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> Bursts Spotted at Milky Way's Black Hole - Yahoo! News
SPACE.com Space.com Staff
space.com 2 hrs 44 mins ago
Outbursts from the black hole at the center of our Milky Way galaxy
generate material that is stretched as it orbits near the
New observations from two telescopes provide a better look at what's
going on down there.
While black holes can't be seen, material swirling into one is
superheated, giving off radiation that can be observed. While the
Milky Way's black hole is not among the most active in the universe,
it is prone to flare-ups.
A team of European and US astronomers used ESO's Very Large Telescope
(VLT) and the Atacama Pathfinder Experiment (APEX) telescope, both in
Chile, to study light from the black hole, called Sagittarius A*, at
near-infrared wavelengths and the longer submillimeter wavelengths
This is the first time that astronomers have recorded an outburst
with these telescopes simultaneously.
"Observations like this, over a range of wavelengths, are really the
only way to understand what's going on close to the black hole," said
Andreas Eckart of the University of Cologne, who led the team.
Sagittarius A* is about 26,000 light-years away. It is a supermassive
black hole with a mass of about 4 million times that of the sun.
Most, if not all, galaxies are thought to have a supermassive black
hole in their centers.
"Sagittarius A* is unique, because it is the nearest of these monster
black holes, lying within our own galaxy," said team member Frederick
K. Baganoff of MIT. "Only for this one object can our current
telescopes detect these relatively faint flares from material
orbiting just outside the event horizon."
The emission from Sagittarius A* is thought to come from gas thrown
off by stars, which then orbits and falls into the black hole.
The researchers detected violently variable infrared emission, with
four major flares over a six-hour period. The submillimeter-
wavelength results showed flares that began more than an hour after
the infrared flares.
The researchers explain that this time delay is probably caused by
the rapid expansion, at speeds of about 3.1 million mph (5 million
kph), of the clouds of gas that are emitting the flares. This
expansion causes changes in the character of the emission over time.
The material was moving at only 0.5 percent of the speed of light. To
escape from the very strong gravity so close to the black hole, the
gas would have to be traveling at half the speed of light 100 times
faster than detected - and so the researchers believe that the gas
cannot be streaming out in a jet. Instead, they suspect that a blob
of gas orbiting close to the black hole is being stretched out, like
dough in a mixing bowl, and this is causing the expansion.