Posted on by Fraser Cain

Audio: Sedna Loses Its Moon

Remember Sedna? It’s that icy object uncovered last year in the outer reaches of the Solar System. When it was first discovered, astronomers noticed it rotated once every 20 days. The only explanation that could explain this slow rotation was a moon, but a moon never showed up in any of their observations. Scott Gaudi is a researcher with the Harvard Smithsonian Centre for Astrophysics. He and his colleagues have been watching the rotation of Sedna with a skeptical eye, and think it’s only rotating once every 10 hours or so. As for the moon? Easy come, easy go.

Listen to the interview: sedna.mp3 (3.8 mb)

Or subscribe to the Podcast: universetoday.com/audio.xml

Posted on by Fraser Cain

Really Big Telescopes are Coming

The largest ground-based optical telescopes in use today use mirrors that are 10 m (33 ft) across. But the prospects for future Extremely Large Telescopes (ELTs) are looking up. According to recent studies by international teams of astronomers and leading astronomical organisations, the next generation of optical telescopes could be 50-100 metres (165 330 ft) in diameter – big enough to fill a sports stadium.

This quantum leap in size has important implications, since astronomers want to capture every photon of light that comes their way, and a 100 m mirror has a collecting area up to 100 times greater than existing instruments. Furthermore, a 100 m telescope would have extremely sharp vision, with the ability to see objects at up to 40 times the spatial resolution of the Hubble Space Telescope.

On Friday 8 April, Dr. Isobel Hook of Oxford University told the RAS National Astronomy Meeting in Birmingham about the compelling scientific case for Extremely Large Telescopes which has been developed at a series of meetings over the past four years. The results of this evaluation process, which involved more than 100 astronomers, have recently been published, coinciding with the start of the European Extremely Large Telescope Design Study. (See Web details at the end of this release).

A team of over 100 European Astronomers has recently produced a brochure summarising the science that could be done, said Dr. Hook. This work is the result of a series of meetings held in Europe over the last 4 years, sponsored by the EC network OPTICON. The new report explains how an ELT will revolutionise all aspects of astronomy, from studies of our own solar system – by producing images of comparable detail to those from space probes – to the edge of the observable Universe.

As the report states: The vast improvement in sensitivity and precision allowed by the next step in technological capabilities, from todays 6-10 m telescopes to the new generation of 50-100 m telescopes with integrated adaptive optics capability, will be the largest such enhancement in the history of telescopic astronomy. It is likely that the major scientific impact of these new telescopes will be discoveries we cannot predict, so that their scientific legacy will also vastly exceed even that rich return which we can predict today.

Astronomers believe that with an ELT it will not only be possible to find planets orbiting other stars, but also to identify and study habitable Earth-like planets by identifying the presence of liquid water, oxygen and methane. Many of the mysteries about the high-energy Universe will also be answered. An ELT would be able to provide key insights into the nature of black holes, galaxy formation, the mysterious dark matter pervading the Universe and the even more mysterious dark energy that is pushing the Universe apart. An ELT will also be sensitive enough to detect the first galaxies that were born only a few hundred million years after the Big Bang, as well as very early supernova explosions, whose light has travelled for over 10 billion years to reach us.

Some of the most exciting discoveries cannot be predicted now, said Dr. Hook. New astronomical instruments have always surprised us with the unexpected. An ELT would make such advances possible for two main reasons – the large collecting area enables it to detect the faintest sources, and the telescopes huge diameter allows extremely sharp images (provided the effects of atmospheric turbulence are corrected by adaptive optics).

Would it be possible to build such a telescope?

Initial studies are very positive, suggesting that a 50-100 m segmented telescope could be built within 10-15 years for a cost of around 1 billion Euros, said Dr. Hook. A major design study is now starting in Europe, aimed at developing the technology needed to build Extremely Large Telescopes. The study has been awarded 8 million Euros from the EC Framework Programme 6 plus additional funds from the participants (the European Southern Observatory, together with universities, institutes and industry around Europe, including the UK).

Original Source: RAS News Release

Posted on by Fraser Cain

Old Star Reignites its Flame

Image credit: NRAO
Astronomers using the National Science Foundation’s Very Large Array (VLA) radio telescope are taking advantage of a once-in-a-lifetime opportunity to watch an old star suddenly stir back into new activity after coming to the end of its normal life. Their surprising results have forced them to change their ideas of how such an old, white dwarf star can re-ignite its nuclear furnace for one final blast of energy.

