Category: Astronomy

XMM-Newton view of hot ionised gas halo in NGC 4631. Image credit: ESA Click to enlarge
Astronomers using ESA’s XMM-Newton observatory have found very hot gaseous haloes around a multitude of spiral galaxies similar to our Milky Way galaxy. These ‘ghost-like’ veils have been suspected for decades but remained elusive until now.

Galaxy ‘haloes’ are often seen in so-called ‘starburst’ galaxies, the locations of concentrated star formation, but the discovery of high-temperature haloes around non-starburst spiral galaxies opens the door to new types of measurements once only dreamed about.

For example, scientists can confirm models of galaxy evolution and infer the star-formation rate in galaxies like our own by ‘calculating backwards’ to estimate how many supernovae are needed to make the observed haloes.

“Most of these ghost-like haloes have never been confirmed before in X-ray energies because they are so tenuous and have a low-surface brightness,” said Ralph T?llmann, from the Ruhr University in Bochum, Germany, lead author of the results.

“We needed the high sensitivity and large light-collecting area of the XMM-Newton satellite to uncover these haloes.”

In starburst galaxies, which have prominent haloes, star formation and star death (supernovae) are concentrated in the core of the galaxy and occur during a short time period over the life of a galaxy. This intense activity forms a halo of gas around the entire galaxy, similar to a volcano sending out a plume.

So how can haloes form in the absence of intense star formation? T?llmann’s group say that the entire disk of a spiral galaxy can ‘simmer’ with star-formation activity. This is spread out over time and distance. Like a giant pot of boiling water, the steady activity of star formation over millions and millions of years percolates outward to form the galaxy halo.

Two of the best-studied galaxies so far out of a group of 32 are NGC 891 and NGC 4634, which are tens of millions of light years away in the constellations Andromeda and Coma Berenices, respectively.

The scientists noted that these observations do not support a recent model of galaxy halo formation, in which gas from the intergalactic medium rains down on the galaxy and forms the halo.

Galaxy halos contain about 10 million solar masses of gas. The scientists say it is a relatively straightforward calculation to determine how many supernovae are needed to create the halo. Supernovae are intricately tied to the rate of star formation in a given galaxy.

“With our data we will be able to establish for the first time a critical rate of star formation that needs to be exceeded in order to create such haloes,” said Dr Ralf-J?rgen Dettmar, a co-author also from Ruhr University.

Once these haloes have formed, the hot gas cools and can fall down onto the galaxy’s disk, the scientists said. The gas is involved in a new cycle of star formation, because pressure from this infalling gas triggers the collapse of gas clouds into new stars.

Some heavy elements might escape the halo into intergalactic space, depending on the energy of the supernovae. Further analysis of the chemical composition of the halo might reveal this.

This would determine the correctness of recent cosmological models on the evolution of galaxies, as well as provide evidence of how the elements necessary for life are distributed through the Universe.

Original Source: ESA Portal

A view of Buffy’s and other Kuiper belt object orbits. Image credit: CFHT Click to enlarge
A team of astronomers working in Canada, France and the United States have discovered an unusual small body orbiting the Sun beyond Neptune, in the region astronomers call the Kuiper belt. This new object is twice as far from the Sun as Neptune and is roughly half the size of Pluto. The body’s highly unusual orbit is difficult to explain using previous theories of the formation of the outer Solar System.

Currently 58 astronomical units from the Sun (1 astronomical unit, or AU, is the distance between the Earth and the Sun), the new object never approaches closer than 50 AU, because its orbit is close to circular. Almost all Kuiper belt objects discovered beyond Neptune are between 30 AU and 50 AU away. Beyond 50 AU, the main Kuiper belt appears to end, and what few objects have been discovered beyond this distance have all been on very high eccentricity (non-circular) orbits. Most of these high-eccentricity orbits are the result of Neptune “flinging” the object outward by a gravitational slingshot. However, because this new object does not approach closer than 50 AU, a different theory is needed to explain its orbit. Complicating the problem, the object’s orbit also has an extreme tilt, being inclined (tilted) at 47 degrees to the rest of the Solar System.

The Discovery and Follow-up

The object, which received the official designation 2004 XR 190 in the International Astronomical Union’s official announcement, was discovered during routine operation of the Canada-France Ecliptic Plane Survey (CFEPS) running as part of the Legacy Survey on the Canada France Hawaii Telescope. For now, the discoverers are using the temporary nickname “Buffy” to identify the new object, although they have proposed a different official name in keeping with normal procedures for naming such objects.

