Category: Astronomy

A scientific researcher from the University of Southampton is leading an international team that has discovered the fastest-yet-seen accreting X-ray pulsar.

Dr Simon Shaw of the University’s School of Physics and Astronomy is UK representative to the INTEGRAL Science Data Centre near Geneva, Switzerland (ISDC is part of the Geneva University Observatory). There he co-ordinates a team that receives and monitors data from INTEGRAL, a European Space Agency (ESA) satellite designed to detect X and gamma-ray radiation from space.

A previously unknown, bright source of X-rays was first spotted in INTEGRAL data at the ISDC in December 2004. It was named ‘IGR J00291+5934’ and its discovery was announced to astronomers around the world shortly after. Follow-up observations made in the next few weeks, during which time the source slowly faded, showed that IGR J00291+5934 was the fastest known accreting binary X-ray pulsar.

A binary system is formed of two stars orbiting each other. If one of these stars undergoes a super-nova explosion it may collapse to form a ‘neutron star’ – an object composed entirely of neutrons. Neutron stars are incredibly dense, weighing slightly more than our Sun but compacted into a sphere with a size similar to Southampton; a spoonful of neutron star material would weigh about the same as the total weight of every person on Earth.

The strong gravitational field around the neutron star causes material to be pulled off the orbiting star, which spirals onto the neutron star, in a process known as ‘accretion’. The magnetic field of the neutron star causes the accreted matter to be channelled onto small ‘hot-spots’ on the neutron star surface where they radiate X and gamma-rays. A ‘pulsar’ is observed when regular flashes, or pulsations, are seen from the hot-spots as the neutron star spins; this can be thought of in exactly the same way as the periodic flashes seen from the rotating beam of light in a lighthouse.

However, this particular lighthouse is rotating approximately 600 times a second, equivalent to the surface of the pulsar moving at 30,000 km/second (10 per cent of the speed of light) – the fastest of its kind yet observed. The orbital period of the system is also impressive; the two stars orbit each other every 2.5 hours, but are separated by roughly the same distance as the Moon and the Earth. On the pulsar in IGR J00291+5934 a day lasts 0.0016 seconds and a year is 147 minutes!

‘The rate at which this object is spinning is truly amazing,’ commented Dr Shaw. ‘It gives us an opportunity to study the effects of such extreme forces of this rotation on the exotic material found in neutron stars, which does not exist on Earth. It is possible that there are more of these objects waiting to be discovered, possibly even faster ones; if they are there, INTEGRAL will find them.’

Dr Shaw is the lead author of a paper on the object accepted for publication by the journal Astronomy and Astrophysics. Pre-print available from http://arxiv.org/abs/astro-ph/0501507

Original Source:
University of Southampton News Release

Image credit: Subaru Telescope
Galaxies often congregate to form clusters of galaxies. At the present day, clusters have tens and hundreds of member galaxies and are the largest astronomical objects in the Universe. Knowing how they formed is a key to understanding the past and future of the Universe.

To study how the Universe has changed over large scales in space and time, it is essential to observe deeply a wide area of the sky. A large number of researchers are now studying the Subaru-XMM Deep Survey Field (SXDS), an approximately one square degree area of the sky in the direction of the constellation Cetus, the Whale, at many wavelengths using several telescopes. (Note 1)

To understand the origin of galaxy clusters, Masami Ouchi, currently at the Space Telescope Science Institute, decided to study how galaxies approximately 12.7 billion light years away (a red shift of 5.7) were distributed in the SXDS. By using the color of galaxies as a guide to their distance, Ouchi and his collaborators found 515 galaxies in a volume 500 million light years in height and width and 100 million light years in depth in images from Subaru’s prime focus camera (Suprime-Cam). (Note 2)

Figure 1 shows a density map of the galaxies in this volume as seen on the sky. This map represents the physical structures in the Universe at the farthest distances and the earliest times that astronomers have been able to observe to date. The yellow regions are where there are the highest concentration of galaxies. (Note 3)

In the bottom portion of this map, the researchers found a concentration of galaxies that could not be explained by chance. By obtaining accurate distance estimates to these galaxies using Subaru’s Faint Object Camera and Spectrograph (FOCAS), the researchers confirmed that there were six galaxies concentrated in a small volume only 3 million light years in diameter, forming a galaxy cluster. Figure 2 identifies the six member galaxies of the cluster.

