Category: Astronomy

Making an extra effort to image a faint, gigantic corkscrew traced by fast protons and electrons shot out from a mysterious microquasar paid off for a pair of astrophysicists who gained new insights into the beast’s inner workings and also resolved a longstanding dispute over the object’s distance.

The astrophysicists used the National Science Foundation’s Very Large Array (VLA) radio telescope to capture the faintest details yet seen in the plasma jets emerging from the microquasar SS 433, an object once dubbed the “enigma of the century.” As a result, they have changed scientists’ understanding of the jets and settled the controversy over its distance “beyond all reasonable doubt,” they said.

SS 433 is a neutron star or black hole orbited by a “normal” companion star. The powerful gravity of the neutron star or black hole draws material from the stellar wind of its companion into an accretion disk of material tightly circling the dense central object prior to being pulled onto it. This disk propels jets of fast protons and electrons outward from its poles at about a quarter of the speed of light. The disk in SS 433 wobbles like a child’s top, causing its jets to trace a corkscrew in the sky every 162 days.

The new VLA study indicates that the speed of the ejected particles varies over time, contrary to the traditional model for SS 433.

“We found that the actual speed varies between 24 percent to 28 percent of light speed, as opposed to staying constant,” said Katherine Blundell, of the University of Oxford in the United Kingdom. “Amazingly, the jets going in both directions change their speeds simultaneously, producing identical speeds in both directions at any given time,” Blundell added. Blundell worked with Michael Bowler, also of Oxford. The scientists’ findings have been accepted by the Astrophysical Journal Letters.

The new VLA image shows two full turns of the jets’ corkscrew on both sides of the core. Analyzing the image showed that if material came from the core at a constant speed, the jet paths would not accurately match the details of the image.

“By simulating ejections at varying speeds, we were able to produce an exact match to the observed structure,” Blundell explained. The scientists first did their match to one of the jets. “We then were stunned to see that the varying speeds that matched the structure of one jet also exactly reproduced the other jet’s path,” Blundell said. Matching the speeds in the two jets reproduced the observed structure even allowing for the fact that, because one jet is moving more nearly away from us than the other, it takes light longer to reach us from it, she added.

The astrophysicists speculate that the changes in ejection speed may be caused by changes in the rate at which material is transferred from the companion star onto the accretion disk.

The detailed new VLA image also allowed the astrophysicists to determine that SS 433 is nearly 18,000 light-years distant from Earth. Earlier estimates had the object, in the constellation Aquila, as near as 10,000 light-years. An accurate distance, the scientists said, now allows them to better determine the age of the shell of debris blown out by the supernova explosion that created the dense, compact object in the microquasar. Knowing the distance accurately also allows them to measure the actual brightness of the microquasar’s components, and this, they said, improves their understanding of the physical processes at work in the system.

The breakthrough image was made using 10 hours of observing time with the VLA in a configuration that maximizes the VLA’s ability to see fine detail. It represents the longest “time exposure” of SS 433 at radio wavelengths, and thus shows the faintest details. It also represents the best such image that can be done with current technology. Because the jets in SS 433 are moving, their image would be “smeared” in a longer observation. In order to see even fainter details in the jets, the astrophysicists must await the greater sensitivity of the Expanded VLA, set to become available in a few years.

SS 433 was the first example of what now are termed microquasars, binary systems with either a neutron star or black hole orbited by another star, and emitting jets of material at high speeds. The strange stellar system received a wealth of media coverage in the late 1970s and early 1980s. A 1981 Sky & Telescope article was entitled, “SS 433 — Enigma of the Century.”

Because microquasars in our own Milky Way Galaxy are thought to produce their high-speed jets of material through processes similar to those that produce jets from the cores of galaxies, the nearby microquasars serve as a convenient “laboratory” for studying the physics of jets. The microquasars are closer and show changes more quickly than their larger cousins.

Katherine Blundell is a University Research Fellow funded by the UK’s Royal Society.

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

An international team of astronomers [2] has succeeded in measuring with high precision the velocities of a large number of planetary nebulae [3] in the intergalactic space within the Virgo Cluster of galaxies. For this they used the highly efficient FLAMES spectrograph [4] on the ESO Very Large Telescope at the Paranal Observatory (Chile).

These planetary nebulae stars free floating in the otherwise seemingly empty space between the galaxies of large clusters can be used as “probes” of the gravitational forces acting within these clusters. They trace the masses, visible as well as invisible, within these regions. This, in turn, allows astronomers to study the formation history of these large bound structures in the universe.

The accurate velocity measurements of 40 of these stars confirm the view that Virgo is a highly non-uniform galaxy cluster, consisting of several subunits that have not yet had time to come to equilibrium. These new data clearly show that the Virgo Cluster of galaxies is still in its making.

They also prove for the first time that one of the bright galaxies in the region scrutinized, Messier 87, has a very extended halo of stars, reaching out to at least 65 kpc. This is more than twice the size of our own galaxy, the Milky Way.

A young cluster
At a distance of approximately 50 million light-years, the Virgo Cluster is the nearest galaxy cluster. It is located in the zodiacal constellation Virgo (The Virgin) and contains many hundreds of galaxies, ranging from giant and massive elliptical galaxies and spirals like our own Milky Way, to dwarf galaxies, hundreds of times smaller than their big brethren. French astronomer Charles Messier entered 16 members of the Virgo cluster in his famous catalogue of nebulae. An image of the core of the cluster obtained with the Wide Field Imager camera at the ESO La Silla Observatory was published last year as PR Photo 04a/03.

Clusters of galaxies are believed to have formed over a long period of time by the assembly of smaller entities, through the strong gravitational pull from dark and luminous matter. The Virgo cluster is considered to be a relatively young cluster because previous studies have revealed small “sub-clusters of galaxies” around the major galaxies Messier 87, Messier 86 and Messier 49. These sub-clusters have yet to merge to form a denser and smoother galaxy cluster.

