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

Rigel
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January 3, 2010
08:48 PM
1,866 views

In the News this month: first observational evidence of a new type of supernova

by Megan in Rigel

Stars the size and mass of our Sun end their lives by first expanding as , then shrinking to . Stars heavier than this however, come to a much more violent end.; For stars with masses between about 10 and 100 times that of the Sun, they continue in the core, until they run out of hydrogen. They then begin to fuse the helium nuclei together to form heavier elements such as carbon, nitrogen and oxygen. This carries on through the elements until iron, at which point the to form either a neutron star or a black hole, and the outer layers are expelled in a giant explosion known as a supernova. For stars heavier than 140 times the mass of the Sun, theory suggests that there may be another mechanism causing the explosion.Counterbalancing gravity inside a star is , the force of the photons themselves which help stop a star collapsing under its own gravitational pull. In very massive stars, when the temperature rises above 1,000,000,000 kelvin, these photons can undergo a process known as where they create an electron and its anti-particle, a positron. This reduces the number of photons in the star, reducing the radiation pressure and, if it happens on a large enough scale, allows the star to begin collapsing. The result is the ignition of oxygen in the core, and the end of the star in what is known as a .Models of this type of supernova are fairly robust, but have never been confirmed observationally. But now a team led by Avishay Gal-yam at the Weizmann Institute of Science in Israel, have discovered of such an explosion taking place. They observed the supernova known as SN 2007bi and compared their observations with predictions from models of pair-instability supernovae. Their data fit the models very well, providing the first clear evidence of this type of explosion. Stars this size and much larger are thought to have been common in the early evolution of the universe, contributing significantly to the chemical evolution of the early galaxies, so confirmation of the models is an important step in understanding how the universe came to be the way we see it today.... Read more »

Gal-Yam, A., Mazzali, P., Ofek, E., Nugent, P., Kulkarni, S., Kasliwal, M., Quimby, R., Filippenko, A., Cenko, S., Chornock, R.... (2009) Supernova 2007bi as a pair-instability explosion. Nature, 462(7273), 624-627. DOI: 10.1038/nature08579

October 5, 2009
07:06 AM
882 views

In the News this month: first results from a panoramic survey of the Andromeda galaxy

by Megan in Rigel

Edwin Hubble's original classification of galaxies into various types based on their visible shapes and structures has been a feature of extra-galactic astronomy since the 1920s. The scheme, originally thought to depict an evolutionary sequence, has two major groups: spiral galaxies with a small central bulge, spiral arms and possibly a central bar, and elliptical galaxies that are more spherical in structure with no spiral arms or disk. There are however, many galaxies which do not fit into this scheme, being neither spherical or disk-like, and these are usually lumped together into a class called the irregulars. These disturbed galaxies are surprisingly common, and many are the result of collisions or close encounters between galaxies. Such interactions happened frequently throughout the history of the universe, but it is also going on right now in our own galactic neighbourhood.The nearest major galaxy to our own is the Andromeda Galaxy, otherwise known as M31, slightly larger than the Milky Way and located 2.5 million light years away. It is heading towards the Milky Way at some 300 km/s and, in a few billion years, the two galaxies will eventually collide. In some cosmological models, galaxies grow over time by disrupting and absorbing smaller galaxies in such collisions. In such violent processes, a significant number of stars should be tossed out of the galaxies involved, forming a diffuse halo which can provide clues to the merger history of a galaxy, if they are bright enough to be detected. In research reported in the journal Nature on the 3rd of September, a team of astronomers led by Alan McConnachie at the Herzberg Institute of Astrophysics in Canada, report a panoramic survey of Andromeda and its nearby neighbour, the Triangulum galaxy, M33, which shows clear evidence of the remnants of galactic mergers.Detecting this evidence is difficult as these stellar populations are extremely faint and distributed over a huge area, so the astronomers are using the MegaCam camera on the 3.6-metre Canada-France-Hawaii telescope to build up a sensitive wide-field survey of the Andromeda galaxy and it's companions. The so-called Pan-Andromeda Archaeological Survey will cover more than 300 square degrees when completed in 2011, but has already produced results showing the vast extent of M31's stellar halo, covering an area of nearly 100 times the classical optical disk of the galaxy.These early results from the survey lend support to the idea that large galaxies build up through the accretion of smaller galaxies. The halo stars discovered away from the disk of M31 are unlikely to have been formed at their present positions because there is not enough gas there for star formation to occur. The most likely explanation is that they have been thrown out in a tidal interaction. Another piece of evidence that they are relics from previous galactic mergers is that the stars in this faint population are often located in huge arcs, loops and other diffuse structures which are characteristic of the gravitational disruption of dwarf galaxies undergoing a merger with a larger galaxy.As well as lending support to the hierarchical model of galaxy formation, the team's results also show a new diffuse stellar structure around M33, M31's largest companion galaxy. This newly discovered feature matches up with a distortion in the disk of M33, as well as a mild warp seen in the outer disk of M31, adding to the evidence of a past tidal interaction between the two galaxies.... Read more »

