Date:30 September 2003
Photo:The location of the black hole is marked with an arrow. The brightness variations, which occur on time scales as short as 40 minutes, reveal that the plasma is much more energetic than previously believed, showing that violent events occur almost continually.
New observations of the supermassive black hole at the center of the Milky Way Galaxy reveal unexpectedly turbulent conditions in the region where matter is sucked beyond the point of no return.
Almost continual violent eruptions of activity occur where astronomers had thought matter disappeared in an orderly flow.
Because neither matter nor light can escape once inside, a black hole can't be seen. But one signature of their existence is the chaos around them. As gas spirals toward one, compelled by gravity, it is accelerated to nearly light-speed and superheated to a fourth state of matter, called plasma. This creates radiation that can span the spectrum, from radio waves to X-rays.
Enormous amounts of radiation have been observed streaming out from the environments of black holes anchoring other galaxies. The Milky Way, being rather mature, is quieter. Its black hole does not seem to excite its environment quite like some do, and this has long puzzled astronomers.
Besides the relative quiescence, the Milky Way's central gravity well has also appeared, until now to emit radiation in a fairly consistent manner.
New view
The new study is the first to detect emissions from superheated gas, called plasma, in the infrared portion of the spectrum.
"Previous observations at radio and X-ray wavelengths suggested that the black hole is dining on a calm stream of plasma that experiences glitches only two percent of the time," said Andrea Ghez, professor of physics and astronomy at UCLA who headed the research team. "Our infrared detection shows for the first time that the black hole's meal is more like the Grand Rapids, in which energetic glitches from shocked gas are occurring almost continually."
Ghez told SPACE.com the situation is akin to changes in the weather.
"It varies dramatically in intensity from week-to-week, day-to-day, and even within a single hour," she said. "It's as if we have been watching the black hole breathing."
The cause of the volatility is not known, but the researchers are on the trail.
"We interpret this as variations in the conditions of the plasma," Ghez said. "Its electrons are being accelerated much more frequently than previously thought."
Looking ahead
The Milky Way's black hole packs a mass equal to about 2.6 million Suns. Unraveling the new mystery could help astronomers understand why it is less active than others, Ghez said. Most researchers assume the galaxy is in a quiet phase at least in part because there isn't much material flowing in. The most active galaxies appear either to be young and developing or to have recently undergone a merger with another large galaxy.
"We now have a completely new and continuously open window to study the material that is falling onto the black hole," Ghez said.
The Milky Way's central black hole is about 26,000 light-years away. Other black holes, only as massive as a handful of stars, exist throughout the galaxy.
The new observations were made using the 10-meter Keck II Telescope at the W.M. Keck Observatory in Hawaii. Seeing the black hole's external activity in infrared was a breakthrough, said Mark Morris, a UCLA professor of physics and astronomy who also worked on the study. Most of the plasma's emissions appear to be in the infrared, the results show.
"The black hole's dirty laundry is hanging right there for us to see," Morris said. "We're peering deep down inside this tumultuous region."
No comments:
Post a Comment