DARK MATTER AND GALACTIC COLLISIONS

New observations on collisions of clusters of remote galaxies have shed further light on the nature of dark matter, enabling some theories to be ruled out.
http://www.bbc.co.uk/news/science-environment-32066013

Astrophysicists studied 72 collisions between galactic clusters. Visible light was recorded by the Hubble Space Telescope, and x-rays by the Chandra Observatory. The researchers tracked the movement of the three main components of galaxies: stars, clouds of gas, and dark matter.

Although dark matter, which makes up 85% of the matter in the universe, does not emit or absorb light, it does have gravity and its presence can be detected by its bending effect on light passing nearby.

Dr Richard Massey of Durham University and colleagues were able to map the dark matter during the galactic collisions. Unlike the gas clouds which interact strongly, and stars which glide past, the dark matter passes through everything and emerges unscathed.

The strongest result from the study was further evidence that dark matter really is present in the galactic clusters. Further, many theories of dark matter can now be ruled out, for example that dark matter is a  'dark version' of ordinary matter, made of 'dark atoms'.

Comment:  Dark matter and energy are slowly yielding their mysteries to these astrophysical observations. It's difficult not to feel that one day there will be a major breakthrough in our understanding.

THE SEARCH FOR DARK MATTER

A highly sensitive particle detector, located one mile underground in a cavern at the bottom of a former gold mine in the Black Hills of South Dakota, is an experiment searching for particles of dark matter.

http://www.bbc.co.uk/news/science-environment-26819792

The detector, called LUX, is inside a steel tank containing 70,000 gallons of pure water, free of any naturally occurring radioactivity that could interfere with the experiment. The detector contains 815 lb of liquid xenon. A dark matter particle interacting with the xenon would cause a tiny flash of light.

LUX failed to detect any of the dark matter particles, called weakly interacting massive particles (WIMPs) during a test run last year, but is now being re-run for a longer period of time.

Professor Rick Gaitskell of Brown University, one of the principal scientists leading the LUX search for dark matter, says 'The hypothesis we are working with at the moment is that a WIMP was the relic left-over from the Big Bang, and in fact dominates over the regular material you and I are made of'.

Dark matter may comprise about 85% of all the matter in the universe.

Other experiments are also searching for evidence of dark matter, including the Large Hadron Collider and space telescopes.