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Brightness Variations of Sun-like Stars: The Mystery Deepens
An extensive study made with ESO’s Very Large Telescope deepens a long-standing mystery in the study of stars similar to the Sun. Unusual year-long variations in the brightness of about one third of all Sun-like stars during the latter stages of their lives still remain unexplained. Over the past few decades, astronomers have offered many possible explanations, but the new, painstaking observations contradict them all and only deepen the mystery. The search for a suitable interpretation is on.
“Astronomers are left in the dark, and for once, we do not enjoy it,” says Christine Nicholls from Mount Stromlo Observatory, Australia, lead author of a paper reporting the study. “We have obtained the most comprehensive set of observations to date for this class of Sun-like stars, and they clearly show that all the possible explanations for their unusual behavior just fail.”
The mystery investigated by the team dates back to the 1930s and affects about a third of Sun-like stars in our Milky Way and other galaxies. All stars with masses similar to our Sun become, towards the end of their lives, red, cool and extremely large, just before retiring as white dwarfs. Also known as red giants, these elderly stars exhibit very strong periodic variations in their luminosity over timescales up to a couple of years.
“Such variations are thought to be caused by what we call ‘stellar pulsations’,” says Nicholls. “Roughly speaking, the giant star swells and shrinks, becoming brighter and dimmer in a regular pattern. However, one third of these stars show an unexplained additional periodic variation, on even longer timescales — up to five years.”
In order to find out the origin of this secondary feature, the astronomers monitored 58 stars in our galactic neighbor, the Large Magellanic Cloud, over two and a half years. They acquired spectra using the high resolution FLAMES/GIRAFFE spectrograph on ESO’s Very Large Telescope and combined them with images from other telescopes, achieving an impressive collection of the properties of these variable stars.
Outstanding sets of data like the one collected by Nicholls and her colleagues often offer guidance on how to solve a cosmic puzzle by narrowing down the plethora of possible explanations proposed by the theoreticians. In this case, however, the observations are incompatible with all the previously conceived models and re-open an issue that has been thoroughly debated. Thanks to this study, astronomers are now aware of their own “ignorance” — a genuine driver of the knowledge-seeking process, as the ancient Greek philosopher Socrates is said to have taught.
“The newly gathered data show that pulsations are an extremely unlikely explanation for the additional variation,” says team leader Peter Wood. “Another possible mechanism for producing luminosity variations in a star is to have the star itself move in a binary system. However, our observations are strongly incompatible with this hypothesis too.”
The team found from further analysis that whatever the cause of these unexplained variations is, it also causes the giant stars to eject mass either in clumps or as an expanding disc. “A Sherlock Holmes is needed to solve this very frustrating mystery,” concludes Nicholls.
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|Image Caption: The life of Sun-like stars Image Credit: ESO/S. Steinhöfel Source: ESO Permalink: http://www.sflorg.com/comm_center/space/p970_19.html Time Stamp: 12/7/2009 at 4:16:26 PM UTC|
Restoration of Asteroid Explorer, HAYABUSA's Return Cruise
The Japan Aerospace Exploration Agency (JAXA) has been studying measures to deal with the anomaly detected in one of the ion engines aboard the Asteroid Explorer "HAYABUSA" as reported on November 9, 2009. As a result, the project team has come up with a recovery operation plan, and the project decided to resume the operations, while carefully watching the status of the ion engines.
JAXA has been studying the characteristics of the neutralizers and the ion sources. During the study, enough thrust is found available for the rest of the cruise, when the neutralizer of the engine-A is combined with the ion source of the engine-B.
While the operation still needs monitored carefully, the project team has concluded the spacecraft can maintain the current return cruise schedule back to the earth around June of 2010, if the new engines configuration continues to work as planned.
|Source: Japan Aerospace Exploration Agency Permalink: http://www.sflorg.com/comm_center/space/p945_18.html Time Stamp: 11/19/2009 at 4:45:00 PM UTC|
Half-baked Asteroids Have Earth-like Crust
Asteroids are hunks of rock that orbit in the outer reaches of space, and scientists have generally assumed that their small size limited the types of rock that could form in their crusts. But two newly discovered meteorites may rewrite the book on how some asteroids form and evolve. Researchers from the Carnegie Institution, the University of Maryland, and the University of Tennessee report in the January 8th edition of Nature that these meteorites are ancient asteroid fragments consisting of feldspar-rich rock called andesite. Similar rocks were previously known only from Earth, making these samples the first of their kind from elsewhere in the Solar System.