Computer simulations had predicted a series of events that would follow such a re-ignition of fusion reactions, but the star didn’t follow the script — events moved 100 times more quickly than the simulations predicted.

“We’ve now produced a new theoretical model of how this process works, and the VLA observations have provided the first evidence supporting our new model,” said Albert Zijlstra, of the University of Manchester in the United Kingdom. Zijlstra and his colleagues presented their findings in the April 8 issue of the journal Science.

The astronomers studied a star known as V4334 Sgr, in the constellation Sagittarius. It is better known as “Sakurai’s Object,” after Japanese amateur astronomer Yukio Sakurai, who discovered it on February 20, 1996, when it suddenly burst into new brightness. At first, astronomers thought the outburst was a common nova explosion, but further study showed that Sakurai’s Object was anything but common.

The star is an old white dwarf that had run out of hydrogen fuel for nuclear fusion reactions in its core. Astronomers believe that some such stars can undergo a final burst of fusion in a shell of helium that surrounds a core of heavier nuclei such as carbon and oxygen. However, the outburst of Sakurai’s Object is the first such blast seen in modern times. Stellar outbursts observed in 1670 and 1918 may have been caused by the same phenomenon.

Astronomers expect the Sun to become a white dwarf in about five billion years. A white dwarf is a dense core left after a star’s normal, fusion-powered life has ended. A teaspoon of white dwarf material would weigh about 10 tons. White dwarfs can have masses up to 1.4 times that of the Sun; larger stars collapse at the end of their lives into even-denser neutron stars or black holes.

Computer simulations indicated that heat-spurred convection (or “boiling”) would bring hydrogen from the star’s outer envelope down into the helium shell, driving a brief flash of new nuclear fusion. This would cause a sudden increase in brightness. The original computer models suggested a sequence of observable events that would occur over a few hundred years.

“Sakurai’s object went through the first phases of this sequence in just a few years — 100 times faster than we expected — so we had to revise our models,” Zijlstra said.

The revised models predicted that the star should rapidly reheat and begin to ionize gases in its surrounding region. “This is what we now see in our latest VLA observations,” Zijlstra said.

“It’s important to understand this process. Sakurai’s Object has ejected a large amount of the carbon from its inner core into space, both in the form of gas and dust grains. These will find their way into regions of space where new stars form, and the dust grains may become incorporated in new planets. Some carbon grains found in a meteorite show isotope ratios identical to those found in Sakurai’s Object, and we think they may have come from such an event. Our results suggest this source for cosmic carbon may be far more important than we suspected before,” Zijlstra added.

The scientists continue to observe Sakurai’s Object to take advantage of the rare opportunity to learn about the process of re-ignition. They are making new VLA observations just this month. Their new models predict that the star will heat very quickly, then slowly cool again, cooling back to its current temperature about the year 2200. They think there will be one more reheating episode before it starts its final cooling to a stellar cinder.

Zijlstra worked with Marcin Hajduk of the University of Manchester and Nikolaus Copernicus University, Torun, Poland; Falk Herwig of Los Alamos National Laboratory; Peter A.M. van Hoof of Queen’s University in Belfast and the Royal Observatory of Belgium; Florian Kerber of the European Southern Observatory in Germany; Stefan Kimeswenger of the University of Innsbruck, Austria; Don Pollacco of Queen’s University in Belfast; Aneurin Evans of Keele University in Staffordshire, UK; Jose Lopez of the National Autonomous University of Mexico in Ensenada; Myfanwy Bryce of Jodrell Bank Observatory in the UK; Stewart P.S. Eyres of the University of Central Lancashire in the UK; and Mikako Matsuura of the University of Manchester.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Original Source: NRAO News Release

Posted on by Fraser Cain

Cosmic Particle Accelerator at the Centre of the Milky Way

Astronomers have found a vast loop-like structure, 20 light years across, adjacent to the most massive star-forming region known in our galaxy. The loop, which was observed in X-ray wavelengths, is 15 times the size of the Arches Cluster, a star-forming region close to the centre of the Milky Way. This is the first time that such a distinctive and huge loop structure has been observed. Dr Masaaki Sakano, from the University of Leicester, will be presenting the discovery at the RAS National Astronomy Meeting at the University of Birmingham on Friday 8th April.

