Monday, October 1, 2007

The view from Hawai'i is shocking—telescopes are showing galaxies colliding and evidence that matter is being ripped apart.

In the artist's illustration shown above (credit CXC/M. Weiss) the red color represents hot gas while the blue represents dark matter. Yellow spots represent individual galaxies. The weirdness: The big pink ball in the middle represents the densest dark matter, but there are no galaxies there. Why are the galaxies and the dark matter separate?

Astrophysicists, writing in an October 2007 issue of The Astrophysical Journal, say are baffled by data that suggests the mysterious “dark matter” is behaving in ways that violate known principles.

Dark matter is a kind of theoretical fix. Astronomers, trying to make sense of calculations that show there's not enough matter in the universe to account for its observed behavior, suggest there's something else out there that we can't see, but which adds significantly to the mass of the universe. Really significant—most of the matter in the universe is believed to be the mysterious dark matter.

In some ways dark matter is believed to act like regular or “light” matter, but it's impossible to detect, except indirectly. It doesn't emit detectable light or radiation. However, while you may not see the dark matter, you know it's there because it has gravity and its presence can bend light.

And it is believed to populate the university generally alongside regular matter.

“Nearly all of our observations and inferences support the conclusion that dark matter and stars concentrate together in the same areas. The abundance of dark matter relative to stars varies with the size of the object under consideration, but we're not accustomed to finding blobs of dark matter 'all by themselves,'” said Adam Bolton, at the University of Hawai'i's Institute for Astronomy, in an email.

So it was a surprise when astronomers pointed NASA's Chandra X-ray Observatory, Mauna Kea's Canada-France-Hawaii Telescope, and Mauna Kea's Subaru Telescope, at a galaxy cluster called Abell 520, where two galaxies were crashing into each other.

What they found was a region that had plenty of galaxies but very little dark matter, and another area with lots of dark matter and hot gas but few galaxies

Astronomers are not easily blow away, but here's what researcher, University of Victoria's Hendrik Hoekstra, said in a press release: “It blew us away that it looks like the galaxies are removed from the densest core of dark matter. This would be the first time we've seen such a thing and could be a huge test of our knowledge of how dark matter behaves."

"These results challenge our understanding of the way clusters merge. Or, they possibly make us even reexamine the nature of dark matter itself," said Dr. Andisheh Mahdavi of the University of Victoria, British Columbia.

The group plans more research to try to figure out what's going on. One of the suggestions is that dark matter may be even stranger than previously thought—that it has its own attractive force in addition to gravity, a force that would keep the dark matter together but would allow light matter to spin away.

Bolton, who was not part of the research team, said he anticipates that more observation will yield clues that suggest that dark matter really isn't misbehaving (at least according to currently accepted rules).

“If more sensitive observations confirm the authors' conclusion, I and many others will be convinced that there is a great puzzle here!” he said.

“Like many scientists, I tend to take a wait-and-see attitude towards a result like this. If it really, truly holds up, then it is extraordinary. But as the old saw goes, extraordinary claims require extraordinary evidence...”

© 2007 Jan W. TenBruggencate

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