Dark Matter Ring Detected by Hubble

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Collision Simulated

Previous research showed that the galaxy cluster formed when two distinct clusters collided one to two billion years ago. That is: Had there been humans on Earth with a Hubble-like telescope one to two billion years ago, astronomers would have been able to witness the collision in process.

Jee and colleagues created a computer simulation of the smash-up to determine what happened when the galaxy clusters collided.

In the simulation, as the clusters smashed together, the dark matter fell to the center of the combined cluster and then sloshed back out.

As the dark matter sloshed out, however, the pull of gravity caused it to slow down and pile up like cars bunched up on a highway, the team explained.

"We conclude that the collision that happened about one or two billion years ago is responsible for the creation of the dark matter ring," Jee said.

A paper on the finding will appear in the June 20 issue of the Astrophysical Journal.

Finding Questioned

Robert Massey is a postdoctoral scholar at the California Institute of Technology and an expert on dark matter. He was not part of the research team, but he was included in the telephone briefing to offer perspective.

He said the new finding, if it stands up to scrutiny, adds further proof for the existence of dark matter and will advance scientific understanding of its mysterious nature.

"However, I do have to say this result is meeting substantial skepticism amongst the astronomical community," he noted.

The galaxy cluster itself is not well understood, he said, and some are concerned the dark matter ring is faint.

The gravitational lensing technique used to detect it may also have been compromised by peculiarities of the camera on Hubble, he added.

"So it's really exciting if it's right," Massey said, "but to be convinced of the ring, astronomers really want to see some independent observations verifying it."

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