Recent observations have shown that the so-called “intracluster” space, the region between galaxies in a cluster, is permeated by a sparse “intracluster population of stars”, which can be used to study in detail the structure of the cluster.

Cosmic wanderers
The first discoveries of intracluster stars in the Virgo cluster were made serendipitously by Italian astronomer, Magda Arnaboldi (Torino Observatory, Italy) and her colleagues, in 1996. In order to study the extended halos of galaxies in the Virgo cluster, with the ESO New Technology Telescope at La Silla, they searched for objects known as “planetary nebulae” [3].

Planetary nebulae (PNe) can be detected out to large distances from their strong emission lines. These narrow emission lines also allow for a precise measure of their radial velocities. Planetary Nebulae can thus serve to investigate the motions of stars in the halo regions of distant galaxies.

In their study, the astronomers found several planetary nebulae apparently not related to any galaxies but moving in the gravity field of the whole cluster. These “wanderers” belonged to a newly discovered intracluster population of stars.

Since these first observations, several hundreds of these wanderers have been discovered. They must represent the tip of the iceberg of a huge population of stars swarming among the galaxies in these enormous clusters. Indeed, as planetary nebulae are the final stage of common low mass stars – like our Sun – they are representative of the stellar population in general. And as planetary nebulae are rather short-lived (a few tens of thousand years – a blitz on astronomical timescales), astronomers can estimate that one star in about 8,000 million of solar-type stars is visible as a planetary nebula at any given moment. There must thus be a comparable number of stars in between galaxies as in the galaxies themselves. But because they are diluted in such a huge volume, they are barely detectable.

Because these stars are predominantly old, the most likely explanation for their presence in the intracluster space is that they formed within individual galaxies, which were subsequently stripped of many of their stars during close encounters with other galaxies during the initial stages of cluster formation. These “lost” stars were then dispersed into intracluster space where we now find them.

Thus planetary nebulae can provide a unique handle on the number, type of stars and motions in regions that may harbour a substantial amount of mass. Their motions contain the fossil record of the history of galaxy interaction and the formation of the galaxy cluster.

Measuring the speed of dying stars
The international team of astronomers [2] went on further to make a detailed study of the motions of the planetary nebulae in the Virgo cluster in order to determine its dynamical structure and compare it with numerical simulations. To this aim, they carried out a challenging research programme, aimed at confirming intracluster planetary nebula candidates they found earlier and measuring their radial velocities in three different regions (“survey fields”) in the Virgo cluster core.

This is far from an easy task. The emission in the main Oxygen emission line from a planetary nebula in Virgo is comparable to that of a 60-Watt light bulb at a distance of about 6.6 million kilometres, about 17 times the average distance to the Moon. Furthermore intracluster planetary nebula samples are sparse, with only a few tens of planetary nebulae in a quarter of a degree square sky field – about the size of the Moon. Spectroscopic observations thus require 8 metre class telescopes and spectrographs with a large field of view. The astronomers had therefore to rely on the FLAMES-GIRAFFE spectrograph on the VLT [4], with its relatively high spectral resolution, its field of view of 25 arcmin and the possibility to take up to 130 spectra at a time.

The astronomers studied a total of 107 stars, among which 71 were believed to be genuine intracluster planetary candidates. They observed between 21 and 49 objects simultaneously for about 2 hours per field. The three parts of the Virgo core surveyed contain several bright galaxies (Messier 84, 86, 87, and NGC 4388) and a large number of smaller galaxies. They were chosen to represent different entities of the cluster.

The spectroscopic measurements could confirm the intracluster nature of 40 of the planetary nebulae studied. They also provided a wealth of knowledge on the structure of this part of the Virgo cluster.

In The Making
In the first field near Messier 87 (M87), the astronomers measured a mean velocity close to 1250 km/s and a rather small dispersion around this value. Most stars in this field are thus physically bound to the bright galaxy M87, in the same way as the Earth is bound to the Sun. Magda Arnaboldi explains: “This study has led to the remarkable discovery that Messier 87 has a stellar halo in approximate dynamical equilibrium out to at least 65 kpc, or more than 200,000 light-years. This is more than twice the size of our own galaxy, the Milky Way, and was not known before.”

The velocity dispersion observed in the second field, which is far away from bright galaxies, is larger than in the first one by a factor four. This very large dispersion, indicating stars moving in very disparate directions at different speeds, also tells us that this field most probably contains many intracluster stars whose motions are barely influenced by large galaxies. The new data suggest as a tantalizing possibility that this intracluster population of stars could be the leftover from the disruption of small galaxies as they orbit M87.

The velocity distribution in the third field, as deduced from FLAMES spectra, is again different. The velocities show substructures related to the large galaxies Messier 86, Messier 84 and NGC 4388. Most likely, the large majority of all these planetary nebulae belong to a very extended halo around Messier 84.

Ortwin Gerhard (University of Basel, Switzerland), member of the team, is thrilled: “Taken together these velocity measurements confirm the view that the Virgo Cluster is a highly non-uniform and unrelaxed galaxy cluster, consisting of several subunits. With the FLAMES spectrograph, we have thus been able to watch the motions in the Virgo Cluster, at a moment when its subunits are still coming together. And it is certainly a view worth seeing!”

More information
The results presented in this ESO Press Release are based on a research paper (“The Line-of-Sight Velocity Distributions of Intracluster Planetary Nebulae in the Virgo Cluster Core” by M. Arnaboldi et al.) that has just appeared in the research journal Astrophysical Journal Letters Vol. 614, p. 33.

Notes
[1]: The University of Basel Press Release on this topic is available at http://www.zuv.unibas.ch/uni_media/2004/20041022virgo.html.

[2]: The members of the team are Magda Arnaboldi (INAF, Osservatorio di Pino Torinese, Italy), Ortwin Gerhard (Astronomisches Institut, Universit?t Basel, Switzerland), Alfonso Aguerri (Instituto de Astrofisica de Canarias, Spain), Kenneth C. Freeman (Mount Stromlo Observatory, ACT, Australia), Nicola Napolitano (Kapteyn Astronomical Institute, The Netherlands), Sadanori Okamura (Dept. of Astronomy, University of Tokyo, Japan), and Naoki Yasuda (Institute for Cosmic Ray Research, University of Tokyo, Japan).