Buffy was extracted from the mountain of Legacy Survey data (about 50 gigabytes per hour of operation) by powerful computers combing through the telescopic images and producing hundreds of candidates. Astronomers then sift through the candidates to identify the distant comets.

Astronomer Lynne Allen of the University of British Columbia was the first to lay eyes on the new object, as she completed the initial identification in the course of processing CFEPS data from December 2004. “It was quite bright compared to the usual Kuiper belt objects we find”, said Dr. Allen, “but what was more interesting was how far away it was.”

The object’s brightness implies it is likely between 500 and 1000 kilometers (300 to 600 miles) in diameter. Buffy is thus a very large Kuiper belt object, but about half a dozen are larger.

“We immediately realized that the object was about twice as far as Neptune from the Sun and that its orbit was potentially nearly circular,” said UBC professor Brett Gladman, who noticed the unusual nature of the object when determining its orbit, “but further observations were required.”

One to two years of observations of a Kuiper belt object are required before their orbits can be precisely measured. The first additional observations of Buffy came in October 2005 when Gladman and Phil Nicholson of Cornell University used the Hale 5-meter telescope to re-observe the object.

Measurement of Buffy’s new position proved that the orbit was not only extremely tilted, inclined (tilted) at 47 degrees to the plane of the planetary system (essentially tying the record for a Kuiper belt object) but confirmed that Buffy was unlike any other previously-known object because it was on a nearly circular orbit while at a very large distance.

More measurements of Buffy’s position on images from telescopes at Kitt Peak National Observatories in Arizona by team members Joel Parker (Southwest Research Institute), as well as JJ Kavelaars (National Research Council of Canada, Herzberg Institute of Astrophysics) and Wes Fraser (University of Victoria), through November 2005 refined the estimate for Buffy’s closest approach to the Sun. Additional observations, to further confirm the orbit, where then provided by the CFHT Legacy Survey project. Astronomers will need to wait until February 2006 to measure the fine details of the Buffy’s orbit.

The team have reported their find to the Minor Planet Center, the clearinghouse for astronomical measurements of new minor planets. “To find the first known object with a nearly circular orbit beyond 50 AU is indeed intriguing,” reacted Brian Marsden, director of the MPC.

Challenging Theories

Although it is neither the smallest, largest, nor most distant object discovered in this region, the new Kuiper belt object has a highly unusual orbit which challenges theories of the evolution of the Solar System.

Why is Buffy’s orbit considered so unusual? Only one other detected object, Sedna, remains further than 50 astronomical units (AUs) from the Sun throughout its entire orbit. However, Sedna is on a very elliptical orbit, swooping in to 76 AU before traveling back out beyond 900 AU. In contrast, Buffy spends all of its time in the narrow range between 52 and 62 AU from the Sun. Combined with the tilt in its orbit, this new object challenges current theories about the history of the early Solar System.

Astronomers have detected other Kuiper belt objects that spend most of their time beyond 50 AU. These are on very elliptical orbits, and almost all approach within 38 AU of the Sun. That close approach places those objects within the reach of the gravitational influence of Neptune. These objects are generally thought to have been scattered out to their present orbits by a gravitational slingshot with Neptune. This group of objects was thus called the “Scattered Disk”.

Prior to the discovery of Buffy, a few other Kuiper belt objects were discovered which spend much of their time beyond 50 AU like those in the “Scattered Disk”, yet did not approach within the gravitational reach of Neptune. This group has been named the “Extended Scattered Disk”. Two of its members are 1995 TL8 and 2000 YW134, which approach to 40 AU of the Sun but have fairly elliptical orbits that take them back out beyond 60 AU. Two more extreme examples of the “Extended Scattered Disk” are 2000 CR105, which approaches to 44 AU, and Sedna, which never comes closer to the Sun than 76 AU.

Due to their large eccentricities, these objects are likely to have been strongly perturbed by something, although it could not have been Neptune because they do not come close enough to be scattered by that planet’s gravitational force. As both Sedna and 2000 CR105 also travel beyond 500 AU from the sun, one theory is that after being scattered by Neptune, a passing star could have pulled their closest approaches away from the Sun.

