Scientists reveal how supermassive black holes bind into pairs duringgalaxy mergers (Forwarded)

News Service
Stanford University
Stanford, Caifornia

Contact:
Dawn Levy, News Service
(650) 725-1944

Comment:
Stelios Kazantzidis, Kavli Institute for Particle Astrophysics and
Cosmology
(650) 926-4786

June 6, 2007

Scientists reveal how supermassive black holes bind into pairs during
galaxy mergers

By Dawn Levy

Picture the Milky Way galaxy -- a disk of stars and gas, a stellar
spheroid and an enormous halo of dark matter. It spirals around a black
hole that is supermassive -- about three million solar masses. The Milky
Way's total mass is about 100 billion solar masses -- enormous to us but
average among galaxies.

Then imagine that galaxy encountering its identical twin. The first galaxy
merges with the second to produce a galaxy that's even grander and
greater. Cosmologists think that's how galaxies grow -- through a complex
process of continuous mergers.

Now, using supercomputers to simulate galaxy mergers, scientists at
Stanford and elsewhere have seen the formation of a new type of structure
-- a central disk of gas that can be from a hundred to a few thousand
light years wide and from a few hundred million to a billion solar masses.
They report the first simulated formation of a supermassive black hole
(SMBH) pair in the June 7 edition of Science Express, an online version of
Science magazine.

"The theory of General Relativity that Einstein developed about 90 years
ago which describes the behavior of gravity has been verified in many of
its predictions," says Stanford co-author Stelios Kazantzidis of the Kavli
Institute for Particle Astrophysics and Cosmology. "However, there is one
major consequence of this theory that has yet escaped verification, and
this is the existence of gravitational waves. Due to the fact that
coalescing SMBH binaries constitute the most powerful sources of
gravitational-wave emission in the universe, it is of primary importance
to establish the necessary conditions leading to the merger of two SMBHs."

Kazantzidis and Lucio Mayer from ETH Zurich (the Swiss Federal Institute
of Technology) and the University of Zurich, the main authors, conceived
the project and designed and conducted the numerical simulations. Monica
Colpi from the University Milano-Bicocca and Piero Madau from the
University of California-Santa Cruz helped interpret the results. Thomas
Quinn from the University of Washington and James Wadsley from McMaster
University wrote the code used to perform the simulations.

A SMBH binary consists of two SMBHs orbiting around their center of mass.
The black holes may or may not merge depending on the existence of a
mechanism that can extract angular momentum from their orbit and reduce
their relative separation, Kazantzidis said.

"A pair of SMBHs may interact with the stars around them or with the gas,"
he said. "Both the gas and the stars exert a frictional force onto the
black holes. This frictional force extracts energy from the orbital motion
of the SMBHs. As a result, the separation between them gradually shrinks."
It is unclear whether it is the friction of the stars or that of the gas
that dominates the process.

To model a galaxy merger, scientists first use a computer program that
builds galaxies based on observations and theoretical predictions. For
example, all galaxies are surrounded by extended, massive dark matter
halos, and spiral galaxies contain a disk of stars. In all self-consistent
models of disk galaxies these two components must be included.

"Once the galaxy models are constructed, we must parameterize the orbits
of involved galaxies and set them on a collision course," Kazantzidis
said.

The scientists found that when the merging galaxies contain some gas,
their SMBHs will form a binary system in most cases. Once paired, the
black holes may keep reducing their separation until they are about as far
apart as our solar system's width, Kazantzidis said.

"At this point we predict that they should begin producing strong
gravitational waves," he said. "Since the emission of waves extract energy
from the binary black hole, the two holes will ultimately merge, less than
a billion years after they had initially formed a binary."

This paper reports the first time that a galactic merger is followed
through the formation of a gravitationally bound SMBH binary and down to
scales of only a few light years.

While many earlier authors have investigated the formation of SMBH
binaries using supercomputer simulations of galaxy collisions, Kazantzidis
and his colleagues followed the processes over a wide range of spatial and
temporal scales.