[3]: Planetary nebulae are Sun-like stars in their final dying phase during which they eject their outer layers into surrounding space. At the same time, they unveil their small and hot stellar core which appears as a “white dwarf star”. The ejected envelope is illuminated and heated by the stellar core and emits strongly in characteristic emission lines of several elements, notably oxygen (at wavelengths 495.9 and 500.7 nm). Their name stems from the fact that some of these nearby objects, such as the “Dumbbell Nebula” (see ESO PR Photo 38a/98) resemble the discs of the giant planets in the solar system when viewed with small telescopes.

[4]: FLAMES, the Fibre Large Array Multi-Element Spectrograph, is installed at the 8.2-m VLT KUEYEN Unit Telescope. It is able to observe the spectra of a large number of individual, faint objects (or small sky areas) simultaneously and covers a sky field of no less than 25 arcmin in diameter, i.e., almost as large as the full Moon. It is the result of a collaboration between ESO, the Observatoire de Paris-Meudon, the Observatoire de Gen?ve-Lausanne, and the Anglo Australian Observatory (AAO).

Original Source: ESO News Release

Most of the stars in our Milky Way galaxy lie in a very flat, pinwheel-shaped disk. Although this disk is prominent in images of galaxies similar to the Milky Way, there is also a very diffuse spherical “halo” of stars surrounding and enclosing the disks of such galaxies.

Recent discoveries have shown that this outer halo of the Milky Way is probably composed of small companion galaxies ripped to shreds as they orbited the Milky Way.

A discovery announced today by the Sloan Digital Sky Survey (SDSS) reveals a clump of stars unlike any seen before. The findings may shed light on how the Milky Way’s stellar halo formed.

This clump of newly discovered stars, called SDSSJ1049+5103 or Willman 1, is so faint that it could only be found as a slight increase in the number of faint stars in a small region of the sky.

“We discovered this object in a search for extremely dim companion galaxies to the Milky Way,” explains Beth Willman of New York University’s Center for Cosmology and Particle Physics. “However, it is 200 times less luminous than any galaxy previously seen.”

Another possibility, adds Michael Blanton, an SDSS colleague of Willman’s at New York University, is that Willman 1 is an unusual type of globular cluster, a spherical agglomeration of thousands to millions of old stars.”

“Its properties are rather unusual for a globular cluster. It is dimmer than all but three known globular clusters. Moreover, these dim globular clusters are all much more compact than Willman 1”, explains Blanton. “If it’s a globular cluster, it is probably being torn to shreds by the gravitational tides of the Milky Way.”

The real distinction between the globular cluster and dwarf galaxy interpretations is that galaxies are usually accompanied by substantial quantities of dark matter, says Julianne Dalcanton, an SDSS researcher at the University of Washington. “Clearly the next step is to carry out additional measurements to determine whether there is any dark matter associated with Willman 1.”

SDSS consortium member Daniel Zucker of the Max Planck Institute for Astronomy in Heidelberg, Germany, says the Sloan Digital Sky Survey has proven to be “a veritable gold mine for studies of the outer parts of our galaxy and its neighbors, as shown by Dr. Willman’s discovery, and by our group’s earlier discovery of a giant stellar structure and a new satellite galaxy around the Andromeda Galaxy.”

If Willman 1 does turn out to be a dwarf galaxy, this discovery could shed light on a long-standing mystery.

The prevailing ‘Cold Dark Matter’ model predicts that our own Milky Way galaxy is surrounded by hundreds of dark matter clumps, each a few hundred light years in size and possibly populated by a dwarf galaxy.

However, only 11 dwarf galaxies have been discovered orbiting the Milky Way. Perhaps some of these clumps have very few embedded stars, making the galaxies particularly difficult to find.

“If this new object is in fact a dwarf galaxy, it may be the tip of the iceberg of a yet unseen population of ultra-faint dwarf galaxies,” suggests Willman.

The Milky Way has been an area of intense research by SDSS consortium members.

“The colors of the stars in Willman 1 are similar to those in the Sagittarius tidal stream, a former dwarf companion galaxy to the Milky Way now in the process of merging into the main body of our Galaxy,” explains Brian Yanny, an SDSS astrophysicist at The Department of Energy’s Fermi National Accelerator Laboratory, a leader in research on the Milky Way’s accretion of material.

Continues Yanny: “If Willman 1 is a globular cluster, then it may have piggybacked a ride into our Galaxy’s neighborhood on one of these dwarf companions, like a tiny mite riding in on a flea as it, in turn, latches onto a massive dog.”

“Whether it is a globular cluster or a dwarf galaxy, this very faint object appears to represent one of the building blocks of the Milky Way,” Willman said.

Original Source: SDSS News Release

A team of European astronomers has discovered that many stars in the vicinity of the Sun have unusual motions caused by the spiral arms of our galaxy, the Milky Way. According to this research, based on data from ESA’s Hipparcos observatory, our stellar neighbourhood is the crossroads of streams of stars coming from several directions. Some of the stars hosting planetary systems could be immigrants from more central regions of the Milky Way.

The Sun and most stars near it follow an orderly, almost circular orbit around the centre of our galaxy, the Milky Way. Using data from ESA’s Hipparcos satellite, a team of European astronomers has now discovered several groups of ‘rebel’ stars that move in peculiar directions, mostly towards the galactic centre or away from it, running like the spokes of a wheel. These rebels account for about 20% of the stars within 1000 light-years of the Sun, itself located about 25 000 light-years away from the centre of the Milky Way.

The data show that rebels in the same group have little to do with each other. They have different ages so, according to scientists, they cannot have formed at the same time nor in the same place. Instead, they must have been forced together. “They resemble casual travel companions more than family members,” said Dr Benoit Famaey, Universit? Libre de Bruxelles, Belgium.

