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Astronomer, outreach coordinator and producer of the monthly news segment of the Jodcast.

Rigel
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October 11, 2011
11:49 AM
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In the news this month: a primitive star in our own backyard

by Megan in Rigel

Our current model of the early universe says that, as it expanded and cooled after the Big Bang, quarks began to coalesce to form protons and neutrons which, when the temperature dropped far enough, began to form simple nuclei. Eventually this material, mainly hydrogen with some helium and trace amounts of lithium, began to clump together, forming the stars and galaxies that we see today. Heavier elements such as carbon, nitrogen and oxygen, in fact pretty much everything that makes up this planet and all the life on it, were created later by processing of this primitive material in stars and supernova explosions. This processing in nuclear fusion reactions produces all the heavier elements that make up the universe. Since less massive stars last longer before running out of fuel, there should be a population of very low mass stars which have been around since the early days of the universe. Such stars would be small, dim, and have an extremely low proportion of elements heavier than hydrogen and helium and, in , a team led by Elisabetta Caffau at the University of Heidelberg in Germany have found just such a star in the halo of the Milky Way, but with an unusual chemical make-up., located in the constellation of Leo and known as , has been found to have the lowest amount of elements heavier than helium of all stars yet studied, a quantity known as metalicity. While a few other primitive stars with very low metalicities have been found, the others all have carbon, nitrogen and oxygen in far greater quantities than would be expected for stars from the very first population. It is thought that low mass stars such as these could only form after the interstellar gas had been enriched by supernova explosions with elements such as carbon and oxygen, since these elements act as a vital cooling agent, reducing the temperature of the gas cloud to the point where gravity can begin to overcome pressure and cause the clumping which eventually leads to stars. This conclusion means that the low abundance of elements including carbon, nitrogen and oxygen in the newly discovered star with current models of star formation in the early universe.A further puzzle with this star is the amount of lithium it contains; it's lithium abundance is at least 50 times smaller than that predicted by big bang nucleosynthesis. The likely explanation is that the stellar material must have experienced temperatures ;2 million K, the temperature required to destroy lithium. While the chemical composition of this star is something of a challenge to current models of early star formation, along with other examples that should be unearthed in planned surveys, it should provide clues which will help in our understanding of the very first stellar population.This blog post is a news story from the , aired in the edition.... Read more »

Caffau, E., Bonifacio, P., François, P., Sbordone, L., Monaco, L., Spite, M., Spite, F., Ludwig, H., Cayrel, R., Zaggia, S.... (2011) An extremely primitive star in the Galactic halo. Nature, 477(7362), 67-69. DOI: 10.1038/nature10377

September 23, 2011
03:43 AM
339 views

Afraid of the dark

by Megan in Rigel

I've never been afraid of the dark.; When it's all you've ever known, it seems a rather silly notion.; But now... well, this seems different somehow.; Now we're all frightened.It wasn't always like this.; We all grew up with the stories about the old times, when there were colonies every few parsecs, all set on planets (artificial or otherwise) around healthy stars, and supply stations strung along the major trade routes likes beads of water on an invisible web.; The galaxy thrived back then, or so the stories go.; Civilisation reaching ever outwards, colonising, trading, cooperating, and fighting, naturally.; There was rarely ever total peace, not in our nature say the historians.; But it's all long gone now.Slowly, imperceptibly at first, night began to fall across the universe.; Complete and total darkness, the end of all things.; Our own star (we knew it as Suryan) faded from glory long before I was born.; I've never known real daylight, never felt the warmth of the midday sunlight on my skin.; Growing up, we were all told the stories and legends of the light times, when Suryan made the sky glow from horizon to horizon and stars filled the sky when Suryan herself slipped below the edge of the world.But all that has faded with the generations.; Long ago our star melted away into the darkness and we were left clinging to this rock, digging ever deeper into its crust just to reach the feeble warmth of the planet's ancient cooling core.; At least we had that, other colonies were not so lucky.; Those who had settled on artificial planets didn't last long when their stars faded, their power systems were never designed to cope with such extreme cold.; The cold metal constructions lost their heat quickly and their inhabitants (those unlucky enough not to make an escape on whatever ships they might have had) froze in a matter of months.; There are those who say that was a better way to go.Suryan isn't completely dead of course, that takes billions of years.; When she ran out of material to fuse, her outer atmosphere expanded, reaching almost as far as our colony here on the fourth planet.; Protected under the colony's thick-walled domes, the inhabitants watched from safety as the star put on its last and greatest show.; While the core began to shrink, those burnt-orange layers continued to expand, becoming a fading wisp-like shell centred on the dying remains of what had once been a giant nuclear fusion reactor.; That remnant core still sits at the centre of this system like the last dying ember of a fire.; It still produces light and heat of course but not enough to be useful, not by a long way.It's been some decades now since the last ship left this system.; When Suryan burnt its last, up there in the sky, there was widespread panic.; People were desperate to leave, to go somewhere else with a star that was still viable.; But there wasn't anywhere to go.; Slowly but surely, the stars were dying everywhere and there was no more gas left to create new ones.; These are the last days of the Universe, but people refused to believe it.; Somewhere there's another star, they said, somewhere.; The ships left, heading out towards whatever points of light they could see in the sky, and those who stayed behind attempted to carry on as normal.; We've known what was coming for generations but there was nothing we could do.; You either accept it and get on with life as best you can, or panic and most likely hasten your demise.; While we have no ships any more, nor the capabilities to construct any, we can still communicate with other colonies although that happens rarely these days.; There isn't anything left to communicate, and it uses power we can little afford to waste.I often wonder what happened to those ships that left.; The records show that they kept in communication with the colony for some time after they set out, promising to return for survivors when they found a new home in the sunlight.; But then the logs stop.; When I was younger I assumed they just stopped transmitting, that they were saving energy or something.; But now, well, I've heard the stories from other colonies of madness and chaos and I wonder if the same fate befell those ships we dispersed into the night like seeds.That's the problem with space flight of course.; It takes time.; Those ships leaving Suryan would each have headed towards a distant glimmer of light, some far-off star that hadn't yet reached the end of its days.; But in the mean time, the light from those little balls would have been travelling for centuries before it reached our system, if not longer.; What would happen to the crew if, after using all of the fuel they could spare to send them rushing onwards towards some distant star, keeping just enough to slow down again at their intended destination, they suddenly saw that their promised Eden was disappearing, fading away before their very eyes?; By that point there would be nothing they could do, no way of changing course without using up the precious fuel they would need in order to slow down once they reached somewhere habitable.; Game over.; What then?I ask myself: what would I do in that situation?; It would be tempting to open an airlock, destroy the safety interlocks and just let everything be pulled out into the vacuum.; Not a pleasant way to go, certainly, but quicker than most options available on a tug.; We were never an exploration colony, merely a mining outpost, and those craft had never been designed for long-term use.; Your options were starvation (water was recycled, even on the tugs, so no problem there), carbon dioxide poisoning (the filters worked pretty well, but were usually replaced every couple of years), or some manner of your own choosing.; Most colonists would rather chose their way out rather than go slowly - we'd all seen it happen, read the case studies.; It was part of basic schooling on these outposts.; Harsh, may be, but the sooner you realised the realities of colony life the better.So, here lies the remains of a once busy and reasonably prosperous colony.; Mirroring the downfall of the empire, it withered with the dying of the light.; There were those who refused to believe it would happen, others who proclaimed it as the ultimate test of faith in whatever deity they served, still others who maintained that we'd find a way out somehow.; But the truth was that we'd known for generations that this was coming.; Ways of restarting stars were proposed, but they all required more energy than the empire could spare, just for a single star.; Society crumbled, the trade routes grew silent, colonies began shutting off their contact with the outside world.; Where colonies were close enough, wars broke out.The stars didn't all go out at once.; It takes time for a star to use up its fuel, and that depends on many things, but larger stars burn up faster.; Despite the dangers, the empire loved placing colonies around massive stars because they were the most profitable.; You could have several large artificial colonies around a massive star where they could harvest huge amounts of energy, and stellar mechanics was developed enough that the onset of a catastrophic supernova explosion, so characteristic of these massive stars, could be predicted to an accuracy of a few months.; Smaller stars like our Suryan were far more sedate.; Not massive enough to go supernova, they took many billions of years to use up their fuel.; While our colony was never rich, we lasted longer then many others simply because our star was a comparative weakling.But even by the time this colony was founded, the universe was old.; Really, it was a wonder our species had lasted as long as it had without destroying itself from within.; Galaxies formed new stars at the rate of a few per standard solar year, but they have to come from something, you need gas to create them.; No more gas, no more stars.; We knew, as a species, that this was what would happen someday but, like countless cultures before us had done throughout history, we always assumed it would be far enough in the future that it would be someone else's problem.; For the most part that was right, but now we are that someone else, and we are scared.Most of the colony, those who didn't leave in the tugs, have chosen to carry on as normal.; Each year we just dig a bit deeper towards the dying heart of the planet to keep the thermal plants supplied with enough energy from our world's cooling interior.; None of us alive now really knew Suryan as anything other than the dying ember that hangs in the sky today, so to us the sight is normal.; I once saw a holograph of an Earthscape - its open spaces and vivid blue sky were nauseating.; There were no stars in that picture either, apart from Sol of course, now long gone.That's the difference.; Their sky was bright and harsh.; Ours is black and cold, as if oblivion had been given form.; I look out every day at that sky and my eyes wander, searching for the last faint pinpricks of light - something I know I'll never see again, now.; Last night, the last star in our sky faded forever.; We knew it had to happen sometime, but it was still something of a shock when it finally came.; None of us can claim to be astronomers, but we all knew the movements of that last star.; We watched it grow fainter and fainter, occasional bursts of light giving unwarranted hope of a reprieve.; Every one of those upward-gazing eyes knew what those fits meant, but still the soul hopes.... may be.The last star.; The final vestiges of warmth are gone from the sky.; Those photons will continue on, travelling out into the darkness long after this little colony has gone.; For all we know, we may be the last, interstellar communication is a luxury that we can no longer afford.; But what's left now?; There will be no more stars, no more colonies, just endless darkness and cold like the long-dead surface of this planet.There's still time for a walk before lights out.; I've nev... 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Braun, R., Popping, A., Brooks, K., & Combes, F. (2011) Molecular gas in intermediate-redshift ultraluminous infrared galaxies. Monthly Notices of the Royal Astronomical Society, 416(4), 2600-2606. DOI: 10.1111/j.1365-2966.2011.19212.x

