Scientists Probe Black Hole's Inner Sanctum
Posted: Friday, January 13, 2006
Source: Naval Research Laboratory
A team of astronomers is announcing today that they have discovered a giant Milky Way-sized tunnel filled with high energy particles in a distant galaxy cluster. These new findings are of special interest to astronomers as they may provide the missing evolutionary link necessary to understand the cycle of birth and death, as well as the environmental impact, of radio jets which result from ravenous supermassive black holes within giant galaxies. The report is being presented to the American Astronomical Society meeting in Washington, DC, by Dr. Tracy Clarke of Interferometrics, Inc. in Herndon, VA, and the Naval Research Laboratory (NRL) in Washington, DC; along with collaborators Dr. Craig Sarazin of the University of Virginia in Charlottesville, VA; Dr. Elizabeth Blanton of Boston University in Boston, MA; Dr. Namir Kassim, also of NRL; and Dr. Doris Neumann of CEA in Saclay, France.
Using the Chandra X-ray Observatory to study the multi-million degree gas in the galaxy cluster Abell 2597, the scientists discovered an unusual X-ray tunnel large enough to fit the entire Milky Way galaxy inside. The cluster, located at a distance of roughly one billion light years, contains a tunnel in the hot gas, which measures nearly 110 thousand light years by 36 thousand light years in size. The tunnel, which appears to originate near the core of the central giant galaxy in the cluster, may be more than 200 million years old.
A constant battle is being waged in the central regions of clusters of galaxies. The hot gas invades the core of the cluster and feeds the supermassive black hole that is lurking there. As the black hole eats more and more, it becomes active and nearby material is funneled into powerful jets of highly energetic particles (so-called radio jets) outward into the hot gas. These relativistic jets, containing particles moving at close to the speed of light, carve out bubbles while they expand, pushing aside the hot gas. Like a poorly planned invasion, these jets cut off the fuel supply to the central black hole, leading to a temporary starvation. Without fuel to maintain the attack, the radio jets cease and the hot gas once again is able to invade the central region of the cluster and the battle begins again.
The new observations of a tunnel connecting from the central supermassive black hole to a distance nearly seven times the radio galaxy size in Abell 2597 suggest that the picture may be more complicated than previously thought. Past radio observations at a wavelength of roughly 4 cm, published in 1995 by Sarazin and collaborators, showed that this system was host to a small radio galaxy only 25 thousand light years across. Recently, Clarke and collaborators obtained new low frequency (90 cm wavelength) radio observations using the National Science Foundation's Very Large Array (VLA), which shed new light on the violent history of the central radio galaxy and its connection to the X-ray tunnel. "Low frequency radio observations are sensitive to the oldest energetic particles thus giving us a means to step even further back in time and look into the past lives of radio galaxies," explains Dr. Clarke. These new observations revealed that the X-ray tunnel is filled with old particles, invisible at shorter wavelengths, which likely originate from the past outbursts of the black hole.
"X-ray and radio observations show that the central supermassive black holes in clusters are at war with the surrounding X-ray gas" says Dr. Sarazin. "In Abell 2597, the small young radio source being inflated by the supermassive black hole at the center of this cluster is the start of a new battle. The tunnel is like a scar left from previous battles, showing that this war has been going on for billions of years. The fact that the tunnel connects back to the supermassive black hole suggests that the black hole is trying the breach the clusters defenses in the same area of the gas where it has been successful in the past."
Astronomers are far from understanding the complex interactions between radio jets and the hot gas in galaxy clusters. Observations of new phenomena such as the tunnel in Abell 2597 are critical as they provide additional clues to how the battle is waged between the inward flow of the hot gas and the outward march of the radio jets. Further progress in the field will require sensitive observations at even longer wavelengths, but unfortunately the current suite of low frequency radio telescopes are already at their limits of sensitivity and resolution.
