Andrew Yee[_1_]
April 15th 08, 05:00 PM
ESA News
http://www.esa.int
15 April 2008
Milky Way's giant black hole awoke from slumber 300 years ago
A team of Japanese astronomers using ESA's XMM-Newton, along with NASA and
Japanese X-ray satellites, has discovered that our galaxy's central black
hole let loose a powerful flare three centuries ago.
The finding helps resolve a long-standing mystery: why is the Milky Way's
black hole so quiescent? The black hole, known as Sagittarius A-star (A*),
is a certified monster, containing about 4 million times the mass of our
Sun. Yet the energy radiated from its surroundings is thousands of millions
of times weaker than the radiation emitted from central black holes in other
galaxies.
"We have wondered why the Milky Way's black hole appears to be a slumbering
giant," says team leader Tatsuya Inui of Kyoto University in Japan. "But now
we realise that the black hole was far more active in the past. Perhaps it's
just resting after a major outburst."
The observations, collected between 1994 and 2005, revealed that clouds of
gas near the central black hole brightened and faded quickly in X-ray light
as they responded to X-ray pulses emanating from just outside the black
hole. When gas spirals inward toward the black hole, it heats up to millions
of degrees and emits X-rays. As more matter piles up near the black hole,
the X-ray output becomes greater.
These X-ray pulses take 300 years to traverse the distance between the
central black hole and a large cloud known as Sagittarius B2, so the cloud
responds to events that occurred 300 years earlier.
When the X-rays reach the cloud, they collide with iron atoms, kicking out
electrons that are close to the atomic nucleus. When electrons from farther
out fill in these gaps, the iron atoms emit X-rays. But after the X-ray
pulse passes through, the cloud fades to its normal brightness.
Amazingly, a region in Sagittarius B2 only 10 light-years across, varied
considerably in brightness in just 5 years. These brightenings are known as
light echoes. By resolving the X-ray spectral line from iron, Suzaku's
observations were crucial for eliminating the possibility that subatomic
particles caused the light echoes.
"By observing how this cloud lit up and faded over 10 years, we could trace
back the black hole's activity 300 years ago," says team member Katsuji
Koyama of Kyoto University. "The black hole was a million times brighter
three centuries ago. It must have unleashed an incredibly powerful flare."
This new study builds upon research by several groups who pioneered the
light-echo technique. Last year, a team led by Michael Muno, who now works
at the California Institute of Technology in, California, USA, used Chandra
observations of X-ray light echoes to show that Sagittarius A* generated a
powerful burst of X-rays about 50 years ago -- about a dozen years before
astronomers had satellites that could detect X-rays from outer space. "The
outburst three centuries ago was 10 times brighter than the one we
detected," says Muno.
The galactic centre is about 26 000 light-years from Earth, meaning we see
events as they occurred 26 000 years ago. Astronomers still lack a detailed
understanding of why Sagittarius A* varies so much in its activity. One
possibility, says Koyama, is that a supernova a few centuries ago plowed-up
gas and swept it into the black hole, leading to a temporary feeding frenzy
that awoke the black hole from its slumber and produced the giant flare.
Notes for editors:
The new study, which will appear in the Publications of the Astronomical
Society of Japan, combines results from Japan's Suzaku and ASCA X-ray
satellites, NASA's Chandra X-ray Observatory, and the ESA's XMM-Newton X-ray
Observatory. The article in which the results appear is titled 'Time
Variability of the Neutral Iron Lines from the Sgr B2 Region and its
Implication of a Past Outburst of Sgr A* ' by T. Inui, K. Koyama, H.
Matsumoto and T. Tsuru
Launched in 2005, Suzaku is the fifth in a series of Japanese satellites
devoted to studying celestial X-ray sources and is managed by the Japan
Aerospace Exploration Agency (JAXA). This mission is a collaborative effort
between Japanese universities and institutions and NASA Goddard.
XMM-Newton, ESA's space-borne X-ray observatory is the biggest scientific
satellite ever built in Europe. Its telescope mirrors are the most sensitive
ever developed in the world, and with its sensitive detectors, it sees much
more than any previous X-ray satellite.
XMM-Newton science operations are handled at ESA's European Space and
Astronomy Centre (ESAC). The satellite was designed and built to return data
for at least a decade. It has detected more X-ray sources than any previous
satellite and is helping solve many cosmic mysteries of the violent
Universe, from what happens in and around black holes to the formation of
galaxies in the early Universe. The satellite uses over 170 wafer-thin
cylindrical mirrors spread over three telescopes.
Its orbit takes it almost a third of the way to the Moon, so that
astronomers can enjoy long, uninterrupted views of celestial objects. NASA's
Marshall Space Flight Center, Alabama, USA manages the Chandra program for
the agency's Science Mission Directorate. The Smithsonian Astrophysical
Observatory controls science and flight operations from the Chandra X-ray
Center in Massachusetts, USA.