The cluster has several properties that reveal its young age. It is one hundred times less massive than present day galaxy clusters and has significantly fewer members. Moreover, its member galaxies are producing stars at one hundred times the rate of galaxies outside the cluster.

The infant galaxy cluster existed at a time when the Universe was only one billion years old. The youngest portraits of galaxy clusters that astronomers previously had were from the Universe at an age of one and a half billion years. As any parent would attest, young children change rapidly. The portrait of a galaxy cluster at a younger age fills a significant gap in our knowledge of the early history of the Universe when stars, galaxies, and clusters were first forming.

“The fact that a cluster is already forming so soon after the Big Bang puts strong constraints on the fundamental structure of the Universe”, says Ouchi. The prevailing theory of cosmology postulates that smaller mass structures form first and then grow into more massive structures. “Our results seem to contradict the prevailing wisdom, but the real challenge is in understanding how well the distribution of visible matter such as galaxies correlates with the distribution of mass in general. As we continue to fill in the gaps in the early history of clusters, we should be able to resolve such ambiguities”, he says.

These results were published in the February 10, 2005, edition of the Astrophysical Journal (ApJ 620, L1-L4) and will be presented at the meeting “The Future of cosmology with clusters of Galaxies” beginning on February 26, 2005, in Waikoloa, Hawaii.

Note 1: For more information on the Subaru/XMM-Newton Deep Survey field, see the June 2004 press release on the SXDS public data release and the SXDS home page.

Note 2 : For more information on how astronomers use colors to look for distant galaxies see the March 2003 press release on the discovery of one the most distant galaxies currently known.

Note 3: Maps of the cosmic microwave background such as those from COBE or WMAP show the unevenness in the heat left over from the Big Bang that eventually led to the physical structures revealed in the new map.

Original Source: Subaru Telescope News Release

Image credit: Astro.Geekjoy
Contrary to what might be expected, it’s actually quite easy to select a telescope, followed by another telescope, followed by another. In fact many amateurs have been known to select dozens.

But here’s the real challenge: Try selecting your last telescope first. To do so comes down to just two things: Views and usability. If a scope doesn’t deliver the views, you won’t use it. And if it isn’t usable, you won’t bother with the views. It’s as simple – and as difficult – as that.

For instance, a very compact telescope on a lightweight mount can easily be transported from house to yard and back again. If it fails to show you anything you want to see however, the instrument will quickly become a “conversation piece” – like that brass telescope in the office at work…

Meanwhile a large telescope may require complex setup and dissassembly – not to mention the brute force needed to carry around as parts. Such a scope – despite bright views – may be rendered useless for lack of spontaneous access. But other reasons can also discourage the observer – such as difficulty orienting a large instrument toward certain regions of the sky or having to stand on a pedestal or ladder to engage the eyepiece. Great views – once you bother to set it all up…

The author has used scopes at both these extremes. One telescope of fine optics gave sharp views but – due to extremely small aperture – was unable to show anything worth viewing. (Despite the fact that the entire assembly – scope AND mount – could easily be carried about in one hand.) Meanwhile the author has also watched fellow observers take nearly an hour setting up a large truss-framed Newtonian telescope on a relatively simple (dobsonian) mount. (All the while the sky darkened and stars drifted a full fifteen degrees across the heavens.) Of course once this particular scope was assembled, the author was more than willing to peek through the eyepiece. So setup time and portability are important factors the thoughtful amateur may want to consider when evaluating telescope types and models for purchase and personal use.

Another important issue to consider is observing position. After long hours on the feet you may not prefer to stand equally long hours observing. Additionally, even slight shifts in balance can complicate seeing fine planetary detail or resolving ultra-close double stars. Of course, measures can be taken to offset ergonomic problems such as these, comfortable observing stands and chairs are available from various suppliers. So if you find yourself spending less time at the eyepiece than you might pay some attention to your body and seek out a workable after-market solution.

But ultimately the telescope you want follows from the type celestial studies you prefer to view. And that, of course, has a lot to do with the kind of conditions you observe through. (Ranging from dark rural skies through well-lit city sidewalks.) But it also has to do with the conditions you observe from. (Inside you, the stuff of your own head – and heart…)

The faintest studies visible in amateur telescopes are of a class known as quasars. These objects are extremely remote and – despite their incredible intrinsic luminosity – are very faint. Like most quasars, the brightest – 3C273 varies in brightness but at peak output (when its supermassive black hole core is about to swallow some star or another) it appears as a faint star of the 13th magnitude. To make a study of the dozen or so quasars accessible through amateur telescopes requires all the aperture possible. (Scopes to thirty inches in aperture are available from manufacturers.) An interest in quasars would place you on the very edge of what is visually possible in amateur astronomy.