September 7, 2011
02:21 PM
477 views

In the news this month: a planet darker than coal

by Megan in Rigel

Stars are bright because they generate heat and light through nuclear fusion processes in their cores, planets are visible because they reflect some of that light.; The percentage of light that is reflected, a quantity known as a planet's , varies depending on the nature of the planet's surface and its atmosphere.; Jupiter, with its thick bands of highly reflective cloud, has an albedo of 52%, while the Earth's is somewhat lower, only reflecting around 37% of the sunlight which falls on the surface.; But now, a duo of astronomers with an exceptionally low albedo, reflecting just 1% of its host star's light, making it less reflective than coal.The planet, discovered by the , is known as TrES-2b and lies about 750 light years away in the constellation of Draco.; David Kipping (of the Harvard-Smithsonian Center for Astrophysics) and David Spiegel (of Princeton University) used data from the to investigate the planet's nature.; To calculate its albedo, the astronomers measured its brightness at two different points in its orbit around the host star, once when it was located directly between us and the star, and again when it was on the far side, just before it went into eclipse.; The difference between the two measurements is therefore the difference in brightness between the day and night sides of the planet, and tells us how much of the star's light is reflected by the surface of TrES-2b.The planet orbits its star at a distance of just five million kilometres, far closer than Mercury is to the Sun.; Mercury is a dense rocky planet with a large iron core and a rocky, silicate surface which has an albedo of 12%.; Surface temperatures on the closest planet to the Sun range between 90 and 700 degrees Kelvin.; In contrast, TrES-2b, an exoplanet in the category of "" shows brightness variations of just 6.5 parts per million, corresponding to an albedo of less than 1%.; But, this assumes that the only cause of the brightness variations is due to the geometry of the planet.; The authors calculate that there is significant emission coming from the day side of the planet.; Its proximity to its host star means that its surface temperature is likely to be around 1000 degrees and any atmosphere it has will likely be composed of chemicals such as vaporised sodium and potassium, or gaseous titanium oxide.; Such a hot temperature also means that the planet actually emits some of its own light, possibly glowing dimly red like an electric bar heater.The Kepler satellite is designed to search for planets using the transit technique, observing one densely-packed star field for its entire operational lifetime, searching for the tiny fluctuations in brightness of a star due to a transiting planet. The exceptional sensitivity of Kepler's instruments has led to this particular discovery in just four months of data acquisition.; In , accepted for publication in the Monthly Notices of the Royal Astronomical Society, the researchers suggest that, over six years of continuous observation, the telescope may be capable of detecting planets with albedos as low as 0.1%.This blog post is a news story from the , aired in the edition.... Read more »

David M. Kipping, & David S. Spiegel. (2011) Detection of visible light from the darkest world. Monthly Notices of the Royal Astronomical Society. arXiv: 1108.2297v2