McConnachie, A., Irwin, M., Ibata, R., Dubinski, J., Widrow, L., Martin, N., Côté, P., Dotter, A., Navarro, J., Ferguson, A.... (2009) The remnants of galaxy formation from a panoramic survey of the region around M31. Nature, 461(7260), 66-69. DOI: 10.1038/nature08327

Astronomy

January 27, 2010
01:21 PM
874 views

Doctor Who and the Silver Spiral

by Megan in Rigel

Far across the universe, something big was about to happen. The explosion would outshine an entire galaxy and be visible billions of kilometres away. Its light would travel across the universe for millions of years but, aside from a few astronomers, it would go unnoticed on the Earth.With a grating, wheezing noise, a small blue box flickered into existence."So, where are we?""Have a look..." the Doctor replied, tapping a control, "but... don't step outside."The door of the TARDIS clicked open, and Martha gave him a quizzical look. "Why, what's out there?""Take a look" he said, a lopsided grin on his face.Gingerly, she pulled open the door of the police box and looked out."Oh my God," exclaimed Martha. "Is that real?" She was looking out at a vast star-scape, hundreds of stars embedded in swirling clouds of gas, stretching out as far as she could see."What? Of course it's real!" he laughed, looking out over her shoulder."It's amazing! Where are we?""A long time ago, in a galaxy far, far away..." he quoted thoughtfully."What?""Sorry. We're in a galaxy the local species call the 'Silver Spiral'. From Earth, it's a tiny, faint speck in the sky, somewhere in the constellation of Perseus. You'd never even notice it without a telescope. These stars are part of a cluster formed just a few million years ago, out in one of the spiral arms.""It's beautiful. But... why are we here?""Why not?" he said. "Have you ever seen a star explode?!"She stared at him."You see that one?" he said, pointing to a large red star to one side of the cluster. "It's just one ordinary star doing what it does but, any minute now, for a tiny fraction of time, it will become brighter than this entire galaxy! The explosion will be visible in the skies of thousands of species across hundreds of galaxies. To most of them it's just another transient star, but not you humans, oh no! Scientists on your planet point as many telescopes as they can at it. They even give it a name: 2007gr."She grimaced."No, not very poetic really," he admitted. "Logical though - because they discover it in 2007. You lot, all you've got to understand the universe are the photons you collect, those tiny little pathetic scraps of energy that travel on through the universe until they hit something. And yet you know so much! That's what I love about you humans, always curious, always trying to understand, study and catalogue the universe, and, even when you don't know all the facts, always blundering on...""You can talk!" retorted Martha."Yeah... gets me into trouble," he said with a grin that stretched from ear to ear, "but that's half the fun!""So it's a star that's actually going to explode?""Yep!" he paused. "Well, technically, there's a collapse first, then an explosion.""Oh." She looked worried. "Hang on, aren't we a bit close? Shouldn't we, well, move out of the way?""Nah! We'll be fine.""But it's made of wood!""Trust me, she's tougher than she looks."Pressing buttons, shifting levers and twisting knobs, the Doctor danced around the console. You'd never guess he was 900 years old, she thought, he acts more like an excitable five year old half the time."Doctor," she asked, looking out at the star through the open door, "why does it collapse?""Hmm?" he said distractedly. "Oh, it runs out of fuel.""Like an engine?""More like a nuclear fusion reactor. The temperature and pressure in the core of a star are so high that hydrogen nuclei fuse together forming helium, that's what creates all that heat and light that keeps Earth from freezing.""The Sun is a giant fusion reactor?" asked Martha in disbelief."Oh yeah, the Sun has been fusing hydrogen for, oooo, five billion years by your time.""Wow. So when a star runs out of hydrogen.... what, it stops?""Then," he said excitedly, "it starts to shrink. The temperature and pressure go up as it collapses until it's hot and dense enough that the helium nuclei start to undergo fusion.""The helium that was made from fusing the hydrogen?""Right. And when it runs out of helium to fuse...""It shrinks and gets hotter, right?"He nodded. "It shrinks, gets hotter, and starts fusing the helium forming carbon, nitrogen, oxygen - the stuff that makes up most of you. Just think, you're made from chemicals that were created in the heart of a star." He grinned at her again.She looked down at her own hands curiously. "All right, say I believe you, you still haven't explained why it explodes!""Ah, well, eventually if a star is heavy enough, that burning process carries on through heavier and heavier elements, going faster and faster until it gets all the way to iron. Once you get to iron, you need a lot of extra energy to keep the fusion going, and there's no where for it to come from. The core starts to collapse again, but