Mapping the invisible: Dark matter charted out to five billion light years (Forwarded)

Royal Astronomical Society
London, U.K.

Issued by RAS Press Officers:

Robert Massey
Tel: +44 (0)20 7734 4582
AND
Anita Heward
Tel: +44 (0)1483 420 904

NATIONAL ASTRONOMY MEETING PRESS ROOM (16 - 20 APRIL ONLY):
Tel: +44 (0)1772 892 613
+44 (0)1772 892 475
+44 (0)1772 892 477

RAS Web site:
http://www.ras.org.uk/

RAS National Astronomy Meeting web site:
http://nam2007.uclan.ac.uk

CONTACT:

Dr Ignacio Ferreras
King's College
University of London
Tel: +44 (0) 20 7848 2150

From 16 to 20 April, Dr Ferreras can be contacted via the NAM press office
(see above).

PRESS INFORMATION NOTE: RAS PN 07/12 (NAM 08)

EMBARGOED FOR 00:01 BST, TUESDAY 17 APRIL 2007

MAPPING THE INVISIBLE: DARK MATTER CHARTED OUT TO FIVE BILLION LIGHT YEARS

Most of the matter in the Universe is not the ordinary kind made up of
protons, neutrons, and electrons, but an elusive "dark matter" detectable
only from its gravity. Like a tenuous gas, dark matter is all around us --
it goes through us all the time without us noticing -- but tends to collect
in large quantities around galaxies and clusters of galaxies and makes up
about one-sixth of the mass of the Universe.

In his talk on Tuesday 17 April at the Royal Astronomical Society National
Astronomy Meeting in Preston, Dr Ignacio Ferreras of King's College London
will present the maps of the distribution of "ordinary" and dark matter in
nine galaxies out to a distance of five billion light-years from the Sun.

Dr Ferreras worked with Dr Prasenjit Saha (University of Zurich,
Switzerland) and Professor Scott Burles (Massachusetts Institute of
Technology, USA) to take advantage of a rare astronomical phenomenon known
as 'gravitational lensing'. The galaxies they studied serendipitously lie in
front of quasars, which are bright sources of light at even greater
distances. The gravity of the nearer galaxy and dark matter distorts the
quasar light, causing the quasar to be seen as two or four images. The
placement of these mirage images, studied using new theoretical techniques
in gravitational lensing, makes it possible to measure the total mass and
effectively gives scientists a telescope for dark matter!

By analysing the starlight from the galaxies using stellar evolution theory,
it is possible to measure the mass of the stars they contain. Combining
these ideas with archival data from the Hubble Space Telescope, Dr Ferreras
and his colleagues were able to make dark-matter maps.

Current theories of galaxy formation can explain some but not all of these
new findings. After the Big Bang, gas should have fallen towards the centres
of dark-matter halos, there igniting to form the stars that go on to make up
a galaxy. But why is there a higher proportion of dark matter in more
massive galaxies? And had these galaxies already finished forming five
billion years ago? These questions will only be answered by future theories
of galaxy formation.

NOTES FOR EDITORS

The 2007 RAS National Astronomy Meeting is hosted by the University of
Central Lancashire. It is sponsored by the Royal Astronomical Society and
the UK Science and Technology Facilities Council.

This year the NAM is being held together with the UK Solar Physics (UKSP)
and Magnetosphere, Ionosphere and Solar-Terrestrial (MIST) spring meetings.
2007 is International Heliophysical Year.

IMAGES:

These are available from
http://www.star.ucl.ac.uk/~ferreras/NAM07.html