September 7, 2011
01:58 PM
479 views

In the news this month: discovery of antimatter in the Earth's Van Allen belts

by Megan in Rigel

is often thought of as something that is only created in particle accelerators (or that only exists in science fiction movies), but it is actually present in small quantities throughout the universe.; Now, a team of researchers the presence of naturally occurring antimatter right here in the neighbourhood of the Earth.; This population of antiparticles originates from cosmic ray interactions in the Earth's upper atmosphere where they are subsequently trapped in the planet's magnetosphere.Anti-protons can be produced in a number of ways, through cosmic rays interacting with the interstellar medium, the natural decay processes of some types of particles from our own atmosphere, or in from high energy particles impacting on the atmosphere, although most of the antiparticles would annihilate with their normal counterparts fairly quickly, especially at lower altitudes where the density of the atmosphere is higher.The existence of anti-protons around the Earth was predicted many years ago, but predictions differ, and experiments on board both and the only succeeded in placing upper limits on their abundance.; The anti-protons found by the PAMELA satellite (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) are located in the Earth's Van Allen belts, doughnut-shaped regions defined by the magnetic field of the Earth.; The magnetic fields trap charged particles, resulting in regions with a relatively high density of positively charged protons, and others with a high density of anti-protons.Launched from the Baikonur Cosmodrome in 2006, is designed to detect cosmic particles with energies between tens of mega electron Volts and hundreds of giga electron Volts. PAMELA's orbit takes it through the area known as the , the region where the Van Allen belts pass closest to the Earth's surface.; Since it began operations in 2006, PAMELA has detected anti-protons at a rate more than 1000 times higher than that expected from Galactic sources.; The researchers say that this implies a belt of anti-protons located between two belts of ordinary matter in the Earth's .The signal detected by PAMELA is ten thousand times times stronger inside the South Atlantic Anomaly than it is outside the Earth's radiation belts, and thousands of times stronger than that expected from Galactic cosmic rays.; The likely explanation, say the researchers, is that the Earth's Van Allen belts are acting in the same way as they trap protons, trapping the anti-protons in a layer around the Earth (at least until they encounter a particle of normal matter and annihilate).Although antimatter is pretty destructive stuff if it comes into contact with ordinary matter, luckily for orbiting spacecraft there isn't that much of it.; In 850 days of data acquisition, PAMELA's detectors collected just 28 anti-protons in the previously unknown antimatter region of the inner Van Allen belts.This blog post is a news story from the , aired in the edition.... Read more »

O. Adriani, G. C. Barbarino, G. A. Bazilevskaya, R. Bellotti, M. Boezio, E. A. Bogomolov, M. Bongi, V. Bonvicini, S. Borisov, S. Bottai.... (2011) The discovery of geomagnetically trapped cosmic ray antiprotons. ApJ, 737, L29, 2011. arXiv: 1107.4882v1

March 2, 2011
06:25 AM
348 views

In the news this month: seasonal changes in the northern dunes of Mars

by Megan in Rigel

This blog post is a news story from the Jodcast, aired in the March 2011 edition.

Hansen CJ, Bourke M, Bridges NT, Byrne S, Colon C, Diniega S, Dundas C, Herkenhoff K, McEwen A, Mellon M, Portyankina G, & Thomas N (2011). Seasonal erosion and restoration of Mars' northern polar dunes. Science (New York, N.Y.), 331 (6017), 575-8 PMID: 21292976... Read more »

Hansen CJ, Bourke M, Bridges NT, Byrne S, Colon C, Diniega S, Dundas C, Herkenhoff K, McEwen A, Mellon M.... (2011) Seasonal erosion and restoration of Mars' northern polar dunes. Science (New York, N.Y.), 331(6017), 575-8. PMID: 21292976

March 2, 2011
05:59 AM
428 views

In the news this month: giant black hole in a dwarf galaxy

by Megan in Rigel

This blog post is a news story from the Jodcast, aired in the March 2011 edition.

Reines, A., Sivakoff, G., Johnson, K., & Brogan, C. (2011). An actively accreting massive black hole in the dwarf starburst galaxy Henize 2-10 Nature, 470 (7332), 66-68 DOI: 10.1038/nature09724... Read more »

Reines, A., Sivakoff, G., Johnson, K., & Brogan, C. (2011) An actively accreting massive black hole in the dwarf starburst galaxy Henize 2-10. Nature, 470(7332), 66-68. DOI: 10.1038/nature09724