[NOTE: Images and weblinks supporting this release are available at
http://www.esa.int/esaSC/SEMV9Z3XQEF_index_1.html ]
http://www.esa.int
15 April 2008
Milky Way's giant black hole awoke from slumber 300 years ago
A team of Japanese astronomers using ESA's XMM-Newton, along with NASA and
Japanese X-ray satellites, has discovered that our galaxy's central black
hole let loose a powerful flare three centuries ago.
The finding helps resolve a long-standing mystery: why is the Milky Way's
black hole so quiescent? The black hole, known as Sagittarius A-star (A*),
is a certified monster, containing about 4 million times the mass of our
Sun. Yet the energy radiated from its surroundings is thousands of millions
of times weaker than the radiation emitted from central black holes in other
galaxies.
"We have wondered why the Milky Way's black hole appears to be a slumbering
giant," says team leader Tatsuya Inui of Kyoto University in Japan. "But now
we realise that the black hole was far more active in the past. Perhaps it's
just resting after a major outburst."
The observations, collected between 1994 and 2005, revealed that clouds of
gas near the central black hole brightened and faded quickly in X-ray light
as they responded to X-ray pulses emanating from just outside the black
hole. When gas spirals inward toward the black hole, it heats up to millions
of degrees and emits X-rays. As more matter piles up near the black hole,
the X-ray output becomes greater.
These X-ray pulses take 300 years to traverse the distance between the
central black hole and a large cloud known as Sagittarius B2, so the cloud
responds to events that occurred 300 years earlier.
When the X-rays reach the cloud, they collide with iron atoms, kicking out
electrons that are close to the atomic nucleus. When electrons from farther
out fill in these gaps, the iron atoms emit X-rays. But after the X-ray
pulse passes through, the cloud fades to its normal brightness.
Amazingly, a region in Sagittarius B2 only 10 light-years across, varied
considerably in brightness in just 5 years. These brightenings are known as
light echoes. By resolving the X-ray spectral line from iron, Suzaku's
observations were crucial for eliminating the possibility that subatomic
particles caused the light echoes.
"By observing how this cloud lit up and faded over 10 years, we could trace
back the black hole's activity 300 years ago," says team member Katsuji
Koyama of Kyoto University. "The black hole was a million times brighter
three centuries ago. It must have unleashed an incredibly powerful flare."
This new study builds upon research by several groups who pioneered the
light-echo technique. Last year, a team led by Michael Muno, who now works
at the California Institute of Technology in, California, USA, used Chandra
observations of X-ray light echoes to show that Sagittarius A* generated a
powerful burst of X-rays about 50 years ago -- about a dozen years before
astronomers had satellites that could detect X-rays from outer space. "The
outburst three centuries ago was 10 times brighter than the one we
detected," says Muno.
The galactic centre is about 26 000 light-years from Earth, meaning we see
events as they occurred 26 000 years ago. Astronomers still lack a detailed
understanding of why Sagittarius A* varies so much in its activity. One
possibility, says Koyama, is that a supernova a few centuries ago plowed-up
gas and swept it into the black hole, leading to a temporary feeding frenzy
that awoke the black hole from its slumber and produced the giant flare.
Notes for editors:
The new study, which will appear in the Publications of the Astronomical
Society of Japan, combines results from Japan's Suzaku and ASCA X-ray
satellites, NASA's Chandra X-ray Observatory, and the ESA's XMM-Newton X-ray
Observatory. The article in which the results appear is titled 'Time
Variability of the Neutral Iron Lines from the Sgr B2 Region and its
Implication of a Past Outburst of Sgr A* ' by T. Inui, K. Koyama, H.
Matsumoto and T. Tsuru
Launched in 2005, Suzaku is the fifth in a series of Japanese satellites
devoted to studying celestial X-ray sources and is managed by the Japan
Aerospace Exploration Agency (JAXA). This mission is a collaborative effort
between Japanese universities and institutions and NASA Goddard.
XMM-Newton, ESA's space-borne X-ray observatory is the biggest scientific
satellite ever built in Europe. Its telescope mirrors are the most sensitive
ever developed in the world, and with its sensitive detectors, it sees much
more than any previous X-ray satellite.
XMM-Newton science operations are handled at ESA's European Space and
Astronomy Centre (ESAC). The satellite was designed and built to return data
for at least a decade. It has detected more X-ray sources than any previous
satellite and is helping solve many cosmic mysteries of the violent
Universe, from what happens in and around black holes to the formation of
galaxies in the early Universe. The satellite uses over 170 wafer-thin
cylindrical mirrors spread over three telescopes.
Its orbit takes it almost a third of the way to the Moon, so that
astronomers can enjoy long, uninterrupted views of celestial objects. NASA's
Marshall Space Flight Center, Alabama, USA manages the Chandra program for
the agency's Science Mission Directorate. The Smithsonian Astrophysical
Observatory controls science and flight operations from the Chandra X-ray
Center in Massachusetts, USA.
[NOTE: Images and weblinks supporting this release are available at
http://www.esa.int/esaSC/SEMV9Z3XQEF_index_1.html ]