The two meteorites were discovered during the Antarctic Search for Meteorites (ANSMET) 2006/2007 field season in a region of the Antarctic ice known as the Graves Nunatak icefield. The light-colored meteorites, designated GRA 06128 and GRA 06129, were immediately recognized as being different from previously known meteorites.
“What is most unusual about these rocks is that they have compositions similar to Earth's andesite continental crust - what makes up the ground beneath our feet,” says University of Maryland’s James Day, lead author of the study. ”No meteorites like this have ever been seen before.”
Andesite is an igneous rock common on Earth in areas where colliding tectonic plates generate volcanoes, such as those of the Andes mountain range. The meteorites contain minerals thought to require large-scale processes such as plate tectonics to concentrate the right chemical ingredients. In view of this, some researchers had suggested that the meteorites were fragments of a planet or the Moon, not an asteroid. But analysis of the meteorites’ oxygen isotopes at the Carnegie Institution’s Geophysical Laboratory by Douglas Rumble ruled out that possibility.
“A number of solar system objects including parent bodies of meteorites, planets, moons, and asteroids have their own oxygen isotope signatures,” says Rumble. “Just by analyzing 16O-17O-18O ratios we can tell if a meteorite came from Mars, from the Moon, or from a particular asteroid. One extensively studied parent is the asteroid 4 Vesta. In the majority of cases the actual location of the parent body is unknown, but a particular group of meteorites may be assigned to the same parent body based on the isotope ratios even if the specific location of the body isn’t known. When the ratios in meteorites are plotted against one another the result is mutually parallel lines offset from one another. The GRA 06128 and GRA 06129 meteorites, and some similar ones called brachinites, plot below Earth-Moon rocks and are nearly coincident with meteorites from 4 Vesta.”
The meteorites’ age, more than 4.5 billion years, suggests that they formed very soon after the birth of the solar system. This makes it unlikely that they came from the crust of a differentiated planet. The chemical signature of some rare precious metals, notably osmium, in the meteorites also points to their origin on an asteroid that was not fully differentiated.
The researchers hypothesize that that the asteroid had a diameter somewhat larger than 100 kilometers, which would be sufficient to hold enough heat for the asteroid’s rocks to partially, but not completely, melt. The asteroid would remain undifferentiated, but the melted portions could erupt on the asteroid’s surface to form the andesitic crust.
“Our work illustrates that the formation of planet-like andesite crust has occurred by processes other than plate tectonics on solar system bodies,” says Day. “Ultimately this may shed light on how evolved crust forms on planets, including Earth, during the earliest stages of their birth.”
This study was supported by the NASA Cosmochemistry Program.
|Image Caption: Field image of the achondrite meteorite GRA 06129, found in blue ice of the Graves Nunatak region of the Antarctica during the ANSMET 2006/2007 field-season. GRA 06129 and its pair, GRA 06128, are achondrite meteorites with compositions unlike any previously discovered Solar System materials. Image courtesy of the Antarctic Search for Meteorites Image Credit: PI – Ralph Harvey, Case Western Reserve University Source: Carnegie Institution for Science Permalink: http://www.sflorg.com/comm_center/space/p828_17.html Time Stamp: 1/9/2009 at 4:06:01 PM UTC|
Zeroing in on Hubble’s Constant
In the early part of the 20th Century, Carnegie astronomer Edwin Hubble discovered that the universe is expanding. The rate of expansion is known as the Hubble constant. Its precise value has been hotly debated for all of the 80 intervening years. The value of the Hubble constant is a key ingredient in determining the age and size of the universe. In 2001, as part of the Hubble Space Telescope Key Project, a team of astronomers led by Carnegie’s Wendy Freedman determined precision distances to individual far-off galaxies and used them to determine that the universe is expanding at the rate of 72 kilometers per second per megaparsec. While the debate had previously raged over a factor-of-two uncertainty in the Hubble constant, Freedman and her team cut that uncertainty down to just 10%. And now that number is about to be decreased to 3% with the new Carnegie Hubble Program (CHP) using NASA’s space-based Spitzer telescope. Freedman, who is director of the Observatories of the Carnegie Institution, will lead the effort, which includes Carnegie staff members Barry Madore and Eric Persson, and Carnegie Spitzer Fellow, Jane Rigby.
