Category: Astronomy

Distribution of stars in galactic companion. Image credit: PSU. Click to enlarge.
A team of scientists from the Sloan Digital Sky Survey (SDSS), including a Penn State astrophysicist, has discovered a companion to the Milky Way galaxy that is so big it previously had been undetectable. The result is the topic of a press conference during the meeting of the American Astronomical Society now taking place in Washington, D.C.

The study, lead by Mario Juric of Princeton and Zeljko Ivezic of the University of Washington, found a collection of stars in the constellation Virgo that covers nearly 5,000 times the size of the full moon. Penn State Professor of Astronomy and Astrophysics Donald Schneider, a coauthor of the investigation, is the Chairman of the SDSS Quasar Science Group and the SDSS Scientific Publications Coordinator. “The star cluster is located only 30,000 light years from Earth,” noted Schneider. “This is the same distance from us as is the Galactic Center, although the cluster lies in a different direction from the Center. It is likely that the cluster is the remnant of a small galaxy that has been captured and disrupted by the gravitational field of our galaxy.”

The galaxy is a huge but very faint structure, containing hundreds of thousands of stars spread over an area area nearly 5,000 times the size of a full moon. Although the structure lies well within the confines of the Milky Way Galaxy, at an estimated distance of 30,000 light years from Earth, it does not follow any of Milky Way’s three main components: a flattened disk of stars in which the Sun resides, a bulge of stars at the center of the Galaxy, and an extended, roughly spherical, stellar halo. Instead, the discoverers believe that the most likely interpretation of the new structure is a dwarf galaxy that is merging into the Milky Way.

“Some of the stars in this Milky Way companion have been seen with telescopes for centuries,” explained Princeton University graduate student Mario Juric, who is principal author of the journal article describing what may well be our closest galactic neighbor. “But because the galaxy is so close, its stars are spread over a huge swath of the sky, and they always used to be lost in the sea of more numerous Milky Way stars. This galaxy is so big, we couldn’t see it before.”

The discovery was made possible by the unprecedented depth and photometric accuracy of the SDSS, which to date has imaged roughly 1/4 of the northern sky. “We used the SDSS data to measure distances to 48 million stars and build a 3-D map of the Milky Way,” explained Zeljko Ivezic of the University of Washington, a co-author of the study. Details of this “photometric parallax” method, which uses the colors and apparent brightnesses of stars to infer their distances, are explained in a paper titled “Milky Way Tomography,” submitted to The Astrophysical Journal.

“It’s like looking at the Milky Way with a pair of 3-d glasses,” said Princeton University co-author Robert Lupton. “This structure that used to be lost in the background suddenly snapped into view.” The new result is reminiscent of the 1994 discovery of the Sagittarius dwarf galaxy, by Rodrigo Ibata and collaborators from Cambridge University. They used photographic images of the sky to identify an excess of stars on the far side of the Milky Way, some 75,000 light years from Earth. The Sagittarius dwarf is slowly dissolving, trailing streams of stars behind it as it orbits the Milky Way and sinks into the Galactic disk.

In the ensuing decade, a new generation of sky surveys using large digital cameras has identified numerous streams and lumps of stars in the outer Milky Way. Some of these lumps are probably new Milky Way companions, while others may be shreds of the Sagittarius dwarf or of other dissolving dwarf galaxies. Earlier SDSS discoveries include an apparent ring of stars that encircles the Milky Way disk and may be the remnant of another disrupted galaxy, and the Ursa Major dwarf, the faintest known neighbor of the Milky Way.

Preliminary evidence for the new dwarf galaxy, found toward the constellation Virgo, appeared in maps of variable stars by the SDSS and by the QUEST survey (a Yale University/University of Chile collaboration). “With so much irregular structure in the outer Galaxy, it looks as though the Milky Way is still growing, by cannibalizing smaller galaxies that fall into it,” said Juric.

Another group of SDSS astronomers, led by Daniel Zucker of the Max Planck Institute of Astronomy in Heidelberg and Cambridge University’s Institute of Astronomy, has used the SDSS to find the two faintest known companions of the Andromeda Galaxy, which is the closest giant spiral galaxy similar in size to the Milky Way. “These new Andromeda companions, alongside the new Milky Way neighbors, suggest that faint satellite galaxies may be plentiful in the Local Group,” said Zucker.

While the SDSS originally was designed to study the distant universe, its wide area, high precision maps of faint stars have made it an invaluable tool for studying the Milky Way and its immediate neighborhood. The 3-D map created by Juric and his collaborators also provides strong new constraints on the shape and extent of the Milky Way’s disk and stellar halo. Another Princeton graduate student, Nick Bond, is using the subtle motions of stars detected over the 5-year span of the SDSS observations to limit the amount of dark matter in the solar neighborhood. University of Washington graduate student Jillian Meyer is mapping the distribution of interstellar dust carefully studying the colors of stars found in both the SDSS and the infrared 2MASS survey.

