An artist's illustration of a light-sail powered by a radio beam (red) generated on the surface of a planet. The leakage from such beams as they sweep across the sky would appear as Fast Radio Bursts (FRBs), similar to the new population of sources that was discovered recently at cosmological distances.
Credit: M. Weiss/CfA
The number of confirmed extra-solar planets has increased by leaps and bounds in recent years. With every new discovery, the question of when we might be able to explore these planets directly naturally arises. There have been several suggestions so far, ranging from laser-sail driven nanocraft that would travel to Alpha Centauri in just 20 years (Breakthrough Starshot) to slower-moving microcraft equipped with a gene laboratories (The Genesis Project).
But when it comes to braking these craft so that they can slow down and study distant stars and orbit planets, things become a bit more complicated. According to a recent study by the very man who conceived of The Genesis Project – Professor Claudius Gros of the Institute for Theoretical Physics Goethe University Frankfurt – special sails that rely on superconductors to generate magnetic fields could be used for just this purpose.
Starshot and Genesis are similar in that both concepts seek to leverage recent advancements in miniaturization. Today, engineers are able to create sensors, thrusters and cameras that are capable of carrying out computations and other functions, but are a fraction of the size of older instruments. And when it comes to propulsion, there are many options, ranging from conventional rockets and ion drives to laser-driven light sails.
Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org
Slowing an interstellar mission down, however, has remained a more significant challenge because such a craft cannot be fitted with braking thrusters and fuel without increasing its weight. To address this, Professor Gros suggests using magnetic sails, which would present numerous advantages over other available methods. As Prof. Gros explained to Universe Today via email:
“Classically, you would equip the spacecraft with rocket engines. Normal rocket engines, as we are using them for launching satellites, can change the velocity only by 5-15 km/s. And even that only when using several stages. That is not enough to slow down a craft flying at 1000 km/s (0.3% c) or 100000 km/s (c/3). Fusion or antimatter drives would help a bit, but not substantially.”
The sail he envisions would consist of a massive superconducting loop that measures about 50 kilometers in diameter, which would create a magnetic field once a lossless current was induced. Once activated, the ionized hydrogen in the interstellar medium would be reflected off the sail’s magnetic field. This would have the effect of transferring the spacecraft’s momentum to the interstellar gas, gradually slowing it down.
According to Gros’ calculations, this would work for slow-travelling sails despite the extremely low particle density of interstellar space, which works out to 0.005 to 0.1 particles per cubic centimeter. “A magnetic sail trades energy consumption with time,” said Gros.”If you turn off the engine of your car and let it roll idle, it will slow down due to friction (air, tires). The magnetic sail does the same, where the friction comes from the interstellar gas.”
Artist concept of lightsail craft approaching the potentially habitable exoplanet Proxima b. Credit: PHL @ UPR Arecibo
One of the advantages of this method is the fact that can be built using existing technology. The key technology behind the magnetic sail is a Biot Savart loop which, when paired with the same kind of superconducting coils used in high-energy physics, would create a powerful magnetic field. Using such a sail, even heavier spacecraft – those that weight up to 1,500 kilograms (1.5 metric tonnes; 3,307 lbs) – could be decelerated from an interstellar voyage.
The one big drawback is the time such a mission would take. Based on Gros’ own calculations, a high speed transit to Proxima Centauri that relied on magnetic momentum braking would require a ship that weighed about 1 million kg (1000 metric tonnes; 1102 tons). However, an interstellar mission involving a 1.5 metric tonne ship would be able to reach TRAPPIST-1 in about 12,000 years. As Gros concludes:
“It takes a long time (because the very low density of the interstellar media). That is bad if you want to see a return (scientific data, exciting pictures) in your lifetime. Magnetic sails work, but only when you are happy to take the (very) long perspective.”
In other words, such a system would not work for a nanocraft like that envisioned by Breakthrough Starshot. As Starshot’s own Dr. Abraham Loeb explained, the main goal of the project is to achieve the dream of interstellar travel within a generation of the ship’s departure. In addition to being the Frank B. Baird Jr. Professor of Science at Harvard University, Dr. Loeb is also the Chair of the Breakthrough Starshot Advisory Committee.
A phased laser array, perhaps in the high desert of Chile, propels sails on their journey. Credit: Breakthrough Initiatives
As he explained to Universe Today via email:
“[Gros] concludes that breaking on the interstellar gas is feasible only at low speeds (less than a fraction of a percent of the speed of light) and even then one needs a sail that is tens of miles wide, weighting tons. The problem is that with such a low speed, the journey to the nearest stars will take over a thousand years.
“The Breakthrough Starshot initiative aims to launch a spacecraft at a fifth of the speed of light so that it will reach the nearest stars within a human lifetime. It is difficult to get people excited about a journey whose completion will not be witnessed by them. But there is a caveat. If the longevity of people could be extended to millennia by genetic engineering, then designs of the type considered by Gros would certainly be more appealing.”
But for missions like The Genesis Project, which Gros originally proposed in 2016, time is not a factor. Such a probe, which would carry single-celled organisms – either encoded in a gene factory or stored as cryogenically-frozen spores – a could take thousands of years to reach a neighboring star system. Once there, it would begin seeding planets that had been identified as “transiently habitable” with single-celled organisms.
For such a mission, travel time is not the all-important factor. What matters is the ability to slow down and establish orbit around a planet. That way, the spacecraft would be able to seed these nearby worlds with terrestrial organisms, which could have the effect of slowly terraforming it in advance of human explorers or settlers.
Given how long it would take for humans to reach even the nearest extra-solar planets, a mission that last a few hundred or a few thousand years is no big deal. In the end, which method we choose to conduct interstellar mission will come down to how much time we’re willing to invest. For the sake of exploration, expedience is the key factor, which means lightweight craft and incredibly high speeds.
But where long-term goals – such as seeding other worlds with life and even terraforming them for human settlement – are concerned, the slow and steady approach is best. One thing is for sure: when these types of missions move from the concept stage to realization, it sure will be exciting to witness!
Artist’s impression of the first interstellar asteroid/comet, "Oumuamua". This unique object was discovered on 19 October 2017 by the Pan-STARRS 1 telescope in Hawaii. Credit: ESO/M. Kornmesser
On October 19th, 2017, the Panoramic Survey Telescope and Rapid Response System-1 (Pan-STARRS-1) telescope in Hawaii picked up the first interstellar asteroid, named 1I/2017 U1 (aka. `Oumuamua). After originally being mistaken for a comet, observations performed by the European Southern Observatory (ESO) and other astronomers indicated that it was actually an asteroid that measures about 400 meters (1312 ft) long.
Thanks to data obtained by the ESO’s Very Large Telescope (VLT) at the Paranal Observatory in Chile, the brightness, color and orbit of this asteroid have been precisely determined. And according to a new study led by Dr. Karen Meech of the Institute for Astronomy in Hawaii, `Oumuamua is unlike any other asteroid we’ve ever seen, in that its shape is highly elongated (i.e. very long and thin).
The VLT was intrinsic to the combined effort to characterize the fast-moving asteroid rapidly, as it needed to be observed before it passed back into interstellar space again. Based on initial calculations of `Oumuamua’s orbit, astronomers had determined that it had already passed the closest point in its orbit to the Sun in September of 2017. Together with other large telescopes, the VLT captured images of the asteroid using its FORS instrument.
What these revealed was that `Oumuamua varies dramatically in terms of brightness (by a factor of ten) as it spins on its axis every 7.3 hours. As Dr. Meech explained in an ESO press release, this was both surprising and highly significant:
“This unusually large variation in brightness means that the object is highly elongated: about ten times as long as it is wide, with a complex, convoluted shape. We also found that it has a dark red colour, similar to objects in the outer Solar System, and confirmed that it is completely inert, without the faintest hint of dust around it.”
These observations also allowed Dr. Meech and her team to constrain Oumuamua’s composition and basic properties. Essentially, the asteroid is now believed to be a dense and rocky asteroid with a high metal content and little in the way of water ice. It’s dark and reddened surface is also an indication of tholins, which are the result of organic molecules (like methane) being irradiated by cosmic rays for millions of years.