February 3, 2011
09:33 AM
390 views

In the news this month: a roundup of stories from the 217th AAS meeting

by Megan in Rigel

In the news this month we roundup of some highlights from the 217th meeting of the American Astronomical Society held in Seattle during January. The annual meetings of the American Astronomical Society are the largest gatherings of astronomers on the planet, and the presentations cover topics across the whole field of astronomy and astrophysics, including observational results, theoretical studies and simulations. Here are some of the highlights from this year's meeting.Starting big, astronomers working on the Sloan Digital Sky Survey released the largest colour map of the sky ever made. It's freely available, but be warned - it's big! Covering a third of the sky and created from millions of 2.8 megapixel images obtained by a dedicated 2.5-m telescope over the last decade, the full image is more than a terapixel in size - that's more than one trillion pixels. But it's not just a pretty picture. The full data release, the eighth from the SDSS project, contains a catalogue of objects as well as spectra allowing astronomers anywhere in the world to use the data as the basis for a diverse range of investigations into questions of galaxy evolution, dark matter and dark energy, the distribution and motion of stars in our own Galaxy, and much, much more.One use for sky surveys like the SDSS is searching for distant galaxies which can tell us about star and galaxy formation in the early universe. Because they are so far away, these first galaxies appear very faint by the time their light reaches us here on Earth. But there is a way around this. Gravitational lensing is the effect whereby the matter in a foreground galaxy can bend the light of a background object, making it appear distorted and magnified. This can be a helpful effect, allowing astronomers to see objects more distant than would otherwise be possible, but in surveys where the aim is to discover the size and brightness distributions of early galaxies, this effect can confuse the results. At the AAS meeting, a team of astronomers led by Stuart Wyithe at the University of Melbourne have estimated that as many as 20 per cent of the most distant galaxies currently detected appear brighter than they actually are, because of this lensing effect. With deeper surveys planned in order to probe the early universe, this lensing effect means that the best place to look for these primitive galaxies is probably near larger foreground galaxies, but understanding the lensing effects will be crucial to determining accurate statistics.Closer to home, spiral galaxies like the Milky Way often have numerous satellite galaxies orbiting around them. Over time, these galaxies slowly spiral inwards and are eventually disrupted, becoming streams of stars that are often only detectable in large surveys. Others are just too dim to see. But Sukanya Chakrabarti, a researcher at the University of California, has developed a new method of detecting such galactic companions. These dwarf galaxies may be too small and dim to be seen directly, but their mass affects the surrounding regions of their parent galaxies, causing ripples in the clouds of hydrogen within the spiral arms. Chakrabarti's method uses these ripples to infer the mass and location of otherwise invisible dwarf galaxies and has already been used to infer the existence of an undiscovered dwarf on the opposite side of the Milky Way to the Earth. The technique has also been tested on spiral galaxies in the nearby universe where high resolution radio observations can map the hydrogen gas in detail, correctly predicting the location of the companion to the Whirlpool galaxy, M51.Many galaxies are spirals, like our own Milky Way, containing large reservoirs of gas from which stars are currently being formed, while other so-called early-type galaxies are largely devoid of gas and no longer producing new stars. One of the current problems with our understanding of galaxy evolution is just how galaxies move from the spiral star-forming phase to the gas-poor "red and dead" phase of ellipticals. In a poster presented at the AAS meeting, a team have discovered that one particular elliptical galaxy is rapidly shedding molecular gas from its core. The galaxy, NGC1266, located in the constellation of Eridanus, is pumping out some 13 solar masses worth of molecular gas each year at speeds of up to 400 kilometres per second. Such a strong outflow could completely strip the galaxy of molecular gas required to form stars in just 100 million years, about 1 per cent of the age of the Milky Way. Many galactic outflows are driven by powerful starformation activity, but in this case there is little starformation occuring and the more likely culprit is a central black hole.The question of which came first, galaxies, or the supermassive black holes at their cores, is an ongoing debate in astrophysics. There is a direct relation between the mass of a spiral galaxy's central bulge of stars and that of its supermassive black hole, suggesting that black holes and bulges affected each others' growth. Previous studies have found galaxies in the early universe where the black holes were more massive than this relationship would suggest, implying that black holes came first. Now, astronomers have discovered a dwarf galaxy with a central supermassive black hole but no central bulge of stars, which they say strengthens the case that black holes did come first. This dwarf galaxy has an irregular shape, and strong radio and X-ray emission characteristic of outflows from the region around a black hole, and is likely to be similar to the first galaxies which formed in the early universe.Black holes are not all supermassive. GRS1915+105 is a binary system in the Milky Way with a black hole just 14 times the mass of the Sun, feeding on material from a companion star. As material from the companion spirals towards the black hole, it forms an X-ray emitting disk with material at its inner edge travelling at speeds of up to 50 per cent of the speed of light. Observations of the system at certain times show short pulses of X-rays being emitted every 50 seconds. Now, using a combination of observations from the Chandra X-ray Observatory and the Rossi X-ray Timing Explorer, a team think they know what's going on. In this phase, the inner region of the disk emits enough radiation to push material away from the black hole. Eventually the disk gets so bright and so hot that it disintegrates and falls towards the black hole, before the cycle begins again. Between pulses, the inner part of the disk refills from material further away from the black hole, while the radiation emitted heats up the outer disk and drives material away from the system, eventually limiting the amount of matter which the black hole can consume, and pushing the system into one of its other known states.More well-known periodic objects are pulsars, compact remnants left over when stars larger than eight times the mass of the Sun end their lives as supernovae. One of the brightest and well-observed pulsars lies in the heart of the Crab nebula in Taurus, a pulsar which has long been thought of as one of the steadiest high energy sources in the sky. So steady, in fact, that X-ray telescopes use it as a calibrator, and the brightness of other sources are often quoted in units of "millicrabs". But now, observations made with several high energy instruments have revealed that the Crab pulsar is far less steady than has been assumed. Observations with the Gamma-ray Burst Monitor on the Fermi satellite suggested that the Crab pulsar was dimming, but to prove it was a real effect rather than an instrumental problem affecting the observations, the team made further observations with several other high energy instruments, confirming that the pulsar has dimmed by seven per cent over two years. The result has implications for the in-flight calibration of X-ray instruments, as well as possible effects on previous results where the Crab pulsar was used to calibrate the observations.It's not just pulsars which vary. A class of stars known as Cepheid variables have a direct relationship between their maximum brightness and their period of variability. If you can measure the period, then you can calculate how bright the star would be at a given distance. By comparing this to how bright the star actually appears, you can calculate how far away it is. This relationship has long been used as a rung on the so-called cosmic distance ladder, allowing the distances of objects throughout the universe to be determined. Since Cepheids are the first rung on this ladder, and each rung on the ladder relies on the accuracy of the previous one, it is vital to much of cosmology that the calibration of Cepheid variability is accurate. But in a study carried out with the Spitzer space telescope, astronomers have discovered that the first star in the class, delta Cephei, is losing mass in a stellar wind at a rate which alters its mass and creates a surrounding nebula which affects the stars' apparent brightness. Further observations showed that as many as 25 per cent of Cepheids are also losing mass at a significant rate, with implications for distance measurements that underpin much of modern cosmology.Even the smallest of stars turn out to be not so constant. A study of more than 215,000 red dwarf stars has found that even these old stars produce flares strong enough to disrupt the atmosphere of any orbiting planets. Originally observed in a survey to search for dimming due to transiting planets, the data were later searched for evidence of flaring and produced several interesting results. The average flare duration was 15 minutes, and some flares increased the brightness of the star by 10 per cent, making them brighter than flares on our own, much larger, Sun. The astronomers also found that variable red dwarfs were about one thousand times more likely to flare than non-variable red dwarfs, possibly due to their strong magnetic fields.P... Read more »

SDSS-III collaboration: Hiroaki Aihara, Carlos Allende Prieto, Deokkeun An, Scott F. Anderson, Éric Aubourg, Eduardo Balbinot, Timothy C. Beers, Andreas A. Berlind, Steven J. Bickerton, Dmitry Bizyaev.... (2011) The Eighth Data Release of the Sloan Digital Sky Survey: First Data from SDSS-III. Astrophysical Journal Supplements. arXiv: 1101.1559v1

Wyithe JS, Yan H, Windhorst RA, & Mao S. (2011) A distortion of very-high-redshift galaxy number counts by gravitational lensing. Nature, 469(7329), 181-4. PMID: 21228870

Sukanya Chakrabarti, Frank Bigiel, Philip Chang, & Leo Blitz. (2011) Finding Dark Galaxies From Their Tidal Imprints. Astrophysical Journal. arXiv: 1101.0815v1

December 17, 2010
02:56 AM
441 views

In the news this (last) month: massive neutron star

by Megan in Rigel

Left over from the explosions of massive stars, are incredibly dense and compact objects, but very little is known about their internal structure. , spinning neutron stars with powerful jets of radio emission which act something like cosmic lighthouses, are useful probes of extreme physics such as and forms of matter so dense that investigating them in laboratories on the Earth is extremely difficult.Various models of the internal structure of a neutron star have been proposed, including various exotic forms of matter, but determining which is closest to reality requires knowledge of the distribution of masses and radii, measurements which require careful observations and depend to some extent on the exact models and assumptions used.Reported in , a team of astronomers using the in the US have discovered a pulsar with a mass twice that of the Sun. have implications not only for our understanding of neutron stars and their formation, but also for our understanding of nuclear physics and matter at very high densities, and suggest that many of the theoretical models of neutron star structure can now be ruled out.Led by Paul Demorest of the in the US, the astronomers observed the binary millisecond pulsar J1614-2230, a pulsar orbiting a white dwarf in a binary system which lies almost edge-on to our line of sight. This geometry was vital, allowing them to make use of an effect known as the , an effect of general relativity. This is the delay of a signal caused as it moves through the gravitational field of the white dwarf companion - a delay which is a maximum when the pulsar lies on the far side of its orbit relative to the Earth. This effect allowed the mass of both the neutron star and its white dwarf companion to be measured precisely.The neutron star was expected to have a mass of about 1.5 times that of the Sun, but they calculated a mass of 1.97 solar masses for the neutron star, the highest mass to be accurately measured for such an object. Combining this mass measurement with predictions based on various different physical models allows several scenarios to be ruled out, including several exotic states of matter containing subatomic particles such as or .The discovery also has implications for other astronomical events. One class of gamma ray burst is thought to be the result of colliding neutron stars. The fact that neutron stars have now been shown to be this massive makes this a viable mechanism for these events.This blog post is a news story from the , aired in the edition.... Read more »

