September 11, 2008, 9:11 PM CT

Upper Mass Limit for Black Holes

There appears to be an upper limit to how big the universe's most massive black holes can get, as per new research led by a Yale University astrophysicist.

Once considered rare and exotic objects, black holes are now known to exist throughout the universe, with the largest and most massive found at the centers of the largest galaxies. These "ultra-massive" black holes have been shown to have masses upwards of one billion times that of our own Sun. Now, Priyamvada Natarajan, an associate professor of astronomy and physics at Yale University and a fellow at the Radcliffe Institute for Advanced Study, and Ezequiel Treister, a postdoctoral fellow at the University of Hawaii, have shown that even the biggest of these gravitational monsters can't keep growing forever. Instead, they appear to curb their own growth - once they accumulate about 10 billion times the mass of the Sun.

These ultra-massive black holes, found at the centers of giant elliptical galaxies in huge galaxy clusters, are the biggest in the known universe. Even the large black hole at the center of our own Milky Way galaxy is thousands of times less massive than these behemoths. But these gigantic black holes, which accumulate mass by sucking in matter from neighboring gas, dust and stars, seem unable to grow beyond this limit regardless of where - and when - they appear in the universe. "It's not just happening today," said Natarajan. "They shut off at every epoch in the universe."........ Posted by: Sean      Read more         Source

September 10, 2008, 8:38 PM CT

The Double Firing Burst

GRB 080319B was so intense that, despite happening halfway across the Universe, it could have been seen briefly with the unaided eye (ESO 08/08). In a paper to appear in the 11 recent issue of Nature, Judith Racusin of Penn State University, Pennsylvania (USA), and a team of 92 co-authors report observations across the electromagnetic spectrum that began 30 minutes before the explosion and followed it for months afterwards.

"We conclude that the burst's extraordinary brightness arose from a jet that shot material almost directly towards Earth at almost the speed of light - the difference is only 1 part in 20 000," says Guido Chincarini, a member of the team.

Gamma-ray bursts are the Universe's most luminous explosions. Most occur when massive stars run out of fuel. As a star collapses, it creates a black hole or neutron star that, through processes not fully understood, drives powerful gas jets outward. As the jets shoot into space, they strike gas previously shed by the star and heat it, thereby generating bright afterglows.

The team believes the jet directed toward Earth contained an ultra-fast component just 0.4 degrees across (this is slightly smaller than the apparent size of the Full Moon). This jet is contained within another slightly less energetic jet about 20 times wider......... Posted by: Sean      Read more         Source

September 2, 2008, 8:40 PM CT

The Thousand-Ruby Galaxy

This dramatic image of the galaxy Messier 83 was captured by the Wide Field Imager at ESO's La Silla Observatory, located high in the dry desert mountains of the Chilean Atacama Desert. Messier 83 lies roughly 15 million light-years away towards the huge southern constellation of Hydra (the sea serpent). It stretches over 40 000 light-years, making it roughly 2.5 times smaller than our own Milky Way. However, in some respects, Messier 83 is quite similar to our own galaxy. Both the Milky Way and Messier 83 possess a bar across their galactic nucleus, the dense spherical conglomeration of stars seen at the centre of the galaxies.

This very detailed image shows the spiral arms of Messier 83 adorned by countless bright flourishes of ruby red light. These are in fact huge clouds of glowing hydrogen gas. Ultraviolet radiation from newly born, massive stars is ionising the gas in these clouds, causing the great regions of hydrogen to glow red. These star forming regions are contrasted dramatically in this image against the ethereal glow of older yellow stars near the galaxy's central hub. The image also shows the delicate tracery of dark and winding dust streams weaving throughout the arms of the galaxy.

Messier 83 was discovered by the French astronomer Nicolas Louis de Lacaille in the mid 18th century. Decades later it was listed in the famous catalogue of deep sky objects compiled by another French astronomer and famous comet hunter, Charles Messier. Recent observations of this enigmatic galaxy in ultraviolet light and radio waves have shown that even its outer desolate regions (farther out than those seen in this image) are populated with baby stars. X-ray observations of the heart of Messier 83 have shown that its centre is a hive of vigorous star formation, held deep within a cloud of superheated gas, with temperatures of 7 million degrees Celsius. Messier 83 is also one of the most prolific producers of supernovae, that is, exploding stars: this is one of the two galaxies, which had 6 supernovae in the past 100 years. One of these, SN 1957D was observable for 30 years!......... Posted by: Sean      Read more         Source

August 27, 2008, 8:52 PM CT

Clash of Clusters Provides Another Clue to Dark Matter

Another powerful collision of galaxy clusters has been captured with NASA's Chandra X-ray Observatory and Hubble Space Telescope. Like its famous cousin, the so-called Bullet Cluster, this clash of clusters provides striking evidence for dark matter and insight into its properties.

Like the Bullet Cluster, this newly studied cluster, officially known as MACS J0025.4-1222, shows a clear separation between dark and ordinary matter. This helps answer a crucial question about whether dark matter interacts with itself in ways other than via gravitational forces.

This finding is important because it independently verifies the results found for the Bullet Cluster in 2006. The new results show the Bullet Cluster is not an exception and that the earlier results were not the product of some unknown error.

Just like the original Bullet Cluster, MACS J0025 formed after an incredibly energetic collision between two large clusters in almost the plane of the sky. In some ways, MACS J0025 can be thought of as a prequel to the Bullet Cluster. At its much larger distance of 5.7 billion light years, astronomers are witnessing a collision that occurred long before the Bullet Cluster's.

