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Cosmologists Ponder the Puzzle of Black Rings

Forget black holes: astronomers are now pondering the properties of black rings.

  • May 6, 2009

A black hole is a region of space in which the gravitational forces are so strong that nothing can escape, including light. They have fascinated cosmologists and physicists since they were first proposed, perhaps as long ago as the 18th century. The term itself is credited to the physicist John Wheeler who first used it in the late 1960s.

A question that various cosmologists have pondered is whether black holes can take on different shapes. The thinking, until recently, has been that they cannot–in four dimensional spacetime other shapes such as black rings collapse into conventional black holes.

But the discovery in the last 20 years that the universe is not only expanding but accelerating away from us changes all that. If the rings can be created on the scale of the cosmological constant, which causes this accelerated expansion, then various groups have calculated that perhaps this accelerated expansion can balance the gravitational collapse, making black rings stable.

Now Masashi Kimura at Osaka City University in Japan has looked at the possibility of black rings forming in higher dimensional space. It turns out that not only are black rings possible in these conditions, but various other shapes should be stable too.

Kimura’s analysis looks at how a thin black ring may have formed early in the Universe’s history and later shrunk into a conventional singularity. He also looks at multi black rings–Olympic-style–and describes how these coalesce.

This and other work marks an interesting new branch of theory for black hole specialists. But cosmologists have yet to address the most important questions of all. If these objects do exist or have existed in the past, what would they look like and how might we spot them?

Ref: arxiv.org/abs/0904.4311: Dynamical Black Rings with a Positive Cosmological Constant

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