Famaey and his colleagues believe that the cause forcing the rebel stars together on their unusual trajectory is a ‘kick’ received from one of the Milky Way’s spiral arms. The spiral arms are not solid structures but rather regions of higher density of gas and stars, called ‘density waves’ and similar to traffic hot-spots along the motorway. An approaching density wave compresses the gas it encounters and favours the birth of new stars, but it can also affect pre-existing stars by deflecting their motion. After the wave has passed, many stars will thus travel together in a stream, all in the same direction, even though they were originally on different trajectories or not even born.

This research has shown that the neighbourhood of the Sun is a crossroads of many streams, made up of stars with different origins and chemical composition. These streams could also account for many of the stars with planetary systems recently discovered near the Sun.

Astronomers know that stars with planetary systems preferentially form in dense gas clouds with a high metal content, such as those located in the more central regions of the Milky Way. The streams discovered by Hipparcos could be the mechanism that brought them closer to the Sun. As Famaey explains, “If these stars are kicked by a spiral arm, they can be displaced thousands of light-years away from their birthplace.” These stars, together with their planets, can thus have migrated closer to the Sun.

To learn more about the structure of our Milky Way, an aggregate of thousands of millions of stars, astronomers look at the way in which stars stay together in a coherent way or move with respect to the Sun and relative to one another. During its four-year mission, ESA’s Hipparcos satellite has measured the distance and motion of more than a hundred thousand stars within a 1000 light-years of the Sun. However, while Hipparcos’s data show in which directions stars are moving on the sky, they cannot tell whether stars are coming towards us or going away from us.

By combining the Hipparcos data with ground-based measurements of their ?Doppler shift?, obtained with a Swiss telescope at the Observatoire de Haute-Provence, France, Famaey and his colleagues could add the missing third dimension, namely the speed with which stars approach us or recede from us. Because of the Doppler shift, the colour of a star appears to change when it travels towards us or away from us, becoming respectively bluer or redder and giving astronomers information about its motion. “By combining all these first-class data, we now have a comprehensive, three-dimensional view of how nearby stars move about us,” said Famaey.

Scientists now wonder how widespread are the streams discovered by Famaey’s team and what role they could play in the evolution of our galaxy. “This result opens up exciting new prospects for our understanding of the dynamics of the Milky Way,” said Dr Michael Perryman, ESA Hipparcos and Gaia project scientist. ESA’s forthcoming mission Gaia, scheduled for launch in 2011, will make it possible to extend this investigation over a much wider region of our galaxy. Gaia will observe more than a thousand million stars and will measure their motion in all three dimensions simultaneously, thanks to the on-board spectrograph providing information on their Doppler shift. “This will give us the clearest view ever of the structure and evolution of the Milky Way,” Perryman said.

Original Source: ESA News Release

Planets are built over a long period of massive collisions between rocky bodies as big as mountain ranges, astronomers announced today.

New observations from NASA’s Spitzer Space Telescope reveal surprisingly large dust clouds around several stars. These clouds most likely flared up when rocky, embryonic planets smashed together. The Earth’s own Moon may have formed from such a catastrophe. Prior to these new results, astronomers thought planets were formed under less chaotic circumstances.

“It’s a mess out there,” said Dr. George Rieke of the University of Arizona, Tucson, first author of the findings and a Spitzer scientist. “We are seeing that planets have a long, rocky road to go down before they become full grown.”

Spitzer was able to see the dusty aftermaths of these collisions with its powerful infrared vision. When embryonic planets, the rocky cores of planets like Earth and Mars, crash together, they are believed to either merge into a bigger planet or splinter into pieces. The dust generated by these events is warmed by the host star and glows in the infrared, where Spitzer can see it.

The findings will be published in an upcoming issue of the Astrophysical Journal. They mirror what we know about the formation of our own planetary system. Recent observations from studies of our Moon’s impact craters also reveal a turbulent early solar system. “Our Moon took a lot of violent hits when planets had already begun to take shape,” Rieke said.

According to the most popular theory, rocky planets form somewhat like snowmen. They start out around young stars as tiny balls in a disc-shaped field of thick dust. Then, through sticky interactions with other dust grains, they gradually accumulate more mass. Eventually, mountain-sized bodies take shape, which further collide to make planets.

Previously, astronomers envisioned this process proceeding smoothly toward a mature planetary system over a few million to a few tens of millions of years. Dusty planet-forming discs, they predicted, should steadily fade away with age, with occasional flare-ups from collisions between leftover rocky bodies.

Rieke and his colleagues have observed a more varied planet-forming environment. They used new Spitzer data, together with previous data from the joint NASA, United Kingdom and the Netherlands’ Infrared Astronomical Satellite and the European Space Agency’s Infrared Space Observatory. They looked for dusty discs around 266 nearby stars of similar size, about two to three times the mass of the Sun, and various ages. Seventy-one of those stars were found to harbor discs, presumably containing planets at different stages of development. But, instead of seeing the discs disappear in older stars, the astronomers observed the opposite in some cases.

“We thought young stars, about one million years old, would have larger, brighter discs, and older stars from 10 to 100 million years old would have fainter ones,” Rieke said. “But we found some young stars missing discs and some old stars with massive discs.”

This variability implies planet-forming discs can become choked with dust throughout the discs’ lifetime, up to hundreds of millions of years after the host star was formed. “The only way to produce as much dust as we are seeing in these older stars is through huge collisions,” Rieke said.

Before Spitzer, only a few dozen planet-forming discs had been observed around stars older than a few million years. Spitzer’s uniquely sensitive infrared vision allows it to sense the dim heat from thousands of discs of various ages. “Spitzer has opened a new door to the study of discs and planetary evolution,” said Dr. Michael Werner, project scientist for Spitzer at NASA’s Jet Propulsion Laboratory, Pasadena, Calif.

“These exciting new findings give us new insights into the process of planetary formation, a process that led to the birth of planet Earth and to life,” said Dr. Anne Kinney, director of the universe division in the Science Mission Directorate at NASA Headquarters, Washington. “Spitzer truly embodies NASA’s mission to explore the universe and search for life,” she said.