The team of astronomers, which includes scientists from the University of Leicester, CEA Saclay and the Max Planke Institute for Extraterrestrial Physics, observed the Arches Cluster repeatedly using the European X-ray satellite, XMM-Newton, as a part of the XMM-Newton Galactic Centre Survey. The galactic centre can only be observed at certain wavelengths, such as X-rays, because large amounts of dust lie in our line of sight and this blocks out optical light.

Dr Sakano says, “The X-ray spectrum of the loop is extraordinary. Most diffuse X-ray sources in the Universe have a characteristic temperature because they are the residual radiation from an event, such as a supernova explosion. However in this case the loop is non-thermal and this means that whatever the origin of the structure is, it is not stationary but rather the result of some ongoing process.”

The most straightforward interpretation of the observations is that powerful particle-acceleration is occurring on-site, producing high energy particles with an energy of up to a thousand trillion electron volts (a thousand times more energetic than those produced in man-made particle accelerators). Such particles have been detected previously in a few supernova remnants and many pulsar nebulae, where a very powerful central source has created them. However, evidence for high-energy particles has never been observed before in star-forming regions of our galaxy.

At this stage it is not clear whether the loop structure is physically related to the Arches Cluster or just happens to be in our line of sight. However, if future observations show that the Arches Cluster is responsible for the feature, this discovery suggests that star-forming activity plays an important role in the energetic Universe.

Original Source: RAS News Release

Posted on by Fraser Cain

Is This the First Photo of an Exoplanet?

Since the discovery in 1995 of the first planet orbiting a normal star other than the Sun, there are now more than 150 candidates of these so-called exoplanets known. Most of them are detected by indirect methods, based either on variations of the radial velocity or the dimming of the star as the planet passes in front of it (see ESO PR 06/03, ESO PR 11/04 and ESO PR 22/04).

Astronomers would, however, prefer to obtain a direct image of an exoplanet, allowing them to better characterize the object’s physical nature. This is an exceedingly difficult task, as the planet is generally hidden in the “glare” of its host star.

To partly overcome this problem, astronomers study very young objects. Indeed, sub-stellar objects are much hotter and brighter when young and therefore can be more easily detected than older objects of similar mass.

Based on this approach, it might well be that last year’s detection of a feeble speck of light next to the young brown dwarf 2M1207 by an international team of astronomers using the ESO Very Large Telescope (ESO PR 23/04) is the long-sought bona-fide image of an exoplanet. A recent report based on data from the Hubble Space Telescope seems to confirm this result. The even more recent observations made with the Spitzer Space Telescope of the warm infrared glows of two previously detected “hot Jupiter” planets is another interesting result in this context. This wealth of new results, obtained in the time span of a few months, illustrates perfectly the dynamic of this field of research.

Tiny Companion
Now, a different team of astronomers [1] has possibly made another important breakthrough in this field by finding a tiny companion to a young star. Since several years these scientists have conducted a search for planets and low-mass objects, in particular around stars still in their formation process – so-called T-Tauri stars – using both the direct imaging and the radial velocity techniques. One of the objects on their list is GQ Lupi, a young T-Tauri star, located in the Lupus I (the Wolf) cloud, a region of star formation about 400 or 500 light-years away. The star GQ Lupi is apparently a very young object still surrounded by a disc, with an age between 100,000 and 2 million years.

The astronomers observed GQ Lupi on 25 June 2004 with the adaptive optics instrument NACO attached to Yepun, the fourth 8.2-m Unit Telescope of the Very Large Telescope located on top of Cerro Paranal (Chile). The instrument’s adaptive optics (AO) overcomes the distortion induced by atmospheric turbulence, producing extremely sharp near-infrared images.

As ESO PR Photo 10a/05 shows, the series of NACO exposures clearly reveal the presence of the tiny companion, located in the close vicinity of the star. This newly found object is only 0.7 arcsecond away, and would have been overlooked without the use of the adaptive optics capabilities of NACO.

