UVic Torch -- Autumn 2007
Autumn 2007,
Volume 28, Number 2

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UNIVERSITY ASTRONOMERS CONDUCTING SOME GALACTIC DETECTIVE WORK may have found evidence that dark matter—thought to form about 90 per cent of the universe—may not behave quite the way generally accepted theories predict.

Andisheh Mahdavi, a research associate with a group including Prof. Arif Babul reported their findings in the October Astrophysical Journal. They based their conclusions on observations of what they term a “cosmic train wreck” involving three large galaxies that collided to form a massive cluster called Abell 520, about three billion light years from earth.

The puzzle lies at the centre of the wreckage where the UVic investigators say they’ve detected dark matter and hot gas, with the galaxies sent to the outer edge of the cluster. That’s not something that’s been observed before and is not predicted by standard theories. Dark matter and stars would normally move together, and not be separated, in galaxy collisions.

In the accompanying image, Abell 520’s centre is filled with hot gas (red) and dark matter (blue) but empty of bright galaxies (yellow and orange).

Further, perhaps more conclusive observations involving the Hubble Space Telescope, are planned for next year. Those results are being awaited by others in the field who were naturally skeptical about the initial findings.

“That’s the way science works,” says Babul. “It’s the task of each one of us to be bold but cautious. It’s the responsibility of the scientific community to resist (new theories) until the evidence mounts sufficiently to overwhelm every opposing idea. It can take at least a decade.”

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