JPL manages the Spitzer Space Telescope for NASA’s Science Mission Directorate. Artist’s concepts and additional information about the Spitzer Space Telescope is available at http://www.spitzer.caltech.edu.

Original Source: NASA/JPL News Release

Just when astronomers thought they might have dug up the last of our galaxy’s “fossils,” they’ve discovered a new one in the galactic equivalent of our own backyard.

Called globular clusters, these ancient bundles of stars date back to the birth of our Milky Way galaxy, 13 or so billion years ago. They are sprinkled around the center of the galaxy like seeds in a pumpkin. Astronomers use clusters as tools for studying the Milky Way’s age and formation.

New infrared images from NASA’s Spitzer Space Telescope and the University of Wyoming Infrared Observatory reveal a never-before-seen globular cluster within the dusty confines of the Milky Way. The findings will be reported in an upcoming issue of the Astronomical Journal.

“It’s like finding a long-lost cousin,” said Dr. Chip Kobulnicky, a professor of physics and astronomy at the University of Wyoming, Laramie, and lead author of the report. “We thought all the galaxy’s globular clusters had already been found.”

“I couldn’t believe what I was seeing,” said Andrew Monson, a graduate student at the University of Wyoming, who first spotted the cluster. “I certainly wasn’t expecting to find such a cluster.”

The newfound cluster is one of about 150 known to orbit the center of the Milky Way. These tightly packed knots of stars are among the oldest objects in our galaxy, having formed about 10 to 13 billion years ago. They contain several hundred thousand stars, most of which are older and less massive than our Sun.

Monson first noticed the cluster while scanning data from the Spitzer Space Telescope’s Galactic Legacy Infrared Mid-Plane Survey Extraordinaire – a survey to find objects hidden within the dusty mid-plane of our galaxy. He then searched archival data for a match and found only one undocumented image of the cluster from a previous NASA-funded infrared survey of the sky, called the Two Micron All-Sky Survey. “The cluster was there in the data but nobody had found it,” said Monson.

“This discovery demonstrates why Spitzer is so powerful – it can see objects that are completely hidden in visible light,” said Dr. Michael Werner of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., project scientist for Spitzer. “This is particularly relevant to the study of the plane of our galaxy, where dust blocks most visible light.”

Follow-up observations with the University of Wyoming Infrared Observatory helped set the distance of the new cluster at about 9,000 light-years from Earth – closer than most clusters — and set the mass at the equivalent of 300,000 Suns. The cluster’s apparent size, as viewed from Earth, is comparable to a grain of rice held at arm’s length. It is located in the constellation Aquila.

The research team consists of astronomers from the University of Wisconsin, Madison; Boston University, Boston, Mass.; the University of Maryland, College Park, Md.; the University of Minnesota, Twin Cities; the Space Science Institute, Boulder, Colo.; and the Spitzer Science Center, Pasadena, Calif. The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire is managed by the University of Wisconsin and led by Dr. Ed Churchwell.

JPL manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington, D.C. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. JPL is a division of Caltech. Spitzer’s infrared array camera, which captured the new cluster, was built by NASA Goddard Space Flight Center, Greenbelt, Md. The camera’s development was led by Dr. Giovanni Fazio of Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.

Additional information about the Spitzer Space Telescope is available at http://www.spitzer.caltech.edu. Additional information about the University of Wyoming Infrared Observatory is available at http://physics.uwyo.edu/~mpierce/WIRO/.

Original Source: NASA/JPL News Release

Cosmologists from the California Institute of Technology have used observations probing back to the remote epoch of the universe when atoms were first forming to detect movements among the seeds that gave rise to clusters of galaxies. The new results show the motion of primordial matter on its way to forming galaxy clusters and superclusters. The observations were obtained with an instrument high in the Chilean Andes known as the Cosmic Background Imager (CBI), and they provide new confidence in the accuracy of the standard model of the early universe in which rapid inflation occurred a brief instant after the Big Bang.

The novel feature of these polarization observations is that they reveal directly the seeds of galaxy clusters and their motions as they proceeded to form the first clusters of galaxies.

Reporting in the October 7 online edition of Science Express, Caltech’s Rawn Professor of Astronomy, and principal investigator on the CBI project, Anthony Readhead and his team say the new polarization results provide strong support for the standard model of the universe as a place in which dark matter and dark energy are much more prevalent than everyday matter as we know it, which poses a major problem for physics. A companion paper describing early polarization observations with the CBI has been submitted to the Astrophysical Journal.

The cosmic background observed by the CBI originates from the era just 400,000 years after the Big Bang and provides a wealth of information on the nature of the universe. At this remote epoch none of the familiar structures of the universe existed–there were no galaxies, stars, or planets. Instead there were only tiny density fluctuations, and these were the seeds out of which galaxies and stars formed under the hand of gravity.

Instruments prior to the CBI had detected fluctuations on large angular scales, corresponding to masses much larger than superclusters of galaxies. The high resolution of the CBI allowed the seeds of the structures we observe around us in the universe today to be observed for the first time in January 2000.

The expanding universe cooled and by 400,000 years after the Big Bang it was cool enough for electrons and protons to combine to form atoms. Prior to this time photons could not travel far before colliding with an electron, and the universe was like a dense fog, but at this point the universe became transparent and since that time the photons have streamed freely across the universe to reach our telescopes today, 13.8 billion years later. Thus observations of the microwave background provide a snapshot of the universe as it was just 400,000 years after the Big Bang–long before the formation of the first galaxies, stars, and planets.

The new data were collected by the CBI between September 2002 and May 2004, and cover four patches of sky, encompassing a total area three hundred times the size of the moon and showing fine details only a fraction of the size of the moon. The new results are based on a property of light called polarization. This is a property that can be demonstrated easily with a pair of polarizing sunglasses. If one looks at light reflected off a pond through such sunglasses and then rotates the sunglasses, one sees the reflected light varying in brightness. This is because the reflected light is polarized, and the polarizing sunglasses only transmit light whose polarization is properly aligned with the glasses. The CBI likewise picks out the polarized light, and it is the details of this light that reveal the motion of the seeds of galaxy clusters.