Building on these many successes, the SEGUE project (Sloan Extension for Galactic Understanding and Exploration) will use the SDSS telescope, its 120-megapixel digital camera, and its 640-fiber optical spectrograph to carry out detailed studies of the structure and chemical evolution of the Milky Way. SEGUE is one of three components of SDSS-II, the three-year extension of the Sloan Survey that will run through mid-2008.

Fermilab scientist Brian Yanny, one of the SEGUE team leaders, is excited at the prospect of examining its just-completed, first season of observations. “The SDSS has already told us surprising things about the Milky Way, but the most exciting discoveries should lie just ahead.”

Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS Web Site is http://www.sdss.org/.

The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions, which include the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, Cambridge University, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPA), the Max-Planck-Institute for Astrophysics (MPIA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington.

Original Source: Eberly College News Release

Artist illustration of Vega. Image credit: NOAO. Click to enlarge.
Strong darkening observed around the equator of Vega suggests that the fifth brightest star in Earth’s sky has a huge temperature difference of 4,000 degrees Fahrenheit from its cool equatorial region to its hot poles.

Models of the star based on these observations suggest that Vega is rotating at 92 percent of the angular velocity that would cause it to physically break apart, an international team of astronomers announced today in Washington, DC, at the 207th meeting of the American Astronomical Society.

This result confirms the idea that very rapidly rotating stars are cooler at their equators and hotter at their poles, and it indicates that the dusty debris disk known to exist around Vega is significantly less illuminated by the star?s light than previously recognized.

“These findings are significant because they resolve some confusing measurements of the star, and they should help us gain a much better understanding of Vega’s circumstellar debris disk,” says Jason P. Aufdenberg, the Michelson Postdoctoral Fellow at the National Optical Astronomy Observatory in Tucson, Arizona.

This debris disk arises mainly from the collision of rocky asteroid-like bodies. “The spectrum of Vega as viewed from its equatorial plane, the same plane as the debris disk, should be about half as luminous as the spectrum viewed from the pole, based on these new results,” Aufdenberg explains.

The team obtained high-precision interferometric measurements of the bright standard star Vega using the Center for High Angular Resolution Astronomy (CHARA) Array, a collection of six 1-meter telescopes located on Mount Wilson, California, and operated by Georgia State University.

With a maximum baseline of 330 meters (1,083 feet), the CHARA Array is capable of resolving details as small as 200 micro-arcseconds, equivalent to the angular size of a nickel seen from a distance of 10,000 miles. The CHARA Array fed the starlight of Vega to the Fiber Linked Unit for Optical Recombination (FLUOR) instrument, developed by the Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique of the Observatoire de Paris.

One major consequence of Vega’s rapid rotation is a significant drop in the effective atmospheric temperature by approximately 2,300 Kelvin (4,000 degrees Fahrenheit) from the pole to the equator. This effect, known as “gravity darkening,” was first predicted by theoretical astronomer E. Hugo von Zeipel in 1924.

The CHARA/FLUOR measurements of the brightness distribution of Vega’s surface also show it to be strongly “limb darkened.” Limb darkening refers to the diminishing brightness in the image of a star from the center of the image to the edge or “limb” of the image.

The new measurements are consistent with the “pole-on” model for Vega first proposed by Richard O. Gray of Appalachian State University, which proposes that Vega?s pole of rotation points toward Earth. The pole-on view of Vega means that the relatively cool equator corresponds to the limb of the star, such that the gravity-darkening effect further enhances the limb-darkening effect.

The CHARA/FLUOR data support the pole-on, gravity darkened model for Vega by showing that Vega’s limb darkening is 2.5 times stronger at a wavelength of 2.2 microns than expected for a star with a single effective atmosphere temperature. Archival observations from the International Ultraviolet Explorer indicate that this model for Vega is not complete. At far ultraviolet wavelengths, below 140 nanometers, the model is generally too bright.

Located at a distance of 25 light-years from Earth in the constellation Lyra, Vega rotates about its axis once every 12.5 hours. For comparison, the Sun’s average rotation period is approximately 27 Earth days. Vega is about 2.5 times more massive than the Sun, and 54 times brighter.

At Vega’s rapid rate of rotation, the star’s atmosphere is distorted, bulging 23 percent wider at its equator compared to its poles. This type of rotational distortion can be seen in images of the planet Saturn, where the planet’s equatorial diameter is roughly 10 percent wider than the polar diameter. A direct measurement of Vega’s rotational distortion is hidden by its pole-on appearance. However, the accurate angular diameter and darkening measured by CHARA/FLUOR are consistent with this distortion.

These results build upon recent measurements of Vega obtained by a team lead by Deane M. Peterson of the State University of New York, Stony Brook, using the Navy Prototype Optical Interferometer.

