January 17, 2008

Pools of Invisible Matter Mapped in Space

A new map
reveals dense pools of invisible matter tipping the scales at 10 trillion times
the mass of the sun and housing a cosmic city of ancient galaxies.

The map,
presented last week at a meeting of the American Astronomical Society in
Austin, Texas, provides indirect evidence for so-called dark matter and how
this mysterious substance affects galaxy formation.

theorize that dark matter, considered to make up about 85 percent of the universe's
matter, acts as scaffolding on which galaxies mature. As
the universe evolves, the tug from dark matter's gravitational field causes
galaxies to collide and swirl into superclusters.

It's all
these gravitational effects, from something that can't be seen, that indicates
dark matter exists.

dark matter halos are what allow the galaxies to form in the first place. The
dark matter is the underlying skeleton of the universe," said Meghan Gray
of the University of Nottingham in the United Kingdom, who was part of the
map-making team. "Most of the universe is dark matter. Galaxies are just
froth on this ocean of dark matter."

invisible matter

Catherine Heymans of the University of British Columbia in Vancouver and
colleagues used NASA's Hubble Space Telescope to observe a supercluster called
Abell 901/902, which resides 2.6 billion light-years from Earth and spans more
than 16 million light-years across.

astrophysicists measured light from a backdrop of more than 60,000 galaxies
after it passed through the supercluster and its dark matter. According to Einstein's general
relativity theory, the presence of matter can bend spacetime, deflecting the
path of a light ray passing through the mass.

matter leaves a signature in distant galaxies" explained study co-author
Ludovic Van Waerbeke of the University of British Columbia. "For example, a
circular galaxy will become more distorted to resemble the shape of a banana if
its light passes near a dense region of dark matter."

averaging the shape-distortions from the thousands of galaxies, the researchers
found four pools of dark matter. And the invisible clumps matched up with the
location of hundreds of ancient galaxies, which have experienced a violent
history in their passage from the outskirts of the supercluster into the
central hubs.

the supercluster wasn't there, you'd still see all of these galaxies in the
background," Gray told SPACE.com. "But you put this massive
object [in front of them] and your view gets distorted. It's a cosmic optical


survey's broader goal is to understand how galaxies are influenced by the
environment in which they live.

"The new
map of the underlying dark matter in the supercluster is one key piece of this
puzzle," Gray said. "At the same time, we're looking in detail at the galaxies

The galaxies in the central hubs, they are finding,
show signs of aging, as they are elliptical, red in color and are no longer
forming stars. Disk galaxies reside on the outskirts of the supercluster. These
youthful galaxies are blue-hued and buzzing with star birth.

It's these
young galaxies that constantly fall into the supercluster, adding to its
galactic girth.

they come in, either they're interacting with each other more or they're
interacting with the dark matter," Gray explained. "Something is
happening to change their properties."

The team
plans to study individual galaxies in an effort to understand how this
supercluster environment shapes and changes galaxies.