The Carnegie Hubble proposal was just selected by the Spitzer Science Center on behalf of NASA as a Cycle-6 Exploration Science Program using Spitzer. This space telescope currently takes images and spectra—chemical fingerprints—of objects by detecting their heat, or infrared (IR) energy, between wavelengths of 3 and 180 microns (a micron equals one-millionth of a meter). Most infrared radiation is blocked by the Earth's atmosphere and thus it has to be detected from space. The Hubble Key Project observed distant objects primarily at optical wavelengths. In its post-cryogenic phase beginning in April 2009 Spitzer will have exhausted its liquid helium coolant but it will still be able to operate two of its imaging detectors that are sensitive to the near-infrared. This portion of the electromagnetic spectrum has numerous advantages, especially when observing Cepheid variable stars, the so-called “standard candles” that are used to determine distances to distant galaxies.
“The power of Spitzer,” explained Freedman, “is that it will allow us to virtually eliminate the dimming and obscuring effects of dust. It offers us the ability to make the most precise measurements of Cepheid distances that have ever been made, and to bring the uncertainty in the Hubble constant down to the few percent level.”
Cepheids are extremely bright, pulsating stars. Their pulsation periods are directly related to their intrinsic luminosities. So, by measuring their periods and apparent brightnesses their individual distances and therefore the distance to their parent galaxies can be determined. By considering the rate at which more distant galaxies are measured to be moving faster away from us in the universe we can calculate the Hubble constant and from that determine the size and the age of the universe.
One of the largest uncertainties plaguing past measurements of the Hubble constant involved the distance to the Large Magellanic Cloud (LMC), a relatively nearby galaxy, orbiting the Milky Way. Freedman and colleagues will begin their 700 hours of observations refining the distance to the LMC using Cepheids newly calibrated based on new Spitzer observations of similar stars in our own Milky Way. They will then measure Cepheid distances to all of the nearest galaxies previously observed from the ground over the past century and by the Key Project, acquiring distances to galaxies in our Local Group and beyond. The Local Group, our galactic neighborhood, is comprised of some 40 galaxies. The team will be able to correct for lingering uncertainties again by observing in the near-IR. Systematic errors such as whether chemical composition differences among Cepheids might affect the period-luminosity relation, will be examined using the infrared data. Spitzer will begin to execute the Carnegie Hubble Program in June 2009 and continue for at least the next two years.
“In the age of precision cosmology one of the key factors in securing the fundamental numbers that describe the time evolution and make-up of our universe is the Hubble constant. Ten percent is simply not good enough. Cosmologists need to know the expansion rate of the universe to as high a precision and as great an accuracy as we can deliver,” remarked Carnegie co-investigator, Barry Madore.
|Image Caption: Artist rendition of Spitzer in its heliocentric orbit. Image Credit: NASA/JPL-Caltech Source: Carnegie Institution for Science Permalink: http://www.sflorg.com/comm_center/space/p820_16.html Time Stamp: 1/5/2009 at 3:59:22 PM UTC|
Students Discover Unique Planet
Three undergraduate students, from Leiden University in the Netherlands, have discovered an extrasolar planet. The extraordinary find, which turned up during their research project, is about five times as massive as Jupiter. This is also the first planet discovered orbiting a fast-rotating hot star.
The students were testing a method of investigating the light fluctuations of thousands of stars in the OGLE database in an automated way. The brightness of one of the stars was found to decrease for two hours every 2.5 days by about one percent. Follow-up observations, taken with ESO's Very Large Telescope in Chile, confirmed that this phenomenon is caused by a planet passing in front of the star, blocking part of the starlight at regular intervals.
According to Ignas Snellen, supervisor of the research project, the discovery was a complete surprise. "The project was actually meant to teach the students how to develop search algorithms. But they did so well that there was time to test their algorithm on a so far unexplored database. At some point they came into my office and showed me this light curve. I was completely taken aback!"
The students, Meta de Hoon, Remco van der Burg, and Francis Vuijsje, are very enthusiastic. "It is exciting not just to find a planet, but to find one as unusual as this one; it turns out to be the first planet discovered around a fast rotating star, and it's also the hottest star found with a planet," says Meta. "The computer needed more than a thousand hours to do all the calculations," continues Remco.
The planet is given the prosaic name OGLE2-TR-L9b. "But amongst ourselves we call it ReMeFra-1, after Remco, Meta, and myself," says Francis.
The planet was discovered by looking at the brightness variations of about 15 700 stars, which had been observed by the OGLE survey once or twice per night for about four years between 1997 and 2000. Because the data had been made public, they were a good test case for the students' algorithm, who showed that for one of stars observed, OGLE-TR-L9, the variations could be due to a transit — the passage of a planet in front of its star. The team then used the GROND instrument on the 2.2 m telescope at ESO's La Silla Observatory to follow up the observations and find out more about the star and the planet.