uncontrollably this time...""Pulled by gravity?"He nodded again. "... until it reaches the density of nuclear matter, effectively becoming one giant atomic nucleus, but then there's nowhere for it to go but back out the way it came, and KABOOM!" he yelled, causing Martha to jump in surprise, "the material in the core rebounds and causes a shock wave which rips through the star, stopping the inward fall of material and causing an explosion.""So does every star do that? Oh my God, is that going to happen to the Sun?""No," he laughed. "The Sun's not nearly heavy enough. It is quite common though, pretty much every star more than about eight times the mass of the Sun will end its life this way.""So why is this one so special?" Martha asked, puzzled."Aha, wait and see!""Look, there, it's about to go! An explosion with the energy of ten octillion megatons of TNT, such a violent comparison..." he paused, with a curious expression on his face. "Ah! I've got it, it's the same energy released in one second as a star like your Sun releases in 30 *billion* years!" he said triumphantly."How long?" Martha exclaimed."Oh, except the Sun isn't going to last that long. It turns into a red giant in, ooo, about the year five billion. Then it expands and swallows the Earth. I should know, I was there."Martha gaped at him."Oh yeah." He paused, "I met the Face of Boe that day.""Oh my God, you're serious!""Always", he grinned again."Any moment now, wait for it.... *there!* And look, there, do you see those jets of material? They're moving at about one hundred and fifty thousand kilometres every second, that's about half the speed of light!"Martha stared at the spectacle in front of her. Where, a moment ago, there had been a fairly ordinary-looking large red star, there was now such a bright light that it hurt to look at it. Peering down she saw a jet of material shooting away from the site of the explosion. She tried to make out what was in it, but it was just a blur."But," she said, turning back to the interior of the TARDIS, "isn't light the fastest thing in the universe?""That's right, nothing travels faster, the ultimate speed limit! You need a lot of energy to travel that fast, and there isn't enough energy even in a supernova to do that. This stuff is pretty quick though, and this is the first time astronomers on the Earth have seen an outflow like that happen.""Hang on," said Martha. "You said astronomers on earth called this explosion 2007gr because they saw it in 2007? But light takes time to travel anywhere, and the Earth must be miles away....""Thirty five million light years, or thereabouts." replied the Doctor.She looked puzzled. "And a light year is...?""The distance light travels in an Earth year. One light year is about, oh, nine and a half thousand billion kilometres.""So does that mean we're way in the past? Are there dinosaurs running around on Earth right now?" Martha asked excitedly."Not likely, they mostly got wiped out sixty five million years before your time. That was quite a day," he muttered. "No, thirty five million years ago mammals were running around on land and there were even sharks starting to appear in the oceans." He leaned on the console and looked at Martha. "Now, there's an idea, how would you like to see prehistoric Earth?" He pushed a couple of buttons on the console, then looked up quickly, his eyes sparkling, focussed behind Martha, looking out the open doors. "I've always wanted to try this..." he said quietly."Try what?" asked Martha suspiciously."This! Here it comes, hang on to something!"A second later, the shockwave hit. Tossed about like a leaf in a hurricane, the TARDIS bounced around, riding the shock front like an insane surfer. Martha grabbed the edge of the console and clung on for dear life. She looked across at the Doctor, but he didn't look worried. Quite the opposite in fact. He had that expression of childlike excitement and wonder on his face. "Woooo hoooooo!" he yelled. "Now that's the way to travel!""You," she exclaimed, "are *completely* mad!""Oh yes!" he grinned back as the shock passed by.The TARDIS slowly righted itself and once more dematerialised.What you have just read is a fictional story. Supernova 2007gr was real, however, and the event described is based on the paper "A mildly relativistic radio jet from the normal Type Ic Supernova 2007gr" by Paragi et al, published in Nature on January 28th 2010. Read the . Hear the .Thanks to everyone who read and commented on early drafts, especially JB!Doctor Who and the TARDIS are trademarks of the BBC.... Read more »

Paragi, Z., Taylor, G., Kouveliotou, C., Granot, J., Ramirez-Ruiz, E., Bietenholz, M., van der Horst, A., Pidopryhora, Y., van Langevelde, H., Garrett, M.... (2010) A mildly relativistic radio jet from the otherwise normal type Ic supernova 2007gr. Nature, 463(7280), 516-518. DOI: 10.1038/nature08713

Crockett, R., Maund, J., Smartt, S., Mattila, S., Pastorello, A., Smoker, J., Stephens, A., Fynbo, J., Eldridge, J., Danziger, I.... (2008) The Birth Place of the Type Ic Supernova 2007gr. The Astrophysical Journal, 672(2). DOI: 10.1086/527299