Co-authors of this result include Antoine M?rand, Vincent Coud? du Foresto, Emmanuel Di Folco, and Pierre Kervella of the Observatoire de Paris-Meudon, France; Olivier Absil of the University of Li?ge, Belgium; Stephen T. Ridgway of the National Optical Astronomy Observatory, Tucson, Arizona and NASA; Harold A. McAlister, Theo A. ten Brummelaar, Judit Sturmann, Laszlo Sturmann, and Nils H. Turner of the Center for High Angular Resolution Astronomy, Georgia State University, Atlanta, Georgia, and Mount Wilson Observatory, California; and David H. Berger of the University of Michigan, Ann Arbor, Michigan.

This work was performed in part under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Michelson Fellowship Program. JPL is managed for NASA by the California Institute of Technology. The CHARA Array is operated by the Center for High Angular Resolution Astronomy, Georgia State University, Atlanta, GA. Additional support comes from the National Science Foundation, the Keck Foundation and the Packard Foundation.

The National Optical Astronomy Observatory is operated by the Association of Universities for Research in Astronomy Inc. (AURA), under a cooperative agreement with the NSF.

Original Source: NOAO News Release

Computer illustration of a binary star. Image credit: Carnegie Institution. Click to enlarge.
New theoretical work shows that gas-giant planet formation can occur around binary stars in much the same way that it occurs around single stars like the Sun. The work is presented today by Dr. Alan Boss of the Carnegie Institution’s Department of Terrestrial Magnetism (DTM) at the American Astronomical Society meeting in Washington, DC. The results suggest that gas-giant planets, like Jupiter, and habitable Earth-like planets could be more prevalent than previously thought. A paper describing these results has been accepted for publication in the Astrophysical Journal.

“We tend to focus on looking for other solar systems around stars just like our Sun,” Boss says. “But we are learning that planetary systems can be found around all sorts of stars, from pulsars to M dwarfs with only one third the mass of our Sun.”

Two out of every three stars in the Milky Way is a member of a binary or multiple star system, in which the stars orbit around each other with separations that can range from being nearly in contact (close binaries) to thousands of light-years or more (wide binaries). Most binaries have separations similar to the distance from the Sun to Neptune (~30 AU, where 1 AU = 1 astronomical unit = 150 million kilometers–the distance from the Earth to the Sun).

It has not been clear whether planetary system formation could occur in typical binary star systems, where the strong gravitational forces from one star might interfere with the planet formation processes around the other star, and vice versa. Previous theoretical work had suggested, in fact, that typical binary stars would not be able to form planetary systems. However, planet hunters have recently found a number of gas-giant planets in orbit around binary stars with a range of separations.

Boss found that if the shock heating resulting from the gravitational forces from the companion star is weak, then gas-giant planets are able to form in planet-forming disks in much the same way as they do around single stars. The planet-forming disk would remain cool enough for ice grains to stay solid and thus permit the growth of the solid cores that must reach multiple-Earth-mass size for the conventional mechanism of gas-giant planet formation (core accretion) to succeed.

Boss’ models show even more directly that the alternative mechanism for gas-giant planet formation (disk instability) can proceed just as well in binary star systems as around single stars, and in fact may even be encouraged by the gravitational forces of the other star. In Boss’ new models, the planet-forming disk in orbit around one of the stars is quickly driven to form dense spiral arms, within which self-gravitating clumps of gas and dust form and begin the process of contracting down to planetary sizes. The process is amazingly rapid, requiring less than 1,000 years for dense clumps to form in an otherwise featureless disk. There would be plenty of room for Earth-like planets to form closer to the central star after the gas-giant planets have formed, in much the same way our own planetary system is thought to have formed.

Boss points out, “This result may have profound implications in that it increases the likelihood of the formation of planetary systems resembling our own, because binary stars are the rule in our galaxy, not the exception.” If binary stars can shelter planetary systems composed of outer gas-giant planets and inner Earth-like planets, then the likelihood of other habitable worlds suddenly becomes roughly three times more probable–up to three times as many stars could be possible hosts for planetary systems similar to our own. NASA’s plans to search for and characterize Earth-like planets in the next decade would then be that much more likely to succeed.

One of the key remaining questions about the theoretical models is the correct amount of shock heating inside the planet-forming disk, as well as the more general question of how rapidly the disk is able to cool. Boss and other researchers are actively working to better understand these heating and cooling processes. Given the growing observational evidence for gas-giant planets in binary star systems, the new results suggest that shock heating in binary disks cannot be too large, or it would prevent gas-giant planet formation.

Original Source: Carnegie News Release

Polaris with its faint companions. Image credit: Greg Bacon (STScI) Click to enlarge
We tend to think of the North Star, Polaris, as a steady, solitary point of light that guided sailors in ages past. But there is more to the North Star than meets the eye – two faint stellar companions. The North Star is actually a triple star system. And while one companion can be seen easily through small telescopes, the other hugs Polaris so tightly that it has never been seen directly – until now.