Unlike other asteroids that have been studied in Near-Earth space and the Solar System at large, `Oumuamua is unique in that it is not bound by the Sun’s gravity. In addition to originating outside of our Solar System, its hyperbolic orbit – which has an eccentricity of 1.2 – means that it will head back out into interstellar space after its brief encounter with our Solar System.
Based on preliminary calculations of its orbit, astronomers have deduced that it came from the general direction of Vega, the brightest star in the northern constellation of Lyra. Traveling at a whopping speed of 95,000 km/hour (59,000 mph), `Oumuamua would have left the Vega system about 300,000 years ago. However, it is also possible that the asteroid may have originated somewhere else entirely, wandering the Milky Way for millions of years.
Astronomers estimate that interstellar asteroids like `Oumuamua pass through the inner Solar System at a rate of about once a year. But until now, they have been too faint and difficult to detect in visible light, and have therefore gone unnoticed. It is only recently that survey telescopes like Pan-STARRS have been powerful enough to have a chance at detecting them.
Hence what makes this discovery so significant in the first place. As the first asteroid of its kind to be detected, further improvements in our instruments will it make it easier to spot the others that are sure to be on the way. And as Olivier Hainaut – a researcher with the ESO and a co-author on the study – indicated, there’s plenty more to be learned from `Oumuamua as well:
“We are continuing to observe this unique object, and we hope to more accurately pin down where it came from and where it is going next on its tour of the galaxy,” he said. “And now that we have found the first interstellar rock, we are getting ready for the next ones!”
And be sure to enjoy this ESOcast video about `Oumuamua, courtesy of the ESO:
The Messier 60 Elliptical Galaxy. Credits: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration
Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the elliptical galaxy known as Messier 60.
In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects he initially mistook for comets. In time, he would come to compile a list of approximately 100 of these objects, hoping to prevent other astronomers from making the same mistake. This list – known as the Messier Catalog – would go on to become one of the most influential catalogs of Deep Sky Objects.
One of the notable objects in this catalog is Messier 60, an elliptical galaxy located approximately 55 million light-years away in the Virgo constellation. Measuring some 60,000 light years across, this galaxy is only about half as large as the Milky Way. However, it still manages to pack in an estimated 400 billion stars which, depending on which estimates you go by, is between four times and the same amount as our own.
What You Are Looking At:
Located about 60 million light years away and spanning about 120 million light years of space, M60 is the third brightest elliptical in the Virgo group and and is the dominant member of a subcluster of four galaxies, which is the closest-known isolated compact group of galaxies. In larger telescopes, you’ll see another nearby galaxy – NGC 4647 – which might first be taken for a interactor, but may very well lay at a different distance since there is no tidal evidence so far found.
Messier 60. Credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona
As L.M. Young (et al.) explained in their 2006 study:
“We present matched-resolution maps of H I and CO emission in the Virgo Cluster spiral NGC 4647. The galaxy shows a mild kinematic disturbance in which one side of the rotation curve flattens but the other side continues to rise. This kinematic asymmetry is coupled with a dramatic asymmetry in the molecular gas distribution but not in the atomic gas. An analysis of the gas column densities and the interstellar pressure suggests that the H2/H I surface density ratio on the east side of the galaxy is 3 times higher than expected from the hydrostatic pressure contributed by the mass of the stellar disk. We discuss the probable effects of ram pressure, gravitational interactions, and asymmetric potentials on the interstellar medium and suggest it is likely that a m = 1 perturbation in the gravitational potential could be responsible for all of the galaxy’s features. Kinematic disturbances of the type seen here are common, but the curious thing about NGC 4647 is that the molecular distribution appears more disturbed than the H I distribution. Thus, it is the combination of the two gas phases that provides such interesting insight into the galaxy’s history and into models of the interstellar medium.”
Although a search for young optical pulsars turned up negative after a recent supernova event, astronomer’s did discover something rather exciting… a supermassive black hole! As Philip J. Humphrey (et al) indicated in their 2008 study:
“We present a Chandra study of the hot ISM in the giant elliptical galaxy NGC4649. In common with other group-centred ellipticals, its temperature profile rises with radius in the outer parts of the galaxy. Under the assumption of hydrostatic equilibrium, we demonstrate that the central temperature spike arises due to the gravitational influence of a quiescent central super-massive black hole. This is the first direct measurement of MBH based on studies of hydrostatic X-ray emitting gas, which are sensitive to the most massive black holes, and is a crucial validation of both mass-determination techniques. This agreement clearly demonstrates the gas must be close to hydrostatic, even in the very centre of the galaxy, which is consistent with the lack of morphological disturbances in the X-ray image. NGC4649 is now one of only a handful of galaxies for which MBH has been measured by more than one method.”
History of Observation:
Both M59 and neighboring M60 were discovered on April 11, 1779 by Johann Gottfried Koehler who wrote: “Two very small nebulae, hardly visible in a 3-foot telescope: The one above the other.” It was independently found one day later by Barnabus Oriani, who missed M59, and four days later, on April 15, 1779, by Charles Messier, who also found nearby M58. In his notes Messier writes:
“Nebula in Virgo, a little more distinct than the two preceding [M58 and M59], on the same parallel as Epsilon [Virginis], which has served for its [position] determination. M. Messier reported it on the Chart of the Comet of 1779. He discovered these three nebulae while observing this Comet which passed very close to them. The latter passed so near on April 13 and 14 that the one and the other were both in the same field of the refractor, and he could not see it; it was not until the 15th, while looking for the Comet, that he perceived the nebula. These three nebulae don’t appear to contain any star.”
William Herschel would later perceive it as a double nebula and so would son John, calling it “A very fine and curious object.” However, it was Admiral Smyth who must have finally had a clear viewing night a took a look at what was all around!
“The hypothesis of Sir John Herschel, upon double nebulae, is new and attracting. They may be stellar systems each revolving round the other: each a universe, according to ancient notions. But as these revolutionary principles of those vast and distant firmamental clusters connot for ages yet be established, the mind lingers in admiration, rather than comprehension of such mysterious collocations. Meantime our clear duty is, so industriously to collect facts, that much of what is now unintelligible, may become plain to our successors, and a portion of the grand mechanism now beyond our conception, revealed. ‘How much,’ exclaims Sir John Herschel, ‘how much is escaping us! How unworthy is it in them who call themselves philosophers, to let these great phenomena of nature, these slow but majestic manifestations of power and the glory of God, glide unnoticed, and drop out of memory beyond the reach of recovery, because we will not take the pains to note them in their unobstrusive and furtive passage, because we see them in their every-day dress, and mark no sudden change, and conclude that all is dead, because we will not look for signs of life; and that all is uninteresting, because we are not impressed and dazzled.’ ….. ‘To say, indeed, that every individual star in the Milky Way, to the amount of eight or ten millions, is to have its place determined, and its motion watched, would be extravagant; but at least let samples be taken, at least let monographs of parts be made with powerful telescopes and refined instruments, that we may know what is going on in that abyss of stars, where at present imagination wanders without a guide!” Such is the enthusiastic call of one, whose father cleared the road by which we are introduced to the grandest phenomena of the stellar universe.'”
Locating Messier 58:
M59 is a telescopic only object and requires patience to find. Because the Virgo Galaxy field contains so many galaxies which can easily be mis-identified, it is sometimes easier to “hop” from one galaxy to the next! In this case, we need to start by locating bright Vindemiatrix (Epsilon Virginis) almost due east of Denebola.
Let’s starhop four and a half degrees west and a shade north of Epsilon to locate one of the largest elliptical galaxies presently known – M60. At a little brighter than magnitude 9, this galaxy could be spotted with binoculars, but stick with your telescope. In the same low power field (depending on aperture size) you may also note faint NGC 4647 which only appears to be interacting with M60.
In a smaller telescope, do not expect to see much. What will appear at low power is a tiny egg-shaped patch of contrast change with a brighter center. As aperture increases, a sharper nucleus will begin to appear as you move into the 4-6″ size range at dark sky locations, but elliptical galaxies do not show details. As with all galaxies, dark skies are a must!
Enjoy your own observations of the Virgo galaxy fields….