Buffy is clearly a member of the “Extended Scattered Disk”. However, Buffy’s almost circular orbit makes it stand out from the other members. In addition, Buffy’s large orbital tilt is not so easily explained by the passing star idea. If a star could have affected Buffy so strongly, it should also have disrupted much of the main Kuiper belt as well. Since astronomers do not detect that strong disruption, a more complex theory is needed to explain Buffy’s orbit.

The elusive explanation may lie in side-effects from rearrangements of the Solar System early in its history. One possibility is that as Neptune’s orbit slowly expanded in the young Solar System, complex gravitational interactions could have caused some Kuiper belt orbits to circularize and tilt. While Buffy’s orbit could have been created this way, this theory would not seem to explain 2000 CR105 and Sedna. This new discovery is exciting because it causes us to rethink our understanding of how the Kuiper belt formed.

The Future

Over the last half decade, theories about the formation of our outer Solar System have been pushed to their limits: unusual Kuiper belt objects, like Buffy, which never come close to Neptune yet have high inclination must be explained.

Although theories that explain individual objects exist, reproducing the entire ensemble of known objects with one process poses a difficult challenge to current solar system models. Because the unusual objects, like Buffy, are very rare, astronomers are still scratching the surface of the dark corners of the Kuiper belt. Future large-scale surveys that systematically explore the Kuiper belt are the only way unlock the mysteries of what happened early in the history of our Solar System.

Original Source: Canada-France-Hawaii Telescope

The new star cluster found by GLIMPSE. Image credit: NASA Click to enlarge
Astronomers have at last found inner light! Only, they didn’t find it through the typical Earthly methods of meditation, exercise and therapy. Instead, the light was discovered inside our Milky Way galaxy after hours of deep self-reflection with NASA’s Spitzer Space Telescope.

The astronomers, who are members of the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) team, used Spitzer’s heat-seeking infrared eyes to gaze at the dust-drenched plane of our galaxy. When they did this, the galaxy’s obscuring clouds of gas and dust became transparent, revealing approximately 100 new star clusters, each containing tens to hundreds of stars.

According to lead investigator Emily Mercer, a graduate student at Boston University, Mass., the new clusters will tell astronomers a great deal about the structure of the Milky Way and star formation within the galaxy.

“These little guys were quite hard to find,” said Mercer. “The discovery required sophisticated computer sifting of GLIMPSE data and careful inspection of the Spitzer images.”

In the past, our galaxy wasn’t so quick to give up its stellar secrets. Because we sit inside its flat, spiral disk, most of the galaxy appears as a thick blurry band of light that stretches across the sky. Many of the stars in this galactic plane cannot be detected with visible-light or ultraviolet telescopes. That’s because the cool clouds of dust and gas that hover around the galaxy’s center and make up galactic spiral arms block their starlight from our view.

Two-thirds of the new star clusters were discovered through a computer method developed by Mercer and her advisor, Dr. Dan Clemens, also of Boston University. They used an algorithm to automatically sift through the GLIMPSE data for clusters. The rest were found using the traditional method of visually scrutinizing images for star clusters.

Mercer also found that there are nearly twice as many star clusters in the southern galactic plane, the portion of the galactic plane visible from the Earth’s southern hemisphere, as in the northern galactic plane. She suspects that this observation may help astronomers map the location of the Milky Way’s spiral arms.

“Emily has done a great job,” says Clemens. “Her computer method for finding clusters has proved to be the most successful automated effort to date.”

Both Clemens and Mercer are members of the multi-institutional GLIMPSE team, which is led by Dr. Edward Churchwell of the University of Wisconsin, Madison. The group was selected to survey the galactic plane with Spitzer’s infrared array camera in November 2000 as part of Spitzer’s Legacy program. So far, more than 30 million stars in the inner Milky Way have already been catalogued by GLIMPSE, and the team expects to identify more than 50 million stars by the end of the project.

“By making the galactic plane transparent, Spitzer opens a new door for astronomers to study the Milky Way,” says Churchwell. “Some of the most interesting science likely to come out of this project will be serendipitous discoveries, which will open up entirely new avenues of inquiry.”

Original Source: Spitzer Space Telescope

Dwarf galaxy I Zwicky 18. Image credit: NASA. Click to enlarge
Clues revealed by the recently sharpened view of the Hubble Space Telescope have allowed astronomers to map the location of invisible “dark matter” in unprecedented detail in two very young galaxy clusters.

A Johns Hopkins University-Space Telescope Science Institute team reports its findings in the December issue of Astrophysical Journal. (Other, less-detailed observations appeared in the January 2005 issue of that publication.)