"But to make sure it was a planet and not a brown dwarf or a small star that was causing the brightness variations, we needed to resort to spectroscopy, and for this, we were glad we could use ESO's Very Large Telescope," says Snellen.
The planet, which is about five times as massive as Jupiter, circles its host star in about 2.5 days. It lies at only three percent of the Earth-Sun distance from its star, making it very hot and much larger than normal planets.
The spectroscopy also showed that the star is pretty hot — almost 7000 degrees, or 1200 degrees hotter than the Sun. It is the hottest star with a planet ever discovered, and it is rotating very fast. The radial velocity method — that was used to discover most extrasolar planets known — is less efficient on stars with these characteristics. "This makes this discovery even more interesting," concludes Snellen.
|Image Caption: During their research project, undergraduate students Francis Vuijsje, Meta de Hoon, and Remco van der Burg (left to right), discovered an extrasolar planet that is larger than and about five times as massive as Jupiter and orbiting a fast-rotating hot star. Image Credit: Leiden Observatory Source: ESO Permalink: http://www.sflorg.com/comm_center/space/p774_15.html Time Stamp: 12/4/2008 at 1:21:52 PM UTC|
Europe Unveils 20-Year Plan for Brilliant Future in Astronomy
Astronomy is enjoying a golden age of fundamental, exciting discoveries. Europe is at the forefront, thanks to 50 years of progress in cooperation. To remain ahead over the next two to three decades, Europe must prioritize and coordinate the investment of its financial and human resources even more closely. The ASTRONET network, backed by the entire European scientific community, supported by the European Commission, and coordinated by the CNRS, today presents its Roadmap for a brilliant future for European astronomy. ESO's European Extremely Large Telescope is ranked as one of two top-priority large ground-based projects.
Europe is a leader in astronomy today, with the world's most successful optical observatory, ESO's Very Large Telescope, and cutting-edge facilities in radio astronomy and in space. In an unprecedented effort demonstrating the potential of European scientific cooperation, all of European astronomy is now joining forces to define the scientific challenges for the future and construct a common plan to address them in a cost-effective manner.
In 2007, a top-level Science Vision was prepared to assess the most burning scientific questions over the next quarter century, ranging from dark energy to life on other planets. European astronomy now presents its Infrastructure Roadmap, a comprehensive 20-year plan to coordinate national and community investments to meet these challenges in a cost-effective manner. The Roadmap not only prioritizes the necessary new frontline research facilities from radio telescopes to planetary probes, in space and on the ground, but also considers such key issues as existing facilities, human resources, ICT infrastructure, education and outreach, and cost — of operations as well as construction.
This bold new initiative — ASTRONET — was created by the major European funding agencies with support from the European Commission and is coordinated by the National Institute for Earth Sciences and Astronomy (INSU) of the CNRS. To build consensus on priorities in a very diverse community, the Science Vision and Roadmap were developed in an open process involving intensive interaction with the community through large open meetings and feedback via e-mail and the web. The result is a plan now backed by astronomers in 28 Member and Associated States of the EU, with over 500 million inhabitants.
Over 60 selected experts from across Europe contributed to the construction of the ASTRONET Roadmap, ensuring that European astronomy has the tools to compete successfully in answering the challenges of the Science Vision. They identified and prioritized a set of new facilities to observe the Universe from radio waves to gamma rays, to open up new ways of probing the cosmos, such as gravitational waves, and to advance in the exploration of our Solar System. In the process, they considered all the elements needed by a successful scientific enterprise, from global-scale cooperation on the largest mega-project to the need for training and recruiting skilled young scientists and engineers.
One of two top-priority large ground-based projects is ESO's European Extremely Large Telescope. Its 42-meter diameter mirror will make the E-ELT the largest optical/near-infrared telescope in the world — "the biggest eye on the sky". The science to be done with the E-ELT is extremely exciting and includes studies of exoplanets and discs, galaxy formation and dark energy. ESO Director General Tim de Zeeuw says: "The top ranking of the E-ELT in the Roadmap is a strong endorsement from the European astronomical community. This flagship project will indisputably raise the European scientific, technological and industrial profile".