The location of Messier 60 in the Virgo constellation. Credit: IAU
And here are the quick facts on this Messier Object to help you get started:
Object Name: Messier 60 Alternative Designations: M60, NGC 4649 Object Type: E2 Galaxy Constellation: Virgo Right Ascension: 12 : 43.7 (h:m) Declination: +11 : 33 (deg:m) Distance: 60000 (kly) Visual Brightness: 8.8 (mag) Apparent Dimension: 7×6 (arc min)
This illustration shows the super-Earth exoplanet 55 Cancri e with its star. What would our Solar System be like if it was home to a super-Earth like this one? Credit: NASA/JPL
The super-Earth 55 Cancri e (aka. Janssen) is somewhat famous, as exoplanet go. Originally discovered in 2004, this world was one of the few whose discovery predated the Kepler mission. By 2016, it was also the first exoplanet to have its atmosphere successfully characterized. Over the years, several studies have been conducted on this planet that revealed some rather interesting things about its composition and structure.
For example, scientists believed at one time that 55 Cancri e was a “diamond planet“, whereas more recent work based on data from the Spitzer Space Telescope concluded that its surface was covered in lakes of hot lava. However, a new study conducted by scientists from NASA’s Jet Propulsion Laboratory indicates that despite its intense surface heat, 55 Cancri e has an atmosphere that is comparable to Earth’s, only much hotter!
The study, titled “A Case for an Atmosphere on Super-Earth 55 Cancri e“, recently appeared in The Astrophysical Journal. Led by Isabel Angelo (a physics major with UC Berkeley) with the assistance of Renyu Hu – a astronomer and Hubble Fellow with JPL and Caltech – the pair conducted a more detailed analysis of the Spitzer data to determine the likelihood and composition of an atmosphere around 55 Cancri e.
Artist’s impression of the super-Earth 55 Cancri e in front of its parent star. Credit: ESA/NASA
Previous studies of the planet noted that this super-Earth (which is twice as large as our planet), orbits very close to its star. As a result, it has a very short orbital period of about 17 hours and 40 minutes and is tidally locked (with one side constantly facing towards the star). Between June and July of 2013, Spitzer observed 55 Cancri e and obtained temperature data using its special infrared camera.
Initially, the temperature data was seen as being an indication that large deposits of lava existed on the surface. However, after re-analyzing this data and combining it with a new model previously develop by Hu, the team began to doubt this explanation. According to their findings, the planet must have a thick atmosphere, since lava lakes exposed to space would create hots spots of high temperatures.
What’s more, they also noted that the temperature differences between the day and night side were not as significant as previously thought – another indication of an atmosphere. By comparing changes in the planet’s brightness to energy flow models, the team concluded that an atmosphere with volatile materials was the best explanation for the high temperatures. As Renyu Hu explained in a recent NASA press statement:
“If there is lava on this planet, it would need to cover the entire surface. But the lava would be hidden from our view by the thick atmosphere. Scientists have been debating whether this planet has an atmosphere like Earth and Venus, or just a rocky core and no atmosphere, like Mercury. The case for an atmosphere is now stronger than ever.”
Using Hu’s improved model of how heat would flow throughout the planet and radiate back into space, they found that temperatures on the day side would average about 2573 K (2,300 °C; 4,200 °F). Meanwhile, temperatures on the “cold” side would average about 1573 – 1673 K (1,300 – 1,400 °C; 2,400 – to 2,600 °F). If the planet had no atmosphere, the differences in temperature would be far more extreme.
As for the composition of this atmosphere, Angelo and Hu revealed that it is likely similar to Earth’s – containing nitrogen, water and even oxygen. While much hotter, the atmospheric density also appeared to be similar to that of Earth, which suggests the planet is most likely rocky (aka. terrestrial) in composition. On the downside, the temperatures are far too hot for the surface to maintain liquid water, which makes habitability a non-starter.
Ultimately, this study was made possible thanks to Hu’s development of a method that makes the study exoplanet atmospheres and surfaces easier. Angelo, who led the study, worked on it as part of her internship with JPL and adapted Hu’s model to 55 Cancri e. Previously, this model had only been applied to mass gas giants that orbit close to their respective suns (aka. “Hot Jupiters”).
Naturally, there are unresolved questions that this study helps to raise, such as how 55 Cancri e has avoided losing its atmosphere to space. Given how close the planet orbits to its star, and the fact that it’s tidally locked, it would be subject to intense amounts of radiation. Further studies may help to reveal how this is the case, and will help advance our understanding of large, rocky planets.
The application of this model to a Super-Earth is the perfect example of how exoplanet research has been evolving in recent years. Initially, scientists were restricted to studying gas giants that orbit close to their stars (as well as their respective atmospheres) since these are the easiest to spot and characterize. But thanks to improvements in instrumentation and methods, the range of planets we are capable of studying is growing.
This map shows Delphinus and Sagitta, both of which are near the bright star Altair at the bottom of the Summer Triangle. You can star hop from the Delphinus "diamond" to the star 29 Vulpecula and from there to the nova or center your binoculars between Eta Sagittae and 29 Vul. Stellarium
Welcome to another edition of Constellation Friday! Today, in honor of the late and great Tammy Plotner, we take a look at “the Dolphin” – the Delphinus constellation. Enjoy!
In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of all the then-known 48 constellations. This treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come, effectively becoming astrological and astronomical canon until the early Modern Age.
One of these is the northern constellation of Delphinus, which translates to “the Dolphin” in Latin. This constellation is located close to the celestial equator and is bordered by Vulpecula, Sagitta, Aquila, Aquarius, Equuleus, and Pegasus. Today, Delphinus is one of the 88 modern constellations recognized by the International Astronomical Union (IAU).
Name and Meaning:
According to classical Greek mythology, Delphinus represented a Dolphin. Once you “see” Delphinus, it is not hard to picture a small dolphin leaping from the waters of the Milky Way. According to Greek legend, Poseidon wanted to marry Amphitrite, a Nereid – or sea nymph. However, she hid from him. Poseidon sent out searchers, one of whom was named Delphinus.
Delphinus is depicted on the left of this card from Urania’s Mirror (1825). Credit: Library of Congress/Sidney Hall
Can you guess who found Amphitrite and talked her into marrying? You got it. In gratitude, Poseidon placed Delphinus’ image among the stars. Not a bad call since the Nereids were known to live in the silvery caves of the deep and the silvery Milky Way is so nearby!
In the other version of the myth, it was Apollo – the god of poetry and music – who placed the dolphin among the constellations for saving the life of Arion, a famed poet and musician. Arion was born on the island of Lesbos and his skill with the lyre made him famous in the 7th century BC.
History of Observation:
The small constellation of Delphinus was one of the original 48 constellations complied by Ptolemy in the Almagest in the 2nd century CE. In Chinese astronomy, the stars of Delphinus are located within the Black Tortoise of the North (Bei Fang Xuán Wu) – one of the four symbols associated with the Chinese constellations. Delphinus was also recognized by some cultures in Polynesia – particularly the people of Pukapuka and the Tuamotu Islands.
Notable Objects:
Located very near the celestial equator, this kite-like asterism is comprised of 5 main stars and contains 19 stellar members with Bayer/Flamsteed designations. It’s primary star, Alpha Delphini (aka. Sualocin), is a multiple star system located 240 light years from Earth which consists of an aging subgiant of 2.82 Solar masses, and a companion that cannot be discerned because it is too close to its primary and too faint.
Next is Beta Delphini (aka. Rotanev), a pair of stars located approximately 101 light years from Earth. This system is comprised of a F5 III class blue-white giant and a F5 IV blue-white subgiant. If you don’t think astronomers have a sense of humor, then you better think again! Sualocin and Rotanev were both named by Italian astronomer Nicolaus Cacciatore, who simply spelled the Latin form of name (Nicolaus Venator) backwards as a practical joke!
Globular cluster NGC 6934. Credit: Hubble Space Telescope
Epsilon Delphini (aka. Deneb Dulfim) is a spectral class B6 III blue-white giant star located about 358 light years from Earth. It’s traditional name comes from the Arabic ðanab ad-dulf?n, meaning “tail of the Dolphin”. Then there’s Rho Aquilae (aka. Tso Ke), a main sequence A2V white dwarf that is 154 light years distant. The star’s traditional name means “the left flag” in Mandarin, which refers to an asterism formed by Rho Aquilae and several stars in the constellation Sagittarius.