In contrast to quasars, the brightest celestial study is the Sun. Due to its brilliance, it takes but a few inches of aperture to get decent views of spots, faculae, granularities, and other fine features. (The Sun is so intense that direct inspection without a solar filter will permanently damage the retina!!!) Solar observing is best pursued with small scopes due to the reality of daylight sky conditions. As the Sun heats the atmosphere, super-fine detail is lost. Because of this, three inch instruments deliver all detail possible (except when observing at high elevations). Solar observing can lead to the purchase of some very expensive accessories. (Super narrow band hydrogen alpha filters can reveal prominences even as they leap off Sol’s limb.) Conceivably you could spend tens of thousands of US dollars putting together the high-precision optics needed to mask the Sun and view the corona as well! But in general – due to the low cost of solar rejection filters and small apertures involved – beginning solar observation is an inexpensive alternative for those astronomers who prefer sleep to late night skies.

Quasars and solar observation mark the two extremes of aperture in scope selection. We might call this the “light-gathering axis”. This is the axis most people think of when considering a scope. But there are other extremes to consider as well…

Very slow telescopes (those with focal lengths greater than twelve times greater than aperture-F12+) are limited in terms of how much of the sky they can show in a single field of view. To specialize in observing extended star fields (M24 in Sagittarius for instance) or nebulosity (the North America Nebula) three plus degree fields are desirable. For this reason small scopes of low – but quite usable magnification (20-30x) – with fine flat fields – make excellent choices. Such scopes are pretty much limited to fast achromatic or apochromatic refractors, or Maksutov-Newtonian models of five inches or less aperture. (Although fast newtonian models are available, such scopes often show pronounced coma at wide angles. In general, scopes that include light-handling refractory collector elements (refractors, Maksutovs and Schmidt’s) give superior off-axis image quality to all but the slowest pure reflector models.

Meanwhile some very fast scopes (F7-) can lack the kind of optical quality needed to specialize in lunar-planetary-double star observing. In such cases, scopes of greater focal ratios (F10+) are preferred. However even these slower scopes require well-corrected optics. Because of high power use, lunar-planetary telescopes ride best on stable mounts able to track against the Earth’s rotation. Such scopes also need enough aperture (four inches or greater) to resolve fine detail or distinguish close stars – especially those of widely dissimilar magnitudes. Outfitting scopes of this type is often quite expensive (several to many thousands of US dollars). But despite the cost, these instruments have great appeal to a very discriminating subset of amateurs – “optophiles” – those who prize sharp, high contrast views – even though appreciably “dimmer” compared to much larger and often far-less expensive instruments.

So with this we’ve explored the limits of the “image-scale” axis. At one extreme are scopes that deliver large flat fields ignoring fine structure, and at the other those with small fields of view providing exceedingly fine gradations of low-contrast detail. On one hand context is king and on the other subtlety is found in the details.

Most observers find that their interests lie between the extremes. An observer may want to take in as much of a faint extended study as possible, while also boosting magnification to glean fine details as well. Such observers are interested in views that include the entire Great Nebula in Orion, while also being able to distinctly reveal gradations visible in Saturn’s ring system. The reality is that such scopes are not likely to take in the entire Cygnus Loop as a single field of view but they should resolve numerous components in the Great Hercules Cluster. For intermediate observations of this type, magnifications ranging from 50 to 200x are needed – a range that doesn’t necessarily require a tracking mount but can keep you busy without one. Meanwhile enough light must be gathered to reveal faint structure.

What’s the best scope¹ for you?

Perhaps its the one that gets you out week after week exploring the Moon, planets, doubles, clusters, nebulae, or galaxies until you have no choice but to get another – along with the observatory to house it in!

¹ The author has found that the Greek aphorism “Know Thyself” is at root of most matters of choice, taste, and aspiration. Selecting an appropriate instrument is a voyage of self-discovery. Enjoy the journey!

