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NASA sheds light on dark matter

First direct evidence?

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NASA says it now has the first direct evidence for the existence of dark matter, thanks to observations of a huge, intergalactic collision.

Researchers using the Chandra-X telescope have been watching two galactic clusters collide, an event they say is the most energetic in the universe, ever, apart from the Big Bang.

They also used Hubble, the European Southern Observatory's Very Large Telescope and the Magellan optical telescopes to track the location of the mass in each cluster using gravitational lensing. This is the phenomenon whereby a sufficiently large mass can actually bend the path of light, so that you can see something that would otherwise be obscured by a massive galaxy, for instance.

As the two galaxy clusters smash into one another, the huge clouds of hot, gaseous normal matter encounter drag, similar to air resistance. Because of this, normal matter is slowed down by the impact of one cluster on another. Dark matter, on the other hand, continues unimpeded since it doesn't interact with normal matter, except through gravity.

This separation of the two types of matter shows up in the data, NASA says, and this provides the evidence that the dark matter is really there.

Most of the matter in the universe is thought to be so-called dark matter. It gets its name because it is effectively invisible, and until now its existence could only be inferred from its gravitational effects.

The term was invented to account for the fact that despite not having enough mass to hold themselves together under their own gravity, galaxies still spectacularly failed to tear themselves apart. Astronomers reasoned that something invisible, but massive, must be holding things together. Hence, dark matter.

However, not all scientists agree (and when do they ever?). Some alternative theories have been put forward, but NASA says only dark matter can explain the observations here.

Doug Clowe of the University of Arizona, and leader of the study, says the work has "closed the loophole" on gravity.

"A universe that's dominated by dark stuff seems preposterous, so we wanted to test whether there were any basic flaws in our thinking," he said "These results are direct proof that dark matter exists." ®

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