Delphinus is also home to numerous Deep Sky Objects, like the relatively large globular cluster NGC 6934. Located near Epsilon Delphini, this cluster is roughly 50,000 light years from Earth and was discovered by William Herschel on September 24th, 1785. Another globular cluster, known as NGC 7006, can be found near Gamma Delphini, roughly 137,000 light-years from Earth.
Delphinus is also home to the small planetary nebulas of NGC 6891 and NGC 6905 (the “Blue Flash Nebula”). Whereas the former is located near Rho Aquilae about 7,200 light years from Earth, the more notable Blue Flash Nebula (named because of its blue coloring) is located between 5,545 and 7,500 light-years from Earth.
Finding Delphinus:
Delphinus is bordered by the constellations of Vulpecula, Sagitta, Aquila, Aquarius, Equuleus and Pegasus. It is visible to all viewers at latitudes between +90° and -70° and is best seen at culmination during the month of September. Are you ready to start exploring Delphinus with binoculars? Then we’ll star with Alpha Delphini, whose name is Sualocin.
The small planetary nebula of NGC 6891. Credit: Judy Schmidt
Sualocin has seven components: A and G, a physical binary, and B, C, D, E, and F, which are optical and have no physical association with A and G. The primary is another rapid rotator star, whipping around at about 160 kilometers per second at its equator – or about 70 times faster than our Sun.
What it’s classification is, is confusing as well. It might a hydrogen-fusing main sequence star, and it subgiant that might just be starting to evolve. Wherever Suolocin lay in the scheme of things, there’s no use trying to resolve out the companion star, because it’s only a fraction of a second of arc away. However, Alpha’s nearby star, still makes for an interesting binocular view!
Now let’s look at Beta Delphini. Are you still ready for a smile? Good old Cacciatore wasn’t done yet. Beta’s name is Rotanev, which is a reversal of his Latinized family name, Venator. Here again we have a multiple star system. Rotanev has five components. Stars A and B are are a true physical binary star, while the others are simply optical companions. This time it’s cool to get out the telescope and split them!
Beta Delphini is a fine target for testing quality optics. At 97 light years from Earth, Rotanev’s components are only separated by about one stellar magnitude and 0.65 seconds of arc. By the way, in case you were wondering…. Nicolaus Venator was the assistant of the one and only Giuseppe Piazzi!
Are you ready for a look at Gamma Delphini? It’s the Y shape on the map. Here we have a binary star very worthy of even a small telescope. Located about a 101 light-years away from Earth, Gamma is one of the best known double stars in the night sky. The primary is a yellow-white dwarf star, a the secondary is an orange subgiant star. Both are separated by about one stellar magnitude and a very comfortable 9.2 seconds of arc apart.
The globular cluster NGC 7006. Credit: NASA
Regardless of their spectral class, take a look at how differently their colors appear in the telescope. While Gamma 1 (to the west) should by all rights be white, it often appears pale yellow orange, while Gamma 2 can appear yellow, green, or blue.
Before we put our binoculars away, let’s have a look at Delta Delphini – the figure “8” on our chart. Delta has no given name, but it has a partner. That’s right, it’s also a binary star. Its identical members are too close together to see separately and only by studying them spectroscopically were astronomers able to detect their 40.58 day orbital period.
Although Delta is officially classed as a type A (A7) giant star, it has a very strange low stellar temperature and an even stranger metal abundance. So what’s going on here? Chances are the Delta pair are really class F subgiants that have just ended core hydrogen fusion and both slightly variable. Do they orbit close to one another? You bet. So close, in fact, there orbit is only about the same distance as Mercury is from our Sun!
Now let’s take out the telescopes and have a look at NGC 7006 (RA 21h 1m 29.4 Dec +16 11′ 14.4) just a few arc minutes due east of Gamma. At magnitude 10, this small and powerful globular cluster might be mistaken for a stellar point in small telescopes at low power, for a very good reason… it’s very, very far away.
It is thought to be about 125 thousand light years from the galaxy’s core and over 135 thousand light years from us – far, far beyond the galaxy’s halo where it belongs. Even though it is a Class 1 globular, the most star dense in the Shapely?Sawyer classification system, and many observers comment that it looks more planetary nebula than it does a globular cluster!
Delphinus Constellation Map. Credit: IAU and Sky&Telescope magazine
Try NGC 6934 instead (RA 20 : 34.2 Dec +07 : 24) . This 50,000 light year distant globular cluster is much brighter and larger, though at Class VIII it doesn’t even come close to having as much stellar concentration. Discovered by Sir William Herschel on September 24, 1785, you’ll enjoy this one just for the rich star field that accompanies it. For larger telescope, you’ll enjoy the resolution and the study in contrasts between these two pairs.
Now let’s take a look at 12th magnitude planetary nebula, NGC 6891 (RA 20 : 15.2 Dec +12 : 42). Here we have an almost stellar appearance, but get tight on that focus and up the magnification to reveal its nature. This is anything but a star. As Martin A. Guerrero (et al) indicated in a 1999 study:
“Narrow-band and echelle spectroscopy observations show a great wealth of structures. The bright central nebula is surrounded by an attached shell and a detached outer halo. Both the inner and intermediate shells can be described as ellipsoids with similar major to minor axial ratios, but different spatial orientations. The kinematical ages of the intermediate shell and halo are 4800 and 28000 years, respectively. The inter-shell time lapse is in good agreement with the evolutionary inter-pulse time lapse. A highly collimated outflow is observed to protrude from the tips of the major axis of the inner nebula and impact on the outer edge of the intermediate shell. Kinematics and excitation of this outflow provide conclusive evidence that it is deflected during the interaction with the outer edge of the intermediate shell.”
If you’d like a real, big, telescope galaxy challenge, try galaxy group NGC 6927, NGC 6928 and NGC 6930. The brightest is NGC 6928 at magnitude 13.5, (RA 20h 32m 51.0s Dec: +09°55’49”). None of them will be easy… But what challenge is?
Artist conception of the James Webb Space Telescope. Credit: NASA
Ever since the project was first conceived, scientists have been eagerly awaiting the day that the James Webb Space Telescope (JWST) will take to space. As the planned successor to Hubble, the JWST will use its powerful infrared imaging capabilities to study some of the most distant objects in the Universe (such as the formation of the first galaxies) and study extra-solar planets around nearby stars.
However, there has been a lot of speculation and talk about which targets will be the JWST’s first. Thankfully, following the recommendation of the Time Allocation Committee and a thorough technical review, the Space Telescope Science Institute (STScI) recently announced that it has selected thirteen science “early release” programs, which the JWST will spend its first five months in service studying.
As part of the JWST Director’s Discretionary Early Release Science Program (DD-ERS), these thirteen targets were chosen by a rigorous peer-review process. This consisted of 253 investigators from 18 counties and 106 scientific institutions choosing from over 100 proposals. Each program has been allocated 500 hours of observing time, once the 6-month commissioning period has ended.
The JWST’s Optical Telescope element/Integrated Science instrument module (OTIS) undergoing testing at NASA’s Johnson Space Center. Credit: NASA/Desiree Stover
As Ken Sembach, the director of the Space Telescope Science Institute (STScI), said in an ESA press statement:
“We were impressed by the high quality of the proposals received. These programmes will not only generate great science, but will also be a unique resource for demonstrating the investigative capabilities of this extraordinary observatory to the worldwide scientific community… We want the research community to be as scientifically productive as possible, as early as possible, which is why I am so pleased to be able to dedicate nearly 500 hours of director’s discretionary time to these early release science observations.”
Each program will rely on the JWST’s suite of four scientific instruments, which have been contributed by NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA). These include the the Near-Infrared Spectrograph (NIRSpec) and the Mid-Infrared Instrument (MIRI) developed by the ESA, as well as the Near-Infrared Camera (NIRCam) developed by NASA and the STScI, and the Near-Infrared Imager and Slitless Spectrograph (NIRISS) developed by the CSA.
The thirteen programs selected include “Through the looking GLASS“, which will rely on the astronomical community’s experience using Hubble to conduct slitless spectroscopy and previous surveys to gather data on galaxy formation and the intergalactic medium, from the earliest epochs of the Universe to the present day. The Principal Investigator (PI) for this program is Tommaso Treu of the University of California Los Angeles.