Demorest, P., Pennucci, T., Ransom, S., Roberts, M., & Hessels, J. (2010) A two-solar-mass neutron star measured using Shapiro delay. Nature, 467(7319), 1081-1083. DOI: 10.1038/nature09466

November 30, 2010
12:31 AM
529 views

In the news this month: record-breaking galaxy

by Megan in Rigel

The most distant object in the known universe is a highly luminous , a single explosion discovered near maximum light, at a of 8.2, a time when the universe was only 630 million years old, less than 5 percent of its current age. The most distant known galaxy lies at a redshift of 6.96, the light we see now left the galaxy just 750 million years after the . However, both these records have now been broken by a galaxy discovered by the Hubble Space Telescope which has a redshift of 8.56 and an estimated distance of 87 , making it the most distant object currently known.First seen in the Hubble , the deepest single image ever taken in near-infrared light, the galaxy (known as UDFy-38135539) was initially classified as a candidate high redshift object based on its colours. Now, a team led by Matthew Lehnert at the in France, has used spectroscopic observations to confirm that the object is the most distant galaxy so far detected.Since the universe is expanding, the further away an object is, the faster it appears to be moving away from us. This results in a shift in wavelength of the light emitted from an object (known as ) with the size of the shift relating to the distance between us and the object. (This is similar to the shift in pitch you hear when a police car travels past at high speed.) This effect allows distances to be calculated by measuring the shift in spectral lines from known chemicals. Lehnert's team used a sensitive spectrograph on the located in Chile to observe the spectrum of this galaxy and found an emission line which is likely to be caused by hydrogen shifted to redder wavelengths by the relative motion between the galaxy and us.This is an exciting discovery because it is the first galaxy discovered in the so-called , the period in the history of the universe where the between the newly formed galaxies was being - the light from young, hot stars stripped electrons from hydrogen atoms. The authors used the measured light from the galaxy to calculate the size of the region of surrounding gas which the galaxy should have been able to ionise on its own and found that, in order to explain the size of the which is consistent with the observations, there must be other sources of radiation. One suggestion is that dwarf galaxies clustering around larger, more easily observed galaxies, may be responsible for this additional radiation, but there are other explanations.While observations such as these are difficult with current ground-based telescopes due to the faint nature of these distant sources, the planned next generation of larger and more sensitive ground- and space-based instruments should make observations of such sources much easier.This blog post is a news story from the , aired in the edition.... Read more »

Lehnert, M., Nesvadba, N., Cuby, J., Swinbank, A., Morris, S., Clément, B., Evans, C., Bremer, M., & Basa, S. (2010) Spectroscopic confirmation of a galaxy at redshift z . Nature, 467(7318), 940-942. DOI: 10.1038/nature09462

November 29, 2010
09:10 PM
420 views

In the news this month: latest results from LCROSS

by Megan in Rigel

Small lumps of rock hit the Moon quite regularly, but in 2009 two artificial projectiles impacted on the lunar surface in an experiment designed to search for water in the permanent shadows of a crater near the lunar south pole. Hints of subsurface water on the Moon had already been found in 1999 when NASA's spacecraft detected signatures of concentrated hydrogen, the "H" in "H2O", near the lunar poles. The Lunar CRater Observation and Sensing Satellite, or , was a low-cost mission launched together with the in June 2009. The mission consisted of the Centaur upper stage of the Atlas-V launch vehicle, and a shepherding spacecraft equipped with various cameras and sensors. Moving at a speed of 1.5 miles per second, the Centaur stage impacted the lunar surface on October 9th 2009, sending up a plume of material from the permanently shadowed floor of the crater Cabeus. The LCROSS spacecraft observed the impact before flying through the plume to impact the surface some four minutes later. In the October 22nd issue of magazine, several teams working on data from the impact publish their findings.Cabeus crater was chosen for the experiment as it contains an area which is permanently in shadow, due to its location close to the lunar south pole. The low temperatures, combined with the movement of soil () by micrometeorite impacts (known as "") which buries accumulated material, makes such craters ideal places to search for - chemicals which are solid only at very low temperatures. from a neutron spectrometer aboard the Lunar Prospector spacecraft suggested that ice could make up between half and one percent of the soil near the lunar poles, and from a neutron detector on the Lunar Reconnaissance Orbiter showed a strong hydrogen signal, originally thought to be from water ice. But observations of the LCROSS plume, made with another instrument (, an ultraviolet spectrograph) on-board LRO, showed that as much of the hydrogen signal comes from as it does from water. Water is thought to have accumulated from cometary impacts, distributing water across the lunar surface in the ejecta, but it is far from certain where the molecular hydrogen originated.The results from the nine instruments on-board the LCROSS shepherding spacecraft, on October 22nd, show signatures of numerous different chemicals, including water vapour, water ice and , a common result of the breaking up of water molecules. Using the spectra obtained, the LCROSS team calculated that the maximum amount of water vapour and ice visible in the field of view of the instruments was 155 kilograms. By estimating the amount of material that was excavated by the Centaur impact and became observable by reaching sunlight, they calculated that the concentration of water in the lunar regolith at the impact site was 5.6 percent. They also found that the observed abundances of other volatile compounds, such as ammonia, sulphur dioxide and carbon monoxide, were far higher than the abundances found in comets, suggesting that molecule formation may be going on in these shadowed regions on the surfaces of cold dust grains.This blog post is a news story from the , aired in the edition.... Read more »

Colaprete, A., Schultz, P., Heldmann, J., Wooden, D., Shirley, M., Ennico, K., Hermalyn, B., Marshall, W., Ricco, A., Elphic, R.... (2010) Detection of Water in the LCROSS Ejecta Plume. Science, 330(6003), 463-468. DOI: 10.1126/science.1186986

Schultz, P., Hermalyn, B., Colaprete, A., Ennico, K., Shirley, M., & Marshall, W. (2010) The LCROSS Cratering Experiment. Science, 330(6003), 468-472. DOI: 10.1126/science.1187454

Gladstone, G., Hurley, D., Retherford, K., Feldman, P., Pryor, W., Chaufray, J., Versteeg, M., Greathouse, T., Steffl, A., Throop, H.... (2010) LRO-LAMP Observations of the LCROSS Impact Plume. Science, 330(6003), 472-476. DOI: 10.1126/science.1186474

Hayne, P., Greenhagen, B., Foote, M., Siegler, M., Vasavada, A., & Paige, D. (2010) Diviner Lunar Radiometer Observations of the LCROSS Impact. Science, 330(6003), 477-479. DOI: 10.1126/science.1197135