By stretching the capabilities of NASA’s Hubble Space Telescope to the limit, astronomers have photographed the close companion of Polaris for the first time. They presented their findings today in a press conference at the 207th meeting of the American Astronomical Society in Washington, DC.

“The star we observed is so close to Polaris that we needed every available bit of Hubble’s resolution to see it,” said Smithsonian astronomer Nancy Evans (Harvard-Smithsonian Center for Astrophysics).

The companion proved to be less than two-tenths of an arcsecond from Polaris – an incredibly tiny angle equivalent to the apparent diameter of a quarter located 19 miles away. At the system’s distance of 430 light-years, that translates into a physical separation of about 2 billion miles.

“The brightness difference between the two stars made it even more difficult to resolve them,” stated Howard Bond of the Space Telescope Science Institute (STScI). Polaris is a supergiant more than two thousand times brighter than the Sun, while its companion is a main-sequence star. “With Hubble, we’ve pulled the North Star’s companion out of the shadows and into the spotlight.”

By watching the motion of the companion star, Evans and her colleagues expect to learn not only the stars’ orbits but also their masses. Measuring the mass of a star is one of the most difficult tasks facing stellar astronomers.

Astronomers want to determine the mass of Polaris accurately because it is the nearest Cepheid variable star. Cepheids are used to measure the distance to galaxies and the expansion rate of the universe, so it is essential to understand their physics and evolution. Knowing their mass is the most important ingredient in this understanding.

“Studying binary stars is the best available way to measure the masses of stars,” said science team member Gail Schaefer of STScI.

“We only have the binary stars that nature provided us,” added Bond. “With the best instruments like Hubble, we can push farther into space and study more of them up close.”

The researchers plan to continue observing the Polaris system for several years. In that time, the movement of the small companion in its 30-year orbit around the primary should be detectable.

“Our ultimate goal is the get an accurate mass for Polaris,” said Evans. “To do that, the next milestone is to measure the motion of the companion in its orbit.”

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: CfA News Release

The Milky Way galaxy. Image credit: Serge Brunier. Click to enlarge
The most prominent of the Milky Way’s satellite galaxies – a pair of galaxies called the Magellanic Clouds – appears to be interacting with the Milky Way’s ghostly dark matter to create a mysterious warp in the galactic disk that has puzzled astronomers for half a century.

The warp, seen most clearly in the thin disk of hydrogen gas permeating the galaxy, extends across the entire 200,000-light year diameter of the Milky Way, with the sun and earth sitting somewhere near the crease. Leo Blitz, professor of astronomy at the University of California, Berkeley, and his colleagues, Evan Levine and Carl Heiles, have charted this warp and analyzed it in detail for the first time, based on a new galactic map of hydrogen gas (HI) emissions.

They found that the atomic gas layer is vibrating like a drum, and that the vibration consists almost entirely of three notes, or modes.

Astronomers previously dismissed the Magellanic Clouds – comprised of the Large and Small Magellanic Clouds – as a probable cause of the galactic warp because the galaxies’ combined masses are only 2 percent that of the disk. This mass was thought too small to influence a massive disk equivalent to about 200 billion suns during the clouds’ 1.5 billion-year orbit of the galaxy.

Nevertheless, theorist Martin D. Weinberg, a professor of astronomy at the University of Massachusetts, Amherst, teamed up with Blitz to create a computer model that takes into account the Milky Way’s dark matter, which, though invisible, is 20 times more massive than all visible matter in the galaxy combined. The motion of the clouds through the dark matter creates a wake that enhances their gravitational influence on the disk. When this dark matter is included, the Magellanic Clouds, in their orbit around the Milky Way, very closely reproduce the type of warp observed in the galaxy.

“The model not only produces this warp in the Milky Way, but during the rotation cycle of the Magellanic Clouds around the galaxy, it looks like the Milky Way is flapping in the breeze,” said Blitz, director of UC Berkeley’s Radio Astronomy Laboratory.

“People have been trying to look at what creates this warp for a very long time,” Weinberg said. “Our simulation is still not a perfect fit, but it has a lot of the character of the actual data.”

Levine, a graduate student, will present the results of the work in Washington, D.C., on Jan. 9 during a 10 a.m. session on galactic structure at the American Astronomical Society meeting. Blitz will summarize the work later that day during a 12:30 p.m. press briefing in the Wilson C Room of the Marriott Wardman Park Hotel.

The interaction of the Magellanic Clouds with the dark matter in the galaxy to produce an enigmatic warp in the hydrogen gas layer is reminiscent of the paradox that led to the discovery of dark matter some 35 years ago. As astronomers built better and better telescopes able to measure the velocities of stars and gas in the outer regions of our galaxy, they discovered these stars moving far faster than would be expected from the observed number and mass of stars in the entire Milky Way. Only by invoking a then-heretical notion, that 80 percent of the galaxy’s mass was too dark to see, could astronomers reconcile the velocities with known theories of physics.

