RESEARCHERS STUDY BLACK HOLES' GRAVITATIONAL FIELD
COLUMBUS, Ohio -- An international team of astronomers from 17 countries has used a novel research technique to measure the gravitational field surrounding suspected black holes.
The team, headed by Bradley Peterson, a professor of astronomy at Ohio State University, used the Hubble Space Telescope to study a quasar in a galaxy 200 million light years away.
Quasars are perhaps the brightest objects in the universe and have long been suspected of harboring supermassive black holes, weighing as much as millions of stars, at their centers. Peterson's group turned to reverberation mapping to track movement of material in and around the centers of galaxies.
Astronomers have been puzzled for years about what exactly is taking place in the centers of these galaxies. Some theories have suggested that material was being explosively hurled outward from the galactic centers, emitting enormous amounts of light in the process. Other more popular theories have explained the intensity of the light as being a byproduct of gas being heated as it falls into a black hole at the center.
"We've believed for a long time that the material in the center of a quasar is strongly affected by what we suspect is an enormous gravitational field," Peterson said.
"By tracing these gases with the reverberation mapping technique, we've learned that the material is not moving outward, meaning gravity is the most important force working on these gases. That alone tells us something about the mass of the black hole."
The researchers obtained more than 100 observations with the International Ultraviolet Explorer satellite and the Hubble Space Telescope in order to follow changes in the gas clouds surrounding the black hole. They were able to do this by comparing the way the light changed in daily observations taken by the HST over a 39-day period.
Scientists observed variations in the brightness of light originating from very close to the black hole and also tracked resulting changes in the multi-color emission lines produced when the white light passed through gas clouds farther away from the black hole.
"We measured the time between the detection of the initial outburst, and the response from the gas clouds," Peterson said. "The response time from the clouds measured from a day to a month. That tells us that there are gas clouds at different distances from the center of the black hole, but they are close enough to the black hole to be strongly affected by it."
Knowing the location of the gas clouds, the scientists were able to determine the distance from the clouds to the center of the black hole, giving them the black hole's mass. They measured the mass to be about 20 million times as massive as the sun.
The group of researchers, called The International AGN Watch, studies active galactic nuclei, objects found at the center of galaxies. AGN are usually small bright phenomena that feature unusual traits, such as unusually wide spectral emission lines. They include a variety of objects, such as quasars, blazars and Seyfert galaxies.
The group's research was one of the largest guest observer programs at the Hubble Space Telescope to date. The team's research will be published in the Astrophysical Journal Supplement Series in April.
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Contact: Bradley Peterson, (614) 292-7886
Written by Kelli Whitlock, (614) 292-9475