About The Author:
Inspired by the early 1900’s masterpiece: “The Sky Through Three, Four, and Five Inch Telescopes”, Jeff Barbour got a start in astronomy and space science at the age of seven. Currently Jeff devotes much of his time observing the heavens and maintaining the website Astro.Geekjoy.

A new theory of how planets form finds havens of stability amid violent turbulence in the swirling gas that surrounds a young star. These protected areas are where planets can begin to form without being destroyed. The theory will be published in the February issue of the journal Icarus.

“This is another way to get a planet started. It marries the two main theories of planet formation,” said Richard Durisen, professor of astronomy and chair of that department at Indiana University Bloomington. Durisen is a leader in the use of computers to model planet formation.

Watching his simulations run on a computer monitor, it’s easy to imagine looking down from a vantage point in interstellar space and watching the process actually happen.

A green disk of gas swirls around a central star. Eventually, spiral arms of yellow begin to appear within the disk, indicating regions where the gas is becoming denser. Then a few blobs of red appear, at first just hints but then gradually more stable. These red regions are even denser, showing where masses of gas are accumulating that might later become planets.

The turbulent gases and swirling disks are mathematical constructions using hydrodynamics and computer graphics. The computer monitor displays the results of the scientists’ calculations as colorful animations.

“These are the disks of gas and dust that astronomers see around most young stars, from which planets form,” Durisen explained. “They’re like a giant whirlpool swirling around the star in orbit. Our own solar system formed out of such a disk.”

Scientists now know of more than 130 planets around other stars, and almost all of them are at least as massive as Jupiter. “Gas giant planets are more common than we could have guessed even 10 years ago,” he said. “Nature is pretty good at making these planets.”

The key to understanding how planets are made is a phenomenon called gravitational instabilities, according to Durisen. Scientists have long thought that if gas disks around stars are massive enough and cold enough, these instabilities happen, allowing the disk’s gravity to overwhelm gas pressure and cause parts of the disk to pull together and form dense clumps, which could become planets.

However, a gravitationally unstable disk is a violent environment. Interactions with other disk material and other clumps can throw a potential planet into the central star or tear it apart completely. If planets are to form in an unstable disk, they need a more protected environment, and Durisen thinks he has found one.

As his simulations run, rings of gas form in the disk at an edge of an unstable region and grow more dense. If solid particles accumulating in a ring quickly migrate to the middle of the ring, the core of a planet could form much faster.

The time factor is important. A major challenge that Durisen and other theorists face is a recent discovery by astronomers that giant gas planets such as Jupiter form fairly quickly by astronomical standards. They have to — otherwise the gas they need will be gone.

“Astronomers now know that massive disks of gas around young stars tend to go away over a period of a few million years,” Durisen said. “So that’s the chance to make gas-rich planets. Jupiter and Saturn and the planets that are common around other stars are all gas giants, and those planets have to be made during this few-million-year window when there is still a substantial amount of gas disk around.”

This need for speed causes problems for any theory with a leisurely approach to forming planets, such as the core accretion theory that was the standard model until recently.

“In the core accretion theory, the formation of gas giant planets gets started by a process similar to the way planets such as Earth accumulate,” Durisen explained. “Solid objects hit each other and stick together and grow in size. If a solid object grows to be about 10 times the mass of Earth, and there’s also gas around, it becomes massive enough to grab onto a lot of the gas by gravity. Once that happens, you get rapid growth of a gas giant planet.”

The trouble is, it takes a long time to form a solid core that way — anywhere from about 10 million to 100 million years. The theory may work for Jupiter and Saturn, but not for dozens of planets around other stars. Many of these other planets have several times the mass of Jupiter, and it’s very hard to make such enormous planets by core accretion.

The theory that gravitational instabilities by themselves can form gas giant planets was first proposed more than 50 years ago. It’s recently been revived because of problems with the core accretion theory. The idea that vast masses of gas suddenly collapse by gravity to form a dense object, perhaps in just a few orbits, certainly fits the available time frame, but it has some problems of its own.

According to the gravitational instability theory, spiral arms form in a gas disk and then break up into clumps that are in different orbits. These clumps survive and grow larger until planets form around them. Durisen sees these clumps in his simulations — but they don’t last long.

“The clumps fly around and shear out and re-form and are destroyed over and over again,” he said. “If the gravitational instabilities are strong enough, a spiral arm will break into clumps. The question is, what happens to them?”

