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Black Holes More Powerful than Expected, And Still Growing
By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET
15 December 2000
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New puzzles
"Often, when you find something out it leads you to ask more questions than the ones you started with in the first place," said Morris Aizenman, senior science associate in the Mathematical and Physical Science Directorate of the National Science Foundation.
For starters, Aizenman said, not all black holes are active. The one believed to be at the center of our Milky Way, for example, is not spewing the kind of energy witnessed in Barger's study.
Black holes are deemed "active" when they are gathering, or accreting great quantities of matter, which swirls toward the center of a giant disk. This matter, heated to millions of degrees under the crushing force of gravity, shines particularly bright in X-ray light, as well as in other wavelengths.
"What causes the black hole at the center of a galaxy to turn off?" asked Aizenman. "And what are the conditions that lead to it being an active galaxy?"
Lennox Cowie, a University of Hawaii scientist who worked with Barger on the new study, had the same questions.
"If, as we suggest, about 10 percent of luminous galaxies are active at any given time, there must be some mechanism which switches the fuelling on and off," Cowie said in an e-mail interview. "We don't know the answer at this time."
Answers on the event horizon
Cowie and Brandt (the Penn State researcher) are collaborating on another study that will look deeper into the X-ray world, and other researchers are conducting parallel studies.
"We should see a lot more information on much larger samples over the coming year," Cowie said.
Cowie, Barger and Karen Rehbock, also of the University of Hawaii, used the Keck and James Clerk Maxwell telescopes on Mauna Kea in Hawaii, plus the Very Large Array of the National Radio Observatories. Optical observations indicated the times at which the black hole activity occurred, while submillimeter and radio measurements revealed the amount of energy emitted in the formation of the supermassive black holes.
The researchers presented their findings December 12 at the annual Texas Symposium on Relativistic Astrophysics in Austin.
Click here for more news and information about black holes.
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