Though no one knows the true identity of this dark matter – the current consensus is that it is exotic matter rather than normal stars too dim to see – astronomers are now taking it into account in their simulations of cosmic dynamics, whether to explain the lensing effect galaxies and galaxy clusters have on the light from background galaxies, or to describe the evolution of galaxy clusters in the early universe.

Some physicists, however, have come up an alternative theory of gravity called Modified Newtonian Dynamics, or MOND, that seeks to explain these observations without resorting to belief in a large amount of undetected mass in the universe, like an invisible elephant in the room. Though MOND can explain some things, Weinberg thinks the theory will have a hard time explaining the Milky Way’s warp.

“Without a dark matter halo, the only thing the gas disk can feel is direct gravity from the Magellanic Clouds themselves, which was shown in the 1970s not to work,” he said. “It looks bad for MOND, in this case.”

Because many galaxies have warped disks, similar dynamics might explain them as well. Either way, the researchers say their work suggests that warps provide a way to verify the existence of the dark matter.

The starting point for this research was new spectral data released this past summer about hydrogen’s 21-centimeter emissions in the Milky Way. The survey, the Leiden-Argentina-Bonn or LAB Survey of Galactic HI, merged a northern sky survey conducted by astronomers in the Netherlands (the Leiden/Dwingeloo Survey) with a southern sky survey from the Instituto Argentino de Radioastronom?a. The data were corrected by scientists at the Institute for Radioastronomy of the University of Bonn, Germany.

Blitz, Levine and Heiles, UC Berkeley professor of astronomy, took these data and produced a new, detailed map of the neutral atomic hydrogen in the galaxy. This hydrogen, distributed in a plane with dimensions like those of a compact disk, eventually condenses into molecular clouds that become stellar nurseries.

With map in hand, they were able to mathematically describe the warp as a combination of three different types of vibration: a flapping of the disk’s edge up and down, a sinusoidal vibration like that seen on a drumhead, and a saddle-shaped oscillation. These three “notes” are about 3 million octaves below middle C.

“We found something very surprising, that we could describe the warp by three modes of vibration, or three notes, and only three,” Blitz said, noting that this rather simple mathematical description of the warp had escaped the notice of astronomers since the warp’s discovery in 1957.

“We were actually trying to analyze a more complex ‘scalloping’ structure of the disk, and this simple, elegant vibrational structure just popped out,” Levine added.

The current warp in the gas disk is a combination of these three vibrational modes, leaving one-half of the galactic disk sticking up above the plane of stars and gas, while the other half dips below the disk before rising upward again farther outward from the center of the galaxy. The results of this analysis will be published in an upcoming issue of the Astrophysical Journal.

Weinberg thought he could explain the observed warp dynamically, and used computers to calculate the effect of the Magellanic Clouds orbiting the Milky Way, plowing through the dark matter halo that extends far out into the orbit of the clouds.

What he and Blitz found is that the clouds’ wake through the dark matter excites a vibration or resonance at the center of the dark matter halo, which in turn makes the disk embedded in the halo oscillate strongly in three distinct modes. The combined motion during a 1.5-billion-year orbit of the Magellanic Clouds is reminiscent of the edges of a tablecloth flapping in the wind, since the center of the disk is pinned down.

“We often think of the warp as being static, but this simulation shows that it is very dynamic,” Blitz said.

Blitz, Levine and Heiles are continuing their search for anomalies in the structure of the Milky Way’s disk. Weinberg hopes to use the UC Berkeley group’s data and analysis to determine the shape of the dark matter halo of the Milky Way.

The research of the UC Berkeley group is supported by the National Science Foundation. Weinberg is partly supported by NASA and the NSF.

Original Source: UC Berkeley News Release

Superbubble complex N44 as imaged with GMOS. Image credit: University of Alaska Anchorage. Click to enlarge
Known as the N44 superbubble complex, this cloudy tempest is dominated by a vast bubble about 325 by 250 light-years across. A cluster of massive stars inside the cavern has cleared away gas to form a distinctive mouth-shaped hollow shell. While astronomers do not agree on exactly how this bubble has evolved for up to the past 10 million years, they do know that the central cluster of massive stars is responsible for the cloud’s unusual appearance. It is likely that the explosive death of one or more of the cluster’s most massive and short-lived stars played a key role in the formation of the large bubble.

“This region is like a giant laboratory providing us with a glimpse into many unique phenomena,” said Sally Oey of the University of Michigan, who has studied this object extensively. “Observations from space have even revealed x-ray-emitting gas escaping from this superbubble, and while this is expected, this is the only object of its kind where we have actually seen it happening.”

