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Posts Tagged ‘black holes’

Surprising Black-Hole Discovery Changes Picture Of Globular Star Clusters

October 4, 2012 1 comment

An unexpected discovery by astronomers using the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) is forcing scientists to rethink their understanding of the environment in globular star clusters, tight-knit collections containing hundreds of thousands of stars.

The astronomers used the VLA to study a globular cluster called Messier 22 (M22), a group of stars more than 10,000 light-years from Earth. They hoped to find evidence for a rare type of black hole in the cluster’s center. They wanted to find what scientists call an intermediate-mass black hole, more massive than those a few or more times the Sun’s mass, but smaller than the supermassive black holes found at the cores of galaxies.

“We didn’t find what we were looking for, but instead found something very surprising — two smaller black holes,” said Laura Chomiuk, of Michigan State University and the National Radio Astronomy Observatory. “That’s surprising because most theorists said there should be at most one black hole in the cluster,” she added.

Full Story: http://www.nrao.edu/pr/2012/m22/

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Gone, With The Wind

October 1, 2012 Leave a comment

The case of the missing quasar gas clouds has been solved by a worldwide team of astronomers, and the answer is blowin’ in the wind.

“We know that many quasars have structures of fast-moving gas caught up in ‘quasar winds,’ and now we know that those structures can regularly disappear from view,” says Filiz Ak, a graduate student at Penn State and lead author of the paper. “But why is this happening?”

Quasars are powered by gas falling into supermassive black holes at the centers of galaxies. As the gas falls into the black hole, it heats up and gives off light. The gravitational force from the black hole is so strong, and is pulling so much gas, that the hot gas glows brighter than the entire surrounding galaxy.

What’s going on here? There are several possible explanations, but the simplest is that, in these quasars, gas clouds that we had seen previously are literally “gone with the wind” —the rotation of the quasar’s disk and wind have carried the clouds out of the line-of-sight between us and the quasar.

Full Story: http://www.sdss3.org/press/thewind.php

Simulations Uncover ‘Flashy’ Secrets Of Merging Black Holes

September 30, 2012 Leave a comment

According to Einstein, whenever massive objects interact, they produce gravitational waves — distortions in the very fabric of space and time — that ripple outward across the universe at the speed of light. While astronomers have found indirect evidence of these disturbances, the waves have so far eluded direct detection. Ground-based observatories designed to find them are on the verge of achieving greater sensitivities, and many scientists think that this discovery is just a few years away.

Catching gravitational waves from some of the strongest sources — colliding black holes with millions of times the sun’s mass — will take a little longer. These waves undulate so slowly that they won’t be detectable by ground-based facilities. Instead, scientists will need much larger space-based instruments, such as the proposed Laser Interferometer Space Antenna, which was endorsed as a high-priority future project by the astronomical community.

A team that includes astrophysicists at NASA’s Goddard Space Flight Center in Greenbelt, Md., is looking forward to that day by using computational models to explore the mergers of supersized black holes. Their most recent work investigates what kind of “flash” might be seen by telescopes when astronomers ultimately find gravitational signals from such an event.

Full Story: http://www.nasa.gov/topics/universe/features/black-hole-secrets.html

Top physicists gather in Jerusalem to mark 40 years Since Jacob Bekenstein’s Famous Essay On The Entropy Of Black Holes

September 3, 2012 Leave a comment

As the scientific community marks 40 years since the publication of Prof. Jacob Bekenstein’s famous paper on black hole entropy, the Hebrew University of Jerusalem’s Institute for Advanced Studies is celebrating the occasion by hosting an international conference featuring the world’s top theoretical physicists. The Sep. 3-7 conference, Forty Years of Black Hole Thermodynamics, is presented in cooperation with the Israel Science Foundation and will focus on recent ramifications of black hole thermodynamics and prospects for the future.

Bekenstein’s groundbreaking proposals about black holes, entropy and thermodynamics were originally contested by renowned physicist Stephen Hawking, who later admitted that Bekenstein was correct and affirmed Bekenstein’s ideas with his famous proposal for the existence of Hawking radiation.

Full Story: http://www.huji.ac.il/cgi-bin/dovrut/dovrut_search_eng.pl?mesge134666067605872560

A Black Hole´s Dinner

June 26, 2012 Leave a comment

A giant gas cloud is on collision course with the black hole in the centre of our galaxy in 2013. This is a unique opportunity to observe how a super massive black hole sucks in material, in real time.The black hole at the centre of the galaxy, formally known as Sagittarius A*, fascinates scientists. By mid-2013 a gas cloud is expected to pass in its vicinity at a distance of only 36 light-hours (equivalent to 40.000.000.000km), which is extremely close in astronomical terms.For the past 20 years, Stefan Gillessen, astrophysicist at the Max Planck Institute for Extraterrestrial Physics in Munich, Germany, has been observing the black hole. “So far there were only two stars that came that close to Sagittarius A*”, he says. “They passed unharmed, but this time will be different: the gas cloud will be completely ripped apart by the tidal forces of the black hole.”  A black hole is what remains after a super massive star dies. When the “fuel” of a star runs low, it will first swell and then collapse to a dense core. If this remnant core has more than three times the mass of our Sun, it will transform to a black hole.

Direct observations of such black holes are impossible because they are coal-black and do not emit light or matter. But astronomers can identify a black hole indirectly due to the gravitational forces observed in their vicinity.

So-called super massive black holes are the largest type of black holes. Their mass equals hundreds of thousands to a billion times the mass of our sun. The centre of all galaxies is thought to contain super massive black holes. But their origin is not fully understood and astrophysicists can only speculate as to what happens inside them. Hence the imminent collision is of great interest to scientists as it should provide some new insights.

Full Story: http://www.youris.com/Environment/Space/A_Black_HoleS_Dinner.kl

Black Hole Growth Found to Be Out of Sync

June 12, 2012 Leave a comment

New evidence from NASA’s Chandra X-ray Observatory challenges prevailing ideas about how black holes grow in the centers of galaxies. Astronomers long have thought that a supermassive black hole and the bulge of stars at the center of its host galaxy grow at the same rate — the bigger the bulge, the bigger the black hole. However, a new study of Chandra data has revealed two nearby galaxies with supermassive black holes that are growing faster than the galaxies themselves.
The mass of a giant black hole at the center of a galaxy typically is a tiny fraction — about 0.2 percent — of the mass contained in the bulge, or region of densely packed stars, surrounding it. The targets of the latest Chandra study, galaxies NGC 4342 and NGC 4291, have black holes 10 times to 35 times more massive than they should be compared to their bulges. The new observations with Chandra show the halos, or massive envelopes of dark matter in which these galaxies reside, also are overweight.
This study suggests the two supermassive black holes and their evolution are tied to their dark matter halos and did not grow in tandem with the galactic bulges. In this view, the black holes and dark matter halos are not overweight, but the total mass in the galaxies is too low.

Full Story: http://www.nasa.gov/mission_pages/chandra/news/H-12-191.html