Rutgers astronomer sheds new light on dark matter

Rutgers astronomy researcher
Licia Verde, together with Dr. Alan Heavens of the University of Edinburgh,
has led an international team of 30 scientists in shedding new light on
dark matter – one of the great mysteries of the universe.  They found
this invisible and mysterious substance distributed in a pattern parallel
to the arrangement of the galaxies, tracing them closely. Refining
its relationship to the galaxies also allowed them to assess its quantity.
Scientists from a dozen institutions in the United States, Britain
and Australia used the largest-ever survey of more than 200,000 galaxies,
made with the Anglo-Australian Telescope, in New South Wales, Australia.
They analyzed in detail how the galaxies are clustered, relating their
distribution to the gravitational pull of the dark matter.
“Where there is matter, there is gravity and its pull has ‘lumped’
the galaxies into an uneven distribution,” said Verde, a postdoctoral
researcher
at Rutgers with a joint appointment to the Princeton University Observatory.
“There is much more dark matter than there is mass in the galaxies, so
the force it exerts has moved the galaxies around.” She explained
that, were it not for the dark matter and its gravitational forces, the
galaxies would be in a much more uniform pattern.

Scientists would like to see where the dark matter mass is, but telescopes
can only see light, from bright objects such as galaxies. Verde explained
that it is like looking at a Christmas tree at night; you
see only the lights, but not the whole tree. This had limited what
researchers could learn from studying galaxy positions.; With the
application of new computer analyses and gravitational theory, the
astronomers
have now been able to work out where the dark matter is. It is just
what is to be expected if galaxies and dark matter are clustered in exactly
the same way.
Verde added, “Knowing how clustered the dark matter is, also reveals
how much of it there is — about seven times as much as ordinary matter;
but only a quarter of what is needed to slow down the expansion of the
universe to a halt.”

The findings are presented in a paper submitted to the Monthly
Notices of the Royal Astronomical Society with Verde as its lead author.
(The paper appears electronically at
http://xxx.lanl.gov/abs/astro-ph/0112161
A second study, led by Dr. Ofer Lahav of Cambridge University,
contrasted the same galaxy distribution map to the distribution of temperature
fluctuations in the cosmic microwave background radiation — a sea of
microwaves
that exists everywhere in the universe and represents an “echo” of the
Big Bang. It is difficult to measure, but tiny fluctuations in its
temperature can reveal the kinds of matter and energy that compose the
universe.
“The second paper looks at the relationship of the galaxies to
a totally different set of phenomena, but the scientists got the same result,
independently confirming our findings,” said Verde.

EDITOR’S NOTE: A computer simulation image of dark matter tracing
galaxies may be downloaded from
http://ur.rutgers.edu/medrel/photos/simulation.jpg
Use of the image should include the credit line: Benson, Baugh, Cole,
Frenk and Lacey (Monthly Notices of the Royal Astronomical Society, 311,
793, 2001).

For additional information, see:
http://www.physics.rutgers.edu/~verde/seeingtheinvisible.html
or contact Dr. Verde at (609) 258 7323 or by e-mail:
verde@physics.rutgers.edu;
or contact Dr. Heavens at (+44) (0)131 668 8352 or by e-mail at
afh@roe.ac.uk.