Using optical images from Hubble, the team was able to infer the distribution of the total mass (colored in blue) -- dark and ordinary matter -- using a technique known as gravitational lensing. The Chandra data enabled the astronomers to accurately map the position of the ordinary matter, mostly in the form of hot gas, which glows brightly in X-rays (pink.)......... Posted by: Sean      Read more         Source

August 27, 2008, 7:07 PM CT

Collision of galaxy clusters captured

Two UC Santa Barbara astronomers are part of a team that has made a stunning discovery using the Hubble Space Telescope and Chandra X-ray Observatory, it was announced recently by the National Aeronautics and Space Administration.

The capture of a collision of galaxy clusters was made by a team led by Marusa Bradac, a postdoctoral researcher and Hubble fellow in UCSB's Department of Physics. The international team also included Tommaso Treu, assistant professor of physics at UCSB.

"It is in our view an important step forward to understanding the properties of the mysterious dark matter," Bradac said. "Dark matter makes up five times more matter in the universe than ordinary matter. This study confirms that we are dealing with a very different kind of matter, unlike anything that we are made of. And were able to study it in a very powerful collision of two clusters of galaxies".

Below is the complete text of the press release issued today by NASA.

(Cambridge, Mass.) A powerful collision of galaxy clusters has been captured with NASA's Chandra X-ray Observatory and Hubble Space Telescope. Like its famous cousin, the so-called Bullet Cluster, this clash of clusters provides striking evidence for dark matter and insight into its properties......... Posted by: Sean      Read more         Source

July 16, 2008, 7:54 PM CT

Diverse, Wet Environments on Ancient Mars

Mars once hosted vast lakes, flowing rivers and a variety of other wet environments that had the potential to support life, as per two new studies based on data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and other instruments on board NASA's Mars Reconnaissance Orbiter (MRO).

"The big surprise from these new results is how pervasive and long-lasting Mars' water was, and how diverse the wet environments were," says Scott Murchie, CRISM's principal investigator at the Johns Hopkins University Applied Physics Laboratory (APL), in Laurel, Md.

One study, reported in the July 17 issue of Nature, shows that vast regions of the ancient highlands of Mars-which cover about half the planet-contain clay minerals, which can form only in the presence of water. Volcanic lavas buried the clay-rich regions during subsequent, drier periods of the planet's history, but impact craters later exposed them at thousands of locations across the planet.

The clay-like minerals, called phyllosilicates, preserve a record of the interaction of water with rocks dating back to what is called the Noachian period of Mars' history, about 4.6 to 3.8 billion years ago. This period corresponds to the earliest years of the solar system, when Earth, the moon and Mars sustained a cosmic bombardment by comets and asteroids. Rocks of this age have largely been destroyed on Earth by plate tectonics; they are preserved on the moon, but were never exposed to liquid water. The phyllosilicate-containing rocks on Mars therefore preserve a unique record of liquid water environments-possibly suitable for life-in the early solar system......... Posted by: Sean      Read more         Source

July 16, 2008, 7:43 PM CT

A new method to weigh giant black holes

How do you weigh the biggest black holes in the universe? One answer now comes from a new and independent technique that UC Irvine researchers and other astronomers have developed using data from NASA's Chandra X-ray Observatory.

By measuring a peak in the temperature of hot gas in the center of the giant elliptical galaxy NGC 4649, researchers have determined the mass of the galaxy's supermassive black hole. The method, applied for the first time, gives results that are consistent with a traditional technique.

Astronomers have been seeking different, independent ways of precisely weighing the largest supermassive black holes, that is, those that are billions of times more massive than the sun. Until now, methods based on observing the motions of stars or of gas in a disk near such large black holes had been used.

"This is tremendously important work since black holes can be elusive, and there are only a couple of ways to weigh them accurately," said Philip Humphrey, leader of the study and an assistant project scientist in the Department of Physics and Astronomy at UCI. David Buote, associate professor of physics and astronomy at UCI, also worked on this study.

"It is reassuring that two very different ways to measure the mass of a big black hole give such similar answers," Humphrey said......... Posted by: Sean      Read more         Source

July 10, 2008, 8:20 PM CT

Nano-sized Electronic Circuit To Universe

A newly developed nano-sized electronic device is an important step toward helping astronomers see invisible light dating from the creation of the universe. This invisible light makes up 98% of the light emitted since the "big bang," and may provide insights into the earliest stages of star and galaxy formation almost 14 billion years ago.

The tiny, new circuit, developed by physicsts at Rutgers University, NASA's Jet Propulsion Laboratory in Pasadena, Calif., and the State University of New York at Buffalo, is 100 times smaller than the thickness of a human hair. It is sensitive to faint traces of light in the far-infrared spectrum (longest of the infrared wavelengths), well beyond the colors humans see.

"In the expanding universe, the earliest stars move away from us at a speed approaching the speed of light," said Michael Gershenson, professor of physics at Rutgers and one of the lead investigators. "As a result, their light is strongly red-shifted when it reaches us, appearing infrared".

Because the Earth's atmosphere strongly absorbs far-infrared light, Earth-based radiotelescopes cannot detect the very faint light emitted by these stars. So researchers are proposing a new generation of space telescopes to gather this light. Yet to take full advantage of space-borne telescopes, detectors that capture the light will have to be far more sensitive than any that exist today......... Posted by: Sean      Read more         Source

Tue, 08 Jul 2008 22:41:58 GMT

Cern's Large Hadron Collider, a big bang

Now here''s a gadget. In fact not just a gadget, but arguably the gadget. It''s the Large Hadron Collider at Cern, the European laboratory for particle physics near Geneva, scheduled to have its Grand Opening next month.

Stephen Hawking explains what the LHC is for:
"It will smash particles together to recreate the moments after the big bang, producing a new golden age of discovery for physicists."

There''s more, lots more, and the Guardian has just unveiled a group of articles and multimedia and podcasts that explains it all. Posted by: Sarah      Read more     Source