One of the mysteries surrounding this object points to the role that supernova explosions (marking the destruction of the most massive of the central cluster’s stars) could have played in sculpting the cloud. Philip Massey of Lowell Observatory, who studied this region along with Oey, adds “When we look at the speed of the gases in this cloud we find inconsistencies in the size of the bubble and the expected velocities of the winds from the central cluster of massive stars. Supernovae, the ages of the central stars, or the orientation and shape of the cloud might explain this, but the bottom line is that there’s still lots of exciting science to be done here and these new images will undoubtedly help.”

The Gemini data used to produce this image are being released to the astronomical community for further research and follow-up analysis. Note to astronomers: Data can be found at the Gemini Science Archive by querying “NGC 1929”. The image provides one of the most detailed views ever obtained of this relatively large region in the Large Magellanic Cloud, a satellite galaxy to the Milky Way, located some 150,000 light-years away and visible from the Southern Hemisphere. The images captured light of specific colors that reveal the compression of material and the presence of gases (primarily excited hydrogen gas and lesser amounts of oxygen and “shocked” sulfur) in the cloud.

Multiple smaller bubbles appear in the image as bulbous growths clinging to the central superbubble. Most of these regions were probably formed as part of the same process that shaped the central cluster. Their formation could also have been “sparked” by compression as the central stars pushed the surrounding gas outward. Our view into this cavern could really be like looking through an elongated tube, which lends the object its monstrous mouth-like appearance.

The images used to produce the color composite were obtained with the Gemini Multi-object Spectrograph (GMOS) at the Gemini South Telescope on Cerro Pachon in Chile. The color image was produced by Travis Rector of the University of Alaska Anchorage and combines three single-color images to produce the image.

Original Source: Gemini Observatory

An artist’s illustartion of the sequence of radioactive decay that gives out gamma rays. Image credit: MPE Click to enlarge
Using ESA’s Integral observatory, an international team of researchers has been able to confirm the production of radioactive aluminium (Al 26) in massive stars and supernovae throughout our galaxy and determine the rate of supernovae – one of its key parameters.

The team, led by Roland Diehl of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, determined that gamma rays from the decay of Al 26 originate from the central regions of our galaxy, implying that production of new atomic nuclei is an ongoing process and occurs in star-forming regions galaxy-wide.

Our environment is composed of chemical elements formed long ago by nuclear fusion reactions in stellar interiors and supernovae. This process of ‘nucleosynthesis’ leads to the emission of gamma rays, which easily reach us from all regions of our galaxy. ESA’s Integral observatory has been measuring such gamma rays since October 2002.

Roland Diehl and his colleagues were able to measure the Al 26 gamma-ray emissions along the plane of the inner galaxy.

However, because the disc of the galaxy rotates about its central axis, with the inner regions orbiting faster, gamma rays from decaying Al 26 observed from these regions should be moderated by the Doppler effect in a characteristic way. It is this characteristic pattern that has been found by Integral.

From this measurement, the team found that Al 26 decay gamma rays do indeed reach us from the inner regions of the galaxy, rather than from foreground regions along the same line of sight possibly caused by local and peculiar Al 26 production. These regions would not have the observed high relative velocity.

From these new observations, it is possible to estimate the total amount of radioactive Al 26 in our galaxy as is equivalent to three solar masses. This is a lot, given that Al 26 is an extremely rare isotope; the fraction estimated for the early Solar System is 5/100 000 of Al 26, in proportion to its stable aluminium isotope (Al 27).

Because astrophysicists had inferred that the likely sources are mainly massive stars, which end their lives as supernovae, they could estimate the rate of such supernova events. They obtained a rate of one supernova every 50 years – consistent with what had been indirectly found from observations of other galaxies and their comparison to the Milky Way.

Integral’s study of gamma rays will continue to operate for several more years. Astrophysicists hope to increase the precision of such measurements. Project leader Roland Diehl said, “These gamma-ray observations provide insights about our home galaxy, which are difficult to obtain at other wavelengths due to interstellar absorption.”

Original Source: ESA Portal

An artist’s impression of the dusty disk orbiting IRS 46. Image credit: NASA/JPL-Caltech Click to enlarge
Astronomers at W. M. Keck Observatory have found ??bf? for the first time ??bf? some of the basic compounds necessary to build organic molecules and one of the bases found in DNA within the inner regions of a planet-forming disk. The object, known as “IRS 46,” is located in the Milky Way galaxy, about 375 light years from Earth, in the constellation Ophiuchus. The results will be published in an upcoming issue of the Astrophysical Journal Letters.

“We see prebiotic organic molecules in comets and the gas giant planets in our own solar system and wonder, where did these chemicals come from?” said Dr. Marc Kassis, support astronomer at the W. M. Keck Observatory. “The Spitzer Space Telescope is letting us study these young stellar objects in new and revealing ways, giving us exciting clues about where life may form in the universe.”

The two organic compounds found — acetylene and hydrogen cyanide — are commonly found in our own solar system, such as the atmospheres of the giant gas planets, the icy surfaces of comets, and the atmosphere of Saturn??bf?s largest moon, Titan. Another carbon-containing species detected, carbon dioxide, is widespread in the atmospheres of Venus, the Earth, and Mars.

