Andrew Yee[_1_]
January 12th 07, 07:50 PM
Media Relations
Northwestern University
MEDIA CONTACT:
Megan Fellman, 847-491-3115
January 9, 2007
Triple Interactions of Supermassive Black Holes Found To Be Common In Early
Universe
EVANSTON, Ill. -- New cosmological computer simulations produced by a team
of astronomers from Northwestern University, Harvard University and the
University of Michigan show for the first time that supermassive black holes
(SMBHs), which exist at the centers of nearly all galaxies, often come
together during triple galaxy interactions.
Frederic Rasio, a theoretical astrophysicist and professor of physics and
astronomy in the Weinberg College of Arts and Sciences at Northwestern
University in Evanston, Ill., will present the findings Jan. 8 at the
meeting of the American Astronomical Society in Seattle.
The theoretical results are of special interest because of the recent
discovery by astronomers at the California Institute of Technology of a
possible triple quasar, findings that also will be reported at the Seattle
meeting.
"SMBHs become visible as quasars when they accrete large quantities of gas
from their host galaxies, releasing prodigious amounts of energy in
radiation," said Rasio. "The observation of three quasars in very close
proximity shows that the kinds of interactions predicted by our computer
simulations are indeed taking place, even in the nearby, present-day
universe."
The existence of binary SMBHs, formed when two galaxies come together, merge
and bring together their central SMBHs, has been discussed by astronomers
for many years. The new work reported by Rasio shows that interactions
between three SMBHs are also quite frequent, occurring perhaps up to a few
times per year within the observable universe. While the merger of a binary
SMBH following the collision between two galaxies simply leads to the
formation of a bigger SMBH at the center of a bigger galaxy, triple black
hole interactions can be much more violent and interesting.
"Three is so much better than two because the dynamics of three
gravitationally interacting bodies is chaotic, as opposed to the much more
regular motion of two bodies simply orbiting each other," said Rasio.
These violent triple interactions were especially frequent at early
cosmological times, when our universe was only about one-tenth of its
present age, and galaxies were smaller and collided much more frequently
than today. At that earlier epoch, galaxies were living in a very crowded
environment, as the universe had yet to expand to its present size. Smaller
galaxies merged together to form some of the much bigger galaxies we see
today. Although slower today, this process is ongoing. Even our own galaxy,
the Milky Way, will experience a "major merger" event when it collides with
its nearest neighbor, the Andromeda galaxy, in about three billion years.
Triple encounters of SMBHs often end in the complete coalescence of an SMBH
pair, guaranteeing a high cosmic merger rate of black holes. They can also
lead to SMBH binaries being kicked out of their parent galaxies and
wandering "naked" through the universe.
"Triple black hole systems undergo complex, chaotic interactions often
ending in the high-velocity ejection of one component, often straight out of
the host galaxy," said Loren Hoffman, a doctoral student at Harvard and a
member of the research team.
"The detection of wandering black hole binaries flying in empty space would
give us a unique signature of triple interactions in the early universe,"
said team member Marta Volonteri, assistant professor of astronomy at the
University of Michigan. "Gravitational waves emission seems to be the only
way of spotting these wandering binaries."
Merging SMBH binaries are key sources of gravitational radiation that
astronomers hope to detect with future observatories such as the Laser
Interferometer Space Antenna (LISA), a billion-dollar joint venture of NASA
and the European Space Agency, which is currently in a design phase and is
expected to begin observations in or around 2017.
In addition to Rasio, Hoffman and Volonteri, the research team includes
Stefan Umbreit, a postdoctoral fellow at Northwestern.
The work was supported by the Astronomy Division of the National Science
Foundation and by the Astrophysics Theory Program at NASA.
Northwestern University
MEDIA CONTACT:
Megan Fellman, 847-491-3115
January 9, 2007
Triple Interactions of Supermassive Black Holes Found To Be Common In Early
Universe
EVANSTON, Ill. -- New cosmological computer simulations produced by a team
of astronomers from Northwestern University, Harvard University and the
University of Michigan show for the first time that supermassive black holes
(SMBHs), which exist at the centers of nearly all galaxies, often come
together during triple galaxy interactions.
Frederic Rasio, a theoretical astrophysicist and professor of physics and
astronomy in the Weinberg College of Arts and Sciences at Northwestern
University in Evanston, Ill., will present the findings Jan. 8 at the
meeting of the American Astronomical Society in Seattle.
The theoretical results are of special interest because of the recent
discovery by astronomers at the California Institute of Technology of a
possible triple quasar, findings that also will be reported at the Seattle
meeting.
"SMBHs become visible as quasars when they accrete large quantities of gas
from their host galaxies, releasing prodigious amounts of energy in
radiation," said Rasio. "The observation of three quasars in very close
proximity shows that the kinds of interactions predicted by our computer
simulations are indeed taking place, even in the nearby, present-day
universe."
The existence of binary SMBHs, formed when two galaxies come together, merge
and bring together their central SMBHs, has been discussed by astronomers
for many years. The new work reported by Rasio shows that interactions
between three SMBHs are also quite frequent, occurring perhaps up to a few
times per year within the observable universe. While the merger of a binary
SMBH following the collision between two galaxies simply leads to the
formation of a bigger SMBH at the center of a bigger galaxy, triple black
hole interactions can be much more violent and interesting.
"Three is so much better than two because the dynamics of three
gravitationally interacting bodies is chaotic, as opposed to the much more
regular motion of two bodies simply orbiting each other," said Rasio.
These violent triple interactions were especially frequent at early
cosmological times, when our universe was only about one-tenth of its
present age, and galaxies were smaller and collided much more frequently
than today. At that earlier epoch, galaxies were living in a very crowded
environment, as the universe had yet to expand to its present size. Smaller
galaxies merged together to form some of the much bigger galaxies we see
today. Although slower today, this process is ongoing. Even our own galaxy,
the Milky Way, will experience a "major merger" event when it collides with
its nearest neighbor, the Andromeda galaxy, in about three billion years.
Triple encounters of SMBHs often end in the complete coalescence of an SMBH
pair, guaranteeing a high cosmic merger rate of black holes. They can also
lead to SMBH binaries being kicked out of their parent galaxies and
wandering "naked" through the universe.
"Triple black hole systems undergo complex, chaotic interactions often
ending in the high-velocity ejection of one component, often straight out of
the host galaxy," said Loren Hoffman, a doctoral student at Harvard and a
member of the research team.
"The detection of wandering black hole binaries flying in empty space would
give us a unique signature of triple interactions in the early universe,"
said team member Marta Volonteri, assistant professor of astronomy at the
University of Michigan. "Gravitational waves emission seems to be the only
way of spotting these wandering binaries."
Merging SMBH binaries are key sources of gravitational radiation that
astronomers hope to detect with future observatories such as the Laser
Interferometer Space Antenna (LISA), a billion-dollar joint venture of NASA
and the European Space Agency, which is currently in a design phase and is
expected to begin observations in or around 2017.
In addition to Rasio, Hoffman and Volonteri, the research team includes
Stefan Umbreit, a postdoctoral fellow at Northwestern.
The work was supported by the Astronomy Division of the National Science
Foundation and by the Astrophysics Theory Program at NASA.