"With very few exceptions, earlier studies did not explore the role of gas
in driving the evolution of a SMBH pair," Kazantzidis added. "Theoretical
and observational evidence do suggest that the central regions of merger
remnants contain significant amounts of gas. Our simulations provide new
insights into how SMBHs form pairs and coalesce, and underscores the vital
role of the gaseous component of galaxies in determining the fate of
SMBHs."

Average galaxies such as the Milky Way do not contain such impressive
gaseous nuclear disks, suggesting that mergers are important in forming
these structures, Kazantzidis said. "Our simulations were the first to
report the formation of such nuclear disks in galaxy mergers. It is
natural to assume that the large reservoir of gas present in these nuclear
disks represents the fuel that feeds the central supermassive black holes
and powers the active galactic nucleus."

The results are good news for LISA, or the Laser Interferometer Space
Antenna experiment, a space-based observatory designed to detect
gravitational waves using laser interferometry over astronomical
distances. The LISA detector is ideal for probing merging supermassive
black holes such as those simulated by Kazantzidis and colleagues. A joint
venture of NASA and the European Space Agency, LISA is expected to begin
observations around 2015.

"Detecting the gravitational waves from the merging supermassive black
holes will not only be the strongest confirmation of one of the most
fundamental theories of physics (General Relativity) but also a
confirmation of our general scenario for galaxy formation and evolution,"
Kazantzidis says. "This is one of the most beautiful examples of the deep
connections between fundamental physics and astrophysics."

Simulations were performed on supercomputers at the Pittsburgh
Supercomputing Center, the University of Zurich and ETH Zurich. "The
numbers of calculations needing to be computed is astronomical,"
Kazantzidis said. "This is why we resort to powerful supercomputers
capable of performing very large numbers of calculations per second.
Supercomputer simulations allow us to effectively compress the vast
cosmological timescales that apply to the largest structures in our
universe down to weeks of virtual time. This gives us a completely new
view of the universe from what is available to us by observation alone."

What's more, the supercomputers provide the closest thing to a physics lab
that is available to the astrophysicist. "The numerical simulations we
conducted constitute the most extensive calculations ever performed on
this topic, consuming several months of supercomputing time each at
various supercomputer centers around the world," he said.

While the merger that the scientists simulated -- one where both galaxies
have equal mass -- is less probable than a merger of unequal galaxies,
it's not at all improbable, Kazantzidis said. In fact, it's the fate of
our own Milky Way.

"Our galaxy is in a collision course with its largest neighbor, Andromeda,
due to take place in approximately three billion years time," Kazantzidis
said. "The result of this collision will be the destruction of the disks
and the formation of an elliptical galaxy."

Support for the work came from the U.S. Department of Energy, NASA and the
Alexander von Humboldt Foundation.

-30-

Editor Note:

Photos of galaxies merging are available on the web at
http://newsphotos.stanford.edu/Hole.jpg [172KB]
and
http://newsphotos.stanford.edu/Hole_composite.jpg [169KB]

Relevant Web URLs:

* Kavli Institute for Particle Astrophysics and Cosmology
http://www-group.slac.stanford.edu/kipac/

On Jun 13, 8:58 pm, Andrew Yee wrote:
News Service
Stanford University
Stanford, Caifornia

Contact:
Dawn Levy, News Service
(650) 725-1944

Comment:
Stelios Kazantzidis, Kavli Institute for Particle Astrophysics and
Cosmology
(650) 926-4786

June 6, 2007

Scientists reveal how supermassive black holes bind into pairs during
galaxy mergers

By Dawn Levy

Picture the Milky Way galaxy -- a disk of stars and gas, a stellar
spheroid and an enormous halo of dark matter. It spirals around a black
hole that is supermassive -- about three million solar masses. The Milky
Way's total mass is about 100 billion solar masses -- enormous to us but
average among galaxies.