Paige, D., Siegler, M., Zhang, J., Hayne, P., Foote, E., Bennett, K., Vasavada, A., Greenhagen, B., Schofield, J., McCleese, D.... (2010) Diviner Lunar Radiometer Observations of Cold Traps in the Moon's South Polar Region. Science, 330(6003), 479-482. DOI: 10.1126/science.1187726

Mitrofanov, I., Sanin, A., Boynton, W., Chin, G., Garvin, J., Golovin, D., Evans, L., Harshman, K., Kozyrev, A., Litvak, M.... (2010) Hydrogen Mapping of the Lunar South Pole Using the LRO Neutron Detector Experiment LEND. Science, 330(6003), 483-486. DOI: 10.1126/science.1185696

August 23, 2010
11:04 AM
488 views

In the news this month: pulsar irregularities

by Megan in Rigel

After massive stars like explode, the object left behind is thought to be either a or a black hole, depending on the final mass of the progenitor star. are neutron stars that have strong magnetic fields and behave somewhat like cosmic lighthouses, projecting beams of radio emission into space as they spin. Studying the pulses of radiation as the beams sweep past the Earth can provide valuable information on the physics of these extreme objects, allowing astronomers to probe physics under conditions which are not possible to create in a terrestrial laboratory. While pulsars are known to be extremely accurate , their pulse rates are very stable over time, there are however unexplained deviations from the expected spin rate, a phenomenon known as timing noise. Now, a team led by Andrew Lyne at the , have uncovered a mechanism which could explain this noise.Over long timescales, the rate at which a pulsar spins (known as the rate) decreases slowly in a predictable way due to the conversion of rotational energy into photons. By studying a large number of pulsars repeatedly over 40 years, the team found that the deviations from the expected spin down rate were actually quasi-periodic on timescales between one and ten years, and that several other pulsar characteristics may be linked to the same phenomenon. One particular pulsar, known as B1931+24, only displays radio pulses intermittently, and long term study showed that it also had two different spin down rates: its spin rate decreased faster when the radio signal was detectable.The team analysed the data on a large sample of pulsars and found a further seventeen which show evidence of quasi-periodic spin down rates, many of which also show variations in the shape of the pulse profile. The authors suggest that the likely explanation is that the pulsar's is switching between two distinct states. Exactly what causes the pulsar to switch between states is not yet known, but if the changes can be accurately modeled then the timing noise can be reduced, and astronomers will find it easier to compensate for errors in pulsar ;clocks; in highly sensitive experiments designed to detect .This blog post is a news story from the , aired in the edition.... Read more »

Lyne, A., Hobbs, G., Kramer, M., Stairs, I., & Stappers, B. (2010) Switched Magnetospheric Regulation of Pulsar Spin-Down. Science, 329(5990), 408-412. DOI: 10.1126/science.1186683

July 2, 2010
05:45 AM
564 views

In the news this month: a drop in eta Carinae's stellar wind

by Megan in Rigel

are the violent explosions of massive stars, so bright that the events can be seen in distant galaxies. But not all apparent explosions are genuine supernovae. Some fall into the category of , the sudden increase in brightness of a star without the terminal explosion. One such impostor event was the , a star which is amongst the most massive known in the Milky Way. Located 7,500 light years away in the constellation of Carina, the star is five million times more luminous than the Sun and an estimated 100 times as massive. underwent a massive but non-terminal explosion 150 years ago, allowing the close-up study of a supernova impostor. During the eruption, the star lost about ten percent of its mass, throwing off the outer layers in the surrounding nebula. Since then, the star has been enshrouded in a thick cloud of dusty debris and has been losing material at the rate of one per year in a strong stellar wind.Now, a team of researchers, led by at the University of Minnesota, have observed dramatic changes in the star's spectrum. Observations over the last decade have shown an increase in the star's magnitude, but with no major long-term changes in its spectrum, something that might be expected following an event causing a major change in brightness. carried out with the on the Hubble Space Telescope by Mehner's team in the emission lines, caused by specific elements in the star's atmosphere. According to the team, the sudden rapid decrease in the brightness of the emission lines (dropping to a third of their original strength in just ten years) suggests a decrease in the strength of the , possibly signifying a much more rapid return to the pre-explosion state than was previously anticipated. With the wind density decreasing, the nebula should begin to thin and the star itself may become visible to modern telescopes for the first time, possibly within the next decade.There are other explanations which may account for the unusual spectroscopic developments, including a change in the latitude dependence of the wind, but the complicated nature of the surrounding nebula and the difficulties constructing accurate models make an accurate assessment problematic.This blog post is a news story from the , aired in the edition.... Read more »

Mehner, A., Davidson, K., Humphreys, R., Martin, J., Ishibashi, K., Ferland, G., & Walborn, N. (2010) A SEA CHANGE IN ETA CARINAE . The Astrophysical Journal, 717(1). DOI: 10.1088/2041-8205/717/1/L22

June 7, 2010
04:20 AM
675 views

In the news this month... Hubble spots a planet-eating star

by Megan in Rigel

Most of the discovered so far are in the class known as "", large gas giants orbiting close to their parent stars, since many of the search techniques used are most sensitive to this type of planet. Usually these planets are located close enough to their parent star that they orbit in just a few days, but a team that is orbiting so close to its parent star that it is actually being disrupted.The planet, known as WASP-12b, is located in the constellation of Auriga and was discovered in the , or WASP, operated by a consortium of eight academic institutions. WASP consists of two robotic observatories, one located at La Palma in the Canary Islands, the other at the South African Astronomical Observatory at Sutherland in South Africa, both scanning the sky for the tiny dimming effects caused when a planet transits in front of a star. This particular planet orbits its parent star, a yellow dwarf known as WASP-12, in just 1.1 Earth days, and shows evidence of an atmosphere which extends far further from the planet than would be expected for a body of this size.Previous observations have shown that at least one other exoplanet displays evidence of such an extended atmosphere, and two different mechanisms have been suggested: either heating from the parent star, or an interaction with the stellar wind. This new planet was first discovered by the WASP survey in 2008, and was predicted to be physically distorted by its proximity to the host star. These new observations, made with the on the Hubble Space Telescope and during May, have verified the prediction. WASP-12b is so close to the star that the tidal forces exerted on it have heated and deformed it far from the normal almost-spherical planetary shape, so far in fact that the internal heating has caused the atmosphere to expand far enough that it is being dragged off onto the surface of the star.Absorption from elements such as , , and was expected in the atmosphere of the star, and the increase in absorption during the transit allowed the astronomers to calculate how common these elements are in the planet's atmosphere. The research, led by Luca Fossati at the in the UK, examined the ultra violet spectrum of the planet's atmosphere and found a much greater abundance of than expected from models of planetary atmospheres. The suggested reason for this unexpected result is that the high amount of incident radiation due to the close proximity of the star, together with tidal effects, cause a large amount of mixing within the atmosphere, pulling heavy elements higher in the atmosphere than they would normally be found. The heating also causes the atmosphere to expand, overflowing what is known as the , the point beyond which particles escape the gravitational pull of the planet and are lost to the surrounding space.From the evidence provided by their ultra-violet observations, the researchers conclude that the planet is probably undergoing by its host star, and the material lost from the atmosphere is forming a diffuse ring around the star along the planet's orbit. While few examples of such systems are currently known, further observations and detailed modelling will help to determine exactly what is going on in these peculiar atmospheres.This blog post is a news story from the , aired in the edition.... Read more »

