Washington, July 03: Using a worldwide combination of diverse telescopes, astronomers have discovered that a giant galaxy’s bursts of very high energy gamma rays are coming from a region very close to the supermassive black hole at its core.
The discovery provides important new information about the mysterious workings of the powerful “engines” in the centers of innumerable galaxies throughout the Universe.
The galaxy M87, 50 million light-years from Earth, harbors at its centre a black hole more than six billion times more massive than the Sun.
Black holes are concentrations of matter so dense that not even light can escape their gravitational pull.
The black hole is believed to draw material from its surroundings - material that, as it falls toward the black hole, forms a tightly-rotating disk.
Processes near this “accretion disk,” powered by the immense gravitational energy of the black hole, propel energetic material outward for thousands of light-years.
This produces the “jets” seen emerging from many galaxies. In 1998, astronomers found that M87 also was emitting flares of gamma rays a trillion times more energetic than visible light.
However, the telescopes that discovered these bursts of very high-energy gamma rays could not determine exactly where in the galaxy they originated.
In 2007 and 2008, the astronomers using these gamma-ray telescopes combined forces with a team using the National Science Foundation’s continent-wide Very Long Baseline Array (VLBA), a radio telescope with extremely high resolving power, or ability to see fine detail.
“Combining the gamma-ray observations with the supersharp radio ‘vision’ of the VLBA allowed us to see that the gamma rays are coming from a region very near the black hole itself,” said Craig Walker, of the National Radio Astronomy Observatory (NRAO).
“Pinning down this location addresses what was an open question and provides important clues for understanding how such highly energetic emissions are produced in the jets of active galaxies,” said Matthias Beilicke, of Washington University in St. Louis.
The radio flare began at about the time of the gamma-ray flares, but continued to increase in brightness for at least two months.
“This tells us that energetic material burst out very close to the black hole, causing the gamma rays to be emitted and the radio flare to begin. As that material traveled down the jet, expanding and losing energy, the gamma-ray emission ceased, but the radio continued to increase in brightness,” Walker explained.
“The VLBA showed us with great precision where the radio emission came from, so we know the gamma rays came from closer in toward the black hole,” he added.
ANI
First Published: Friday, July 03, 2009, 18:32