Soderberg, A., Chakraborti, S., Pignata, G., Chevalier, R., Chandra, P., Ray, A., Wieringa, M., Copete, A., Chaplin, V., Connaughton, V.... (2010) A relativistic type Ibc supernova without a detected γ-ray burst. Nature, 463(7280), 513-515. DOI: 10.1038/nature08714

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

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

February 2, 2010
12:02 AM
691 views

In the news this month: the coolest brown dwarf yet

by Megan in Rigel

An international team, led by astronomers at the University of Hertfordshire have discovered what may be the coolest sub-stellar body ever found outside our own solar system. Using the United Kingdom Infrared Telescope (UKIRT) in Hawaii, the , smaller than other stars but larger than gas giant planets such as Jupiter. The object, known as SDSS1416+13B, is only visible in infra-red light and is in a wide orbit around a somewhat brighter and warmer known as SDSS1416+13A. This discovery is "the fourth time in three years that UKIRT has made a record breaking discovery of the coolest known brown dwarf, with an estimated temperature not far above 200 degrees Celsius," said the University of Hertfordshire's Dr Philip Lucas.The light detected from the star is rather unusual, it appears far bluer at near infra-red wavelengths than any other brown dwarf detected so far. A near infrared spectrum, taken with the Japanese Subaru Telescope in Hawaii, showed that it belongs to a class of objects known as T dwarfs, and that is has a lot of methane in its atmosphere but with peculiar features including a big gap at certain wavelengths. Using the Spitzer space telescope to measure its colour at mid-infrared wavelengths,the researchers found that it is also the reddest known brown dwarf at these wavelengths by some margin. A comparison with theoretical models of brown dwarf atmospheres results in a temperature estimate of just 500 Kelvin or 227 degrees Celsius. In comparison, our own Sun has a surface temperature of approximately 6000 Kelvin. Both stars are also lacking in heavy elements, an indication that they may be very old which fits in with the low temperature of the fainter star - fainter stars use up their fuel much slower and can last for many billions of years.The has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.... Read more »

Ben Burningham, S. K. Leggett, P. W. Lucas, D. J. Pinfield, R. L. Smart, A. C. Day-Jones, H. R. A. Jones, D. Murray, E. Nickson, M. Tamura.... (2010) The discovery of a very cool binary system. MNRAS. arXiv: 1001.4393v1

March 4, 2010
01:16 AM
687 views

In the News this month: the explosion mechanism behind type Ia supernovae

by Megan in Rigel

Supernova explosions are initially by the chemical signatures in their optical spectra. While some are caused by the catastrophic collapse of stars more than eight times as massive as the Sun, others are thought to be caused by , stars like the Sun which have already evolved off the main sequence and shrunk in size. Called Type Ia supernovae, such explosions are thought to have a fixed brightness, allowing them to be used as to measure distances to galaxies and test cosmological models of the expansion of the universe. There are two possible models for these Type Ia supernovae, both involving the explosion of white dwarf stars. Of these theories, the one thought to be the most likely involves the accumulation of material from a companion star onto the surface of a white dwarf. When the mass of the white dwarf exceeds a certain limit, known as the , it becomes unstable and explodes. The second theory is that the explosion is caused by the merger of two white dwarfs in orbit around each other. While the first theory was thought to be the most likely explanation, research published in on the 18th February suggests that the second model may, in fact, be far more likely than was previously assumed.The X-ray signatures of these two different explosion mechanisms are quite different, with far more pre-explosion X-ray emission expected from an accreting white dwarf than from the merger scenario, so two researchers at the in Germany used data from the and the to examine several nearby galaxies. The ongoing accretion process prior to a supernova explosion would generate significant amounts of X-ray emission detectable by Chandra, while a binary white dwarf system heading towards a merger would not generate such emission. The infra-red luminosity of a particular galaxy, taken from the Spitzer data, gives an estimate of the number of white dwarfs in the galaxy, leading to an estimate of the expected X-ray luminosity if accretion is the dominant mechanism. The astronomers examined observations of five nearby elliptical galaxies, as well as the bulge of , the nearest spiral galaxy to the Milky Way, and found in all cases that the predicted X-ray luminosity was between 30 and 50 times lower than expected if the accretion scenario was the main cause of type Ia supernovae.The results imply that, at least in , the dominant mechanism behind type Ia supernovae is white dwarf merger rather than accretion. The researchers calculate that, in ellipticals, it may be that less than five per cent of type Ia supernovae explosions are caused by accretion. The story is slightly different in spiral galaxies however, where clouds of neutral gas and thick dust lanes typical of star formation in spiral galaxies could be obscuring the X-ray radiation created in the pre-explosion phase of the accretion scenario.These new results may have for cosmological studies, since the assumed standard luminosity of type Ia supernovae is used to calculate the expansion velocity of the universe. Since the two merging stars may have slightly different masses in different systems, the total explosion luminosity may not be as standard as thought.... Read more »