Among other recommendations, the Roadmap considers how to maximize the future scientific impact of existing facilities in a cost-effective manner. It also identifies a need for better access to state-of-the art computing and laboratory facilities, and for a stronger involvement of European high-tech industry in the development of future facilities. Moreover, success depends critically upon an adequate supply of qualified scientists, and of engineers in fields ranging from IT to optics. Finally, the Roadmap proposes a series of measures to enhance the public understanding of astronomy as a means to boost recruitment in science and technology in schools and universities across Europe.
Europe currently spends approximately €2 billion a year on astronomy in the broadest sense. Implementing the ASTRONET Roadmap will require a funding increase of around 20% — less than €1 per year per European citizen. Global cooperation will be needed — and is being planned — for several of the largest projects.
ASTRONET first developed a Science Vision for European Astronomy (published October 2007), which reviewed and prioritized the main scientific questions that European astronomy should address over the next 10–20 years. Based on this effort, the ASTRONET Roadmap was developed primarily on scientific grounds by a Working Group appointed by the ASTRONET Board. Existing and proposed infrastructure projects — over 100 in all — were reviewed by three specialist panels of European scientists. Two other panels considered the needs for theory, computing and data archiving, and human resources, including education, recruitment, public outreach and industrial involvement.
The Roadmap addresses projects primarily requiring new funds of €10 million or more from European sources and on which spending decisions are required after 2008. Each project was examined for its potential scientific impact, originality, level of European input, size of the astronomical community that would benefit, and its relevance to advancing European high technology industry. Feedback from the community on an advanced complete draft of the report was invited through both a web-based forum and a large symposium held in Liverpool in June 2008.
Some top-priority projects from the full list are
Among large-scale projects on the ground:
Scientifically compelling instruments in a lower cost range include:
Among the largest space missions proposed for the coming decade, the top priorities for ASTRONET include:
Equally challenging, but less costly top-priority space projects include:
|Roadmap Full Report: http://www.sflorg.com/comm_center/space/pdfs/p752_14_01.pdf Image Caption: ESO's European Extremely Large Telescope is ranked as one of two top-priority large ground-based projects in the ASTRONET Roadmap for European astronomy which is backed by the entire European scientific community and supported by the European Commission. The current design of the E-ELT in its enclosure is seen here. This dome will have an approximate height of 90m and a footprint of about 90m diameter. Hi-Res Version: http://www.sflorg.com/comm_center/space/images/p752_14_02.jpg Image Credit: ESO Source: ESO Permalink: http://www.sflorg.com/comm_center/space/p752_14.html Time Stamp: 11/25/2008 at 4:22:35 PM UTC|
Astronomers detect matter torn apart by black hole
VLT and APEX team up to study flares from the black hole at the Milky Way's core
Astronomers have used two different telescopes simultaneously to study the violent flares from the supermassive black hole in the center of the Milky Way. They have detected outbursts from this region, known as Sagittarius A*, which reveal material being stretched out as it orbits in the intense gravity close to the central black hole.
The team of European and US astronomers used ESO's Very Large Telescope (VLT) and the Atacama Pathfinder Experiment (APEX) telescope, both in Chile, to study light from Sagittarius A* at near-infrared wavelengths and the longer submillimeter wavelengths respectively. This is the first time that astronomers have caught a flare with these telescopes simultaneously. The telescopes' location in the southern hemisphere provides the best vantage point for studying the Galactic Center.
"Observations like this, over a range of wavelengths, are really the only way to understand what's going on close to the black hole," says Andreas Eckart of the University of Cologne, who led the team.
Sagittarius A* is located at the center of our own Milky Way Galaxy at a distance from Earth of about 26 000 light-years. It is a supermassive black hole with a mass of about four million times that of the Sun. Most, if not all, galaxies are thought to have a supermassive black hole in their center.
"Sagittarius A* is unique, because it is the nearest of these monster black holes, lying within our own galaxy," explains team member Frederick K. Baganoff of the Massachusetts Institute of Technology (MIT) in Cambridge, USA. "Only for this one object can our current telescopes detect these relatively faint flares from material orbiting just outside the event horizon."
The emission from Sagittarius A* is thought to come from gas thrown off by stars, which then orbits and falls into the black hole.
Making the simultaneous observations required careful planning between teams at the two telescopes. After several nights waiting at the two observatory sites, they struck lucky.
"At the VLT, as soon as we pointed the telescope at Sagittarius A* we saw it was active, and getting brighter by the minute. We immediately picked up the phone and alerted our colleagues at the APEX telescope," says Gunther Witzel, a PhD student from the University of Cologne.