The team’s results lend credence to the theory that the galaxies we can see form at the densest regions of “cosmic webs” of invisible dark matter, just as froth gathers on top of ocean waves, said study co-author Myungkook James Jee, assistant research scientist in the Henry A. Rowland Department of Physics and Astronomy in Johns Hopkins’ Krieger School of Arts and Sciences.

“Advances in computer technology now allow us to simulate the entire universe and to follow the coalescence of matter into stars, galaxies, clusters of galaxies and enormously long filaments of matter from the first hundred thousand years to the present,” Jee said. “However, it is very challenging to verify the simulation results observationally, because dark matter does not emit light.”

Jee said the team measured the subtle gravitational “lensing” apparent in Hubble images ? that is, the small distortions of galaxies’ shapes caused by gravity from unseen dark matter ? to produce its detailed dark matter maps. They conducted their observations in two clusters of galaxies that were forming when the universe was about half its present age.

“The images we took show clearly that the cluster galaxies are located at the densest regions of the dark matter haloes, which are rendered in purple in our images,” Jee said.

The work buttresses the theory that dark matter ? which constitutes 90 percent of matter in the universe ? and visible matter should coalesce at the same places because gravity pulls them together, Jee said. Concentrations of dark matter should attract visible matter, and as a result, assist in the formation of luminous stars, galaxies and galaxy clusters.

Dark matter presents one of the most puzzling problems in modern cosmology. Invisible, yet undoubtedly there ? scientists can measure its effects ? its exact characteristics remain elusive. Previous attempts to map dark matter in detail with ground-based telescopes were handicapped by turbulence in the Earth’s atmosphere, which blurred the resulting images.

“Observing through the atmosphere is like trying to see the details of a picture at the bottom of a swimming pool full of waves,” said Holland Ford, one of the paper’s co-authors and a professor of physics and astronomy at Johns Hopkins.

The Johns Hopkins-STScI team was able to overcome the atmospheric obstacle through the use of the space-based Hubble telescope. The installation of the Advanced Camera for Surveys in the Hubble three years ago was an additional boon, increasing the discovery efficiency of the previous HST by a factor of 10.

The team concentrated on two galaxy clusters (each containing more than 400 galaxies) in the southern sky.

“These images were actually intended mainly to study the galaxies in the clusters, and not the lensing of the background galaxies,” said co-author Richard White, a STScI astronomer who also is head of the Hubble data archive for STScI. “But the sharpness and sensitivity of the images made them ideal for this project. That’s the real beauty of Hubble images: they will be used for years for new scientific investigations.”

The result of the team’s analysis is a series of vividly detailed, computer-simulated images illustrating the dark matter’s location. According to Jee, these images provide researchers with an unprecedented opportunity to infer dark matter’s properties.

The clumped structure of dark matter around the cluster galaxies is consistent with the current belief that dark matter particles are “collision-less,” Jee said. Unlike normal matter particles, physicists believe, they do not collide and scatter like billiard balls but rather simply pass through each other.

“Collision-less particles do not bombard one another, the way two hydrogen atoms do. If dark matter particles were collisional, we would observe a much smoother distribution of dark matter, without any small-scale clumpy structures,” Jee said.

Ford said this study demonstrates that the ACS is uniquely advantageous for gravitational lensing studies and will, over time, substantially enhance understanding of the formation and evolution of the cosmic structure, as well as of dark matter.

“I am enormously gratified that the seven years of hard work by so many talented scientists and engineers to make the Advanced Camera for Surveys is providing all of humanity with deeper images and understandings of the origins of our marvelous universe,” said Ford, who is principal investigator for ACS and a leader of the science team.

The ACS science and engineering team is concentrated at the Johns Hopkins University and the Space Telescope Science Institute on the university’s Homewood campus in Baltimore. It also includes scientists from other major universities in the United States and Europe. ACS was developed by the team under NASA contract NAS5-32865 and this research was supported by NASA grant NAG5-7697.

Original Source: JHU News Release

James Webb Space Telescope (JWST). Image credit: NASA Click to enlarge
Carl Zeiss Optronics, in Oberkochen, Germany, and the Max Planck Institute for Astronomy in Heidelberg (MPIA), are developing the main fine mechanical optical technology for two instruments to be part of the James Webb Space Telescope (JWST). Over the next eight years, under administration of the European Space Agency and NASA in the USA, the JWST (with a mirror of 6.5 metres) will shape up to be the successor to the legendary HUBBLE Space Telescope. Carl Zeiss and the Max Planck Institute signed a contract on November 29 to co-operate in their work on the MIRI and NIRSpec instrumentation of the JWST.