“If you add hydrogen cyanide, acetylene and water together in a test tube, and give them an appropriate surface on which to be concentrated and react, you’ll get a slew of organic compounds including amino acids and a DNA purine base called adenine,” said Keck Astronomer Dr. Geoffrey Blake, of the California Institute of Technology in Pasadena and co-author of the paper. “Now, we can detect these same molecules in the planet zone of a star hundreds of light-years away.”

The presence of gas-rich disks around young stars is well known, but little is understood about the chemical structure inside. The discovery of acetylene and hydrogen cyanide in one of these disks will help astronomers better understand these disks, where future solar systems may someday form and possibly result in life.

“Spitzer found something very unique — a young protostar with a dusty disk that, when viewed from Earth, appears tilted on the sky, similar to how some galaxies appear,” Kassis explained. “This viewing angle let the team use Keck-NIRSPEC data to study the inner regions of the disk. The results told the team exactly how the disk was moving and suggest there may be a stellar wind coming from the inner region. Keck also helped measure the high temperatures and the particle concentration in the disk.”

The dust and gas surrounding a young star blocks visible light, but lets longer wavelengths, such as infrared light, pass through. Astronomers can find out what this gas and dust is made of by separating the light into its component wavelengths, or colors.

Since 2003, the NASA Spitzer Space Telescope has allowed astronomers to use this technique to study molecular compounds in protoplanetary disks of young stellar objects. The Spitzer “c2d legacy program” has looked at more than 100 sources in five nearby star-forming regions and only one ??bf? IRS 46 ??bf? showed clear evidence of containing the organic compounds in the warm regions close to the star where terrestrial planets are most likely to form.

“This infant system might look a lot like ours did billions of years ago, before life arose on Earth,” said Fred Lahuis of Leiden Observatory in the Netherlands and the SRON Netherlands Institute for Space Research. Lahuis is the lead author of the paper describing the results.

While the precise events leading up to self-replicating nucleic acids remains unclear, the molecules of acetylene (C2H2) and hydrogen cyanide (HCN) have been shown to produce the base compounds necessary to build RNA and DNA. The team found that the abundance of hydrogen cyanide (HCN) was nearly 10,000 times higher than that found in cold interstellar gas from which stars and planets are born.

Models of early solar-system chemistry have historically centered on data from our own primitive solar system, but now discoveries of protoplanetary disks have opened the field to solar systems other than our own. Theoretical models have suggested that large quantities of complex organic molecules would be present in the inner-most regions of these disks, but until now, no observational tests have been possible.

To help determine where, exactly, the organic-rich gas resides in IRS 46, the team also used submillimeter data from the James Clerk Maxwell Telescope on Mauna Kea. The faint signals observed again suggest that the material originates from the inner disk, perhaps no more 10 astronomical units from the parent star, similar in distance to where Saturn orbits the Sun in our own solar system. However, much additional work remains to be done to know this for certain.

“The gases are very warm, close to or somewhat above the boiling point of water on Earth,” said Dr. Adwin Boogert, also of Caltech. “These high temperatures helped to pinpoint the location of the gases in the disk.”

The Keck-NIRSPEC results point to the presence of a stellar wind emerging from the inner region of the disk orbiting IRS 46. The wind may eventually blow away the dusty debris in the disk, perhaps revealing the presence of rocky, Earth-like planets in several million years.

The Jet Propulsion Laboratory manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech. JPL is a division of Caltech.

The W. M. Keck Observatory is managed by the California Association for Research in Astronomy, a non-profit 501 (c) (3) corporation. The Keck I and Keck II 10-meter telescopes probe the faintest objects in the optical and infrared Universe.

Original Source: W. M. Keck Observatory

Composite Image of Geminga. Image credit: XMM-Newton Click to enlarge
A team led by Dr. Patrizia Caraveo of the Italian National Institute for Astrophysics (INAF) in Milan discovered this cometary trail with data from NASA’s Chandra X-ray Observatory Archive. The discovery follows the team’s discovery in 2003 using ESA’s XMM-Newton of Geminga’s twin X-ray tails stretching for billions of chilometers.

Together, these observations provide unique insight into the contents and density of the interstellar “ocean” Geminga is plowing through, as well as the physics of Geminga itself. Not only is Geminga close, only about 500 light years from Earth, it is cutting across our line of sight, offering a spectacular view of a pulsar in motion.

“Geminga is the only isolated pulsar we know of showing both a small comet-like trail and a larger tail structure,” said Dr. Andrea De Luca of INAF’s Istituto di Astrofisica Spaziale e Fisica Cosmica, lead author on an article about this discovery in Astronomy and Astrophysics. “This jettison from Geminga’s journey through interstellar space provides unprecedented information about the physics of pulsars.”

