Post by Chicago Astronomer - Astro Joe on Feb 7, 2006 7:38:50 GMT -6
Dark matter comes out of the cold
Astronomers have for the first time put some real numbers on the physical characteristics of dark matter.
This strange material that dominates the Universe but which is invisible to current telescope technology is one of the great enigmas of modern science.
That it exists is one of the few things on which researchers have been certain.
But now an Institute of Astronomy, Cambridge, team has at last been able to place limits on how it is packed in space and measure its "temperature".
"It's the first clue of what this stuff might be," said Professor Gerry Gilmore. "For the first time ever, we're actually dealing with its physics," he told the BBC News website.
Science understands a great deal about what it terms baryonic matter - the "normal" matter which makes up the stars, planets and people - but it has struggled to comprehend the main material from which the cosmos is constructed.
'Magic volume'
Astronomers cannot detect dark matter directly because it emits no light or radiation.
Its presence, though, can be inferred from the way galaxies rotate: their stars move so fast they would fly apart if they were not being held together by the gravitational attraction of some unseen material.
Using the biggest telescopes in the world, including the Very Large Telescope facility in Chile, the group has made detailed 3D maps of the galaxies, using the movement of their stars to "trace" the impression of the dark matter among them and weigh it very precisely.
With the aid of 7,000 separate measurements, the researchers have been able to establish that the galaxies contain about 400 times the amount of dark matter as they do normal matter.
"If this temperature for the dark matter is correct, then it has huge implications for direct searches for these mysterious particles (it seems [science] may be looking in the wrong place for them) and for how we thought the galaxies and clusters of galaxies evolve in the Universe.
"Having 'hotter' dark matter makes it harder to form the smallest galaxies, but does help to make the largest structures. This result will generate a lot of new research."
"It turns out the Milky Way is more massive than we thought," said Professor Gilmore. "It now looks as though the Milky Way is the biggest galaxy in the local Universe, bigger even than Andromeda. It was thought until just a few months ago that it was the other way around."
Read the full story here from the BBC: news.bbc.co.uk/2/hi/science/nature/4679220.stm
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I wonder what mysteries will be found within the dark matter.