Fossati, L., Haswell, C., Froning, C., Hebb, L., Holmes, S., Kolb, U., Helling, C., Carter, A., Wheatley, P., Cameron, A.... (2010) METALS IN THE EXOSPHERE OF THE HIGHLY IRRADIATED PLANET WASP-12b. The Astrophysical Journal, 714(2). DOI: 10.1088/2041-8205/714/2/L222

June 7, 2010
04:00 AM
710 views

In the news this month... runaway star in 30 Doradus

by Megan in Rigel

One of the most spectacular examples of a star formation region in the nearby universe is , also known as the , located in the Large Magellanic Cloud. This region is a giant stellar nursery, similar to the , but much larger, containing many clusters of recently formed young, hot stars. Some of the young stars in the nebula are many tens of times more massive than the Sun, making them some of the most massive stars known. New observations, on May 5th, show that one particular star is travelling away from the nebula at high velocity.The star, known as 30 Dor 016, was first spotted in 2006 when it was observed by the at Siding Spring Observatory in Australia. It was found to be an exceptionally hot, massive blue-white star, located relatively far from any cluster in which such stars are usually found. More recent observations made during the calibration of the , installed on the Hubble Space Telescope during servicing mission four in May 2009, showed that the star had an unusually fast stellar wind, almost 3500 km/s, one of the most powerful ever detected and a strong indication that the star is incredibly massive - it is estimated to be roughly 90 times the mass of the Sun. Its size means that it must be young - stars this large only live for a few million years before exploding as core collapse supernovae.Archive images taken by Hubble's in 1995, show that the star is at one end of an egg-shaped cavity in the surrounding interstellar gas which points towards 30 Doradus, in the direction of a cluster of massive stars known as R136, the likely birthplace of the star. Further observations, made with the in Chile, have shown that the star's velocity is more than 400,000 kilometres an hour, a speed that would get you from the Earth to the Moon in an hour. The measured velocity could have been due to orbital motion if the star had a companion, but the VLT observations show that it is a single massive star, and the velocity is due to motion away from the nebula.Stars can end up with such high velocities as a result of nearby explosions. In the case of 016 however, this is unlikely since the stars in 30 Doradus are still too young to have exploded as supernovae. The more likely explanation, , led by Chris Evans at the in Edinburgh, is that it was ejected from the cluster by dynamical interactions with other massive stars, one of the clearest examples yet of such a process.This blog post is a news story from the , aired in the edition.... Read more »

Evans, C., Walborn, N., Crowther, P., Hénault-Brunet, V., Massa, D., Taylor, W., Howarth, I., Sana, H., Lennon, D., & van Loon, J. (2010) A MASSIVE RUNAWAY STAR FROM 30 DORADUS. The Astrophysical Journal, 715(2). DOI: 10.1088/2041-8205/715/2/L74

June 7, 2010
03:45 AM
509 views

In the news this month... a possible new class of supernova

by Megan in Rigel

Most supernovae are classified as one of two different types of explosion: single massive short-lived stars that explode when their cores run out of fuel at the end of their lives and undergo gravitational collapse, and old evolved white dwarfs in binary systems which accrete hydrogen from a companion star before exploding catastrophically.; are generally seen only in regions of ongoing star formation since, by stellar standards, their supergiant progenitors do not live for very long. In contrast, in binary systems are produced by old, evolved stars and so are seen in all galaxy types, even those which show no signs of recent star formation. However, in the May 20th issue of the journal Nature, two groups of astronomers with characteristics that do not fit into existing categories of supernovae, and come to very different conclusions about their progenitors.The first event, , was observed in the edge-on spiral galaxy in 2005 and was initially classified as a type Ib (core collapse) supernova based on the chemical elements detected in its optical spectrum soon after explosion. Located in the , rather than the disk of the galaxy, the surrounding environment is composed of an old stellar population with no recent star formation, an unlikely location for a core collapse supernova. While some of its properties show similarities to type Ia explosions, the lightcurve shows a much faster decline than is expected for the thermonuclear explosion of a white dwarf. The mass ejected in the explosion, less than a third of a solar mass, is also low for this class of supernova, and analysis of the spectra showed significant differences from what is expected from either explosion mechanism. lead Dr Perets' team to conclude that the progenitor was something unusual, likely to be a helium-rich low mass star, probably a helium-accreting white dwarf, making 2005E the first example of a new class of supernova.However, 2005E is not the only supernova with these unusual characteristics; several other calcium-rich, subluminous supernovae, spectroscopically classified as type Ib/c events, have also been observed. One such event is SN 2005cz, in the same issue of Nature. While 2005cz shares many properties with 2005E, Kawabata's team reaches a different conclusion on the cause of the explosion. According to their study, supernovae in this class are more likely to originate via the core collapse mechanism, but from stars with masses at the lower end of the range of those that explode. Unlike 2005E, SN2005cz is located in an . These galaxies are generally made up of old stellar populations, but NGC4589 has a relatively young stellar population (for an elliptical galaxy) so the explosion of a star by core collapse is not ruled out.Since most supernova searches are more likely to detect bright events, the number of faint 2005E-like events currently known is small. More sensitive surveys are planned, however, and these should result in many more examples and further insights into this non-standard class of supernova.This blog post is a news story from the , aired in the edition.... Read more »

Perets, H., Gal-Yam, A., Mazzali, P., Arnett, D., Kagan, D., Filippenko, A., Li, W., Arcavi, I., Cenko, S., Fox, D.... (2010) A faint type of supernova from a white dwarf with a helium-rich companion. Nature, 465(7296), 322-325. DOI: 10.1038/nature09056

Kawabata, K., Maeda, K., Nomoto, K., Taubenberger, S., Tanaka, M., Deng, J., Pian, E., Hattori, T., & Itagaki, K. (2010) A massive star origin for an unusual helium-rich supernova in an elliptical galaxy. Nature, 465(7296), 326-328. DOI: 10.1038/nature09055

May 31, 2010
02:09 PM
842 views

In the news this month... volcanoes on Venus

by Megan in Rigel

Closer to home, the planet Venus shows large amounts of evidence of volcanic activity. Despite being shrouded under a thick layer of cloud, spacecraft have been able to map the surface of our nearest neighbour using radar, leading to the realisation that much of the planet's surface is comparatively young, suggesting that at some point in the recent past the planet underwent a complete resurfacing. However the question remains whether Venus is currently a geologically active planet.... Read more »

Smrekar, S., Stofan, E., Mueller, N., Treiman, A., Elkins-Tanton, L., Helbert, J., Piccioni, G., & Drossart, P. (2010) Recent Hotspot Volcanism on Venus from VIRTIS Emissivity Data. Science, 328(5978), 605-608. DOI: 10.1126/science.1186785