Gilfanov, M., & Bogdán, A. (2010) An upper limit on the contribution of accreting white dwarfs to the type Ia supernova rate. Nature, 463(7283), 924-925. DOI: 10.1038/nature08685

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

October 5, 2009
06:50 AM
606 views

In the News this month: discovery of water on the Moon

by Megan in Rigel

It is thought that the Moon was formed about four and a half billion years ago by the collision of a Mars-sized object with the Earth. The heat from the impact and subsequent accretion of material created a magma ocean which would have caused the loss of most of the volatile materials from the surface, so-called because they have low boiling points and evaporate easily. In a press conference at NASA on Thursday 24th September, results were announced from three separate spacecraft showing evidence of water on the lunar surface in far greater quantities than has previously been seen. Two of these spacecraft, Cassini and Deep Impact, observed the Moon as they passed by on their way to other parts of the solar system while the third, India Space Research Organisation's Chandrayaan-1, observed the lunar surface from orbit around the Moon.What each of these probes detected was an absorption feature in the infra-red part of the spectrum at a wavelength of about 3 microns, a wavelength characteristic of absorption by hydroxyl - a hydrogen atom joined together with an oxygen atom. Add another hydrogen to hydroxyl and you produce H20, water, which also absorbs infra-red light near 3-microns. It has been known since the observations of the Lunar Prospector spacecraft in the late 1990s that there is an estimated 10 to 300 million metric tones of water ice buried in permanently shadowed craters at the lunar poles. These new results however, show that the hydroxyl and water signature is in fact present over large parts of the lunar surface, not just at the poles.Launched on October 22nd 2008, India's Chandrayaan-1 carried several scientific instruments on board. One of these was the Moon Mineralogy Mapper, or M3, built by NASA, a spectrograph operating in the infra-red part of the spectrum. Although Chandrayaan-1 sadly ceased operations last month, it had already returned many months of usable data from the instruments on board. When the data from the M3 experiment was analysed, researchers found absorption features consistent with patterns expected for water and hydroxyl over most of the lunar surface. Although M3 only probed the top few millimetres of the lunar regolith, they found a strong hydroxyl signature across the surface, stronger towards the lunar poles at higher latitudes, and varying throughout the lunar cycle, suggesting that the Sun has some effect on the distribution.According to the scientists, the most likely origin for this water is a reaction between protons in the solar wind and oxygen atoms already present in the lunar dirt. The M3 results were subsequently confirmed by observations by the Deep Impact spacecraft which also has instruments that observe in the infra-red and regularly uses observations of the Moon for calibration purposes, and also in old data from the Cassini spacecraft which observed the Moon during a flyby in 1999. The data show that there may be as much as 0.1 to 1 per cent water by weight in the regolith, in contrast to the rocks brought back by the Apollo missions which were incredibly dry. This is roughly equivalent to a litre of water per cubic metre of regolith but, since it is only present in the top few millimetres of soil, extracting usable amounts of water would require processing a very large surface area.The results from the three spacecraft were announced together to coincide with the publication of three papers in the journal Science on September 24th, and come just two weeks before another spacecraft, NASA's LCROSS, the Lunar Crater Observation and Sensing Satellite, is due to crash into the Moon's surface near the south pole in an attempt to kick up water ice buried in the regolith in craters which rarely see sunlight.... Read more »

Sunshine, J., Farnham, T., Feaga, L., Groussin, O., Merlin, F., Milliken, R., & A'Hearn, M. (2009) Temporal and Spatial Variability of Lunar Hydration as Observed by the Deep Impact Spacecraft. Science. DOI: 10.1126/science.1179788

Pieters, C., Goswami, J., Clark, R., Annadurai, M., Boardman, J., Buratti, B., Combe, J., Dyar, M., Green, R., Head, J.... (2009) Character and Spatial Distribution of OH/H2O on the Surface of the Moon Seen by M3 on Chandrayaan-1. Science. DOI: 10.1126/science.1178658

Clark, R. (2009) Detection of Adsorbed Water and Hydroxyl on the Moon. Science. DOI: 10.1126/science.1178105