Co-authors of the paper are IU doctoral student Kai Cai and two of Durisen’s former students: Annie C. Mejia, postdoctoral fellow in the Department of Astronomy, University of Washington; and Megan K. Pickett, associate professor of physics and astronomy, Purdue University Calumet.

Original Source: Indiana University News Release

Cosmic gamma-ray bursts produce more energy in the blink of an eye, than the Sun will release in its entire lifetime. These short-lived explosions appear to be the death throes of massive stars, and, many scientists believe, mark the birth of black holes. Testing these ideas has been difficult, however, because the bursts fade so quickly and rapid action is required. Now a team of Carnegie and Caltech astronomers, led by Carnegie-Princeton and Hubble fellow Edo Berger, has made crucial strides toward answering these cosmic quandaries. The team was able to discover and study burst afterglows thanks to the exquisite performance of NASA’s new Swift satellite and rapid follow-up with telescopes in both the southern and northern hemispheres.

“I’m thrilled,” said Berger. “We’ve shown that we can chase the Swift bursts at a moment’s notice, even right before Christmas! This is a great sign of exciting advances down the road.” The discoveries herald a new era in the study of gamma-ray bursts, hundreds of which are expected to be discovered and scrutinized in the next several years.

The Swift satellite detected the first of the four bursts on December 23, 2004, in the constellation Puppis, and Carnegie astronomers used telescopes at the Las Campanas Observatory in Chile to pinpoint the visual afterglow within several hours. This was the first burst detected solely by the new Swift satellite to be pinpointed with sufficient accuracy to study the remains. The next three bursts came in quick succession between January 17 and 26 and were immediately pinpointed by a team of Carnegie and Caltech astronomers using the Palomar Mountain 200-inch Hale telescope in California and the Keck Observatory 10-meter telescopes in Hawaii.

“The Las Campanas telescopes are ideal for their flexibility to follow up targets like gamma-ray bursts, which quickly fade out of view,” said Carnegie Observatories director Wendy Freedman. “This is a wonderful example of science that comes from the synergy between telescopes on the ground and in space, and between public and private observatories.”

Because Swift allows a response to new gamma-ray bursts within minutes, astronomers hope to use the intense light from gamma-ray bursts as cosmic “flashlights.” They plan to use the bright visual afterglows to trace the formation of the first galaxies, only a few hundred million years after the Big Bang, and the composition of the gas that permeates the universe. “This is much like using a flashlight to study the contents of a dark room,” said Berger. “But because the flashlight is on for only a few hours, we have to act quickly.”

“Swift’s rapid response is opening a new window on the universe. I can’t wait to see what we catch,” remarked Neil Gehrels of Goddard Space Flight Center, principal investigator for Swift.

Swift, launched on November 20, 2004, is the most sensitive gamma-ray burst satellite to date, and the first to have X-ray and optical telescopes on-board, allowing it to relay very accurate and rapid positions to astronomers on the ground. The satellite is a collaboration between NASA’s Goddard Space Flight Center, Penn State University, Leicester University and the Mullard Space Science Laboratory (both in England), and the Osservatorio Astronomico di Brera in Italy.

In the next few years the Swift satellite is expected to find several hundred gamma-ray bursts. Follow-up observations on-board Swift and using telescopes on the ground should move us a few steps closer to answering some of the most fundamental puzzles in astronomy, such as the birth of black holes, the first stars, and the first galaxies.

The team that identified and studied the afterglows of the first Swift bursts?in addition to Berger, Freedman and Gehrels?includes Mario Hamuy, Wojtek Krzeminski, and Eric Persson from Carnegie Observatories, Shri Kulkarni, Derek Fox, Alicia Soderberg, and Brad Cenko from Caltech, Dale Frail from the National Radio Astronomy Observatory, Paul Price from the University of Hawaii, Eric Murphy from Yale University, and Swift team members David Burrows, John Nousek, and Joanne Hill from Penn State University, Scott Barthelmy from Goddard Space Flight Center, and Alberto Moretti from Osservatorio Astronomico di Brera.