The JAMES WEBB Space Telescope is going to replace the Hubble Space Telescope in the next few decades as the most important tool for astronomical observation. The most important scientific goal of the mission is to discover the “first light” of the early universe – the formation of the first stars out of the slowly cooling Big Bang. The light from these first stars and galaxies has shifted into the infrared spectrum because its wavelength has stretched out some twenty times, as the universe has been expanding. The infrared (warm) radiation of the telescope and its instruments could disturb these weak cosmic signals. In order to prevent this, the telescope has to be essentially deep frozen.

For this reason, the JWST will be stationed at the “Lagrangian point L2”, 1.5 million kilometres outside the Earth?s orbit. The gravitational forces of the Sun and the Earth balance each other at L2, so the JWST can maintain a position synchronous with the sun and the Earth, permanently on the far side of the Earth from the sun. Here, the telescope and its instruments will cool down to -230 degrees Celsius. The extremely high sensitivity and resolution of the huge telescope will lead to entirely new insights about the formation of stars and planets in the Milky Way Galaxy. These investigations are only possible in the infrared spectrum. Unlike visible light, infrared light can pass through the thick gas and dust clouds, in which planets and stars form, without being appreciably weakened.

The telescope and its instruments make immense demands. They will be subject to initial stress at an acceleration much higher than the Earth?s, and then cooled down to a temperature almost reaching absolute zero (-273 degrees Celsius). After the telescope is put into operation at its final location, its astronomical instruments will be adjusted to a high level of accuracy and have to be kept there – roughly equivalent to targeting the point of a needle from a one-kilometre distance.

The Space Telescope has three instruments on board for data recording: MIRI, NIRSpec, and NIRCam. MIRI and NIRSpec are being developed and built in Europe. Carl Zeiss and the MPIA will be making a major contribution, as the only European representatives, to both instruments.

For the MIRI and NIRSpec, Carl Zeiss will deliver the filter and grating changing mechanisms which allow the instruments to be precisely configured for various types of observation. The MPIA will also be participating in their development and testing. Futhermore, Carl Zeiss will be delivering two filter and grating mechanisms for the NIRSpec instrument to EADS Astrium. The contract that Carl Zeiss and the MPIA signed specifies that they will co-operate in producing both instruments.

The MIRI and NIRSpec mechanisms are similar, related projects. Their development and testing will take place in the next two-and-a-half years; after that, Carl Zeiss and the MIPA will install them. It is planned that in the year 2013, a European Ariane 5 rocket will bring the JWST to the Lagrangian point L2. The entire operation with MIRI and NIRSpec is being organised by the European Space Agency, the German Aerospace Center, and the Max Planck Society.

Carl Zeiss and the Max Planck Institute for Astronomy have already worked together successfully on challenging projects developing space instruments. One example is ISOPHOT, a major contribution to the success of the European Infrared Space Observatory, ISO. Recently, they began co-operating on the PACS instrument of the HERSCHEL European space observatory, set to start operations in 2008.

Carl Zeiss and the MPIA have won a great deal of trust from international partners through their co-operation. Now, the two organisations are setting foot on terra nova: astronomers from Heidelberg hope to observe the borders of the cosmic “dark ages”, before stars started to form. Together, they are looking forward to developing optomechanical systems of unprecedented quality. They will guarantee both success for the astronomical “flagship” mission JWST, and a competitive edge for all kinds of imaginable future applications.

Original Source: Max Planck Society

Newly found galaxy collisions in the nearby universe. Image credit: NOAO. Click to enlarge
More than half of the largest galaxies in the nearby universe have collided and merged with another galaxy in the past two billion years, according to a new study using hundreds of images from two of the deepest sky surveys ever conducted.

The idea of large galaxies being assembled primarily by mergers rather than evolving by themselves in isolation has grown to dominate cosmological thinking. However, a troubling inconsistency within this general theory has been that the most massive galaxies appear to be the oldest, leaving minimal time since the Big Bang for the mergers to have occurred.

?Our study found these common massive galaxies do form by mergers. It is just that the mergers happen quickly, and the features that reveal the mergers are very faint and therefore difficult to detect,? says Pieter van Dokkum of Yale University, lead author of the paper in the December 2005 issue of the Astronomical Journal.