At the distance of GQ Lupi, the separation between the star and its feeble companion is about 100 astronomical units (or 100 times the distance between the Sun and the Earth). This is roughly 2.5 times the distance between Pluto and the Sun.

The companion, called GQ Lupi B or GQ Lupi b [2], is roughly 250 times fainter than GQ Lupi A as seen in this series of image. Further images obtained with NACO in August and September confirmed the presence and the position of this companion.

Moving in the same direction
The astronomers then uncovered that the star had been previously observed by the Subaru telescope as well as by the Hubble Space Telescope. They retrieved the corresponding images from the data archives of these facilities for further analysis.

The older images, taken in July 2002 and April 1999, respectively, also showed the presence of the companion, giving the astronomers the possibility of precisely measuring the position of the two objects over a period of several years. This in turn allowed them to determine if the stars move together in the sky – as should be expected if they are gravitationally bound together – or if the smaller object is only a background object, just aligned by chance.

From their measurements, the astronomers found that the separation between the two objects did not change over the five-year period covered by the observations (see ESO PR Photo 10b/05). For the scientists this is a clear proof that both objects are moving in the same direction in the sky. “If the faint object would be a background object”, says Ralph Neuh?user of the University of Jena (Germany) and leader of the team, “we would see a change in separation as GQ Lup would be moving in the sky. From 1999 to 2004, the separation would have changed by 0.15 arcsec, while we are confident that the change is a least 20 times smaller.”

Exoplanet or brown dwarf?
To further probe the physical nature of the newly discovered object, the astronomers used NACO on the VLT to take a series of spectra. These showed the typical signature of a very cool object, in particular the presence of water and CO bands. Taking into account the infrared colours and the spectral data available, atmospheric model calculations point to a temperature between 1,600 and 2,500 degrees and a radius that is twice as large as Jupiter (see PR Photo 10c/05). According to this, GQ Lupi B is thus a cold and rather small object.

But what is the nature of this faint object? Is it a bona-fide exoplanet or is it a brown dwarf, those “failed” stars that are not massive enough to centrally produce major nuclear reactions? Although the borderline between the two is still a matter of debate, one way to distinguish between the two is by their mass (as this is also done between brown dwarfs and stars): (giant) planets are lighter than about 13 Jupiter-masses (the critical mass needed to ignite deuterium fusion), brown dwarfs are heavier.

What about GQ Lupi b?
Unfortunately, the new observations do not provide a direct estimate of the mass of the object. Thus the astronomers must rely on comparison with theoretical models of such objects. But this is not as easy as it sounds. If, as astronomers generally accept, GQ Lupi A and B formed simultaneously, the newly found object is very young. The problem is that for such very young objects, traditional theoretical models are probably not applicable. If they are used, however, they provide an estimate of the mass of the object that lies somewhere between 3 to 42 Jupiter-masses, i.e. encompassing both the planet and the brown dwarf domains.

These early phases in brown dwarf and planet formation are essentially unknown territory for models. It is very difficult to model the early collapse of the gas clouds given the conditions around the forming parent star. One set of models, specifically tailored to model the very young objects, provide masses as low as one to two Jupiter-masses. But as Ralph Neuh?user points out “these new models still need to be calibrated, before the mass of such companions can be determined confidently”.

The astronomers also stress that from the comparison between their VLT/NACO spectra and the theoretical models of co-author Peter Hauschildt from Hamburg University (Germany), they arrive at the conclusion that the best fit is obtained for an object having roughly 2 Jupiter radii and 2 Jupiter masses. If this result holds, GQ Lupi b would thus be the youngest and lightest exoplanet to have been imaged.

Further observations are still required to precisely determine the nature of GQ Lupi B. If the two objects are indeed bound, then the smallest object will need more than 1,000 years to complete an orbit around its host star. This is of course too long to wait but the effect of the orbital motion might possibly be detectable – as a tiny change in the separation between the two objects – in a few years. The team therefore plans to perform regular observations of this object using NACO on the VLT, in order to detect this motion. No doubt that in the mean time, further progress on the theoretical side will be achieved and that many sensational discoveries in this field will be made.