Once deployed, the JWST will conduct a variety of science missions aimed at improving our understanding of the Universe. Credit: NASA/STScI
Another is the Cosmic Evolution Early Release Science (CEERS) program, which will conduct overlapping observations to create a coordinated extragalactic survey. This survey is intended to let astronomers see the first visible light of the Universe (ca. 240,000 to 300,000 years after the Big Bang), as well as information from the Reionization Epoch (ca. 150 million to 1 billion years after the Big Bang) and the period when the first galaxies formed. The PI for this program is Steven Finkelstein of the University of Texas at Austin.
Then there’s the Transiting Exoplanet Community Early Release Science Program, which will build on the work of the Hubble, Spitzer, and Kepler space telescopes by conducting exoplanet surveys. Like its predecessors, this will consist of monitoring stars for periodic dips in brightness that are caused by planets passing between them and the observer (aka. Transit Photometry).
However, compared to earlier missions, the JWST will be able to study transiting planets in unprecedented detail, which is anticipated to reveal volumes about their respective atmospheric compositions, structures and dynamics. This program, for which the PI is Imke de Pater from the University of California Berkeley, is therefore expected to revolutionize our understanding of planets, planet formation, and the origins of life.
Also focused on the study of exoplanets is the High Contrast Imaging of Exoplanets and Extraplanetary Systems program, which will focus on directly imaged planets and circumstellar debris disks. Once again, the goal is to use the JWST’s enhanced capabilities to provide detailed analyses on the atmospheric structure and compositions of exoplanets, as well as the cloud particle properties of debris disks.
Artist’s impression of the planet orbiting a red dwarf star. Credit: ESO/M. Kornmesser
But of course, not all the programs are dedicated to the study of things beyond our Solar System, as is demonstrated by the program that will focus on Jupiter and the Jovian System. Adding to the research performed by the Galileo and Juno missions, the JWST will use its suite of instruments to characterize and produce maps of Jupiter’s cloud layers, winds, composition, auroral activity, and temperature structure.
This program will also focus on some of Jupiter’s largest moons (aka. the “Galilean Moons”) and the planet’s ring structure. Data obtained by the JWST will be used to produce maps of Io’s atmosphere and volcanic surface, Ganymede’s tenuous atmosphere, provide constrains on these moons thermal and atmospheric structure, and search for plumes on their surfaces. As Alvaro Giménez, the ESA Director of Science, proclaimed:
“It is exciting to see the engagement of the astronomical community in designing and proposing what will be the first scientific programs for the James Webb Space Telescope. Webb will revolutionize our understanding of the Universe and the results that will come out from these early observations will mark the beginning of a thrilling new adventure in astronomy.”
During its mission, which will last for a minimum of five years (barring extensions), the JWST will also address many other key topics in modern astronomy, probing the Universe beyond the limits of what Hubble has been capable of seeing. It will also build on observations made by Hubble, examining galaxies whose light has been stretched into infrared wavelengths by the expansion of space.
The James Webb Space Telescope’s 18-segment primary mirror, a gold-coated beryllium mirror has a collecting area of 25 square meters. Credit: NASA/Chris Gunn
Beyond looking farther back in time to chart cosmic evolution, Webb will also examine the Supermassive Black Holes (SMBH) that lie at the centers of most massive galaxies – for the purpose of obtaining accurate mass estimates. Last, but not least, Webbwill focus on the birth of new stars and their planets, initially focusing on Jupiter-sized worlds and then shifting focus to study smaller super-Earths.
John C. Mather, the Senior Project Scientist for the JWST and a Senior Astrophysicist at NASA’s Goddard Space Flight Center, also expressed enthusiasm for the selected programs. “I’m thrilled to see the list of astronomers’ most fascinating targets for the Webb telescope, and extremely eager to see the results,” he said. “We fully expect to be surprised by what we find.”
For years, astronomers and researchers have been eagerly awaiting the day when the JWST begins gathering and releasing its first observations. With so many possibilities and so much waiting to be discovered, the telescope’s deployment (which is scheduled for 2019) is an event that can’t come soon enough!
This artist's impression shows the temperate planet Ross 128 b, with its red dwarf parent star in the background. Credit: ESO/M. Kornmesser
In August of 2016, the European Southern Observatory (ESO) announced the discovery of a terrestrial (i.e. rocky) extra-solar planet orbiting within the habitable zone of the nearby Proxima Centauri star system, just 4.25 light-years away. Naturally, news of this was met with a great deal of excitement. This was followed about six months later with the announcement of a seven-planet system orbiting the nearby star of TRAPPIST-1.
Well buckle up, because the ESO just announced that there is another potentially-habitable planet in our stellar neighborhood! Like Proxima b, this exoplanet – known as Ross 128b – is relatively close to our Solar System (10.8 light years away) and is believed to be temperate in nature. But on top of that, this rocky planet has the added benefit of orbiting a quiet red dwarf star, which boosts the likelihood of it being habitable.
This artist’s impression shows the temperate planet Ross 128b, with its red dwarf parent star in the background. Credit: ESO/M. Kornmesser
The discovery was made using the ESO’s High Accuracy Radial velocity Planet Searcher (HARPS), located at the La Silla Observatory in Chile. This observatory relies on measurements of a star’s Doppler shift in order to determine if it moving back and forth, a sign that it has a system of planets. Using the HARPS data, the team determined that a rocky planet orbits Ross 128 (an M-type red dwarf star) at a distance of about 0.05 AU with a period of 9.9 days.
Despite its proximity to its host star, Ross 128b receives only 1.38 times more irradiation than the Earth. This is due to the cool and faint nature of red dwarf stars like Ross 128, which has a surface temperature roughly half that of our Sun. From this, the discovery team estimated that Ross 128b’s equilibrium temperature is likely somewhere between -60 and 20°C – i.e. close to what we experience here on Earth.
As Nicola Astudillo-Defru of the Geneva Observatory – and a co-author on the discovery paper – indicated in an ESO press release:
“This discovery is based on more than a decade of HARPS intensive monitoring together with state-of-the-art data reduction and analysis techniques. Only HARPS has demonstrated such a precision and it remains the best planet hunter of its kind, 15 years after it began operations.”
But what is most encouraging is the fact that Ross 128 is the “quietest” nearby star that is also home to an exoplanet. Compared to other classes of stars, M-type red dwarfs are particularly low in mass, dimmer and cooler. They are also the most common type of star in the Universe, accounting for 70% of the stars in spiral galaxies and more than 90% of all stars in elliptical galaxies.
Unfortunately, they are also variable and unstable compared to other classes of star, which means they experience regular flare ups. This means that any planets which orbit them will be periodically subjected to deadly ultraviolet and X-ray radiation. In comparison, Ross 128 is much quieter, meaning it experiences less in the way of flare activity, and planets orbiting it are therefore exposed to less radiation over time.
This means that, relative to Proxima b or those planets located within TRAPPIST-1’s habitable zone – Ross 128b is more likely to retain an atmosphere and support life. For those who are engaged in searches for exoplanets around M-type stars – or are of the opinion that red dwarfs are the best bet for finding habitable worlds – this latest discovery would seem to confirm that they are looking in the right spots!
As noted, red dwarfs are the most common in the Universe, and in recent years, many rocky planets (sometimes even a multi-planet system) have been found orbiting these stars. Combined with their natural longevity – which can remain in their main sequence phase for up to 10 trillion years – red dwarf stars have understandably become a popular target for exoplanet-hunters.
In fact, lead author Xavier Bonfils named their HARPS program “The Shortcut to Happiness” for this very reason. As he and his colleagues indicated, it is easier to detect small cool planets of Earth around smaller, dimmer M-type stars than it is around stars that are more similar to the Sun.
However, many in the scientific community have remained skeptical about the likelihood that any of these planets could be habitable (again, due to their variable nature). But this most recent discovery, along with recent research that indicates how tidally-locked planets that orbit red dwarf stars could hold onto their atmospheres, is another possible indication that these fears may be for naught.
Being at a distance of about 11 light-years from Earth, Ross 128b is currently the second-closest exoplanet to our Sun. However, Ross 128 itself is slowly moving closer towards us and will become our nearest stellar neighbor in roughly 79,000 years. At this point, Ross 128b will replace Proxima b and become the closest exoplanet to Earth!
