April 13, 2009, 2:03 PM CT

Challenge To Galaxy Formation Theories

A team led by an Indiana University astronomer has found a sample of massive galaxies with properties that suggest they may have formed relatively recently. This would run counter to the widely-held belief that massive, luminous galaxies (like our own Milky Way Galaxy) began their formation and evolution shortly after the Big Bang, some 13 billion years ago. Further research into the nature of these objects could open new windows into the study of the origin and early evolution of galaxies.

John Salzer, principal investigator for the study published recently in Astrophysical Journal Letters, said that the 15 galaxies in the sample exhibit luminosities (a measure of their total light output) that indicate that they are massive systems like the Milky Way and other so-called "giant" galaxies. However, these particular galaxies are unusual because they have chemical abundances that suggest very little stellar evolution has taken place within them. Their relatively low abundances of "heavy" elements (elements heavier than helium, called "metals" by astronomers) imply the galaxies are cosmologically young and may have formed recently.

The chemical abundances of the galaxies, combined with some simple assumptions about how stellar evolution and chemical enrichment progress in galaxies in general, suggest that they may only be 3 or 4 billion years old, and therefore formed 9 to 10 billion years after the Big Bang. Most theories of galaxy formation predict that massive, luminous systems like these should have formed much earlier......... Posted by: Sean      Read more         Source

March 31, 2009, 4:10 PM CT

A new X-ray spectroscopic tool

Astronomy & Astrophysics is publishing the first clear detection of signatures long sought in the spectra of X-ray astronomical sources. These signatures, the so-called EXAFS standing for "Extended X-ray Absorption Fine Structure", were observed with an X-ray spectroscopic technique that is common in materials sciences. Up to now, EXAFS studies of astronomical sources have been unsuccessful because of the weak X-ray signals received from celestial objects. Using the Reflection Grating Spectrometer (RGS) onboard the XMM-Newton satellite, Dutch astronomers C.P. de Vries and E. Costantini have obtained high-quality X-ray spectra of Scorpius X-1, one of the brightest X-ray sources in the sky, located about 2800 parsecs from the Earth. For the first time, they have found clear evidence of an EXAFS signature coming from the dust seen toward a celestial source.

EXAFS is a powerful tool for studying the structure of grains in the interstellar medium (ISM). It is based on the phenomenon that X-ray photons can eject electrons from atoms inside solid particles, which in turn can be backscattered onto the emitting atom by atoms in their immediate neighborhood. This causes characteristic sinusoidal absorption features in the X-ray spectrum of a distant source that depend on the structure of the absorbing solid material......... Posted by: Sean      Read more         Source

March 25, 2009, 9:54 PM CT

The Erratic Black Hole

New results from NASA's Chandra X-ray Observatory have made a major advance in explaining how a special class of black holes may shut off the high-speed jets they produce. These results suggest that these black holes have a mechanism for regulating the rate at which they grow.

Black holes come in a number of sizes: the supermassive ones, including those in quasars, which weigh in at millions to billions of times the mass of the Sun, and the much smaller stellar-mass black holes which have measured masses in the range of about 7 to 25 times the Sun's mass. Some stellar-mass black holes launch powerful jets of particles and radiation, like seen in quasars, and are called "micro-quasars".

The newly released study looks at a famous micro-quasar in our own Galaxy, and regions close to its event horizon, or point of no return. This system, GRS 1915+105 (GRS 1915 for short), contains a black hole about 14 times the mass of the Sun that is feeding off material from a nearby companion star. As the material swirls toward the black hole, an accretion disk forms.

This system shows remarkably unpredictable and complicated variability ranging from timescales of seconds to months, including 14 different patterns of variation. These variations are caused by a poorly understood correlation between the disk and the radio jet seen in GRS 1915......... Posted by: Sean      Read more         Source

March 25, 2009, 9:29 PM CT

Asteroid monitored from outer space to ground impact

Reports by researchers of meteorites striking Earth in the past have resembled police reports of so a number of muggings - the offenders came out of nowhere and then disappeared into the crowd, making it difficult to get more than very basic facts.

Now an international research team has been able to identify an asteroid in space before it entered Earth's atmosphere, enabling computers to determine its area of origin in the solar system as well as predict the arrival time and location on Earth of its shattered surviving parts.