More information
The research presented in this ESO Press Release is published in a Letter to the Editor accepted for publication by Astronomy and Astrophysics (“Evidence for a co-moving sub-stellar companion of GQ Lup” by R. Neuh?user et al.) and available in PDF form at http://www.edpsciences.org/articles/aa/pdf/forthpdf/aagj061_forth.pdf.

Note
[1]: The team is composed of Ralph Neuh?user, G?nther Wuchterl, Markus Mugrauer, and Ana Bedalov (University of Jena, Germany), Eike Guenther (Th?ringer Landessternwarte Tautenburg, Germany), and Peter Hauschildt (Hamburger Sternwarte, Germany).

[2]: In the astronomical literature, the convention is to put capitals for stars member of multiple systems, but small letters for planets. If the companion to GQ Lupi A turns out to be a planet, it would be called GQ Lupi b, while if it is a brown dwarf, it would be identified as GQ lupi B. Given the present uncertainty, we have therefore used both denominations in this press release, as did the authors in the original scientific paper.

Original Source: ESO News Release

Posted on by Fraser Cain

Europe Planning a Mars Rover Mission

European space scientists have strongly recommended a mission equipped with a Rover as the next scientific mission to Mars as part of the European Space Agency?s [ESA] Aurora programme of planetary exploration.

The mission would conduct a detailed analysis of the Martian environment and search for traces of past or present life. A launch in June 2011, followed by a two year journey, would arrive on the Red Planet in June 2013. A detailed proposal will be prepared for consideration by ESA member states at the agency?s Council Meeting at Ministerial Level in December 2005.

The recommendation was made by European scientists at an international space workshop held at Aston University, Birmingham, England on the 6th and 7th April 2005. The ESA workshop, hosted by the UK?s Particle Physics and Astronomy Research Council [PPARC], brought together space scientists and agency officials from Europe, Canada, North America and the international space community in order to debate robotic mission options up to 2013 in the first phase of the Aurora programme.

Three candidate missions were considered: BeagleNet, ExoMars and its variant ExoMars-Lite. Consideration was also given to the preparatory activities needed to develop a sustainable, long-term Mars Exploration programme and how efforts to 2011 address the requirements of a Mars Sample Return [MSR] mission within an overall Aurora roadmap.

Following scientific and technology presentations of each candidate mission an evaluation process was undertaken by the scientists measured against key criteria. The outcome and consensus of the workshop recommended a mission which blended key technologies and objectives from each of the candidate missions as the first robotic mission in the Aurora programme. This recommendation will form the basis of a detailed proposal by the scientific community to be considered at the ESA?s Council Meeting at Ministerial Level in December 2005.

The recommended mission will consist of a Soyuz launcher to deliver a probe which includes at least one Rover for scientific exploration of the Martian environment. Telecommunications [data relay] between the probe and Earth will be achieved via NASA orbiting spacecraft. The Rover would be equipped with a suite of scientific instruments designed to search for traces of past or present life on Mars; to characterise the shallow subsurface water/geochemical composition and its vertical distribution profile; and to identify surface and environmental hazards to future human missions. Taking into account the exciting and scientifically intriguing results from ESA?s Mars Express orbiter the recommended mission will also incorporate instruments to specifically measure seismic phenomena which could be caused by volcanoes, hydrothermal activity or Marsquakes. The Rover will also contain a drill capable of penetrating the surface to a depth of 2m and a Beagle 2 type life marker experiment such as a Gas Analysis Package [GAP] capable of studying stable isotopes in the atmosphere, rocks, and soil. The entry, descent and landing system [EDLS] will utilise key technologies involving airbags and possibly retrorockets. To be launched by a Soyuz Fregat 2b vehicle in June 2011 from ESA?s spaceport at Kourou in French Guiana the probe and Rover would arrive on the surface of Mars in June 2013 after a two year voyage.

Looking beyond 2011 the scientists confirmed their commitment to collaborating in an international Sample Return Mission in 2016 [which would include sample acquisition and handling, mobility and planetary protection], as a logical sequence to the recommended mission in the future roll out of ESA?s Aurora programme.

Commenting on the workshop Prof. Jean Pierre Swings, Chair of ESA?s Exploration Programme Advisory Committee, said,? This workshop has brought an extremely wide range of scientists together from a diverse range of disciplines to recommend what will be a tremendously exciting mission for European space. It builds upon the success of ESA?s Mars Express whilst driving new technologies that will form the foundation for the future development of the Aurora programme?.

