http://www.tehrantimes.com/index_View.asp?code=196490
June 11, 2009
Giant black holes just got bigger
Some of the biggest black holes in the nearby Universe may be much larger than
previously thought.
A reassessment of the monster hole at the core of the M87 galaxy suggests it
could have 6.4 billion times the mass of our own Sun.
This result is two to three times the estimates from earlier studies. Dr. Karl
Gebhardt told an American Astronomical Society meeting that his investigations
led him to believe many other holes were under-recorded, also.
Most galaxies are thought to contain gargantuan central black holes. Indeed,
there is thought to be a very tight correlation between the size of a galaxy
and the core which consumes all matter that comes too close to it.
If a hole gets too big, too fast, however, it starts to push back, spewing
high-velocity jets of matter out into space.
"There are processes that happen around the black hole that affect how much
material you can dump on it," explained Dr. Karl Gebhardt from the University
of Texas at Austin.
"Eventually, it gets so massive that the jets that are common in these galaxies
blow out and they can actually halt the material that falls in."
But if supermassive black holes are actually bigger than previously thought,
the assumptions that help describe the relationship to their host galaxies
might now have to be re-evaluated, the researcher said.
Astronomers weigh supermassive black holes by studying the size of their host
galaxies and, critically, the speed with which stars move around inside those
galaxies.
The new study used novel computer modeling techniques to tease apart the
relative contributions to the total mass of M87 from its visible stars, its
black hole and its "dark halo".
The dark halo is a spherical region surrounding the galaxy that extends beyond
its main visible structure.
It contains "dark matter", an as yet unidentified material that cannot be
directly detected by telescopes but which astronomers know is there from its
gravitational interaction with everything else that can be seen.
"In order to get the small-scale analysis correct, you have to include what the
stars are doing at the outer envelope of the galaxy, ie you have to understand
the effect of the dark halo because that is where the dark halo lives - at the
edge of the galaxy."
Dr. Gebhardt and colleague Dr Jens Thomas, from the Max Planck Institute for
Extraterrestrial Physics, are the first group to incorporate the dark halo into
the mass calculations and the complexity of their effort required the use of a
supercomputer.
"This model took a few days to run whereas in the past it would have taken 10
years," Dr. Gebhardt said.
The results of the research, presented at the 214th meeting of the AAS in
Pasadena, California, suggest that all black hole masses for the biggest
galaxies may have been underestimated.
Dr. Gebhardt told the meeting that this assessment was supported by data coming
from the most recent - although not yet published - observations using the
world's most sophisticated telescopes.
Realizing that nearby supermassive black holes are actually bigger than
previously thought also goes some way to solving a paradox concerning the
masses of giant black holes in the distant Universe.
The black holes that power quasars - the compact but extremely luminous
galaxies seen in early cosmic history - are considerably bigger than anything
seen in the local Universe. This has always puzzled astronomers.
"By increasing masses of local black holes by two to three, it almost makes
that problem go away," Dr. Gebhardt said.
"That is, we're beginning to resolve the differences between the masses of the
black holes in quasars and the masses of black holes from nearby galaxies.
That's quite exciting when things start to come together."
(Source: BBC)
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