at this time.
The duration of the current episode and its depth are similar to that observed during the previous extreme fading episode which began circa JD 2438200 (June 1963) and continued with only one brief interruption until circa JD 2439100 (December 1965). During the 1963-1965 event, a few AAVSO observers estimated that R CrB reached m(vis) around 14.9-15.0, although the average visual estimate remained around 14.2-14.3 at minimum. The current episode seems to have reached the same depth; there is no way to tell whether the fade will continue, although the light curve has been flat or trending weakly downward for several months. As J. Toone pointed out, the current magnitude is very close to if not fainter than the historic minimum for this star.”
Of course, nearing magnitude 15 isn’t within the territory of binoculars or small telescopes – but it is within the grasp of many of our amateur astronomer UT readers with larger equipment, clear skies and the willingness to seize the opportunity to record this historic astronomical event. (I dislike the term “amateur” – it only means you don’t get paid for it, folks… Not that you’re any less serious or talented!) One such astronomer is Dr. Joseph Brimacombe, who took up the gauntlet immediately. Although Joe hails from Australia where R Coronae Borealis isn’t visible, today’s astronomy world is far different than it used to be. Thanks to the magic of the Internet, he immediately set about the task of capturing the star on January 30, 2009 via a robotic telescope located in New Mexico and shared his results with us.
R Coronae Borealis True Color - J. Brimacombe
R CrB Chart - AAVSOFor those wishing to also participate in the quest for R Coronae Borealis, you’ll find it located at the following (J2000) coordinates: RA: 15 48 34.40 , Dec: +28 09 24.0 and you may use this field chart provided by the AAVSO to further refine your observations. If R is too faint for your equipment now? Don’t worry. It’s a variable star and within a few months it will return to its easily spotted magnitude 6 self – and a very delightful red star in binoculars. As always, be kind to science and contribute! Please promptly submit all observations to the AAVSO using the name “R CRB” and take part in astronomy history!
My many thanks to Joe Brimacombe of Northern Galactic for his superb talents and to the AAVSO for keeping us on alert!