In the total intensity we see a series of peaks and valleys, where the peaks are successive harmonics of a fundamental “tone.” In the polarized emission we also see a series of peaks and valleys, but the peaks in the polarized emission coincide with the valleys in the total intensity, and vice versa. In other words, the polarized emission is exactly out of step with the total intensity. This property of the polarized emission being out of step with the total intensity indicates that the polarized emission arises from the motion of the material.

The first detection of polarized emission by the Degree Angular Scale Interferometer (DASI), the sister project of the CBI, in 2002 provided dramatic evidence of motion in the early universe, as did the measurements by the Wilkinson Microwave Anisotropy Probe (WMAP) in 2003. The CBI results announced today significantly augment these earlier findings by demonstrating directly, and on the small scales corresponding to galaxy clusters, that the polarized emission is out of step with the total intensity.

Other data on the cosmic microwave background polarization were released just two weeks ago by the DASI team, whose three years of results show further compelling evidence that the polarization is indeed due to the cosmic background and is not contaminated by radiation from the Milky Way. The results of these two sister projects therefore complement each other beautifully, as was the intention of Readhead and John Carlstrom, the principal investigator of DASI and a coauthor on the CBI paper, when they planned these two instruments a decade ago.

According to Readhead, “Physics has no satisfactory explanation for the dark energy which dominates the universe. This problem presents the most serious challenge to fundamental physics since the quantum and relativistic revolutions of a century ago. The successes of these polarization experiments give confidence in our ability to probe fine details of the polarized cosmic background, which will eventually throw light on the nature of this dark energy.”

“The success of these polarization experiments has opened a new window for exploring the universe which may allow us to probe the first instants of the universe through observations of gravitational waves from the epoch of inflation,” says Carlstrom.

The analysis of the CBI data is carried out in collaboration with groups at the National Radio Astronomy Observatory (NRAO) and at the Canadian Institute for Theoretical Astrophysics (CITA).

“This is truly an exciting time in cosmological research, with a remarkable convergence of theory and observation, a universe full of mysteries such as dark matter and dark energy, and a fantastic array of new technology–there is tremendous potential for fundamental discoveries here” says Steve Myers of the NRAO, a coauthor and key member of the CBI team from its inception.

According to Richard Bond, director of CITA and a coauthor of the paper, “As a theorist in the early eighties, when we were first showing that the magnitude of the cosmic microwave background polarization would likely be a factor of a hundred down in power from the minute temperature variations that were themselves a heroic effort to discover, it seemed wishful thinking that even in some far distant future such minute signals would be revealed. With these polarization detections, the wished-for has become reality, thanks to remarkable technological advances in experiments such as CBI. It has been our privilege at CITA to be fully engaged as members of the CBI team in unveiling these signals and interpreting their cosmological significance for what has emerged as the standard model of cosmic structure formation and evolution.”

The next step for Readhead and his CBI team will be to refine these polarization observations significantly by taking more data, and to test whether or not the polarized emission is exactly out of step with the total intensity with the goal of finding some clues to the nature of the dark matter and dark energy.

The CBI is a microwave telescope array comprising 13 separate antennas, each about three feet in diameter and operating in 10 frequency channels, set up in concert so that the entire instruments acts as a set of 780 interferometers. The CBI is located at Llano de Chajnantor, a high plateau in Chile at 16,800 feet, making it by far the most sophisticated scientific instrument ever used at such high altitudes. The telescope is so high, in fact, that members of the scientific team must each carry bottled oxygen to do the work.

The upgrade of the CBI to polarization capability was supported by a generous grant from the Kavli Operating Institute, and the project is also the grateful recipient of continuing support from Barbara and Stanley Rawn Jr. The CBI is also supported by the National Science Foundation, the California Institute of Technology, and the Canadian Institute for Advanced Research, and has also received generous support from Maxine and Ronald Linde, Cecil and Sally Drinkward, and the Kavli Institute for Cosmological Physics at the University of Chicago.

In addition to the scientists mentioned above, today’s Science Express paper is coauthored by C. Contaldi and J. L. Sievers of CITA, J.K. Cartwright and S. Padin, both of Caltech and the University of Chicago; B. S. Mason and M. Pospieszalski of the NRAO; C. Achermann, P. Altamirano, L. Bronfman, S. Casassus, and J. May all of the University of Chile; C. Dickinson, J. Kovac, T. J. Pearson, and M. Shepherd of Caltech; W. L. Holzapfel of UC Berkeley; E. M. Leitch and C. Pryke of the University of Chicago; D. Pogosyan of the University of Toronto and the University of Alberta; and R. Bustos, R. Reeves, and S. Torres of the University of Concepci?n, Chile.

Original Source: Caltech News Release

Astronomers using the Gemini North and Keck II telescopes have peered inside a violent binary star system to find that one of the interacting stars has lost so much mass to its partner that it has regressed to a strange, inert body resembling no known star type.

Unable to sustain nuclear fusion at its core and doomed to orbit with its much more energetic white dwarf partner for millions of years, the dead star is essentially a new, indeterminate type of stellar object.

“Like the classic line about the aggrieved partner in a romantic relationship, the smaller donor star gave, and gave, and gave some more until it had nothing left to give,” says Steve B. Howell, an astronomer with Wisconsin-Indiana-Yale-NOAO (WIYN) telescope and the National Optical Astronomy Observatory, Tucson, AZ. “Now the donor star has reached a dead end – it is far too massive to be considered a super-planet, its composition does not match known brown dwarfs, and it is far too low in mass to be a star. There’s no true category for an object in such limbo.”

The binary system, known as EF Eridanus (abbreviated EF Eri), is located 300 light-years from Earth in the constellation Eridanus. EF Eri consists of a faint white dwarf star with about 60 percent of the mass of the Sun and the donor object of unknown type, which has an estimated bulk of only 1/20th of a solar mass.