May 31, 2010
09:49 AM
509 views

In the news this month... the strange atmosphere of GJ 436b

by Megan in Rigel

Most known extrasolar planets are massive gas giants orbiting close to their parent stars. If one of these planets happens to pass directly between us and its parent star during its orbit, then sensitive spectroscopy can be used to determine the chemical make-up of its atmosphere. Models of such atmospheres predict which gases should be present and in what relative abundances, based on physical conditions such as the temperature. Recent infra red observations carried out with the have provided the first details of the atmospheric composition of a so-called hot Neptune.The planet, known as , orbits an M-type dwarf star in the constellation of Leo. It is similar to Neptune in size, but orbits its parent star in just 2.6 days. Previous observations of the planet showed that its surface temperature was estimated to be 712 K, higher than predicted due to stellar heating alone, and the new observations () suggest that its atmosphere may not be in equilibrium. The team, led by Kevin Stevenson at the University of Central Florida, observed the planet's day side as it passed around the far side of the star and examined the infra red spectrum for various chemical signatures. What they found was a high abundance of carbon monoxide and a deficiency of methane compared to predictions from atmospheric models at this temperature for an atmosphere thought to be dominated by hydrogen. In an atmosphere such as this, methane (one carbon atom and four hydrogen atoms) should be the main carbon-bearing molecule, but the observations show the actual abundance is less than that predicted by a factor of seven thousand. The large amount of absorption due to carbon monoxide is also unexpected, the results suggesting that the atmosphere may not be in thermochemical equilibrium.One alternative explanation considered by the authors is that the atmosphere may not be dominated by hydrogen, but this is unlikely given the dominance of hydrogen in planet forming disks. Another possibility is that vertical mixing within the atmosphere may dredge up carbon monoxide from lower, hotter parts of the atmosphere, although the authors point out that, in order to explain the observed abundances, the amount of mixing would have to be large. These new data will provide useful information for future atmospheric modeling.This blog post is a news story from the , aired in the edition.... Read more »

Stevenson, K., Harrington, J., Nymeyer, S., Madhusudhan, N., Seager, S., Bowman, W., Hardy, R., Deming, D., Rauscher, E., & Lust, N. (2010) Possible thermochemical disequilibrium in the atmosphere of the exoplanet GJ 436b. Nature, 464(7292), 1161-1164. DOI: 10.1038/nature09013

May 31, 2010
08:19 AM
512 views

In the news this month... the nature of the eclipsing binary system epsilon Aurigae

by Megan in Rigel

Many stars vary in brightness, sometimes due to changes within the star itself such as novae or Cepheid variables, others because of external factors. One is , an F-type supergiant in the constellation of Auriga, located at an estimated distance of 625 parsecs (2,100 light years). Since its variable nature was discovered in the 1820s, the star has been seen to fade in brightness every 27.1 years. During these eighteen-month-long eclipses, the brightness of the star fades to around 50 per cent of its normal magnitude. While the variability of the system has been well-studied, the exact physical nature of the eclipsing companion is less certain as it has remained undetected, and many models have been put forward to explain the unusual nature of the system. Observations of epsion Aurigae show that the star and its darker companion have a similar mass which, until recently, was thought to be around 15 times the mass of the Sun. have shown that the supergiant star has a much lower mass of between two and three solar masses, and that the companion may be a single B5V-type star embedded within a disk of opaque material.Now, using the CHARA interferometer, an array of infrared telescopes located on Mount Wilson in California, a team led by Brian Kloppenborg from the University of Denver have . This is the first time a spatially resolved observation of an eclipsing binary has been made. Their observations show that the eclipsing object is an opaque disk of dust, tilted to our line of sight by an estimated 84 degrees. From the motion of the disk between two observations carried out in November and December 2009, the team infer that the companion object is more massive than the visible F-type supergiant. Assuming the B-type star within the disk has a typical mass of 5.9 solar masses, the researchers calculate a mass of 3.6 solar masses for the F-type supergiant. They also calculate that if the disk is composed entirely of dust, then its mass is less than 10 per cent of the Earth's.While the nature of the disk is now clearer, there are still several unanswered questions which remain. The model that best fits the data is of a geometrically thin disk tilted to our line of sight, rather than a thick disk seen edge on. However, the fact that it is opaque suggests that its nature is more like a debris disk than a dusty accretion disk around a young stellar object. The tilted disk model also predicts a central hole which should cause a mid-eclipse brightening of the F-type star. Observers the world-over will continue to monitor the system during the eclipse, and the data should help build up a profile of the disk and constrain the evolutionary history of the system.This blog post is a news story from the , aired in the edition.... Read more »

Kloppenborg, B., Stencel, R., Monnier, J., Schaefer, G., Zhao, M., Baron, F., McAlister, H., ten Brummelaar, T., Che, X., Farrington, C.... (2010) Infrared images of the transiting disk in the ε Aurigae system. Nature, 464(7290), 870-872. DOI: 10.1038/nature08968

March 4, 2010
02:31 AM
566 views

In the News this month: emission from methane in the atmosphere of an extrasolar planet

by Megan in Rigel

In just fifteen years, have been discovered around stars other than the Sun using a variety of techniques. Even without the ability to directly image these other worlds, some of their properties can be determined. Most extra solar planets found so far are massive orbiting close to their parent stars, since these are the types of planets that the detection methods are most sensitive to. As develop and improve, astronomers are finding out more and more about these other worlds, including the composition of their atmospheres.The chemical make-up of planetary atmospheres can provide clues to a whole variety of processes, including both , but often our own atmosphere gets in the way, hampering attempts to detect the spectral signatures of certain molecules. To get a full picture of what is going on often requires both ground-based and space-based observations. Satellite observations have previously detected the absorption signatures of , , and in the atmospheres of two so-called , planets with masses similar to or greater than that of Jupiter, but orbiting far closer to their parent star.In research published in on the 4th of February, a team led by Mark Swain of the in California, have detected the in the atmosphere of one particular exoplanet known as HD-189-733-b. Using the NASA Infrared Telescope Facility located on Mauna Kea, the team discovered an unexpectedly strong emission feature at a wavelength of 3.25 microns, corresponding to the presence of methane in the planet's atmosphere.This is not the first time that methane fluorescence has been seen, but it is the first time it has been detected in the spectrum of an exoplanet. It has previously been seen in our own solar system in the atmospheres of Jupiter, Saturn and Titan, although HD-189-733-b is much closer to its parent star and so offers a chance to study a planetary atmosphere under very different physical conditions.... Read more »

Swain, M., Deroo, P., Griffith, C., Tinetti, G., Thatte, A., Vasisht, G., Chen, P., Bouwman, J., Crossfield, I., Angerhausen, D.... (2010) A ground-based near-infrared emission spectrum of the exoplanet HD 189733b. Nature, 463(7281), 637-639. DOI: 10.1038/nature08775

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