Macarena García-Marín, also from Cologne, was waiting at APEX, where the observatory team had made a special effort to keep the instrument on standby. "As soon as we got the call we were very excited and had to work really fast so as not to lose crucial data from Sagittarius A*. We took over from the regular observations, and were in time to catch the flares," she explains.
Over the next six hours, the team detected violently variable infrared emission, with four major flares from Sagittarius A* . The submillimeter-wavelength results also showed flares, but, crucially, this occurred about one and a half hours after the infrared flares.
The researchers explain that this time delay is probably caused by the rapid expansion, at speeds of about 5 million km/h, of the clouds of gas that are emitting the flares. This expansion causes changes in the character of the emission over time, and hence the time delay between the infrared and submillimeter flares.
Although speeds of 5 million km/h may seem fast, this is only 0.5% of the speed of light. To escape from the very strong gravity so close to the black hole, the gas would have to be traveling at half the speed of light – 100 times faster than detected – and so the researchers believe that the gas cannot be streaming out in a jet. Instead, they suspect that a blob of gas orbiting close to the black hole is being stretched out, like dough in a mixing bowl, and this is causing the expansion.
The simultaneous combination of the VLT and APEX telescopes has proved to be a powerful way to study the flares at multiple wavelengths. The team hope that future observations will let them prove their proposed model, and discover more about this mysterious region at the center of our Galaxy.
|Image Caption: (image left) This is a color composite image of the central region of our Milky Way galaxy, about 26 000 light years from Earth. Giant clouds of gas and dust are shown in blue, as detected by the LABOCA instrument on the Atacama Pathfinder Experiment (APEX) telescope at submillimeter wavelengths (870 micron). The image also contains near-infrared data from the 2MASS project at K-band (in red), H-band (in green), and J-band (in blue). The image shows a region approximately 100 light-years wide. (image right) This series of three images shows an artist’s impression of a bright “blob” of gas in the disk of material surrounding the black hole in the center of our Galaxy, Sagittarius A*. This blob of material is responsible for the flares detected by the researchers. As the blob orbits the black hole, it is stretched out, and this expansion over time causes the delay between flares being detected at near-infrared wavelengths (with the VLT) and at submillimeter wavelengths (with APEX). Image Credit: ESO/APEX/2MASS/A. Eckart et al. , ESO/L. Calçada Hi-Res Version: http://www.sflorg.com/observatories/eso/eso_15 Source: ESO Permalink: http://www.sflorg.com/comm_center/space/p737_13.html Time Stamp: 11/20/2008 at 1:18:39 PM UTC|
The NASA/ESA Hubble Space Telescope is back in business
The Hubble Space Telescope is back in business with a snapshot of the fascinating galaxy pair Arp 147.
Just a couple of days after the orbiting observatory was brought back online, Hubble aimed its prime working camera, the Wide Field Planetary Camera 2 (WFPC2), at a particularly intriguing target, a pair of gravitationally interacting galaxies called Arp 147.
The image demonstrated that the camera is working exactly as it was before going offline, thereby scoring a "perfect 10" both for performance and beauty.
And literally "10" for appearance too, due to the chance alignment of the two galaxies. The left-most galaxy, or the "one" in this image, is relatively undisturbed, apart from a smooth ring of starlight. It appears nearly edge-on to our line of sight. The right-most galaxy, the "zero" of the pair, exhibits a clumpy, blue ring of intense star formation.
The blue ring was formed after the galaxy on the left passed through the galaxy on the right. Just as a pebble thrown into a pond creates an outwardly moving circular wave, or ripples, an outwardly propagating ring of higher density was generated at the point of impact of the two galaxies. As this excess density collided with outer material that was moving inwards due to the gravitational pull of the two galaxies, shocks and dense gas were produced, stimulating star formation.
The dusty reddish knot at the lower left of the blue ring probably marks the location of the original nucleus of the galaxy that was hit.
Arp 147 appears in the Arp Atlas of Peculiar Galaxies, compiled by Halton Arp in the 1960s and published in 1966. This picture was assembled from WFPC2 images taken with three separate filters. The colours blue, green, and red represent the blue, visible-light, and infrared filters respectively.
The galaxy pair was photographed on 27-28 October 2008. Arp 147 lies in the constellation of Cetus, more than 400 million light-years away from Earth
|Image Caption: Hubble scores a perfect ten Image Credit: NASA, ESA and M. Livio (STScI) Hi-Res and Full Caption: http://www.sflorg.com/observatories/hubble/hubble_43 Source: ESA Permalink: http://www.sflorg.com/comm_center/space/p663_12.html Time Stamp: 10/30/2008 at 2:02:48 PM UTC|
Keck Telescope and "Cosmic Lens" Team-up to Demonstrate Eventual Power of Thirty Meter Telescope
at the California Institute of Technology (Caltech) and their
colleagues used a rare cosmic alignment and modern adaptive
optics to image a distant galaxy with similar exquisite
resolution promised by the future Thirty Meter Telescope (TMT).
