MILKY WAY MONSTER STARS
IN COSMIC REALITY SHOW
longest X-ray look at the supermassive black hole at the Milky Way's center has
given astronomers unprecedented access to its life and times. The new data from
NASA's Chandra X-ray Observatory revealed that our galaxy's central black hole
is a frequent "bad actor," prone to numerous outbursts and occasional large
The observations of the
black hole, Sagittarius A* or Sgr A*, occurred over a two-week period with a
total exposure time of 164 hours. During this time Sgr A* flared up in X-ray
intensity several times. Astronomers also found evidence that suggests it had an
even more boisterous past. These discoveries will help unlock the secrets of how
Sgr A* grows and interacts with its environment.
"We are getting a look at
the everyday life of a supermassive black hole like never before," said
Frederick K. Baganoff of the Massachusetts Institute of Technology (MIT) in
Cambridge, Mass., who presented these new results on behalf of an international
team at a press conference today at the American Astronomical Society meeting in
Seattle. "We see it flaring on an almost daily basis," he said.
The cause of the flares is
not understood, but the rapidity with which they rise and fall indicates they
are occurring near the event horizon, or point of no return, around the black
hole. Even when it flares, the intensity of the X-ray emission from the vicinity
of the black hole is relatively weak, which suggests that Sgr A*, weighing in at
3 million times the mass of the Sun, is a starved black hole.
"Although it appears to
snack often, this black hole is definitely on a severe diet," said Baganoff.
"This could be because explosive events in the past blew away much of the gas
from the neighborhood of the black hole," he explained.
Indeed, evidence for such
events, which astronomers are viewing 26,000 years later due to the time it
takes light to travel to Earth from the center of the galaxy, can be found in
the image. A faint streak of X-rays about one light-year long has been
discovered 1.5 light-years from Sgr A*. The streak points at Sgr A*, suggesting
the streak may be a jet of particles expelled at nearly the speed of light from
just outside the event horizon of the black hole. The intensity and size of this
jet indicate the flaring activity has been occurring for many years.
On a much larger scale,
huge lobes of 20-million-degree-Centigrade gas, extending over dozens of
light-years on either side of the black hole, have also been discovered. "These
lobes show that enormous explosions have occurred several times over the last
10,000 years," said Mark Morris of UCLA, lead author of a second paper on Sgr
A*, who also participated in the press conference.
Sangwook Park, of Penn
State University, University Park, Pa., and Michael Muno, of MIT, were lead
authors of two other papers presented at the meeting. These papers focused on
the extraordinarily rich region around the central black hole, where they
detected more than 2,000 X-ray sources.
NASA's Marshall Space
Flight Center in Huntsville, Ala., manages the Chandra program, and TRW, Inc.,
Redondo Beach, Calif., is the prime contractor for the spacecraft. The
Smithsonian's Chandra X-ray Center controls science and flight operations from
Cambridge, Mass., for the Office of Space Science at NASA Headquarters,
Images and additional
information about this result are available at:
Marshall Space Flight Center, Huntsville, Ala.
Chandra X-ray Observatory Center, CFA, Cambridge, Mass.
|Jan. 6, 2003
RELEASE: 03-002 BY
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