Then imagine that galaxy encountering its identical twin. The first galaxy
merges with the second to produce a galaxy that's even grander and
greater. Cosmologists think that's how galaxies grow -- through a complex
process of continuous mergers.

Now, using supercomputers to simulate galaxy mergers, scientists at
Stanford and elsewhere have seen the formation of a new type of structure
-- a central disk of gas that can be from a hundred to a few thousand
light years wide and from a few hundred million to a billion solar masses.
They report the first simulated formation of a supermassive black hole
(SMBH) pair in the June 7 edition of Science Express, an online version of
Science magazine.

"The theory of General Relativity that Einstein developed about 90 years
ago which describes the behavior of gravity has been verified in many of
its predictions," says Stanford co-author Stelios Kazantzidis of the Kavli
Institute for Particle Astrophysics and Cosmology. "However, there is one
major consequence of this theory that has yet escaped verification, and
this is the existence of gravitational waves. Due to the fact that
coalescing SMBH binaries constitute the most powerful sources of
gravitational-wave emission in the universe, it is of primary importance
to establish the necessary conditions leading to the merger of two SMBHs."

Kazantzidis and Lucio Mayer from ETH Zurich (the Swiss Federal Institute
of Technology) and the University of Zurich, the main authors, conceived
the project and designed and conducted the numerical simulations. Monica
Colpi from the University Milano-Bicocca and Piero Madau from the
University of California-Santa Cruz helped interpret the results. Thomas
Quinn from the University of Washington and James Wadsley from McMaster
University wrote the code used to perform the simulations.

A SMBH binary consists of two SMBHs orbiting around their center of mass.
The black holes may or may not merge depending on the existence of a
mechanism that can extract angular momentum from their orbit and reduce
their relative separation, Kazantzidis said.

"A pair of SMBHs may interact with the stars around them or with the gas,"
he said. "Both the gas and the stars exert a frictional force onto the
black holes. This frictional force extracts energy from the orbital motion
of the SMBHs. As a result, the separation between them gradually shrinks."
It is unclear whether it is the friction of the stars or that of the gas
that dominates the process.

To model a galaxy merger, scientists first use a computer program that
builds galaxies based on observations and theoretical predictions. For
example, all galaxies are surrounded by extended, massive dark matter
halos, and spiral galaxies contain a disk of stars. In all self-consistent
models of disk galaxies these two components must be included.

"Once the galaxy models are constructed, we must parameterize the orbits
of involved galaxies and set them on a collision course," Kazantzidis
said.

The scientists found that when the merging galaxies contain some gas,
their SMBHs will form a binary system in most cases. Once paired, the
black holes may keep reducing their separation until they are about as far
apart as our solar system's width, Kazantzidis said.

"At this point we predict that they should begin producing strong
gravitational waves," he said. "Since the emission of waves extract energy
from the binary black hole, the two holes will ultimately merge, less than
a billion years after they had initially formed a binary."

This paper reports the first time that a galactic merger is followed
through the formation of a gravitationally bound SMBH binary and down to
scales of only a few light years.

While many earlier authors have investigated the formation of SMBH
binaries using supercomputer simulations of galaxy collisions, Kazantzidis
and his colleagues followed the processes over a wide range of spatial and
temporal scales.

"With very few exceptions, earlier studies did not explore the role of gas
in driving the evolution of a SMBH pair," Kazantzidis added. "Theoretical
and observational evidence do suggest that the central regions of merger
remnants contain significant amounts of gas. Our simulations provide new
insights into how SMBHs form pairs and coalesce, and underscores the vital
role of the gaseous component of galaxies in determining the fate of
SMBHs."

Average galaxies such as the Milky Way do not contain such impressive
gaseous nuclear disks, suggesting that mergers are important in forming
these structures, Kazantzidis said. "Our simulations were the first to
report the formation of such nuclear disks in galaxy mergers. It is
natural to assume that the large reservoir of gas present in these nuclear
disks represents the fuel that feeds the central supermassive black holes
and powers the active galactic nucleus."