But of course, much remains to be found about this latest exoplanet. While the discovery team consider Ross 128b to be a temperate planet based on its orbit, it remains uncertain as to whether it lies within, beyond, or on the cusp of the star’s habitable zone. However, further studies are expected to shed more light on this and other questions relating this potentially-habitable world.
Astronomers also anticipate that more temperature exoplanets will be discovered in the coming years, and that future surveys will be able to determine a great deal more about their atmospheres, composition and chemistry. Instruments like the James Webb Space Telescope (JWST) and the ESO’s Extremely Large Telescope (ELT) are expected to play a major role.
Not only will these and other instrument help turn up more exoplanet candidates, they will also be used in the hunt for biosignatures in planet’s atmospheres (i.e. oxygen, nitrogen, water vapor, etc.). As Bonfils concluded:
“New facilities at ESO will first play a critical role in building the census of Earth-mass planets amenable to characterization. In particular, NIRPS, the infrared arm of HARPS, will boost our efficiency in observing red dwarfs, which emit most of their radiation in the infrared. And then, the ELT will provide the opportunity to observe and characterize a large fraction of these planets.”
At this juncture, the process of exoplanet discovery is moving beyond detection and getting into the process of characterization and detailed study. Even so, it is nice that we are still making groundbreaking discoveries in the field of detection. In the coming years, we may transition from looking for an Earth 2.0 to a point where weare actively studying several at once!
The summer constellations of Cygnus and Lyra. The position of KIC 9832227 is shown with a red circle. It is in line with the three stars of the cross bar and, if it reaches 2nd magnitude in outburst, as it might, will be as bright as they are. Credit: calvin.edu
Welcome to another edition of Constellation Friday! Today, in honor of the late and great Tammy Plotner, we take a look at the “Swan” – the Cygnus constellation. Enjoy!
In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of all the then-known 48 constellations. This treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come, effectively becoming astrological and astronomical canon until the early Modern Age.
One of the constellations identified by Ptolemy was Cygnus, otherwise known as “the Swan”. The constellation is easy to find in the sky because it features a well-known asterism known as the Northern Cross. Cygnus was first catalogued the by Greek astronomer Ptolemy in the 2nd century CE and is today one of the 88 recognized by the IAU. It is bordered by the constellations of Cepheus, Draco, Lyra, Vulpecula, Pegasus and Lacerta.
Name and Meaning:
Because the pattern of stars so easily resembles a bird in flight, Cygnus the “Swan” has a long and rich mythological history. To the ancient Greeks, it was at one time Zeus disguising himself to win over Leda, and eventually father Gemini, Helen of Troy, and Clytemnestra. Or perhaps it is poor Orpheus, musician and muse of the gods, who when he died was transformed into a swan and placed in the stars next to his beloved lyre.
Artist’s conception of what Cygnus’ figure looks like, against the backdrop of stars that make up the constellation. Credit: Wendy Stenzel (first published on NASA Kepler website)
It could be king Cycnus, a relative of Phaethon, son of Apollo, who crashed dear old dad’s fiery sky chariot and died. Cygcus was believed to have driven up and down the starry river so many times looking for Phaethon’s remains that he was finally transformed into stars. No matter what legend you choose, Cygnus is a fascinating place… and filled with even more fascinating areas to visit!
History of Observation:
Because of its importance in ancient Greek mythology and astrology, the sprawling constellation of Cygnus was one of Ptolemy’s original 48 constellations. To Hindu astronomers, the Cygnus constellation is also associated with the “Brahma Muhurta” (“Moment of the Universe”). This period, which lasts from 4:24 AM to 5:12 AM, is considered to be the best time to start the day.
Cygnus is also highly significant to the folklore and mythology of many people in Polynesia, who also viewed it as a separate constellation. These include the people of Tonga, the Tuamatos people, the Maori (New Zealand) and the people of the Society Islands. Today, Cygnus is one of the official 88 modern constellations recognized by the IAU.
Notable Objects:
Flying across the sky in a grand position against the backdrop of the Milky Way, Cygnus consists of 6 bright stars which form an asterism of a cross comprised of 9 main stars and there are 84 Bayer/Flamsteed designated stars within its confines. It’s most prominent star, Deneb (Alpha Cygni), takes it name from the Arabic word dhaneb, which is derived from the Arabic phrase Dhanab ad-Dajajah, which means “the tail of the hen”.
Cygnus as depicted in Urania’s Mirror, a set of constellation cards published in London c.1825. Surrounding it are Lacerta, Vulpecula and Lyra. Credit: Sidney Hall/US Library of Congress
Deneb is a blue-white supergiant belonging to the spectral class A2 Ia, and is located approximately 1,400 light years from Earth. In addition to being the brightest star in Cygnus, it is one of the most luminous stars known. Being almost 60,000 times more luminous than our Sun and about 20 Solar masses, it is also one of the largest white stars known.
Deneb serves as a prototype for a class of variable stars known as the Alpha Cygni variables, whose brightness and spectral type fluctuate slightly as a result of non-radial fluctuations of the star’s surface. Deneb has stopped fusing hydrogen in its core and is expected to explode as a supernova within the next few million years. Together with the stars of Altair and Vega, Deneb forms the Summer Triangle, a prominent asterism in the summer sky.
Next up is Gamma Cygni (aka. Sadr), whose name comes from the Arabic word for “the chest”. It is also sometimes known by its Latin name, Pectus Gallinae, which means “the hen’s chest.” This star belongs to the spectral class F8 lad, making it a blue-white supergiant, and is located approximately 1,800 light years from Earth.
It can easily seen in the night sky at the intersection of the Northern Cross thanks to its apparent magnitude of 2.23, which makes it one of the brightest stars that can be seen in the night sky. It is also believed to be only about 12 million years old and consumes its nuclear fuel more rapidly because of its mass (12 Solar masses).
Gamma Cygni (Sadr) is surrounded by a diffuse emission nebula, IC 1318, also known as the Sadr region or the Gamma Cygni region. Credit: Eric Larsen
Then there’s Epsilon Cygni (ak. Glenah), an orange giant of the spectral class K0 III that is 72.7 light years distant. It’s traditional name comes from the Arabic word janah, which means “the wing” (this name is shared with Gamma Corvi, a star in the Corvus constellation). It is 62 times more luminous than the Sun and measures 11 Solar radii.
Delta Cygni (Rukh), is a triple star system in Cygnus, which is located about 165 light years away. The system consists of two stars lying close together and a third star located a little further from the main pair. The brightest component is a blue-white fast-rotating giant belonging to the spectral class B9 III. The star’s closer companion is a yellow-white star belonging to the spectral class F1 V, while the third component is an orange giant.
Last, there’s Beta Cygni (aka. Albireo) which is only the fifth brightest star in the constellation Cygnus, despite its designation. This binary star system, which appears as a single star to the naked eye, is approximately 380 light-years distant. The traditional name is the result of multiple translations and misunderstandings of the original Arabic name, minqar al-dajaja (“the hen’s beak”). It is one of the stars that form the Northern Cross.
The binary system consists of a yellow star which is itself a close binary star that cannot be resolved as two separate objects. Its second star is a fainter blue fast-rotating companion star with an apparent magnitude of 5.82 that is located 35 arc seconds apart from its primary.
Albireo A, the primary star of Beta Cygni (which is itself a binary system). Credit: Henryk Kowalewski
Cygnus is also home to a number of Deep Sky Objects. These include Messier 29 (NGC 6913), an open star cluster that is about 10 million years old and located about 4,000 light years from Earth. It can be spotted with binoculars a short distance away from Gamma Cygni – 1.7 degrees to the south and a little east.
Next up is Messier 39 (NGC 7092), another open star cluster that is located about 800 light-years away and is between 200 and 300 million years old. All the stars observed in this cluster are in their main sequence phase and the brightest ones will soon evolve to the red giant stage. The cluster can be found two and a half degrees west and a degree south of the star Pi-2 Cygni.
There is also the Fireworks Galaxy (NGC 6946), an intermediate spiral galaxy that is approximately 22.5 million light-years distant. The galaxy is located near the border of the constellation Cepheus and lies close to the galactic plane, where causes it to become obscured by the interstellar matter of the Milky Way.