This achievement provided detailed insight into the nature of a
young star-forming galaxy as it appeared only two billion years
after the Big Bang, and determined how that galaxy may eventually
evolve to become a system like our own Milky Way.
Gravitational lensing enlarged the distant galaxy in angular size by a factor of about eight in each direction. Together with the enhanced resolution using adaptive optics, this allowed the team to determine the internal velocity structure of the remote galaxy, located 11 billion light-years from Earth, and hence its likely future evolution.
The researchers found that the distant galaxy, which is typical in many respects to others at that epoch, shows clear signs of orderly rotation. The finding, in association with observations conducted at millimeter wavelengths, which are sensitive to cold molecular gas (an indicator of galactic rotation), suggests that the source is in the early stages of assembling a spiral disk with a central nucleus similar to those seen in spiral galaxies at the present day.
The research, described in the October 9 issue of the journal Nature, provides a remarkable demonstration of the likely power of the future TMT, the first of a new generation of large telescopes designed to exploit AO.
"This is the most detailed view we have yet seen of a young, early-epoch galaxy, and it has given us unique insight into how such systems begin to take on the familiar characteristics of spiral galaxies like our own Milky Way," said Richard Ellis, Steele Professor of Astronomy at Caltech, co-author of the Nature paper, and a member of the TMT science advisory committee. “It is an exciting discovery that heralds the kind of science that will be routine when the Thirty Meter Telescope comes on-line.”
When completed in the latter half of the next decade, TMT's giant primary mirror and improved optics will produce images with an angular resolution three times better than the 10-meter Keck and 12 times better than the Hubble Space Telescope, at similar wavelengths. Because of the spectacular improvement in angular resolution provided by AO, the TMT will be able to study the internal properties of small distant galaxies, seen as they were when the Universe was young.
Likewise, the Atacama Large Millimeter Array (ALMA), a large interferometer being completed in Chile, will provide a huge step forward in mapping the extremely faint emission from cold hydrogen gas -- the principal component of young, distant galaxies and a clear marker of cold molecular gas -- compared to the coarser capabilities of present facilities. In their recent research, the Caltech-led team has provided an impressive glimpse of what can be done with the superior performance expected of TMT and ALMA.
Using the Hubble Space Telescope, the team located a distinctive galaxy dubbed the "Cosmic Eye" because its form is distorted into a ring-shaped structure by the gravitational field of a foreground galaxy.
"Gravity has effectively provided us with an additional zoom lens, enabling us to study this distant galaxy on scales approaching only a few hundred light-years. This is ten times finer sampling than hitherto possible," explains Postdoctoral Research Scholar Dan Stark of Caltech, leader of the study. "As a result, we can see, for the first time, that a typical-sized young galaxy is spinning and slowly evolving into a spiral galaxy much like our own Milky Way," he says.
The key spectroscopic observations were made with the OSIRIS instrument, developed specifically for the Keck AO system by astrophysicist James Larkin and collaborators at the University of California, Los Angeles. Stark and his co-workers used the OSIRIS instrument to map the velocity across the source in fine detail, allowing them to demonstrate that it has a primitive rotating disk.
To aid in their analysis, the researchers combined data from the Keck Observatory with data taken at millimeter wavelengths by the Plateau de Bure Interferometer (PdBI) located in the French Alps. This PdBI instrument is sensitive to the distribution of cold gas that has yet to collapse to form stars. These observations give a valuable glimpse of what will soon be routine with the ALMA telescope.
"Remarkably, the cold gas traced by our millimeter observations shares the rotation shown by the young stars seen in the Keck observations. The distribution of gas seen with our amazing resolution indicates we are witnessing the gradual build up of a spiral disk with a central nuclear component," explains co-investigator Mark Swinbank of Durham University, who was involved in both the Keck and PBI observations.
This breakthrough demonstrates how important angular resolution has become in ensuring progress in extragalactic astronomy. This will be the key gain of both the TMT and ALMA facilities.