Astronomy

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

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

February 1, 2010
11:18 PM
555 views

In the news this month: Chandra tells tails of extragalactic star formation

by Megan in Rigel

Star formation is usually thought of as occurring mainly in the spiral arms of galaxies. In close encounters or collisions between galaxies, the orbits of these stars around the galactic disk can be disrupted, resulting in some stars being thrown out into intergalactic space. But new results from the Chandra X-ray Observatory suggest that, at least in some cases, stars can form outside the normal boundaries of galactic disks.A team led by Ming Sun at the University of Virginia used the orbiting Chandra telescope to observe galaxies in a nearby rich cluster known as Abell 3627. What they found were , trailing behind galaxies located in the cluster. Tails like these are made up of X-ray emitting gas which is stripped from a galaxy as it moves through the cluster. One of these galaxies, , was already known to have one X-ray tail which extends approximately 260 thousand light years from the galaxy itself, but in these observations the team found a second tail apparently associated with the same galaxy. This new tail is of a similar length to the first, but is both fainter and narrower. Both the widths and temperatures of the tails remain surprisingly constant over their entire lengths, and these properties present challenges to current models and simulations of such systems. A similar tail of about half the length was also detected behind ESO 137-002, another similar galaxy in the same cluster.Together with observations using telescopes operating in other parts of the electromagnetic spectrum, the research also shows the first unambiguous evidence of star formation in the material stripped from a galaxy. Rather than forming in the galactic disk as normal, these stars are forming in the gas stripped from the disk as the galaxy moves through the tenuous gas in the cluster.X-ray tails are rare, and double-tails are extremely rare, so one question is, why should there be two bright X-ray tails visible in the same cluster? In their paper, published in the Astrophysical Journal, the researchers suggest that (aside from coincidence) the high ambient pressure in this particular cluster could play a role, making the X-ray tails denser and more luminous. If this is the case, the high pressure environment would also be helping the process of extra-galactic star formation.... Read more »

Sun, M., Donahue, M., Roediger, E., Nulsen, P., Voit, G., Sarazin, C., Forman, W., & Jones, C. (2010) SPECTACULAR X-RAY TAILS, INTRACLUSTER STAR FORMATION, AND ULXs IN A3627. The Astrophysical Journal, 708(2), 946-964. DOI: 10.1088/0004-637X/708/2/946

October 31, 2009
06:13 AM
554 views

In the news this month... another impressive exoplanet haul from HARPS

by Megan in Rigel

2009 has been a good year for exoplanets, and one team of astronomers have discovered most of them. Since the first planet was found orbiting a star other than the Sun, many more have been discovered using increasingly sensitive instruments and sophisticated techniques. Because they are so faint compared to their parent stars, most planets are discovered through indirect methods. One of the most successful has been the which uses the principle of the Doppler effect to detect the tiny changes in velocity of a star caused by an orbiting planet.This is the technique used by the High Accuracy Radial Velocity Planet Searcher, or , instrument, mounted on the European Southern Observatory's 3.6-m telescope at La Silla in Chile which repeatedly measures the radial velocities of stars that might host planetary systems. On the 19th of October, members of the HARPS team presented their latest results: the discovery of , bringing the total number of known exoplanets to more than 400. The radial velocity technique is most sensitive to large planets orbiting close to their parent star, but due to its high precision HARPS is capable of detecting smaller planets known as super-Earths. The new batch of exoplanets range in size from just five times the mass of the Earth to up to 10 times the mass of Jupiter.HARPS has been largely responsible for the detection of 24 of the 28 known planets with masses below 20 times that of Earth and has now discovered more than 75 of the 400 , making it the most productive current planet finder. However, HARPS will soon have competition in the form of , a NASA satellite launched in March with the aim of detecting Earth-sized planets in the habitable zone, the region around a star where water can exist as a liquid.; Rather than measuring the wobble of stars, Kepler will monitor their brightness looking for the tiny dips in intensity caused by planetary transits.... Read more »

Mayor, M.; Pepe, F.; Queloz, D.; Bouchy, F.; Rupprecht, G.; Lo Curto, G.; Avila, G.; Benz, W.; Bertaux, J.-L.; Bonfils, X.; dall, Th.; Dekker, H.; Delabre, B.; Eckert, W.; Fleury, M.; Gilliotte, A.; Gojak, D.; Guzman, J. C.; Kohler, D.; Lizon, J.-L.; Long. (2003) Setting New Standards with HARPS. Messenger, 20-24. info:other/2003Msngr.114..20M