The results are good news for LISA, or the Laser Interferometer Space
Antenna experiment, a space-based observatory designed to detect
gravitational waves using laser interferometry over astronomical
distances. The LISA detector is ideal for probing merging supermassive
black holes such as those simulated by Kazantzidis and colleagues. A joint
venture of NASA and the European Space Agency, LISA is expected to begin
observations around 2015.

"Detecting the gravitational waves from the merging supermassive black
holes will not only be the strongest confirmation of one of the most
fundamental theories of physics (General Relativity) but also a
confirmation of our general scenario for galaxy formation and evolution,"
Kazantzidis says. "This is one of the most beautiful examples of the deep
connections between fundamental physics and astrophysics."

Simulations were performed on supercomputers at the Pittsburgh
Supercomputing Center, the University of Zurich and ETH Zurich. "The
numbers of calculations needing to be computed is astronomical,"
Kazantzidis said. "This is why we resort to powerful supercomputers
capable of performing very large numbers of calculations per second.
Supercomputer simulations allow us to effectively compress the vast
cosmological timescales that apply to the largest structures in our
universe down to weeks of virtual time. This gives us a completely new
view of the universe from what is available to us by observation alone."

What's more, the supercomputers provide the closest thing to a physics lab
that is available to the astrophysicist. "The numerical simulations we
conducted constitute the most extensive calculations ever performed on
this topic, consuming several months of supercomputing time each at
various supercomputer centers around the world," he said.

While the merger that the scientists simulated -- one where both galaxies
have equal mass -- is less probable than a merger of unequal galaxies,
it's not at all improbable, Kazantzidis said. In fact, it's the fate of
our own Milky Way.

"Our galaxy is in a collision course with its largest neighbor, Andromeda,
due to take place in approximately three billion years time," Kazantzidis
said. "The result of this collision will be the destruction of the disks
and the formation of an elliptical galaxy."

Support for the work came from the U.S. Department of Energy, NASA and the
Alexander von Humboldt Foundation.

-30-

Editor Note:

Photos of galaxies merging are available on the web at
http://newsphotos.stanford.edu/Hole.jpg[172KB]
and
http://newsphotos.stanford.edu/Hole_composite.jpg[169KB]

Relevant Web URLs:

* Kavli Institute for Particle Astrophysics and Cosmology
http://www-group.slac.stanford.edu/kipac/

I replied to this same subject earlier and I put this copy below.

Hannu

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From: Hannu Poropudas
Newsgroups: sci.physics,sci.physics.relativity
Subject: How Supermassive Black Holes Come Together
Date: Mon, 11 Jun 2007 09:18:36 -0700
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On Jun 9, 4:26 am, Sam Wormley wrote:
How Supermassive Black Holes Come Together
http://www.universetoday.com/2007/06...e-black-holes-...

Galaxies get bigger and bigger through galactic mergers. Two small
galaxies come together, merge their stars, and you get a bigger
galaxy. But astronomers have always wondered, what happens with the
two supermassive black holes that seem to always lurk at the heart of
galaxies. What happens when two compact objects with millions of
times the mass of our sun collide? Good question.

An international team of physicists have developed a computer
simulation designed to answer this very question. And in a recent
article in Science Express, they published the results of the
simulation.

See:http://www.universetoday.com/2007/06...e-black-holes-...

I don't agree so peacefull results of their interaction (simulation
result may be ok,
if interaction is quite distant with these two supermassive black-
holes so that their
event horizonts would not overlap):

I think that if these two supermassive black holes interacts deeply
(if their two nuclei
"neutrino stars" comes close enough to each others so that their
"color electricity flames"
interacts) then huge EXPLOSION would follow and jets of quarks and
leptons would result
in the first place and they possible then again later combine somehow
to jets of protons and
electrons which again later combine to hydrogen gas ?

Hannu