In terms of UK involvement Dr. Mark Sims, University of Leicester and Chair of PPARC?s Aurora Advisory Committee was buoyant,? This is a great result for European planetary exploration with significant involvement for the UK. The UK community has worked hard to ensure that the Aurora programme reflects the scientific and industrial expertise we have in the UK and the recommended mission builds upon the heritage of Beagle 2 and Huygens. We look forward to making major contributions to this scientific mission of discovery to the Red Planet?.

Original Source: ESA News Release

Posted on by Fraser Cain

Gamma Ray Bursts Could Have Led to Extinctions

Scientists at NASA and the University of Kansas say that a mass extinction on Earth hundreds of millions of years ago could have been triggered by a star explosion called a gamma-ray burst. The scientists do not have direct evidence that such a burst activated the ancient extinction. The strength of their work is their atmospheric modeling — essentially a “what if” scenario.

The scientists calculated that gamma-ray radiation from a relatively nearby star explosion, hitting the Earth for only ten seconds, could deplete up to half of the atmosphere’s protective ozone layer. Recovery could take at least five years. With the ozone layer damaged, ultraviolet radiation from the Sun could kill much of the life on land and near the surface of oceans and lakes, and disrupt the food chain.

Gamma-ray bursts in our Milky Way galaxy are indeed rare, but the scientists estimate that at least one nearby likely hit the Earth in the past billion years. Life on Earth is thought to have appeared at least 3.5 billion years ago. This research, supported by a NASA Astrobiology grant, represents a thorough analysis of the “mass extinction” hypothesis first announced by members of this science team in September 2003.

“A gamma-ray burst originating within 6,000 light years from Earth would have a devastating effect on life,” said Dr. Adrian Melott of the Department of Physics and Astronomy at the University of Kansas. “We don’t know exactly when one came, but we’re rather sure it did come — and left its mark. What’s most surprising is that just a 10-second burst can cause years of devastating ozone damage.”

A scientific paper describing this finding appears in Astrophysical Journal Letters. The lead author is Brian Thomas, a Ph.D. candidate at University of Kansas whom Melott advises.

Gamma-ray bursts are the most powerful explosions known. Most originate in distant galaxies, and a large percentage likely arise from explosions of stars over 15 times more massive than our Sun. A burst creates two oppositely-directed beams of gamma rays that race off into space.

Thomas says that a gamma-ray burst may have caused the Ordovician extinction 450 million years ago, killing 60 percent of all marine invertebrates. Life was largely confined to the sea, although there is evidence of primitive land plants during this period.

In the new work, the team used detailed computer models to calculate the effects of a nearby gamma-ray burst on the atmosphere and the consequences for life.

Thomas, with Dr. Charles Jackman of NASA’s Goddard Space Flight Center in Greenbelt, Md., calculated the effect of a nearby gamma-ray burst on the Earth’s atmosphere. Gamma rays, a high-energy form of light, can break molecular nitrogen (N2) into nitrogen atoms, which react with molecular oxygen (O2) to form nitric oxide (NO). NO will destroy ozone (O3) and produce nitrogen dioxide (NO2). NO2 will then react with atomic oxygen to reform NO. More NO means more ozone destruction. Computer models show that up to half the ozone layer is destroyed within weeks. Five years on, at least 10 percent is still destroyed.

Next Thomas and fellow student Daniel Hogan, an undergraduate, calculated the effect of ultraviolet radiation on life. Deep-sea creatures living several feet below water would be protected. Surface-dwelling plankton and other life near the surface, however, would not survive. Plankton is the foundation of the marine food chain.

Dr. Bruce Lieberman, a paleontologist at the University of Kansas, originated the idea that a gamma-ray burst specifically could have caused the great Ordovician extinction, 200 million years before the dinosaurs. An ice age is thought to have caused this extinction. But a gamma-ray burst could have caused a fast die-out early on and also could have triggered the significant drop in surface temperature on Earth.