"I would say that this work demonstrates, for the first time, the ability of astronomers to discover and predict the impact of a space object," says Sandia National Laboratories researcher Mark Boslough, a member of the research team.

Perhaps more importantly, the event tested the ability of society to respond very quickly to a predicted impact, says Boslough. "In this case, it was never a threat, so the response was scientific. Had it been deemed a threat - a larger asteroid that would explode over a populated area - an alert could have been issued in time that could potentially save lives by evacuating the danger zone or instructing people to take cover."

The profusion of information in this case also helps meteoriticists learn the orbits of parent bodies that yield various types of meteorites......... Posted by: Sean      Read more         Source

March 16, 2009, 8:26 PM CT

A Curious Pair of Galaxies

Sometimes objects in the sky that appear strange, or different from normal, have a story to tell and prove scientifically very rewarding. This was the idea behind Halton Arp's catalogue of Peculiar Galaxies that appeared in the 1960s. One of the oddballs listed there is Arp 261, which has now been imaged in more detail than ever before using the FORS2 instrument on ESO's Very Large Telescope. The image proves to contain several surprises.

Arp 261 lies about 70 million light-years distant in the constellation of Libra, the Scales. Its chaotic and very unusual structure is created by the interaction of two galaxies that are engaged in a slow motion, but highly disruptive close encounter. Eventhough individual stars are very unlikely to collide in such an event, the huge clouds of gas and dust certainly do crash into each other at high speed, leading to the formation of bright new clusters of very hot stars that are clearly seen in the picture. The paths of the existing stars in the galaxies are also dramatically disrupted, creating the faint swirls extending to the upper left and lower right of the image. Both interacting galaxies were probably dwarfs not unlike the Magellanic Clouds orbiting our own galaxy.

The images used to create this picture were not actually taken to study the interacting galaxies at all, but to investigate the properties of the inconspicuous object just to the right of the brightest part of Arp 261 and close to the centre of the image. This is an unusual exploding star, called SN 1995N, that is believed to be the result of the final collapse of a massive star at the end of its life, a so-called core collapse supernova. SN 1995N is unusual because it has faded very slowly - and still shows clearly on this image more than seven years after the explosion took place! It is also one of the few supernovae to have been observed to emit X-rays. It is thought that these unusual characteristics are a result of the exploding star being in a dense region of space so that the material blasted out from the supernova ploughs into it and creates X-rays......... Posted by: Sean      Read more         Source

March 3, 2009, 6:21 AM CT

The lower atmosphere of Pluto revealed

Using ESO's Very Large Telescope, astronomers have gained valuable new insights about the atmosphere of the dwarf planet Pluto. The researchers found unexpectedly large amounts of methane in the atmosphere, and also discovered that the atmosphere is hotter than the surface by about 40 degrees, eventhough it still only reaches a frigid minus 180 degrees Celsius. These properties of Pluto's atmosphere appears to be due to the presence of pure methane patches or of a methane-rich layer covering the dwarf planet's surface.

"With lots of methane in the atmosphere, it becomes clear why Pluto's atmosphere is so warm," says Emmanuel Lellouch, main author of the paper reporting the results.

Pluto, which is about a fifth the size of Earth, is composed primarily of rock and ice. As it is about 40 times further from the Sun than the Earth on average, it is a very cold world with a surface temperature of about minus 220 degrees Celsius!.

It has been known since the 1980s that Pluto also has a tenuous atmosphere [1], which consists of a thin envelope of mostly nitrogen, with traces of methane and probably carbon monoxide. As Pluto moves away from the Sun, during its 248 year-long orbit, its atmosphere gradually freezes and falls to the ground. In periods when it is closer to the Sun - as it is now - the temperature of Pluto's solid surface increases, causing the ice to sublimate into gas......... Posted by: Sean      Read more         Source

February 25, 2009, 5:30 AM CT

Observing first moments of universe

During the next decade, a delicate measurement of primordial light could reveal convincing evidence for the popular cosmic inflation theory, which proposes that a random, microscopic density fluctuation in the fabric of space and time gave birth to the universe in a hot big bang approximately 13.7 billion years ago.