Original Source: Carnegie News Release

Using a new computer model of galaxy formation, researchers have shown that growing black holes release a blast of energy that fundamentally regulates galaxy evolution and black hole growth itself. The model explains for the first time observed phenomena and promises to deliver deeper insights into our understanding of galaxy formation and the role of black holes throughout cosmic history, according to its creators. Published in the Feb. 10 issue of Nature, the results were generated by Carnegie Mellon University astrophysicist Tiziana Di Matteo and her colleagues while at the Max Planck Institut fur Astrophysik in Germany. Di Matteo?s collaborators include Volker Springel at Max-Planck Institut for Astrophysics and Lars Hernquist at Harvard University.
“In recent years, scientists have begun to appreciate that the total mass of stars in today?s galaxies corresponds directly to the size of a galaxy?s black hole, but until now, no one could account for this observed relationship,” said Di Matteo, assistant professor of physics at Carnegie Mellon. “Using our simulations has given us a completely new way to explore this problem.”

The key to the researchers? breakthrough was incorporating calculations for black hole dynamics into a computational model of galaxy formation.

As galaxies formed in the early universe, they likely contained small black holes at their centers. In the standard scenario of galaxy formation, galaxies grow by coming together with one another by the pull of gravity. In the process, the black holes at their center merge together and quickly grow to reach their observed masses of a billion times that of the Sun; hence, they are called supermassive black holes. Also at the time of merger, the majority of stars form from available gas. Today?s galaxies and their central black holes must be the result of a series of such events.

Di Matteo and her colleagues simulated the collision of two nascent galaxies and found that when the two galaxies came together, their two supermassive black holes merged and initially consumed the surrounding gas. But this activity was self-limiting. As the remnant galaxy?s supermassive black hole sucked up gas, it powered a luminescent state called a quasar. The quasar energized the surrounding gas to such a level that it was blown away from the vicinity of the supermassive black hole to the outside of the galaxy. Without nearby gas, the galaxy?s supermassive black hole could not “eat” to sustain itself and became dormant. At the same time, gas was no longer available to form any more stars.

“We?ve discovered that the energy released by black holes during a quasar phase powers a strong wind that prevents material from falling into the black hole,” Springel said. “This process inhibits further black hole growth and shuts off the quasar, just as star formation stops inside a galaxy. As a result, the black hole mass and the mass of stars in a galaxy are closely linked. Our results also explain for the first time why the quasar lifetime is such a short phase compared to the life of a galaxy.”

In their simulations, Di Matteo, Springel and Hernquist found that the black holes in small galaxies self-limit their growth more effectively than in those in larger galaxies. A smaller galaxy contains smaller amounts of gas so that a small amount of energy from the black hole can quickly blow this gas away. In a large galaxy, the black hole can reach a greater size before its surrounding gas is energized enough to stop falling in. With their gas quickly spent, smaller galaxies make fewer stars. With a longer-lived pool of gas, larger galaxies make more stars. These findings match the observed relation between black hole size and the total mass of stars in galaxies.

“Our simulations demonstrate that self-regulation can quantitatively account for observed facts associated with black holes and galaxies,” said Hernquist, professor and chair of astronomy in Harvard?s Faculty of Arts and Sciences. “It provides an explanation for the origin of the quasar lifetime and should allow us to understand why quasars were more plentiful in the early universe than they are today.”

“With these computations, we now see that black holes must have an enormous impact on the way galaxies form and evolve,” Di Matteo said. “The successes obtained so far will allow us to implement these models within larger simulated universes, so that we can understand how large populations of black holes and galaxies influence each other in a cosmological context.”

The team ran their simulations with the extensive computing resources of the Center for Parallel Astrophysical Computing at the Harvard-Smithsonian Center for Astrophysics and at the Rechenzentrum der Max-Planck-Gesellschaft in Garching.

Original Source: Max Planck Institute News Release

Moons circle planets, and planets circle stars. Now, astronomers have learned that planets may also circle celestial bodies almost as small as planets.

NASA’s Spitzer Space Telescope has spotted a dusty disk of planet-building material around an extraordinarily low-mass brown dwarf, or “failed star.” The brown dwarf, called OTS 44, is only 15 times the mass of Jupiter. Previously, the smallest brown dwarf known to host a planet-forming disk was 25 to 30 times more massive than Jupiter.

The finding will ultimately help astronomers better understand how and where planets — including rocky ones resembling our own — form.

“There may be a host of miniature solar systems out there, in which planets orbit brown dwarfs,” said Dr. Kevin Luhman, lead author of the new study from the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass. “This leads to all sorts of new questions, like ‘Could life exist on such planets?’ or ‘What do you call a planet circling a planet-sized body? A moon or a planet?'”