A pulsar is a type of rapidly spinning neutron star that emits steady pulses of radiation with each rotation, funnelled along strong magnetic field lines, much like a lighthouse beam sweeping across space. A neutron star is the core remains of an exploded star once at least eight times as massive as the sun.

These dense stars, only about 20 kilometers across, still contain roughly the mass of the sun. Neutron stars contain the densest material known. Like many neutron stars, Geminga got a “kick” from the explosion that created it and has been flying through space like a cannonball ever since.

De Luca said that Geminga’s complex phenomenology of tails and a trail must be from high-energy electrons escaping the pulsar magnetosphere following paths clearly driven by the pulsar??bf?s motion in the interstellar medium.

Most pulsars emit radio waves. Yet Geminga is “radio quiet” and was discovered 30 years ago as a unique “gamma-ray only” source (only later was Geminga seen in the X-ray and optical light wavebands). Geminga generates gamma rays by accelerating electrons and positrons, a type of antimatter, to high speeds as it spins like a dynamo four times per second.

“Astronomers have known that only a fraction of these accelerated particles produce gamma rays, and they have wondered what happens to the remaining ones,” said Caraveo, a co-author on the Astronomy & Astrophysics article. “Thanks to the combined capabilities of Chandra and XMM-Newton, we now know that such particles can escape. Once they reach the shock front, created by the supersonic motion of the star, the particles lose their energy radiating X-rays.”

Meanwhile, an equal number of particles (with a different electric charge) should move in the opposite direction, aiming back at the star. Indeed, when they hit the star’s crust they create tiny hotspots, which have been detected through their varying X-ray emission.

The next generation of high-energy gamma-ray instruments – namely, the planned Italian Space Agency’s AGILE mission and NASA’s GLAST mission – will explore the connection between the X-ray and gamma ray behaviour of pulsars to provide clues to the nature of unknown gamma-ray sources, according to Prof. Giovanni Bignami, a co-author and director of the Centre d’Etude Spatiale des Rayonnements (CESR) in Toulouse, France. Of the 271 higher-energy gamma-ray objects detected by a NASA telescope called EGRET, 170 remained unidentified in other wavebands. These unidentified objects could be “gamma-ray pulsars” like Geminga, whose optical and X-ray light might be visible only because of its nearness to Earth.

Only about a dozen other radio-quiet isolated neutron stars are known, and Geminga is the only one with tails and trails and copious gamma-ray emission. Bignami named Geminga for “Gemini gamma-ray source” in 1973. In his local Milan dialect, the name is a pun on “ghe minga,” which means “it is not there.” Indeed, Geminga was unidentified in other wavelengths until 1993, twenty years after its discovery.

The discovery team also includes Drs. Fabio Mattana and Alberto Pellizzoni of the INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica.

Original Source: INAF News Release

NGC 2467 and Surroundings. Image credit: ESO Click to enlarge
Just like Charles Dickens’ Christmas Carol takes us on a journey into past, present and future in the time of only one Christmas Eve, two of ESO’s telescopes captured various stages in the life of a star in a single image.

ESO’s first image shows the area surrounding the stellar cluster NGC 2467, located in the southern constellation of Puppis (“The Stern”). With an age of a few million years at most, it is a very active stellar nursery, where new stars are born continuously from large clouds of dust and gas.

The image, looking like a colourful cosmic ghost or a gigantic celestial Mandrill, contains the open clusters Haffner 18 (centre) and Haffner 19 (middle right: it is located inside the smaller pink region – the lower eye of the Mandrill), as well as vast areas of ionised gas.

The bright star at the centre of the largest pink region on the bottom of the image is HD 64315, a massive young star that is helping shaping the structure of the whole nebular region.

The first image was taken with the Wide-Field Imager camera at the 2.2m MPG/ESO telescope located at La Silla, in Chile.

Another image of the central part of this area is shown in ESO’s second image. It was obtained with the FORS2 instrument at ESO’s Very Large Telescope on Cerro Paranal, also in Chile.

NGC 2467 and Surroundings. Image credit: ESO Click to enlarge
However, the second image zooms in on the open stellar cluster Haffner 18, perfectly illustrating three different stages of this process of star formation: In the centre of the picture, Haffner 18, a group of mature stars that have already dispersed their birth nebulae, represents the completed product or immediate past of the star formation process. Located at the bottom left of this cluster, a very young star, just come into existence and, still surrounded by its birth cocoon of gas, provides insight into the very present of star birth. Finally, the dust clouds towards the right corner of the image are active stellar nurseries that will produce more new stars in the future.

Haffner 18 contains about 50 stars, among which several short lived, massive ones. The massive star still surrounded by a small, dense shell of hydrogen, has the rather cryptic name of FM3060a. The shell is about 2.5 light-years wide and expands at a speed of 20 km/s. It must have been created some 40,000 years ago. The cluster is between 25,000 and 30,000 light-years away from us.

Original Source: ESO News Release