Light shed on dark matter

Brussels, 06 Feb 2006

Dark Matter forms up to 95 per cent of all matter in the universe, but ever since its discovery, there has been no clue as to what it is, as it emits no radiation or light while appearing to be everywhere. Astronomers from the Cambridge institute of Astronomy have discovered the first clues as to what this mysterious substance is.

Dark Matter was first observed when astronomers noticed that galaxies move too quickly compared to their mass - suggesting a force other than gravity must be in play.

The researchers have now managed to estimate the temperature of dark matter, which gives the team further information on this mysterious substance. 'It's the first clue of what this stuff might be. For the first time ever, we're actually dealing with its physics,' the Institute's Professor Gerry Gilmore told the BBC.

The team used the Very Large Telescope (VLT) in Chile to make maps of the cosmos, taking advantage of a phenomenon known as 'weak lensing'. Lensing occurs when objects of very high mass distort the space-time around it. This, in effect, gives astronomers a vast natural lens far out in space. If the lensing effect is larger than it ought to be for the size of the galaxies causing the effect, then the presence of dark matter can be inferred, and can even be mapped.

From studying 12 'dwarf' galaxies in great detail, the team has managed to make the first detailed, 3-D map of those galaxies. This has allowed the team to weigh the dark matter for the first time.

This weighing led to a host of further data. The first thing the team discovered is that there is about 400 times more dark matter than 'normal' matter in those galaxies. This has also given the team the opportunity to estimate the density, or 'speed' of the dark matter particles.

'The distribution of dark matter bears no relationship to anything you will have read in the literature up to now. It comes in a 'magic volume' which happens to correspond to an amount which is 30 million times the mass of the sun,' explained Professor Gilmore.

The team has estimated that the particles are travelling at 9 km/s. 'These are the first properties other than existence that we've been able to determine,' he said.

These speeds put the temperature of dark matter at about 10,000 degrees Celsius, considerably warmer than previous estimates, which assumed that dark matter moved slowly and was extremely cold. This is significant, as it means that astronomers searching for dark matter have been looking in the wrong place.

The most likely candidate particle for dark matter remains the so-called 'wimp', or weakly interacting massive particle, which fits certain models for the creation of the Universe. Whatever dark matter is, there is now some light thrown on this astronomically mysterious entity, and further light should be expected.

Further information

CORDIS RTD-NEWS/© European Communities, 2005
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