Brown dwarfs are something of misfits in the astronomy world. These cool orbs of gas have been called both failed stars and super planets. Like planets, they lack the mass to ignite and produce starlight. Like stars, they are often found alone in space, with no parent body to orbit.

“In this case, we are seeing the ingredients for planets around a brown dwarf near the dividing line between planets and stars. This raises the tantalizing possibility of planet formation around objects that themselves have planetary masses,” said Dr. Giovanni Fazio, an astronomer at the Harvard Smithsonian Center for Astrophysics and a co-author of the new study.

The results were presented today at the Planet Formation and Detection meeting at the Aspen Center for Physics, Aspen, Colo., and will be published in the Feb. 10th issue of The Astrophysical Journal Letters.

Planet-forming, or protoplanetary, disks are the precursors to planets. Astronomers speculate that the disk circling OTS 44 has enough mass to make a small gas giant planet and a few Earth-sized, rocky ones. This begs the question: Could a habitable planet like Earth sustain life around a brown dwarf?

“If life did exist in this system, it would have to constantly adjust to the dwindling temperatures of a brown dwarf,” said Luhman. “For liquid water to be present, the planet would have to be much closer to the brown dwarf than Earth is to our Sun.”

“It’s exciting to speculate about the possibilities for life in such as system, of course at this point we are only beginning to understand the unusual circumstances under which planets arise,” he added.

Brown dwarfs are rare and difficult to study due to their dim light. Though astronomers recently reported what may be the first-ever image of a planet around a brown dwarf called 2M1207, not much is understood about the planet-formation process around these odd balls of gas. Less is understood about low-mass brown dwarfs, of which only a handful are known.

OTS 44 was first discovered about six months ago by Luhman and his colleagues using the Gemini Observatory in Chile. The object is located 500 light-years away in the Chamaeleon constellation. Later, the team used Spitzer’s highly sensitive infrared eyes to see the dim glow of OTS 44’s dusty disk. These observations took only 20 seconds. Longer searches with Spitzer could reveal disks around brown dwarfs below 10 Jupiter masses.

Other authors of this study include Dr. Paola D’Alessia of the Universidad Nacional Autonoma de Mexico; and Drs. Nuria Calvet, Lori Allen, Lee Hartmann, Thomas Megeath and Philip Myers of the Harvard-Smithsonian Center for Astrophysics.

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington, D.C. Science operations are conducted at the Spitzer Science Center, Pasadena, Calif. JPL is a division of Caltech. The infrared array camera, which spotted the protoplanetary disk around OTS 44, was built by NASA Goddard Space Flight Center, Greenbelt, Md.; its development was led by Fazio.

Original Source: Spitzer News Release

Using the MMT Observatory in Tucson, AZ, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) are the first to report the discovery of a star leaving our galaxy, speeding along at over 1.5 million miles per hour. This incredible speed likely resulted from a close encounter with the Milky Way’s central black hole, which flung the star outward like a stone from a slingshot. So strong was the event that the speedy star eventually will be lost altogether, traveling alone in the blackness of intergalactic space.

“We have never before seen a star moving fast enough to completely escape the confines of our galaxy,” said co-discoverer Warren Brown (CfA). “We’re tempted to call it the outcast star because it was forcefully tossed from its home.”

The star, catalogued as SDSS J090745.0+24507, once had a companion star. However, a close pass by the supermassive black hole at the galaxy’s center trapped the companion into orbit while the speedster was violently flung out. Astronomer Jack Hills proposed this scenario in 1998, and the discovery of the first expelled star seems to confirm it.

“Only the powerful gravity of a very massive black hole could propel a star with enough force to exit our galaxy,” explained Brown.

While the star’s speed offers one clue to its origin, its path offers another. By measuring its line-of-sight velocity, it suggests that the star is moving almost directly away from the galactic center. “It’s like standing curbside watching a baseball fly out of the park,” said Brown.

Its composition and age provide additional proof of the star’s history. The fastest star contains many elements heavier than hydrogen and helium, which astronomers collectively call metals. “Because this is a metal-rich star, we believe that it recently came from a star-forming region like that in the galactic center,” said Brown. Less than 80 million years were needed for the star to reach its current location, which is consistent with its estimated age.