“One unknown variable is the rate of local gamma-ray bursts,” said Thomas. “The bursts we detect today originated far away billions of years ago, before the Earth formed. Among the billions of stars in our Galaxy, there’s a good chance that a massive one relatively nearby exploded and sent gamma rays our way.” The Swift mission, launched in November 2004, will help determine recent burst rates. Other team members are Dr. Claude Laird of the University of Kansas, and Drs. Richard Stolarski, John Cannizzo, and Neil Gehrels of NASA Goddard.

Original Source: NASA News Release

Posted on by Fraser Cain

Dark Matter at the Heart of Galaxy Groups

Researchers at the University of Birmingham have used the new generation of X-ray space observatories to study fossil galaxies – ancient galaxy groups in which all of the large galaxies have gradually merged to form one central giant galaxy.

The astronomers discovered a remarkable concentration of dark and normal matter in the cores of these isolated star systems, compared with the mass distribution in normal galaxy groups.

Many galaxies, including our Milky Way, reside in groups. Sometimes they experience close encounters with other members of the group. Computer simulations predict that such interactions cause large galaxies to spiral slowly towards the centre of the group, where they can merge to form a single giant galaxy, which progressively swallows all its neighbours.

Since many galaxy groups possess extended halos of hot gas and dark matter, it was predicted ten years ago that a class of systems dubbed fossil groups should exist, in which all the major galaxies have merged to form one central giant galaxy. This would be surrounded by an X-ray-bright cloud of hot gas that extends outward to many galactic radii.

When we first discovered the large halos of hot gas in which some very compact groups of galaxies are embedded, we realised that just a few billion years of further evolution would leave a single, giant, merged galaxy sitting at the centre of a bright X-ray halo, said Trevor Ponman, the leader of the Birmingham group who made this prediction and then discovered the first fossil group in 1994.

Theories also suggested that fossil groups which fall into even larger clusters of galaxies may account for the giant elliptical galaxies which are often found in the centres of such clusters.

The Birmingham team has observed six likely fossil groups in the past two years, taking advantage of the sharp vision of NASAs Chandra X-Ray Space Observatory and the high sensitivity of ESAs orbiting XMM-Newton X-ray observatory. The six fossil groups are located up to two billion light years from Earth. The teams main objective was to explore the mechanisms by which fossil groups and giant elliptical galaxies are formed.

The key to the study was the distribution of dark matter in the fossil groups. This mysterious matter comprises over 80 per cent of the mass of the Universe, yet its nature is unknown. Dark matter has never been detected directly, but its presence is inferred through its gravitational influence on ordinary matter.

The large elliptical galaxy NGC 6482 was of special interest to the team, since it is the closest known fossil group, and could be studied in great detail. This isolated giant, which shines with the equivalent of 110 billion Suns, is located 100 million light years away in the constellation Hercules. Using Chandras Advanced CCD Imaging Spectrometer, Habib Khosroshahi, Trevor Ponman and Laurence Jones, used observations of the hot gas to trace the distribution of dark matter in NGC 6482. The gas is heated to a temperature of 10 million degrees Celsius, mainly due to shock heating as a result of gravitational collapse.

Speaking today at the RAS National Astronomy Meeting in Birmingham, Habib Khosroshahi described the discovery of a remarkable concentration of dark matter in the core of NGC 6482. Khosroshahi also described two more examples of high mass concentration in more massive and more distant fossil galaxies studied by both the Chandra and the XMM-Newton telescopes, although the case of NGC 6482 is unique, since it is possible to probe the centre of the system with higher accuracy.

According to Khosroshahi, the concentration of mass at the centre of these ancient galaxy groups, which is mostly in the form of dark matter, was found to be typically five times higher than in normal galaxy groups with similar mass and halo size. This central concentration of mass supports the idea that fossil groups such as NGC 6482 are very old structures which collapsed long before the typical groups of galaxies formed. “The explanation for such a centralised dark matter distribution could be that the system formed at very high redshift when the Universe was very young and dense, said Khosroshahi.

The great advantage of fossil groups compared to normal groups is that no major galaxy interaction, which can stir the hot gas, is taking place, he added. Therefore, they provide ideal laboratories to study the properties of visible matter in the form of gas and stars as well as their container, the dark matter.

Original Source: RAS News Release

Posted on by Fraser Cain

Discovery Reaches the Launch Pad

NASA’s Space Shuttle Discovery arrived at its launch pad completing the next major milestone for Return to Flight of America’s Space Shuttle program. The Shuttle arrived at its launch pad at 12:30 a.m. This was approximately three hours later than its scheduled arrival.