Among the cosmologists searching for these weak signals will be John Carlstrom, the S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics at the University of Chicago. Carlstrom operates the South Pole Telescope (SPT) with a team of researchers from nine institutions in their search for evidence about the origins and evolution of the universe.

Now on their agenda is putting cosmic inflation theory to its most stringent observational test so far. The test: detecting extremely weak gravity waves, which Einstein's theory of general relativity predicts that cosmic inflation should produce.

"If you detect gravity waves, it tells you a whole lot about inflation for our universe," Carlstrom said. It also would rule out various competing ideas for the origin of the universe. "There are fewer than there used to be, but they don't predict that you have such an extreme, hot big bang, this quantum fluctuation, to start with," he said. Nor would they produce gravity waves at detectable levels......... Posted by: Sean      Read more         Source

February 16, 2009, 10:00 PM CT

The first moments of universe

During the next decade, a delicate measurement of primordial light could reveal convincing evidence for the popular cosmic inflation theory, which proposes that a random, microscopic density fluctuation in the fabric of space and time gave birth to the universe in a hot big bang approximately 13.7 billion years ago.

Among the cosmologists searching for these weak signals will be John Carlstrom, the S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics at the University of Chicago. Carlstrom operates the South Pole Telescope (SPT) with a team of researchers from nine institutions in their search for evidence about the origins and evolution of the universe.

Now on their agenda is putting cosmic inflation theory to its most stringent observational test so far. The test: detecting extremely weak gravity waves, which Einstein's theory of general relativity predicts that cosmic inflation should produce.

"If you detect gravity waves, it tells you a whole lot about inflation for our universe," Carlstrom said. It also would rule out various competing ideas for the origin of the universe. "There are fewer than there used to be, but they don't predict that you have such an extreme, hot big bang, this quantum fluctuation, to start with," he said. Nor would they produce gravity waves at detectable levels......... Posted by: Sean      Read more         Source

January 26, 2009, 11:42 PM CT

Astronauts on International Space Station

Astronauts spending months in space lose significant bone strength, making them increasingly at risk for fractures during the later part of life.

UC Irvine and UC San Francisco led a study evaluating 13 astronauts who spent four to six months on the International Space Station and observed that, on average, astronauts' hipbone strength decreased 14 percent. Three astronauts experienced losses of 20 percent to 30 percent, rates comparable to those seen in older women with osteoporosis.

These results alarmed scientists because they revealed a greater rate of bone deterioration than previously measured using less powerful technologies.

"If preventive measures are not taken, some of our astronauts appears to be at increased risk for age-related fractures decades after their missions," said study leader Joyce Keyak, UCI orthopedic surgery and biomedical engineering professor.

For as long as there have been astronauts, scientists have studied why the microgravitational environment of space makes bones more fragile. While prior studies looked at bone mineral density, this study is the first to specifically evaluate bone strength.

Keyak and her colleagues used a novel computer program she developed over the past 20 years to identify hipbone fracture risk in people with osteoporosis. The study team used this program to analyze structurally the hipbone Computerized axial tomography scans of one female and 12 male International Space Center crewmembers......... Posted by: Sean      Read more         Source

January 15, 2009, 6:34 PM CT

Solving an old astronomy mystery

Researchers may have solved one of the most longstanding astrophysical mysteries of all times: How massive stars - up to 120 times the mass of our sun - form without blowing away the clouds of gas and dust that feed their growth.

New research by Lawrence Livermore National Laboratory, University of California, Santa Cruz and UC Berkeley has shown how a massive star can grow despite outward-flowing radiation pressure that exceeds the gravitational force pulling material inward. The study appears in the Jan. 15 online edition of Science Express.

Using 3-D radiation hydrodynamics simulations, the group, which includes Livermore's Richard Klein, who also is an adjunct professor at UC Berkeley, and his LLNL postdoc Andrew Cunningham, unexpectedly discovered that these massive stars also tend to occur in binary or multiple star systems.

"Originally, we were just exploring the physics of massive star formation," Klein said. "As we were looking at the physics, we observed that gravitational instabilities cause companion stars to form around massive stars".

Massive stars produce so much light that the radiation pressure they exert on the gas and dust around them is stronger than their gravitational attraction, a circumstance that has long been expected to prevent them from growing by accretion (the growth of a massive object by gravitationally attracting more matter)......... Posted by: Sean      Read more         Source