The paper uses two recent deep surveys done with the National Science Foundation?s 4-meter telescopes at Kitt Peak National Observatory and Cerro Tololo Inter-American Observatory, known as the NOAO Deep Wide-Field Survey and the Multiwavelength Survey by Yale/Chile. Together, these surveys covered an area of the sky 50 times larger than the size of the full Moon.

?We needed data that are very deep over a very wide area to provide statistically meaningful evidence,? van Dokkum explains. ?As happens so often in science, fresh observations helped inform new conclusions.?

Van Dokkum used images from the two surveys to look for telltale tidal features around 126 nearby red galaxies, a color selection biased to select the most massive galaxies in the local universe. These faint tidal features turn out to be quite common, with 53 percent of the galaxies showing tails, broad fans of stars trailing behind them or other obvious asymmetries.

?This implies that there is a galaxy that has endured a major collision and subsequent merger event for every single other ?normal? undisturbed field galaxy,? van Dokkum notes. ?Remarkably, the collisions that precede the mergers are still ongoing in many cases. This allows us to study galaxies before, during, and after the collisions.?

Though there are not many direct star-to-star encounters in this merger process, such galaxy collisions can have profound effects on star formation rates and the shape of the resulting galaxy.

These mergers do not resemble the spectacular mergers of blue spiral galaxies that are featured in several popular Hubble Space Telescope images. But these red galaxy mergers appear to be much more common. Their ubiquity represents a direct confirmation of predictions by the most common models for the formation of large-scale structure in the Universe, with the added benefit of helping solve the apparent-age problem.

?In the past, people equated stellar age with the age of the galaxy,? van Dokkum explains. ?We have found that, though their stars are generally old, the galaxies that result from these mergers are relatively young.?

It is not yet understood why the merging process does not lead to enhanced star formation in the colliding galaxies. It may be that massive black holes in the centers of the galaxies provide the energy to heat or expel the gas that needs to be able to cool in order to form new stars. Ongoing detailed study of the newly found mergers will provide better insight into the roles that black holes play in the formation and evolution of galaxies.

A series of images of different galaxies in this study that, taken together, represent a time sequence of a typical red galaxy merger, is available here. More information, including an animation of the mergers, is available from Yale University.

Based in Tucson, AZ, the National Optical Astronomy Observatory (NOAO) consists of Kitt Peak National Observatory near Tucson, AZ, Cerro Tololo Inter-American Observatory near La Serena, Chile, and the NOAO Gemini Science Center. NOAO is operated by the Association of Universities for Research in Astronomy (AURA) Inc., under a cooperative agreement with the National Science Foundation.

Original Source: NOAO News Release

Perseus Cluster. Image credit: NASA Click to enlarge
An accumulation of 270 hours of Chandra observations of the central regions of the Perseus galaxy cluster reveals evidence of the turmoil that has wracked the cluster for hundreds of millions of years. One of the most massive objects in the universe, the cluster contains thousands of galaxies immersed in a vast cloud of multimillion degree gas with the mass equivalent of trillions of suns.

Enormous bright loops, ripples, and jet-like streaks are apparent in the image. The dark blue filaments in the center are likely due to a galaxy that has been torn apart and is falling into NGC 1275, a.k.a. Perseus A, the giant galaxy that lies at the center of the cluster.

Special processing designed to bring out low and high pressure regions in the hot gas has uncovered huge low pressure regions (shown in purple in the accompanying image overlay, and outlined with the white contour). These low pressure regions appear as expanding plumes that extend outward 300,000 light years from the supermassive black hole in NGC 1275.

The hot gas pressure is assumed to be low in the plumes because unseen bubbles of high-energy particles have displaced the gas. The plumes are due to explosive venting from the vicinity of the supermassive black hole.

The venting produces sound waves which heat the gas throughout the inner regions of the cluster and prevent the gas from cooling and making stars at a high rate. This process has slowed the growth of one of the largest galaxies in the Universe. It provides a dramatic example of how a relatively tiny, but massive, black hole at the center of a galaxy can control the heating and cooling behavior of gas far beyond the confines of the galaxy.

Original Source: Chandra X-ray Observatory

Spitzer captured galaxy interaction in this image of NGC 5291. Image credit: NASA/JPL Click to enlarge
When galaxies collide (as our galaxy, the Milky Way, eventually will with the nearby Andromeda galaxy), what happens to matter that gets spun off in the collision’s wake?