March 4, 2010
01:58 AM
551 views

In the News this month: the molecular content of early galaxies

by Megan in Rigel

A long-standing question in the study of is whether the process was more efficient in the early universe than it is today. Stars form through the collapse of clouds of cold gas. As the collapse progresses, the of the cloud gets denser and hotter until begins and a star is born. In the local universe, however, cold molecular gas is relatively rare so star formation occurs slowly; the Milky Way forms new stars at a rate of only a few per year. More distant galaxies formed stars at a much higher rate, but in order to determine whether this is due to a more efficient star formation process or a more ready supply of molecular gas, it is necessary to investigate their gas content.Star formation within these clouds is very difficult to observe directly since the gas absorbs much of the visible light produced by young proto-stars. Once they begin to shine, the of young stars begins to dispel the surrounding gas and the star becomes visible. The gas itself is hard to detect but some molecules, such as , are visible through the radiation they emit at infrared wavelengths.A team of researchers used the to examine the gas content of two samples of galaxies which are so distant that we see them as they were when the universe was only 40 and 24 percent of its current age. Because they are so distant, the infrared radiation from the carbon monoxide molecules in these galaxies is into the part of the spectrum where wavelengths are measured in millimetres. Using new receivers recently installed on the antennas of the interferometer at the Plateau de Bure in France, Linda Tacconi and colleagues imaged the molecular gas content of these galaxies. Many previous studies have focused on highly extreme examples, galaxies forming stars at very high rates due to powerful central black holes or systems where galaxies are merging, but Tacconi's team studied more modest examples likely to be more typical of normal star forming galaxies.Published in the journal on February 11th, their results show that distant star forming galaxies were in fact gas rich, containing three to ten times more cold gas (as a fraction of the galaxy's total mass) than equivalent galaxies in the local universe today. Their results also show that the fraction of gas does not vary greatly with : the galaxies in the more distant sample, seen when the universe was just three billion years old, contained 44 percent molecular gas while those in the closer sample, seen when the universe was 5.5 billion years old, contained 34 percent gas.The results also suggest that there is a mechanism replenishing the molecular gas in these galaxies. The rate at which stars are forming can be used to estimate how long it would take to use up the entire supply of molecular gas, the timescale turns out to be less than the time interval between the two samples, suggesting that either the gas is replenished, or that the two galaxy populations studied have experienced different evolutionary paths.... Read more »

Tacconi, L., Genzel, R., Neri, R., Cox, P., Cooper, M., Shapiro, K., Bolatto, A., Bouché, N., Bournaud, F., Burkert, A.... (2010) High molecular gas fractions in normal massive star-forming galaxies in the young Universe. Nature, 463(7282), 781-784. DOI: 10.1038/nature08773

October 31, 2009
05:31 AM
550 views

In the news this month... a record-breaking distant cluster

by Megan in Rigel

Look deep enough with a sensitive telescope and a seemingly empty patch of sky is full of galaxies. Look closely and you'll see that they are often gathered together in clusters. These massive collections of galaxies are the largest gravitationally bound objects in the universe, but it is uncertain how long ago these clusters formed. Now, using a variety of instruments, a team led by Stefano Andreon of the in Milan, Italy, has the most distant galaxy cluster ever found.The cluster, known as JKCS041, is located in the constellation of Cetus and lies about 10.2 billion light years away, beating the previous record holder by almost one billion light years. It is so far away that the light now arriving at Earth was produced by the cluster when the universe was only about a quarter of its current age.The astronomers first discovered the galaxy in infra-red observations made with the UK Infra Red Telescope, , in 2006. The optical light from galaxies this far away is shifted into the infra-red part of the spectrum due to the expansion of the universe, so old galaxies like these are often detected by infra-red telescopes. Further observations with both optical and infra-red telescopes confirmed the distance to the object, but could not rule out the possibility that, rather than being a genuine gravitationally bound cluster, the object could just be a chance alignment of galaxies along our line of sight. To test this, the team examined X-ray observations from the space telescope.Nearby galaxy clusters have extended X-ray emission, caused by hot gas in the space between the galaxies. This gas, known as the hot , is only observed in genuine gravitationally bound clusters of galaxies and so is a good test of whether a group of galaxies just lie along the same line of sight by chance, or are physically associated. When the astronomers examined the Chandra observations of JKCS041, they found a significant amount of extended X-ray emission within the cluster coming from hot gas of the intra-cluster medium, showing that it is a physically connected group of galaxies.This is an important discovery because this is close to the distance limit expected for a galaxy cluster based on how long it should take for them to assemble following the big bang, and studying its characteristics can reveal more about how the universe evolved.... Read more »

Andreon, S., Maughan, B., Trinchieri, G., & Kurk, J. (2009) JKCS041: a colour-detected galaxy cluster at zphot~1.9 with deep potential well as confirmed by X-ray data. Astronomy and Astrophysics. DOI: 10.1051/0004-6361/200912299

Astronomy

November 30, 2010
12:31 AM
528 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