The slight delay was caused when Shuttle processing team members had to replace a Programmable Logic Controller (PLC) circuit card on the Crawler Transporter during the final leg of its journey. The Crawler Transporter is the vehicle which transports the Space Shuttle and its Mobile Launcher Platform to the launch pad. The PLC is an indicator that relays height measurements to the Crawler’s operators while it’s in motion.

The issue occurred during Discovery’s initial attempt to climb the incline ramp leading to Pad 39B. When observed, technicians decided to stop the rollout and then reverse Discovery back down the incline ramp to level ground to test and then replace the circuit card. Once the new card was in place, the Crawler functioned normally and the rollout was completed. The Space Shuttle remained level and in a safe configuration throughout all movements and during the changeout of the card.

Once in place at the launch pad, the shuttle team continued preparation of Discovery for its scheduled launch set for a window of May 15 to June 3.

Original Source: NASA News Release

Posted on by Fraser Cain

Early Galaxy Growth Spurt Spotted

Distant galaxies undergoing intense bursts of star formation have been shown by NASA’s Chandra X-ray Observatory to be fertile growing grounds for the largest black holes in the Universe. Collisions between galaxies in the early Universe may be the ultimate cause for both the accelerated star formation and black hole growth.

By combining the deepest X-ray image ever obtained with submillimeter and optical observations, an international team of scientists has found evidence that some extremely luminous adolescent galaxies and their central black holes underwent a phenomenal spurt of growth more than 10 billion years ago. This concurrent black hole and galaxy growth spurt is only seen in these galaxies and may have set the stage for the birth of quasars – distant galaxies that contain the largest and most active black holes in the Universe.

“The extreme distances of these galaxies allow us to look back in time, and take a snapshot of how today’s largest galaxies looked when they were producing most of their stars and growing black holes,” said David Alexander of the University of Cambridge, UK, and lead author of a paper in the April 7, 2005 issue of Nature that describes this work.

The galaxies studied by Alexander and his colleagues are known as submillimeter galaxies, so-called because they were originally identified by the James Clerk Maxwell submillimeter telescope (JCMT) on Mauna Kea in Hawaii. The submillimeter observations along with optical data from Keck indicate these galaxies had an unusually large amount of gas. The gas in each galaxy was forming into stars at a rate of about one per day, or 100 times the present rate in the Milky Way galaxy. The Chandra X-ray data show that the supermassive black holes in the galaxies were also growing at the same time.

These galaxies are very faint and it is only with the deepest observations of the Universe that they can be detected at all. “The deeper we look into the Universe with Chandra, the more fascinating things we find” says Niel Brandt of Penn State University in University Park. “Who knows what nature has in store for us as we push the boundaries yet further.”

The X-ray observations also showed that the black holes are surrounded by a dense shroud of gas and dust. This is probably the material that will be consumed by the growing black holes.

Hubble Space Telescope observations indicate that most of the submillimeter galaxies are actually two galaxies that are colliding and merging. Recent sophisticated computer simulations performed by Tiziana Di Matteo of Carnegie Mellon University in Pittsburgh, Penn., and her collaborators have shown that such mergers drive gas toward the central regions of galaxies, triggering a burst of star formation and providing fuel for the growth of a central black hole.

“It is exciting that these recent observations are in good agreement with our simulation,” says Di Matteo, “We seem to be converging on a consistent picture of galaxy formation with both observations and theory.” In particular, this work will help scientists to understand the observed link in the present epoch between the total mass of stars in the central bulges of large galaxies and the size of their central, supermassive black holes.

The James Clerk Maxwell Telescope (JCMT) is operated on behalf of the United Kingdom, Canada & Netherlands by the Joint Astronomy Centre. With its 15-meter (50-foot) diameter dish the JCMT detects light with “submillimeter” wavelengths, between infrared light and radio waves on the wavelength scale. The W. M. Keck Observatory is operated by the California Association for Research in Astronomy.

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate, Washington. Northrop Grumman of Redondo Beach, Calif., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Additional information and images are available at: http://chandra.harvard.edu and http://chandra.nasa.gov

Original Source: Chandra News Release