To address this shortcoming, astronomers at several institutions, collectively known as the Southwest Consortium, are contributing to an effort to build the world's largest and most sensitive low-frequency telescope, called the Long Wavelength Array (LWA). The LWA will operate at wavelengths between 15 and 3.75 meters (or 20 and 80 Megahertz) and has the potential to revolutionize future studies of radio galaxies and galaxy clusters.
Current plans call for the LWA to be sited near the VLA in New Mexico. "Ironically the LWA will operate at the same frequencies at which Carl Jansky first discovered extra-terrestrial radio emission, thus representing a return to the very roots of radio astronomy," notes Dr. Namir Kassim, a radio astronomer in NRL's Remote Sensing Division.
This project was supported by the National Aeronautics and Space Administration through Chandra X-ray Observatory awards. Basic research in radio astronomy at NRL is supported by the Office of Naval Research. The National Radio Astronomy Observatory operates the VLA for the National Science Foundation under a cooperative agreement by Associated Universities, Inc.
The original news release can be found at:
Send page by E-Mail Scientists Find Black Hole's 'Point Of No Return'
Posted: Wednesday, January 11, 2006
Source: Massachusetts Institute of Technology
Scientists have found new evidence that black holes are performing the disappearing acts for which they are known.
A team from MIT and Harvard has found that a certain type of X-ray explosion common on neutron stars is never seen around their black hole cousins, as if the gas that fuels these explosions has vanished into a void.
This is strong evidence, the team said, for the existence of a theoretical border around a black hole called an event horizon, a point from beyond which nothing, not even light, can escape.
Ron Remillard of the Kavli Institute for Astrophysics and Space Research at MIT led the analysis and is discussing his team's result Jan. 9 at a press conference at the 207th meeting of the American Astronomical Society in Washington, D.C. His colleagues are Dacheng Lin of MIT and Randall Cooper and Ramesh Narayan of the Harvard-Smithsonian Center for Astrophysics in Cambridge.
The scientists studied a complete sample of transient X-ray sources detected with NASA's Rossi X-ray Timing Explorer during the last nine years. They detected 135 X-ray bursts from the 13 sources believed to be neutron stars, but none from the 18 suspected black holes.
Gas released by a nearby star can accumulate on the hard surface of a neutron star, and it will eventually erupt in a thermonuclear explosion. The more massive compact objects in this study suspected of being black holes appeared to have no surface. Gas falling toward the black hole seems to disappear.
"Event horizons are invisible by definition, so it seems impossible to prove their existence," said Remillard. "Yet by looking at dense objects that pull in gas, we can infer whether that gas crashes and accumulates onto a hard surface or just quietly vanishes. For the group of suspected black holes we studied, there is a complete absence of surface explosions called X-ray bursts."
A black hole forms when a very massive star runs out of fuel. Without energy to support its mass, the star implodes. If the star is more than 25 times more massive than our sun, the core will collapse to a point of infinite density with no surface. Within a boundary of about 50 miles from the black hole center, gravity is so strong that not even light can escape its pull. This boundary is the theoretical event horizon.
Stars of about 10 to 25 solar masses will collapse into compact spheres about 10 miles across, called neutron stars. These objects have a hard surface and no event horizon.
Black holes and their neutron star cousins are sometimes located in binary systems, orbiting a relatively normal star companion. Gas from these stars, lured by strong gravity, can flow toward the compact object periodically. This process, called accretion, releases large amounts of energy, predominantly in the form of X-rays.
Gas can accumulate on a neutron star surface, and when conditions are ripe, the gas will ignite in a thermonuclear explosion that is visible as a one-minute event called a Type I X-ray burst. The suspected black holes -- that is, the more massive types of compact objects in this study -- behave as if they have no surface and are located behind event horizons.
The idea of using the absence of X-ray bursts to confirm the presence of event horizons in black holes was proposed in 2002 by Harvard's Narayan and Jeremy Heyl of the University of British Columbia in Vancouver.
The Rossi Explorer, launched on Dec. 30, 1995, is operated by NASA Goddard Space Flight Center in Greenbelt, Md.
For more information, including images, visit http://universe.nasa.gov/press/event_horizon/event_horizon.html.
The original news release can be found at:
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