Then there’s the famous X-ray source known as Cygnus X-1, which is one of the strongest that can be seen from Earth. Cygnus X-1 is notable for being the first X-ray source to be identified as a black hole candidate, with a mass 8.7 times that of the Sun. It orbits a blue supergiant variable star some 6,100 light-years away, which is one of two stars form a binary system.
Over time, an accretion disk of material brought from the star by a stellar wind has formed around Cygnus X-1, which is the source of its X-ray emissions.
Finding Cygnus:
Cygnus is visible to all observers at latitudes between +90° and -40° and is best seen at culmination during the month of September. For a period of 15 days around the peak date of August 20, watch for the Kappa Cygnid meteor shower. This annual meteor shower has a radiant near the bright star Deneb and an average fall rate of about 12 meteors per hour. It is noted to have many bright fire balls called “bolides” and the best time to watch is when the constellation is directly overhead.
Because Cygus is so rich in things to visit, we shall only touch very briefly on just a few. Let’s begin with our unaided eye as we take a look at the brightest star of the constellation, Alpha Cygni – Deneb. Here we have not only an extremely luminous blue super giant star – but a pulsing variable star, too. Its changes are minor – only about 1/10 of a stellar magnitude, but Deneb is its own prototype.
Its stellar oscillations are very complex, consisting of multiple pulsation frequencies as well as a fundamental one. This means changes in brightness occur between 5 and 10 days apart, but that’s a good thing. If the changes weren’t small, Deneb would blow itself to bits!
If you are looking at Cygnus for an area well away from city lights on a night when there is no Moon, look just northwest of Deneb for the North America Nebula (NGC 7000). This is an excellent emission nebula that covers as much area of the sky as 10 full Moons! At 3 full degrees, you’ll be looking for a vague, misty patch of silver-ness that about as broad as your thumb held at arm’s length.
While telescopes and binoculars are grand, remember this particular region is so large that you can easily over magnify it and often your unaided eye is all you need to catch this elusive interstellar cloud of ionized hydrogen (H II region). Now, get out your binoculars and let’s dance!
Messier 29 is very easy and bright and you can find it about a fingerwidth south and a little east of Gamma Cygni – the “8” shape on our map. This open cluster of stars has just a handful of bright members and will look like a small rendition of the “Big Dipper”. M29 is about 7,200 light years away from Earth, so the fact we can see it at all in binoculars is pretty impressive! Now, try Messier 39.
You’ll find this one about a fingerwidth west and southwest of Pi2, which looks like TT2 on our map. This galactic star cluster is far brighter and richer than the last. It will show as a triangle shape with bright stars in each corner and a couple of dozen fainter stars captured within the center. M39 is only about 800 light years away from our solar system, but it could be as much as 300 million years old!
Don’t put your binoculars away just yet. You’ve got to visit Omega 2 before you stop! Its name is Ruchbah and it’s a double star about 500 light years from Earth, consisting of a magnitude 5.44 star of spectral class M2 and a 6.6 magnitude star of spectral class A0. The stars are well separated at 256″ apart and can be seen in binoculars and totally glorious in a telescope. Because of the color contrast (red main star and blue companion), Ruchba is a beautiful object for amateur astronomers.
The northern Cygnus constellation. Credit: IAU
Now try Beta Cygni – Albireo. It is also known as one of the most attractive and colorful double stars in the sky. Beautiful Beta 1 is an orange giant K star and Beta 2 is a main-sequence B star of a soft, blue hue. If you can’t separate them in your binoculars, use a telescope! This seasonal favorite is one that’s not to be missed! Now, let’s try a couple objects for the telescope.
One of the true prizes of the Cygnus region for any telescope is the Holy Veil (NGC 6960, 6962, 6979, 6992, and 6995). You’ll find it just south of Epsilon Cygni and the easiest segment to find is 6960, which runs through the star 52 Cygni. This is an ancient supernova remnant covering approximately 3 degrees of the sky and an experience you won’t soon forget if you are viewing from a dark sky site.
The source supernova exploded some 5,000 to 8,000 years ago and it is simply amazing to think that anything remains to be seen. It was discovered on 1784 September 5 by William Herschel. He described the western end of the nebula as “Extended; passes thro’ 52 Cygni… near 2 degree in length.” and described the eastern end as “Branching nebulosity… The following part divides into several streams uniting again towards the south.”
Even though it is any where from from 1,400 to 2,600 light-years light years away, you’ll find long and wondrous tongues of material to capture your interest and delight your eye and you follow them to their ends!
More challenging is the Crescent Nebula (NGC 6888 or Caldwell 27) located at RA 20h 12m 7s Dec +38 21.3′. This is an emission nebula fueled by a Wolf-Rayet star located about 5000 light years away. It is formed by the fast stellar wind careening off illuminating the slower moving wind ejected by the star when it went into the red giant star stage. What’s left is a collision… a shell and two shock waves… one moving outward and one moving inward. A what a grand one it is!
The Fireworks Galaxy (NGC 6946) taken by the Subaru Telescope. Credit: NAOJ/Robert Gendler
For galaxy fans, you have got to point your telescope towards NGC 6946, the “Fireworks Galaxy” (RA 20h 34m 52.3s Dec +60 09 14). Who cares if this barred spiral galaxy 10 million light years away? This is one supernovae active baby! At one time, it was widely believed that NGC 6946 was a member of our Local Group; mainly because it could be easily resolved into stars.
There was a reddening observed in it, believed to be indicative of distance – but now know to be caused by interstellar dust. But it isn’t the shrouding dust cloud that makes NGC 6946 so interesting, it’s the fact that so many supernova and star-forming events have sparkled in its arms in the last few years that has science puzzled! So many, in fact, that they’ve been recorded every year or two for the last 60 years…
Now, for the really cool part – understanding barred structure. Thanks to the Hubble Space Telescope and a study of more than 2,000 spiral galaxies – the Cosmic Evolution Survey (COSMOS) – astronomers understand that barred spiral structure just didn’t occur very often some 7 billion years ago in the local universe. Bar formation in spiral galaxies evolved over time.
A team led by Kartik Sheth of the Spitzer Science Center at the California Institute of Technology in Pasadena discovered that only 20 percent of the spiral galaxies in the distant past possessed bars, compared with nearly 70 percent of their modern counterparts. This makes NGC 6946 very rare, indeed… Since its barred structure was noted back in Herschel’s time and its age of 10 billion years puts it beyond what is considered a “modern” galaxy.
It that all there is? Not hardly. Try NGC 6883, an open cluster located about 3 degrees east/northeast of Eta Cygni. It’s a nice, tight cluster that involves a well-resolved double star and a bonus open cluster – Biurakan 2 – as well. Or how about NGC 6826 located about 1.3 degrees east/northeast of Theta. This one is totally cool… the “Blinking Planetary”!
This planetary nebula is fairly bright and so is the central star… but don’t stare at it, or it will disappear! Look at it averted and the central star will appear again. Neat trick, huh? Now try NGC 6819 about 8 degrees west of Gamma. Here you’ll find a very rich, bright open cluster of about 100 stars that’s sure to please. It’s also known as Best 42!
There’s many more objects in Cygnus than just what’s listed here, so grab yourself a good star chart and fly with the “Swan”!
A team of Brazilian scientists recently observed a binary star system consisting of a white dwarf and a brown dwarf companion. Credit: FAPESP
Eclipsing binary star systems are relatively common in our Universe. To the casual observer, these systems look like a single star, but are actually composed of two stars orbiting closely together. The study of these systems offers astronomers an opportunity to directly measure the fundamental properties (i.e. the masses and radii) of these systems respective stellar components.
Recently, a team of Brazilian astronomers observed a rare sight in the Milky Way – an eclipsing binary composed of a white dwarf and a low-mass brown dwarf. Even more unusual was the fact that the white dwarf’s life cycle appeared to have been prematurely cut short by its brown dwarf companion, which caused its early death by slowly siphoning off material and “starving” it to death.
