Posted on 02/07/2006 3:56:57 AM PST by PatrickHenry
Astronomers have measured the temperature of dark matter for the first time. The discovery should help particle hunters to identify exactly what this mysterious substance is made of.
Although dark matter cannot be seen, its existence can be inferred from its gravitational interaction with stars around it, which stops rapidly rotating galaxies from flying apart. Astronomers estimate that, on average, dark matter must be about six times more abundant than normal, visible matter in our Universe.
But very little else is known about dark matter. "Even knowing it was dark was pretty profound," says Gerry Gilmore of Cambridge University, UK, who led the research. From this, researchers have extrapolated that it must have no electrical charge, no magnetism, and does not interact with light or any other radiation.
Now Gilmore and his colleagues have managed to map out its temperature and distribution in nearby dwarf galaxies. "These are the first properties of dark matter, other than its existence, that we've been able to determine," says Gilmore.
And the end result is startling: it seems that dark matter is whizzing about at some 10,000 °C . The work, which has not yet been submitted for publication, should provide some major clues to dark matter's other properties, says Gilmore.
A matter of temperature
The team used the Very Large Telescope array at the Paranal Observatory in Atacama, Chile, to measure the distance and speeds of hundreds of stars contained in 12 dwarf galaxies orbiting the Milky Way. Plotting their trajectories then revealed the invisible dark matter in between.
The team found that each galaxy seemed to contain the same amount of dark matter: roughly 30 million times the mass of the Sun. They say this is no coincidence. Instead, it represents the minimum amount of dark matter needed for a stable clump to hang together.
This finding implies that individual dark-matter particles must be moving at about 9 kilometres per second. Any faster, and a clump of dark matter of that mass would fly apart; any slower, and more dark matter would accumulate into the same space.
From this speed, the team could work out the temperature of the matter, just as the speed of water molecules bouncing around in a glass relates to its bulk temperature. The result is surprising: it seems that dark matter is much more 'tepid' than conventional 'cold' dark models have predicted, they say.
"I think this will be a major result," says Bob Nichol, an astrophysicist at the University of Portsmouth, UK. "Every now and again a result like this comes along that's a quantum leap in our understanding."
The findings were presented at a press conference in London, UK, on 3 February.
Getting warmer
The so-called cold dark matter model, in which particles move no faster than a few millimetres per second, has had tremendous success in explaining the structure of the Universe over the past decade or so, says Nichol.
But over the past few years, some astronomers have been suggesting that turning up the heat could solve some outstanding problems. The conventional cold dark matter model predicts that galaxies should have thousands of smaller satellite galaxies, along with extremely dense cores, explains Gilmore; yet neither has been found by astronomers1.
Some have posited the existence of a bit of very hot dark matter, such as neutrinos travelling close to the speed of light. But these are expected to make up a tiny portion of the total, so it wouldn't significantly affect the bulk temperature of dark matter.
'Tepid' dark matter may be a boon for theorists, says Nichol. "It could actually help us to solve some problems," he explains.
The team has yet to explain why its dark-matter particles are moving so fast, but says that the results are consistent with dark matter being made of some kind of weakly interacting, massive particles (WIMPS) never seen before. Gilmore hopes that the particles could be generated by the Large Hadron Collider, an immense particle accelerator currently being built at CERN in Geneva.
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Global warming?
Since they cannot see dark matter and do not know where it is, or how much there is, how can they measure the temperature. Must be because of global warming.
Galactic warming???
...Bush, Cheney, Rove, Haliburton at fault.
Isn't God awesome! He put something out there that we cannot see, but we can infer its presence by the effects it has; how apropos!
Luminiferous aether.
Could it be second-hand smoke from the democracks? (Only kidding)
If this same phrase was applied to Intelligent Design imagine how livid scientists would be that inference was applied to existence.
The difference is that there is empirical evidence by which to infer the existence of dark matter, whereas not only is there no empirical evidence by which to infer the existence of intelligence design, but rather all the empirical evidence suggests its nonexistence.
Nice article. Tks for posting.
I take issue with the "there must be about 6 times as much dark matter as ordinary matter" hypothesis.
Why 'must' it be so? Turns out that only under the above hypothesis can Scientists show that the expanding universe will at some point eventually stop and recontract. Turns out that a universe that suddenly popped into existence (at God's command?) is indigestible to our scientific brethren.
As for ID, it can neither be proved nor disproved at this point. To (dis)prove it, evidence from 'outside' the universe will be needed, which by construction, is impossible to have.
Ever heard of the Big Bang?
Hot milk glow-bull warning for the gullah bull
Precisely what I'm talking about.
The Big bang is nothing but the universe popping into existence.
What existed before the big bang? The dark matter hypothesis is nothng but an attempt to potray the expansion and contraction of the universe as some kinda endless birth and death cycle at a cosmic scale so that the idea of a creator intervening can be put aside.
Have a nice day.
I don't know - the fact that we can observe a pretty universal belief in God seems to be empirical to me.
Anyone who thinks that dark matter cannot be seen has never been to a dairy farm.
Dark matter heating up - Bush's faulkt for not signing Kyoto!
Isn't 10,000 °C kind of hot to use the term "tepid" in the headline? Matter at that temperature should be emitting light at about the color of our sun.
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