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RAS PN 07/12 (NAM 08): MAPPING THE INVISIBLE: DARK MATTER CHARTED OUT TO FIVE BILLION LIGHT YEARS

Last Updated on Wednesday, 07 April 2010 18:28
Published on Tuesday, 17 April 2007 00:00
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.

ROYAL ASTRONOMICAL SOCIETY PRESS INFORMATION NOTE

EMBARGOED FOR 00:01 BST, TUESDAY 17 APRIL 2007
Ref.: PN 07/ 12 (NAM 08)
 
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AND

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NATIONAL ASTRONOMY MEETING PRESS ROOM (16 - 20 APRIL ONLY):

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                          892 477
 
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CONTACT DETAILS ARE LISTED AT THE END OF THIS RELEASE.


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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.


CONTACT(s):


Dr Ignacio Ferreras
King’s College
University of London
Tel:  +44 (0) 20 7848 2150
Mob: +44 (0)
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.


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


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 will be posted on the NAM website at www.nam2007.uclan.ac.uk/press.php and are also available from http://www.star.ucl.ac.uk/~ferreras/NAM07.html


FIGURE CAPTIONS:


Figure 1. A false colour map of the dark matter distribution in the
sample of nine galaxies. The colour represents the ratio between total
and ordinary (or baryonic) matter so that dark matter dominates the regions that appear blue, whereas in the red areas matter is mostly baryonic.


Figure 2. The relationship between ordinary and dark matter in a galaxy. On the left is the ordinary matter that makes up the galaxy and its shape indicates how it was assembled. In the centre the spectral energy distribution gives information about the ages of the stars in the galaxy (i.e. information about its star formation history). Finally, on the right the map of dark matter shows how it extends over a much larger area than the visible part of the galaxy.

Figure 3. Gravitational lensing at work, illustrated with an image of the old observatory at University College, London observatory. On the left is the normal view and on the right we see it, as it would appear if there were a massive but transparent galaxy hiding in the quadrangle.