With help from the Spitzer Space Telescope’s infrared spectrograph (IRS) and infrared array camera (IRAC), Cornell astronomers are beginning to piece together an answer to that question. Specifically, they are gaining new insight into how some ubiquitous dwarf galaxies form, interact, and arrange themselves into new systems.

Dwarf galaxies, with stellar masses around 0.1 percent that of the Milky Way, are far more common than their more massive spiral or starburst counterparts. Some may be primordial remnants of the Big Bang; but others — called tidal dwarfs — formed later as a result of gravitational interactions after galactic collisions.

To understand which dwarf galaxies are tidal in origin and how those galaxies differ from primordial dwarf galaxies, Cornell researcher Sarah Higdon and her colleagues studied a galactic merger called NGC 5291, which is 200 million light-years from Earth and roughly four times the size of the Milky Way. At the system’s center are two colliding galaxies; behind them trail a string of much smaller dwarfs.

The researchers focused on the system because they knew from earlier analyses that the trailing dwarfs were formed tidally as a result of the central collision. Until recently, though, they hadn’t been able to look closely enough at the tidal dwarfs to catalog their properties for comparison with those of similar galaxies.

Spitzer’s sharp eye has changed that. Using it to look for compounds that indicate star-forming activity, Higdon’s team found that when it comes to fostering new star formation, the colliding galaxies at the system’s center are fairly dull. The exciting place to be, they found, is in the tidal dwarfs at the system’s edges.

Specifically, the team found that the tidal dwarfs show strong emission from organic compounds, found in crude petroleum, burnt toast, and (more relevantly) stellar nurseries, known as PAHs — for polycyclic aromatic hydrocarbons. And for the first time, the researchers detected warm molecular hydrogen — another indicator of star formation, and one that has never before been directly measured in tidal dwarf galaxies.

“We know molecular hydrogen is out there. Now we have the sensitivity to measure it,” Higdon said.

Higdon and Cornell colleagues James Higdon and Jason Marshall describe the features of the NGC 5291 system in a forthcoming issue of the Astrophysical Journal.

“Nearly everything at some stage interacts,” Higdon said. “This is a part of the puzzle. But we’ve only just started looking. We don’t know how long lived [the tidal dwarf galaxies] will be, or how many formed like this.”

Next, the team plans to search for new tidal dwarf galaxies using the Spitzer surveys and compare their properties to the newly cataloged galaxies in NGC 5291.

Original Source:Spitzer Space Telescope

An artist’s concept of the miniature solar system (top) compared to a known solar sytem. Image credit: NASA/JPL Click to enlarge
Scientists using a combination of ground-based and orbiting telescopes have discovered a failed star, less than one-hundredth the mass of the Sun, possibly in the process of forming a solar system. It is the smallest known star-like object to harbor what appears to be a planet-forming disk of rocky and gaseous debris, which one day could evolve into tiny planets and create a solar system in miniature. A team led by Kevin Luhman, assistant professor of astronomy and astrophysics at Penn State University, will discuss this finding in the 10 December 2005 issue of Astrophysical Journal Letters.

The discovered object, called a brown dwarf, is described as a “failed star” because it is not massive enough to sustain nuclear fusion like our Sun. The object is only eight times more massive than Jupiter. The fact that a brown dwarf this small could be in the midst of creating a solar system challenges the very definition of star, planet, moon and solar system.

“Our goal is to determine the smallest ‘sun’ with evidence for planet formation,” said Luhman. “Here we have a sun that is so small it is the size of a planet. The question then becomes, what do we call any little bodies that might be born from this disk: planets or moons?” If this protoplanetary disk does form into planets, the whole system would be a miniaturized version of our solar system — with the central “sun”, the planets, and their orbits all roughly 100 times smaller.

Luhman’s team detected the brown dwarf, called Cha 110913-773444, with NASA’s Spitzer Space Telescope, the Hubble Space Telescope, and two telescopes in the Chilean Andes, the Blanco telescope of the Cerro Tololo Inter-American Observatory and the Gemini South telescope, both international collaborations funded in part by the National Science Foundation. Luhman led a similar observation last year that uncovered a 15-Jupiter-mass brown dwarf with a protoplanetary disk.