The Observatorio del Roque de los Muchachos, located on the island of La Palma. Credit: IAC
For the sake of their study, the team conducted observations of a binary star system between 2005 and 2013 using the Pico dos Dias Observatory in Brazil. This data was then combined with information from the William Herschel Telescope, which is located in the Observatorio del Roque de los Muchachos on the island of La Palma. This system, known as of HS 2231+2441, consists of a white dwarf star and a brown dwarf companion.
White dwarfs, which are the final stage of intermediate or low-mass stars, are essentially what is left after a star has exhausted its hydrogen and helium fuel and blown off its outer layers. A brown dwarf, on the other hand, is a substellar object that has a mass which places it between that of a star and a planet. Finding a binary system consisting of both objects together in the same system is something astronomers don’t see everyday.
As Leonardo Andrade de Almeida explained in a FAPESP press release, “This type of low-mass binary is relatively rare. Only a few dozen have been observed to date.”
This particular binary pair consists of a white dwarf that is between twenty to thirty percent the Sun’s mass – 28,500 K (28,227 °C; 50,840 °F) – while the brown dwarf is roughly 34-36 times that of Jupiter. This makes HS 2231+2441 the least massive eclipsing binary system studied to date.
This artist’s impression shows an eclipsing binary star system. Credit: ESO/L. Calçada.
In the past, the primary (the white dwarf) was a normal star that evolved faster than its companion since it was more massive. Once it exhausted its hydrogen fuel, its formed a helium-burning core. At this point, the star was on its way to becoming a red giant, which is what happens when Sun-like stars exit their main sequence phase. This would have been characterized by a massive expansion, with its diameter exceeding 150 million km (93.2 million mi).
At this point, Almeida and his colleagues concluded that it began interacting gravitationally with its secondary (the brown dwarf). Meanwhile, the brown dwarf began to be attracted and engulfed by the primary’s atmosphere (i.e. its envelop), which caused it it lose orbital angular momentum. Eventually, the powerful force of attraction exceeded the gravitational force keeping the envelop anchored to its star.
Once this happened, the primary star’s outer layers began to be stripped away, exposing its helium core and sending massive amounts of matter to the brown dwarf. Because of this loss of mass, the remnant effectively died, becoming a white dwarf. The brown dwarf then began orbiting its white dwarf primary with a short orbital period of just three hours. As Almeida explained:
“This transfer of mass from the more massive star, the primary object, to its companion, which is the secondary object, was extremely violent and unstable, and it lasted a short time… The secondary object, which is now a brown dwarf, must also have acquired some matter when it shared its envelope with the primary object, but not enough to become a new star.”
Artist’s impression of a brown dwarf orbiting a white dwarf star. Credit: ESO
This situation is similar to what astronomers noticed this past summer while studying the binary star system known as WD 1202-024. Here too, a brown dwarf companion was discovered orbiting a white dwarf primary. What’s more, the team responsible for the discovery indicated that the brown dwarf was likely pulled closer to the white dwarf once it entered its Red Giant Branch (RGB) phase.
At this point, the brown dwarf stripped the primary of its atmosphere, exposing the white dwarf remnant core. Similarly, the interaction of the primary with a brown dwarf companion caused premature stellar death. The fact that two such discoveries have happened within a short period of time is quite fortuitous. Considering the age of the Universe (which is roughly 13.8 billion years old), dead objects can only be formed in binary systems.
In the Milky Way alone, about 50% of low-mass stars exist as part of a binary system while high mass stars exist almost exclusively in binary pairs. In these cases, roughly three-quarters will interact in some way with a companion – exchanging mass, accelerating their rotations, and eventually en merging.
As Almeida indicated, the study of this binary system and those like it could seriously help astronomers understand how hot, compact objects like white dwarfs are formed. “Binary systems offer a direct way of measuring the main parameter of a star, which is its mass,” he said. “That’s why binary systems are crucial to our understanding of the life cycle of stars.”
It has only been in recent years that low-mass white dwarf stars were discovered. Finding binary systems where they coexist with brown dwarfs – essentially, failed stars – is another rarity. But with every new discovery, the opportunities to study the range of possibilities in our Universe increases.
This artist’s impression shows how the newly discovered belts of dust around the closest star to the Solar System, Proxima Centauri, may look. Credit: ESO/M. Kornmesser
Proxima Centauri, in addition to being the closest star system to our own, is also the home of the closest exoplanet to Earth. The existence of this planet, Proxima b, was first announced in August of 2016 and then confirmed later that month. The news was met with a great deal of excitement, and a fair of skepticism, as numerous studies followed t were dedicated to determining if this planet could in fact be habitable.
Another important question has been whether or not Proxima Centauri could have any more objects orbiting it. According to a recent study by an international team of astronomers, Proxima Centauri is also home to a belt of cold dust and debris that is similar to the Main Asteroid Belt and Kuiper Belt in our Solar System. The existence of this dusty belt could indicate the presence of more planets in this star system.
View of the Atacama Large Millimeter/submillimeter Array (ALMA) site in the Atacama Desert of northern Chile. Credit: A. Marinkovic/X-Cam/ALMA (ESO/NAOJ/NRAO)
For their study, the team relied on data obtained by the Atacama Large Millimeter/submillimter Array (ALMA) at the ALMA Observatory in Chile. These observations revealed the glow of a cold dust belt that is roughly 1 to 4 AUs from Proxima Centauri – one to four times the distance between the Earth and the Sun. This puts it significantly further out than Proxima b, which orbits its sun at a distance of 0.0485 AU (~5% of Earth’s distance from the Sun).
Dust belts are essentially the leftover material that did not form into larger bodies withing a star system. The particles of rock and ice in these belts vary in size from being smaller than a millimeter across to asteroids that are many kilometers in diameter. Based on their observations, the team estimated that the belt in Proxima Centauri has a total mass that is about one-hundredth the mass of Earth.
The team also estimated that this belt experiences temperatures of about 43 K (-230°C; -382 °F), making it as cold as the Kuiper Belt. As Dr. Anglada explained the significance of these findings in a recent ESO press release:
“The dust around Proxima is important because, following the discovery of the terrestrial planet Proxima b, it’s the first indication of the presence of an elaborate planetary system, and not just a single planet, around the star closest to our Sun.”
This infographic compares the orbit of the planet around Proxima Centauri (Proxima b) with the same region of the Solar System. Credit: ESO
The ALMA data also provided indications that Proxima Centauri might also have another belt located about ten times further out. In other words, Proxima Centauri may have two belts, just like our Solar System. If confirmed, this could indicate that this neighboring star also has a system of planets that fall within and between belts of unconsolidated material, which in turn is leftover from the early days of planet formation. As Dr. Anglada explained:
“This result suggests that Proxima Centauri may have a multiple planet system with a rich history of interactions that resulted in the formation of a dust belt. Further study may also provide information that might point to the locations of as yet unidentified additional planets.”
The very cold environment of this outer belt could also have some interesting implications, since its parent star is much dimmer than our own. Pedro Amado, who also hails from the Astrophysical Institute of Andalusia, was similarly enthusiastic about these findings. As he indicated, they are just the beginning of what is sure to be a long process of discovery about this system.
“These first results show that ALMA can detect dust structures orbiting around Proxima,” he said. “Further observations will give us a more detailed picture of Proxima’s planetary system. In combination with the study of protoplanetary discs around young stars, many of the details of the processes that led to the formation of the Earth and the Solar System about 4600 million years ago will be unveiled. What we are seeing now is just the appetiser compared to what is coming!”
Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org
This study is also likely to be of interest to those planning on conducting direct observations of the Alpha Centauri system, such as Project Blue. In the coming years, they hope to deploy a space telescope that will observe Alpha Centauri directly to study any exoplanets it may have. With a slight adjustment, this telescope could also take a gander at Proxima Centauri and aid in the hunt for a system of planets there.
And then there’s Breakthrough Starshot, the first proposed interstellar voyage which hopes to send a laser sail-driven nanocraft to Alpha Centauri in the coming decades. Recently, the scientists behind Starshot discussed the possibility of extending the mission to include a stopover in Proxima Centauri. Before such a mission can take place, the planners need to know what kind of dusty environment awaits it.
And of course, future studies will benefit from the deployment of next-generation instruments, like the James Webb Space Telescope (scheduled for launch in 2019) and the ESO’s Extremely Large Telescope (ELT) – which is expected to collect its first light in 2024.
