Spin of Supermassive Black Holes Measured for First Time (Forwarded)

Office of University Communications
University of Maryland

Contacts:
Lee Tune, 301 405 4679

For Immediate Release: May 29, 2007

Spin of Supermassive Black Holes Measured for First Time

COLLEGE PARK, Md. -- Astronomers at the University of Maryland have made the
first quantitative measurements of the spin of several supermassive black
holes, information that is essential to understanding how these giant black
holes develop and grow.

University of Maryland astronomy graduate student Laura Brenneman and
Associate Professor of astronomy Christopher Reynolds have used observations
's XMM-Newton X-ray telescope to examine the relativistically altered shape
of the iron spectral line emitted from the accretion disks around these
black holes. Comparing these data with new theoretical models for this
spectral line, developed by Brenneman, they have generated measures of
angular momentum, or the spin rate, of these objects. The black hole for
which they have the best data is found at the center of the galaxy
MCG-06-30-15. Their analysis indicates that this black hole is spinning very
fast indeed, at least 98.7 percent of the maximum possible spin rate allowed
's Theory of General Relativity.

Brenneman and Reynolds, her thesis advisor at the University of Maryland,
presented their findings at a press briefing at the American Astronomical
s meeting in Honolulu Hawaiion May 29th.

really know very little about how supermassive black holes form and grow,
said Reynolds. have models for how it can happen, but being able to
determine spin rate is critical to our understanding of the process by which
it actually happens.

One mechanism by which black holes can grow to be supermassive is through
accretion of massive amounts of material, explained Reynolds, who together
with Brenneman presented their findings. When black holes suck in matter
they spin faster, thus a rapid rate of spin would indicate growth by
accretion. Supermassive black holes can also be the product of a collision
between black holes. Models indicate that such collisions tend to result in
a supermassive black hole that spins at only a modest rate. Black holes can
be completely defined by their mass and spin. Scientists have long been able
to measure the mass of a black hole (through any number of methods), but,
until now, measuring spin has been far more challenging.

Supermassive black holes have masses that are hundreds of thousands to
billions of times that of the Sun. It is currently thought that most, if not
all galaxies, including the Milky Way, contain supermassive black holes at
their galactic centers.

The research of Reynolds and Brenneman was supported in part by the National
Science Foundation and NASA.