Howell and Thomas E. Harrison of New Mexico State University made high-precision infrared measurements of the binary star system using the spectrographic capabilities of the Near Infrared Imager (NIRI) on the Gemini North telescope and NIRSPEC on Keck II both on Mauna Kea in December 2002 and September 2003, respectively. Supporting observations were made with the 2.1-meter telescope at Kitt Peak National Observatory near Tucson in September 2002.

EF Eri is a type of binary star system known as magnetic cataclysmic variables. This class of systems may produce many more of these ‘dead’ objects than scientists have realized, says Harrison, co-author of a paper on the discovery to be published in the October 20 issue of the Astrophysical Journal. “These types of systems are not generally accounted for within the usual census figures of star systems in a typical galaxy,” Harrison says. “They certainly should be considered more carefully.”

The white dwarf in EF Eri is a compressed, burnt-out remnant of a solar-type star that is now about the same diameter as the Earth, though it still emits copious amounts of visible light. Howell and Harrison observed EF Eri in the infrared because infrared light from the pair is naturally dominated by heat and longer wavelength emissions from the secondary object.

The scientific detective work to deduce the components of this binary system was complicated greatly by the cyclotron radiation emitted as free electrons spiral down the powerful magnetic field lines of the white dwarf. The white dwarf’s magnetic field is about 14 million times as powerful as the Sun’s. The resulting cyclotron radiation is emitted primarily in the infrared part of the spectrum.

“In our initial spectroscopy of EF Eri, we noted that some parts of the infrared continuum light became about 2-3 times brighter for a time period, then went away. This brightening repeated every orbit, and thus had to have an origin within the binary,” Howell explains. “We first thought the brightness change resulted from the difference between a heated side and a cooler side of the donor object, but further observations with Gemini and Keck instead pointed to cyclotron radiation. We ‘see’ this additional infrared component at the phases which occur when the radiation is beamed in our direction, and we do not see it when the beaming points in other directions.”

The 81-minute orbital period of the two objects was probably four or five hours when the mass transfer process began about five billion years ago. Originally, the secondary object may also have been similar in size to the Sun, with perhaps 50-100 percent of a solar mass.

“When this interactive process of mass transfer from the secondary star to the white dwarf begin, and why it stopped, both remain unknown to us,” Howell says. During this process, repeated outbursts and novae explosions were very likely. The physics of the process also caused the two objects to spiral closer to each other. Today, the two objects orbit each other at about the same separation as the distance from the Earth to the Moon. The donor object has regressed to a body with a diameter roughly equal to the planet Jupiter.

The combined observing power of the Gemini 8-meter and Keck 10-meter telescopes and their large primary mirrors, which were essential to this research, Howell says, makes it clear that neither spectral features of the donor nor its composition match any known type of brown dwarf or planet.

Derek Homeier University of Georgia created a series of computer models that attempt to replicate the conditions at EF Eri, but even the best of these do not match perfectly.

The shape of the spectra indicate a very cool object (about 1,700 degrees Kelvin, equivalent to a cool brown dwarf), yet they do not have the same detailed shape or key features of brown dwarf spectra. The coolest normal stars (very low mass M-type stars) are about 2,500 degrees K, and Jupiter is 124 degrees K. The close-in “hot Jupiter” exoplanets detected indirectly by other astronomers using their gravitational effect on their parent stars are estimated to be 1,000-1,600 degrees K.

There is a small chance that the EF Eri system could have originally consisted of the progenitor of the present-day white dwarf star and some sort of “super-planet” that survived the evolution of the white dwarf to result in the system observed now, but this is considered unlikely.

“There are about 15 other known binary systems out there that may be similar to EF Eri, but none has been studied enough to tell,” Howell says. “We are working on some of them right now, and trying to improve our models to better match the infrared spectra.”

Co-authors of this paper on EF Eri are Paula Szkody of the University of Washington in Seattle, and Joni Johnson and Heather Osborne of New Mexico State.

The WIYN 3.5-meter telescope is located at Kitt Peak National Observatory, 55 miles southwest of Tucson, AZ. Kitt Peak National Observatory is part of the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation (NSF).

The national research agencies that form the Gemini Observatory partnership include: the US National Science Foundation (NSF), the UK Particle Physics and Astronomy Research Council (PPARC), the Canadian National Research Council (NRC), the Chilean Comisi?n Nacional de Investigaci?n Cientifica y Tecnol?gica (CONICYT), the Australian Research Council (ARC), the Argentinean Consejo Nacional de Investigaciones Cient?ficas y T?cnicas (CONICET) and the Brazilian Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq). The Observatory is managed by AURA under a cooperative agreement with the NSF.

The W.M. Keck Observatory is operated by the California Association for Research in Astronomy (CARA), a scientific partnership of the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration.

Original Source: Gemini News Release

Four hundred years ago, sky watchers, including the famous astronomer Johannes Kepler, best known as the discoverer of the laws of planetary motion, were startled by the sudden appearance of a “new star” in the western sky, rivaling the brilliance of the nearby planets.

Modern astronomers, using NASA’s three orbiting Great Observatories, are unraveling the mysteries of the expanding remains of Kepler’s supernova, the last such object seen to explode in our Milky Way galaxy.

When a new star appeared Oct. 9, 1604, observers could use only their eyes to study it. The telescope would not be invented for another four years. A team of modern astronomers has the combined abilities of NASA’s Great Observatories, the Spitzer Space Telescope, Hubble Space Telescope and Chandra X-ray Observatory, to analyze the remains in infrared radiation, visible light, and X-rays. Ravi Sankrit and William Blair of the Johns Hopkins University in Baltimore lead the team.

The combined image unveils a bubble-shaped shroud of gas and dust, 14 light-years wide and expanding at 6 million kilometers per hour (4 million mph). Observations from each telescope highlight distinct features of the supernova, a fast-moving shell of iron-rich material, surrounded by an expanding shock wave sweeping up interstellar gas and dust.