October 5, 2009
06:21 AM
518 views

In the News this month: first evidence of a solid exoplanet

by Megan in Rigel

Using various techniques, astronomers have, over the last decade, discovered many hundreds of planets outside our own solar system. Most of these techniques are indirect because planets are much fainter than the stars they orbit, and so are very hard to detect directly. Because their effects are easier to spot, larger planets are easier to find, but smaller and smaller planets are being discovered as techniques and technology improve. One of the smallest exoplanets known to date is CoRoT-7b, a planet discovered by the CoRoT satellite in February 2009, orbiting an otherwise unremarkable 11th magnitude star catalogued as TYC 4799-1733-1, located almost 500 light years away in the constellation of Monoceros. Most of the known exoplanets are thought to be larger versions of Jupiter, likely to be large gas giants, but new observations of CoRoT-7b suggest that it is far more like our own Earth.A team of astronomers, led by Didier Queloz at the Geneva Observatory in Switzerland, used the HARPS instrument on ESO's 3.6-metre telescope at the La Silla observatory in Chile, to observe the CoRoT-7 system and try and determine the mass of CoRoT-7b. HARPS, or the High Accuracy Radial velocity Planet Searcher, is a high resolution spectrograph which enables astronomers to measure the tiny changes in velocity of a star as it is gently tugged by the gravitational pull of it's orbiting planets. These velocity shifts are extremely small, so very accurate spectrographs are needed to see the effects.In the case of CoRoT-7b, the planet is so close to its parent star that it completes one orbit every 20.4 hours, blocking out a tiny fraction of the stars' light for just one hour during each orbit. Because the planet is so small, the team had to obtain more than 70 hours of observations to see the tiny changes in the stars' spectrum that would tell them about the planet. What the team found was that CoRoT-7b is one of the lightest exoplanets known, with a mass of just 4.8 times that of the Earth, putting it in the category of so-called "super-Earths". Since the planet directly transits the star, passing directly between the star and us, astronomers have already been able to determine that the planet's radius is less than twice that of Earth. If you know both the mass and the radius of a planet, you can calculate its density. The team did this and found that CoRoT-7b has a density of 5.5 grams per cubic centimetre, very similar to the density of the Earth. This suggests that CoRoT-7b is a rocky planet, not a gas giant like Jupiter, and is likely to be composed mainly of silicates with a small iron core, the first time such a determination has been made for such a small exoplanet.As well as determining the mass and density of CoRoT-7b, the team also discovered a new planet, CoRoT-7c, which is slightly larger with a mass of 8.4 times that of Earth. Unfortunately, this planet does not directly transit the star, so its radius, and hence density, cannot be determined. The research will be published in the journal Astronomy and Astrophysics on October 22nd.... Read more »

Queloz, D., Bouchy, F., Moutou, C., Hatzes, A., Hebrard, G., Alonso, R., Auvergne, M., Baglin, A., Barbieri, M., Barge, P.... (2009) The CoRoT-7 planetary system: two orbiting super-Earths. Astronomy and Astrophysics. DOI: 10.1051/0004-6361/200913096

Astronomy

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

February 1, 2010
11:50 PM
511 views

In the news this month: coronal loops imaged around another star

by Megan in Rigel

Most of our knowledge of the processes and morphology of stellar coronae comes from observing our nearest star, the Sun. Coronal loops are associated with sunspot groups which affect the streams of charged particles leaving the Sun as the solar wind, so an understanding of the processes in these loops has implications for space weather predictions which can impact on satellite operations and the safety of astronauts.Studying the same processes in other stars is difficult due to the distances involved and the high resolution required to see any detail. Some of the highest resolution observations possible in astronomy are made using arrays of radio telescopes linked together in a process known as very long baseline interferometry; the more widely separated the telescopes in the array, the higher the resolution of the final images.Using this technique, , have detected a large coronal loop on another star.Using a very sensitive array of radio telescopes which included the ten antennas of the Very Long Baseline Array in the US, the 100-m Green Bank Telescope in West Virginia, the Very Large Array in New Mexico and the 100-m Effelsberg telescope in Germany, the astronomers imaged in Perseus. Algol is an eclipsing binary system consisting of a large main sequence B-class star and a cooler K-class sub-giant in orbit around each other. The two stars are very close, just 6% of the distance between the Earth and our own Sun, and orbit each other every 2.86 days. The results show a gigantic coronal loop stretching out from the surface of Algol B, the K-class sub-giant star, towards its companion Algol A, with the two ends of the loop located at the magnetic poles of the sub-giant star. Throughout the orbit, this loop continues to point towards Algol A.The researchers say that Algol B's coronal loop is similar to those seen on the Sun, but is much larger, and the magnetic field at Algol is about 1,000 times more powerful. The size of the coronal loop is larger than predicted by stellar models, and the suggestion is that this is probably due to the tidal effects of the companion star distorting the loop and stretching it.The results, the first time a coronal loop has been imaged on another star, were .... Read more »

Peterson, W., Mutel, R., Güdel, M., & Goss, W. (2010) A large coronal loop in the Algol system. Nature, 463(7278), 207-209. DOI: 10.1038/nature08643

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