The star is traveling twice as fast as galactic escape velocity, meaning that the Milky Way’s gravity will not be able to hold onto it. Like a space probe launched from Earth, this star was launched from the galactic center onto a never-ending outward journey. It faces a lonely future as it leaves our galaxy, never to return.

Brown’s co-authors on the paper announcing this find are Margaret J. Geller, Scott J. Kenyon and Michael J. Kurtz (Smithsonian Astrophysical Observatory). This study will be published in an upcoming issue of The Astrophysical Journal.

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

Fitted with its new compound eye on the heavens, the National Science Foundation’s (NSF) Arecibo Observatory telescope, the world’s largest and most sensitive single-dish radio telescope, early tomorrow morning begins a years-long survey of distant galaxies, perhaps discovering elusive “dark galaxies” — galaxies that are devoid of stars.

Astronomers at Arecibo Observatory hope the new sky survey will result in a comprehensive census of galaxies out to a distance of 800 million light years from our galaxy, the Milky Way, in nearly one-sixth of the sky — or some 7,000 square degrees.

The search, conducted by an international team of students and scholars, is the first of a series of large-scale Arecibo surveys that will take advantage of a the telescope’s new instrument, installed last year, called ALFA (for Arecibo L-Band Feed Array). The device is essentially a seven-pixel camera with unprecedented sensitivity for making radio pictures of the sky, allowing astronomers to collect data about seven times faster than at present. The project has been dubbed ALFALFA, for Arecibo Legacy Fast Alfa Survey.

“Fast” does not refer to the time necessary to carry out the survey, which will require thousand hours of telescope time and a few years to complete, but rather to the observing technique, which consists in fast sweeps of broad swaths of sky.

The survey is supported by the National Astronomy and Ionosphere Center (NAIC) at Cornell University, Ithaca, N.Y., which manages the Arecibo Observatory for the NSF. In addition, support is being provided through research grants from the NSF and the Brinson Foundation to the project’s leader, Cornell professor of astronomy Riccardo Giovanelli, and to Martha Haynes, a Goldwin Smith Professor of Astronomy at Cornell.

Giovanelli explains that ALFA operates at radio frequencies near 1420 MegaHertz (MHz), a frequency range that includes a spectral line emitted by neutral atomic hydrogen, the most abundant element in the universe. ALFA detects this signature of hydrogen, which hopefully signals the presence of an undiscovered galaxy. Nearly every previous sky survey has been of optically, infrared- or X-ray-selected galaxies.

ALFALFA will be six times more sensitive — meaning that it will go much deeper in distance — than the only previous hydrogen wide-field survey carried out in Australia in the late 1990s. “What has made ALFALFA possible is the completion of the Gregorian upgrade to the Arecibo telescope in 1997, which allowed feed arrays to be placed in the telescope focal plane and expanded the instantaneous frequency coverage of the telescope,” he says.

Besides providing a comprehensive census of the gaseous content of the near universe, ALFALFA will explore galaxies in groups and clusters and investigate the efficiency by which galaxies convert gas into stars. What particularly intrigues astronomers is that ALFALFA could determine whether gas-rich systems of low mass that have not been able to convert their cosmic material into stars — the so-called dark galaxies — actually exist. Because these galaxies, being starless, are optically inert, it is hoped that they can be detected by their hydrogen signature.

The galaxy survey is feasible now because ALFA lets the telescope see seven spots — seven pixels — on the sky at once, greatly reducing the time needed to make all-sky surveys. The Australian-built detector, on the 305-meter (1,000-foot) diameter Arecibo radio telescope, provides the imaging speed and sensitivity that astronomers will need for their search.

Robert Brown, the NAIC’s director, said that a significant fraction of the Arecibo telescope time in the next few years will be devoted to extensive surveys with the ALFA array, such as ALFALFA. The new survey consortium consists of 38 scientists from 10 countries, including the United States, France, the United Kingdom, Italy, Spain, Israel, Argentina, Chile, Russia and the Ukraine.

Several of the members are graduate students who will base their Ph.D. theses on ALFALFA data. Among them are Cornell graduate students Brian Kent, Sabrina Stierwalt and Amelie Saintonge.

Says Giovanelli: “My one and only paper published in an engineering journal proposed the construction of a feed array at the upgraded Arecibo telescope to carry out hydrogen line surveys of the sky. It took 15 years of waiting, but I am finally going to do the experiment.”

Original Source: Cornell News Release