Brown dwarfs are born like stars, condensing out of thick clouds of gas and dust. But unlike stars, brown dwarfs do not have enough mass — and therefore do not have enough pressure and temperature in their cores — to sustain nuclear fusion. They remain relatively cool objects visible in lower-energy wavelengths such as infrared. A protoplanetary disk is a flat disk made up of dust and gas that is thought to clump together to form planets. Our solar system was formed from such a disk about five billion years ago. NASA’s Spitzer telescope has found dozens of disk-sporting brown dwarfs so far, several of which show the initial stages of the planet-building process. The material in these disks is beginning to stick together into what may be the “seeds” of planets.

With Spitzer, the science team spotted Cha 110913-773444 about 500 light years away in the constellation Chamaeleon. This brown dwarf is young, only about 2 million years old. The team studied properties of the brown dwarf with infrared instruments on the other observatories. The cool, dim protoplanetary disk was detectable only with Spitzer’s Infrared Array Camera, which was developed at the Harvard-Smithsonian Center for Astrophysics.

In the past decade, advances in astronomy have led to the detection of small brown dwarfs and massive extra-solar planets, which has brought about a quandary in taxonomy. “There are two camps when it comes to defining planets versus brown dwarfs,” said team member Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics. “Some go by size, and others go by how the object formed. For instance, this new object would be called a planet based on its size, but a brown dwarf based on how it formed.” If one were to call the object a planet, Fazio said, then Spitzer may have discovered its first “moon-forming” disk. No matter what the final label may be, one thing is clear: The universe produces some strange solar systems very different from our own. Other members of the discovery team are Lucia Adame and Paola D’Alessio of the National Autonomous University of Mexico and Nuria Calvet and Lee Hartmann of the University of Michigan.

The 4-meter Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile 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. The nearby 8-meter Gemini South telescope also is managed by AURA. NASA’s Goddard Space Flight Center, Greenbelt, Md., built Spitzer’s Infrared Array Camera. The instrument’s principal investigator is Giovanni Fazio. The Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer mission for NASA. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena.

Original Source:Penn State University

SOHO is celebrating ten years in space on 2nd December. Image credit: SOHO Click to enlarge
The world’s flagship solar probe, the Solar and Heliospheric Observatory (SOHO), is celebrating ten years in space on 2nd December. Scientists are gathering at CCLRC Rutherford Appleton Laboratory on the anniversary of the launch to celebrate the achievements of SOHO which has revolutionised our understanding of our star, the Sun, and its impacts on the Earth.

The 12 instruments on board SOHO probe the Sun’s every detail. One, the Coronal Diagnostic Spectrometer (CDS), is led from the UK, another was partly built in the UK, and UK scientists are involved in the operations and research of all instruments. SOHO’s instruments are monitoring the complex, violent solar atmosphere, the charged gases that the Sun expels into space and examining the solar interior.

“Never before have we had such a detailed view of a star. All life on Earth is dependent on the Sun’s energy, and when the Sun ejects clouds into space which engulf the Earth it can have severe consequences for satellite systems, navigation, communication and power distribution systems. We need to understand how the Sun works and how to predict how its activity impacts on the Earth”, said Professor Richard Harrison, from the CDS team.

“SOHO has provided us with a comprehensive, detailed examination of a star over an extended period, and has operated superbly during that time. The advances generated by this mission are incredible”, commented Professor Len Culhane of the UCL Mullard Space Science Laboratory.

The mission has revealed the true nature of the Sun’s violent atmosphere as it flings clouds into space and as huge magnetic loops tie themselves in knots to generate solar flare explosions. Scientists have discovered that the solar atmosphere is riddled with Earth-sized explosions and occasional tornadoes and the mission has also revealed how the interior of the Sun rotates. SOHO has even discovered over 1000 comets as they pass close to the Sun – a world record. Sophisticated observations have allowed scientists to monitor the far-side of the Sun and instruments have enabled weather maps of the Sun’s atmosphere – probing temperatures, densities, solar wind speeds and even what the Sun is made of, from a distance of 150 million km.

Professor Keith Mason, Chief Executive Officer of the Particle Physics and Astronomy Research Council, the main funder of the UK involvement in the mission, said “SOHO continues to be a stunning success and over its extended lifetime has provided the scientific community and the public with a wealth of data about the Sun. Its success is testimony to the expertise of the scientists and industrialists, in the US and Europe, including the UK, that have worked on its design and operation.”

Original Source: PPARC News Release