FOR RELEASE: 9:00am PST, January 13, 2011 
Contact: Dr. David Pooley, Eureka Scientific, 617-230-1098, davepooley@me.com

ASTRONOMERS MAP OUT DARK MATTER IN MASSIVE GALAXIES

A team of astronomers led by Dr. David Pooley of Eureka Scientific has
made an important determination of the amount of dark matter in massive
galaxies using NASA's Chandra X-ray Observatory, providing independent
evidence for the dark matter.  In addition, these results help map out
the distribution of dark matter in elliptical galaxies, which is vital
in understanding both galaxy formation and the nature of dark matter.

The team studied 14 massive galaxies averaging about 6 billion light
years away, which appear almost directly in front of even more distant
galaxies nearly three times farther away. Those more distant galaxies
each harbor a supermassive black hole in the center, known as a quasar,
which produces an enormous amount of light.

Because of the special configuration of these galaxies, the light from
the distant quasar is "gravitationally lensed" by the intervening galaxy
to produce four images of the quasar as seen from Earth’s vantage point.
According to Einstein's general theory of relativity, the gravitational
field of a massive object, like one of these galaxies, can bend the path
of light in its vicinity, acting as a lens and producing multiple
images, or mirages, of the background object.

"We compared what those four images were supposed to look like according
to lensing theory to what we actually saw with Chandra," said Dr.
Pooley, who presented the results at the American Astronomical Society
meeting in Seattle.  "We found some major differences."

[EDITORS: example images available at http://www.deadlyastroninja.com/aas217/]

Based on the configuration of the images and the lensing galaxy, general
relativity can predict the amount of matter needed in the lensing galaxy
to produce the images of the background quasar.  However, it does not
address the form of the matter.

The team's explanation for the anomalies seen with Chandra lies in the
makeup of the matter in the lensing galaxies.  The aggregate
gravitational field from all the matter in the lensing galaxy produces
the effect strong enough to make the four distinct images of the
background quasar.  Along those four paths through the lensing galaxy,
the light from the quasar can be further affected.

The stars in a galaxy have their own gravitational fields, which further
perturb the light from the background quasar.  "It's lensing on top of
lensing," said Dr. Pooley.  The degree to which the light is further
affected is a sensitive function of the number of stars and the amount
of dark matter at the locations in the galaxy where the quasar's light
passes through.

A galaxy made entirely of stars, without any dark matter, would not
produce what Dr. Pooley and his team saw with Chandra.  Neither would a
galaxy made entirely of dark matter.  To produce what was observed, the
galaxies must consist of approximately 85-95% dark matter in the regions
where the background quasar's light passes through.  Typically, those
regions are located about 15,000 to 25,000 light years from the centers
of the lensing galaxies, similar to the distance of the Solar System
from the center of the Milky Way.

"This is one of the most direct measurements of the amount of dark
matter at a specific location in a galaxy," said Dr. Pooley.  Other
studies have determined the amount of dark matter in clusters of
galaxies, such as the Bullet Cluster.  In those cases, the dark matter
being studied is mainly outside of the individual galaxies in the vast
expanse between them.  These results, on the other hand, are probing
well inside individual galaxies.

Having determined the amount of matter in stars and dark matter at these
locations, the team's next step is to determine the mass-to-light ratio.
It will be the most direct measurement yet of an important quantity used
in almost all areas of astronomy.

Earlier work in this area was presented by Professor Paul Schechter of
the Massachusetts Institute of Technology and Professor Joachim
Wambsganss of the University of Heidelberg, who worked with observations
in optical light. Those results were ambiguous because the size of the
region emitting the optical light was unknown, but these new X-ray
results give a very clean determination of the amount of dark matter.
Both Schechter and Wambsganss are members of the team presenting the
X-ray results, along with Professor Saul Rappaport of MIT and Dr.
Jeffrey Blackburne of Ohio State University.

These results will be further refined as more gravitationally lensed
quasars are discovered and then observed with Chandra.  The discovery of
additional systems will be greatly aided by emerging large-area surveys
undertaken by ground-based observatories, such as the Panoramic Survey
Telescope & Rapid Response System project and the Large Synoptic Survey
Telescope project.