Friday, February 10, 2006

Grey matter unravels dark matter

I watched Horizon last night, more mind-blowing ideas and fantastic feats of imagination, calculation and dogged research. One team has had no positive results for 18 years, but they are in for the long haul because what they are investigating are the most fundamental things about the universe - and much of it seemed to be missing !

Even more recent research has weighed our galaxy (don't ask me how) and found that, contrary to what was believed until only months ago, the Milky Way is the biggest galaxy in the the "local universe".

It makes you kinda proud - Springsteen should write a new song: "Born in the Milky Way ! Born in the Milky Way !..."

"Most of Our Universe Is Missing"

"Horizon discovers that 96% of the universe is missing. Only a tiny 4% of the universe is made of stuff we understand. Some scientists claim they know what the rest is, but others insist that nothing's missing at all, and that the real problem is far, far worse. They say that Newton, gravity and science itself is wrong, and needs to be re-written.

Dark matter, dark energy and variable gravity are put under the spotlight, as the world's leading cosmologists attempt to explain the biggest problem in science today."

Since the programme was made there has been progress, and, as so often with science, the results of observation have led to a radical rethink. It seems dark matter is travelling much faster and is therefore much hotter than theorists thought:

"Dark matter comes out of the cold"
By Jonathan Amos, BBC News science reporter

"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.

Such observations have established this dark material makes up about 80-85% of the Universe that is matter.

Now, the Cambridge team has provided new information with its detailed study of 12 dwarf galaxies that skirt the edge of our own Milky Way. 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.

"The distribution of dark matter bears no relationship to anything you will have read in the literature up to now," explained Professor Gilmore.

"It comes in a 'magic volume' which happens to correspond to an amount which is 30 million times the mass of the Sun.

"It looks like you cannot ever pack it smaller than about 300 parsecs - 1,000 light-years; this stuff will not let you. That tells you a speed actually - about 9km/s - at which the dark matter particles are moving because they are moving too fast to be compressed into a smaller scale.

"These are the first properties other than existence that we've been able determine."

Knowledge advance

The speed is a big surprise. Current theory had predicted dark matter particles would be extremely cold, moving at a few millimetres per second; but these observations prove the particles must actually be quite warm (in cosmic terms) at 10,000 degrees.

Weighing our galaxy

The Cambridge efforts have produced an additional, independent result: the detailed study of the dwarf galaxies has allowed the scientists to weigh our own galaxy more precisely than ever before.

"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."

For more on dark matter see;


Anonymous Anonymous said...

Jesus Ted, how can you sleep at night with interests like this?
Maybe you don't. That's why you out prowling around Paris til 6am..
Star gazing..perhaps?

Blogger sybariter said...

Jesus, LK, how could you not be interested in stuff like this ? :-) Curiosity keeps me reading about this kind of thing AND prowling the streets of Paris. To paraphrase Wilde, we are all in the gutter (Parisian if we're lucky), but some of us are weighing the stars.


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