"For decades, astronomers were content to build bigger telescopes, arguing that light-gathering power was the primary measure of a telescope's ability," explains Ellis. "However, adaptive optics and interferometry are now providing ground-based astronomers with the additional gain of angular resolution. The combination of a large aperture and exquisite resolution is very effective for studying the internal properties of distant and faint sources seen as they were when the Universe was young. This is the exciting future we can expect with TMT and ALMA and, thanks to the magnification of a gravitational lens, we have an early demonstration here in this study," he says.
The W. M. Keck Observatory operates twin 10-meter telescopes located on the summit of Mauna Kea. The Observatory, made possible by grants from the W. M. Keck Foundation totaling over $138 million, is managed as a non-profit corporation whose board of directors includes representatives from Caltech and the University of California.
The TMT is currently in the final stages of its design phase. The plan is to initiate construction in 2010 with ‘first light’ in early 2018. This project is a partnership among the California Institute of Technology, the University of California, and ACURA, an organization of Canadian universities. The Gordon and Betty Moore Foundation has provided $50 million for the design phase of the project and has pledged an additional $200 million for the construction of the telescope. ACURA committed an additional $17.5 million for the design and development of TMT.
Co-authors on the paper, "The formation and assembly of a typical star-forming galaxies at redshift z~3," are Simon Dye of Cardiff University in Cardiff, Wales; Ian R. Smail of Durham University in Durham, England; and Johan Richard of Caltech.
|Image Caption 1: How Adaptive Optics Works Image Caption 2: Demonstrating a Sharp Future Image Credits: Thirty Meter Telescope Source: Thirty Meter Telescope Permalink: http://www.sflorg.com/comm_center/space/p604_11.html Time Stamp: 10/8/2008 at 17:00:02 UTC|
Young Galaxy's Magnetism Surprises Astronomers
Astronomers have made the first direct measurement of the magnetic field in a young, distant galaxy, and the result is a big surprise.
Looking at a faraway protogalaxy seen as it was 6.5 billion years ago, the scientists measured a magnetic field at least 10 times stronger than that of our own Milky Way. They had expected just the opposite.
"This new measurement indicates that magnetic fields may play a more important role in the formation and evolution of galaxies than we have realized," said Arthur Wolfe, of the University of California-San Diego (UCSD).
At its great distance, the protogalaxy is seen as it was when the Universe was about half its current age. According to the leading theory, cosmic magnetic fields are generated by the dynamos of rotating galaxies -- a process that would produce stronger fields with the passage of time. In this scenario, the magnetic fields should be weaker in the earlier Universe, not stronger.
The new, direct magnetic-field measurement comes on the heels of a July report by Swiss and American astronomers who made indirect measurements that also implied strong magnetic fields in the early Universe.
"Our results present a challenge to the dynamo model, but they do not rule it out," Wolfe said.
There are other possible explanations for the strong magnetic field seen in the one protogalaxy Wolfe's team studied. "We may be seeing the field close to the central region of a massive galaxy, and we know such fields are stronger toward the centers of nearby galaxies. Also, the field we see may have been amplified by a shock wave caused by the collision of two galaxies," he said.
The protogalaxy studied with the GBT, called DLA-3C286, consists of gas with little or no star formation occurring in it. The astronomers suspect that the strong magnetic field may prevent the gravitational collapse that is needed for stars to form.
To make their measurement, the scientists studied radio waves emitted by an even more-distant object, the quasar 3C 286, behind the protogalaxy. As these electromagnetic waves passed through the protogalaxy, some were absorbed by Hydrogen atoms in the protogalaxy. Normally, the atoms would absorb only a single, specific frequency. However, because the atoms were affected by the protogalaxy's magnetic field, they absorbed at two closely-spaced frequencies. This phenomenon, called the Zeeman Effect, allows scientists to measure the strength of the magnetic field affecting the Hydrogen gas through which the waves passed.
The GBT observations of the protogalaxy were the first measurements using the Zeeman Effect made on a celestial object at such a great distance.
Wolfe worked with Regina Jorgenson, a UCSD graduate student; Carl Heiles of the University of California-Berkeley; Timothy Robishaw, a graduate student at UC-Berkeley; and Jason X. Prochaska of the University of California-Santa Cruz. The scientists reported their findings in the October 2 issue of the journal Nature. Their research was supported by grants from the National Science Foundation.
The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
|Image Caption: Robert C. Byrd Green Bank Telescope Image Credit: NRAO/AUI/NSF Source: National Radio Astronomy Observatory Permalink: http://www.sflorg.com/comm_center/space/p590_10.html Time Stamp: 10/1/2008 at 6:13:36 PM UTC|