“Multi-wavelength studies are absolutely essential for putting together a complete picture of how supernova remnants evolve,” Sankrit said. Sankrit is an associate research scientist, Center for Astrophysical Sciences at Hopkins and lead for Hubble astronomer observations.

“For instance, the infrared data are dominated by heated interstellar dust, while optical and X-ray observations sample different temperatures of gas,” Blair added. Blair is a research professor, Physics and Astronomy Department at Hopkins and lead astronomer for Spitzer observations. “A range of observations is needed to help us understand the complex relationship that exists among the various components,” Blair said.

The explosion of a star is a catastrophic event. The blast rips the star apart and unleashes a roughly spherical shock wave that expands outward at more than 35 million kilometers per hour (22 million mph) like an interstellar tsunami. The shock wave spreads out into surrounding space, sweeping up any tenuous interstellar gas and dust into an expanding shell. The stellar ejecta from the explosion initially trail behind the shock wave. It eventually catches up with the inner edge of the shell and is heated to X-ray temperatures.

Visible-light images from Hubble’s Advanced Camera for Surveys reveal where the supernova shock wave is slamming into the densest regions of surrounding gas. The bright glowing knots are dense clumps that form behind the shock wave. Sankrit and Blair compared their Hubble observations with those taken with ground-based telescopes to obtain a more accurate distance to the supernova remnant of about 13,000 light-years.

The astronomers used Spitzer to probe for material that radiates in infrared light, which shows heated microscopic dust particles that have been swept up by the supernova shock wave. Spitzer is sensitive enough to detect both the densest regions seen by Hubble and the entire expanding shock wave, a spherical cloud of material. Instruments on Spitzer also reveal information about the chemical composition and physical environment of the expanding clouds of gas and dust ejected into space. This dust is similar to dust which was part of the cloud of dust and gas that formed the Sun and planets in our solar system.

The Chandra X-ray data show regions of very hot gas. The hottest gas, higher-energy X-rays, is located primarily in the regions directly behind the shock front. These regions also show up in the Hubble observations and also align with the faint rim of material seen in the Spitzer data. Cooler X-ray gas, lower-energy X-rays, resides in a thick interior shell and marks the location of the material expelled from the exploded star.

There have been six known supernovas in our Milky Way over the past 1,000 years. Kepler’s is the only one for which astronomers do not know what type of star exploded. By combining information from all three Great Observatories, astronomers may find the clues they need. “It’s really a situation where the total is greater than the sum of the parts,” Blair said. “When the analysis is complete, we will be able to answer several questions about this enigmatic object.”

Images and additional information are available at http://www.nasa.gov, http://hubblesite.org/news/2004/29, http://chandra.harvard.edu , http://spitzer.caltech.edu ,http://www.jhu.edu/news_info/news/, http://heritage.stsci.edu/2004/29 and http://www.nasa.gov/vision/universe/starsgalaxies/kepler.html.

Original Source: NASA/JPL News Release

Life near the center of our galaxy never had a chance. Every 20 million years on average, gas pours into the galactic center and slams together, creating millions of new stars. The more massive stars soon go supernova, exploding violently and blasting the surrounding space with enough energy to sterilize it completely. This scenario is detailed by astronomer Antony Stark (Harvard-Smithsonian Center for Astrophysics) and colleagues in the October 10, 2004, issue of The Astrophysical Journal Letters.

The team’s discovery was made possible using the unique capabilities of the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO). It is the only observatory in the world able to make large-scale maps of the sky at submillimeter wavelengths.

The gas for each starburst comes from a ring of material located about 500 light-years from the center of our galaxy. Gas collects there under the influence of the galactic bar-a stretched oval of stars 6,000 light-years long rotating in the middle of the Milky Way. Tidal forces and interactions with this bar cause the ring of gas to build up to higher and higher densities until it reaches a critical density or “tipping point.” At that point, the gas collapses down into the galactic center and smashes together, fueling a huge burst of star formation.

“A starburst is star formation gone wild,” says Stark.

Astronomers see starbursts in many galaxies, most often colliding galaxies where lots of gas crashes together. But starbursts can happen in isolated galaxies too, including our own galaxy, the Milky Way.

The next starburst in the Milky Way is coming relatively soon, predicts Stark. “It likely will happen within the next 10 million years.”

That assessment is based on the team’s measurements showing that the gas density in the ring is nearing the critical density. Once that threshold is crossed, the ring will collapse and a starburst will blaze forth on an unimaginably huge scale.

Some 30 million solar masses of matter will flood inward, overwhelming the 3 million solar mass black hole at the galactic center. The black hole, massive as it is, will be unable to consume most of the gas.

“It would be like trying to fill a dog dish with a firehose,” says Stark. Instead, most of the gas will form millions of new stars.

The more massive stars will burn their fuel quickly, exhausting it in only a few million years. Then, they will explode as supernovae and irradiate the surrounding space. With so many stars packed so close together as a result of the starburst, the entire galactic center will be impacted dramatically enough to kill any life on an Earth-like planet. Fortunately, the Earth itself lies about 25,000 light-years away, far enough that we are not in danger.

The facility used to make this discovery, AST/RO, is a 1.7-meter-diameter telescope that operates in one of the most challenging environments on the planet-the frigid desert of Antarctica. It is located at the National Science Foundation’s Amundsen-Scott Station at the South Pole. The air at the South Pole is very dry and cold, so radiation that would be absorbed by water vapor at other sites can reach the ground and be detected.

“These observations have helped advance our understanding of star formation in the Milky Way,” says Stark. “We hope to continue those advancements by collaborating with researchers who are working on the Spitzer Space Telescope’s Legacy Science Program. AST/RO’s complementary observations would uniquely contribute to that effort.”

Stark’s co-authors on the paper announcing this finding are Christopher L. Martin, Wilfred M. Walsh, Kecheng Xiao and Adair P. Lane (Harvard-Smithsonian Center for Astrophysics), and Christopher K. Walker (Steward Observatory).

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