black hole Nearly naked black hole lost its ‘clothes’ to a gravity rip tide

[Reefa]

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It’s a supermassive streaker. When one galaxy zipped through a larger one, the lesser galaxy’s stars were mostly stripped away by a gravitational rip tide. It fled the confrontation with just a thin veil of stars cloaking the gargantuan black hole at its center.

 

That’s what Jim Condon of the National Radio Astronomy Observatory in Charlottesville, Virginia, and his team think they have seen using radio telescopes: a bright fountain of radiation that only huge black holes can produce. Follow-up observations with the Hubble Space Telescope showed that the object, about 2.2 billion light years away, has just a small belt of stars around it rather than the sprawling galaxy that a black hole of its size ought to have.

 

If confirmed, it would be the first time astronomers have found a supermassive black hole stripped bare by a larger galaxy. His group has searched the skies for nearly nude black holes for years, so it was exciting but not surprising for them to see one at last.

 

What is strange is that only one of 492 black holes they examined was in this state, Condon says. “Nearly every black hole was just sitting there [in a galaxy] like it was supposed to.” Cosmological theory predicts that scantily clad singularities should often form when galaxies collide, and Condon hopes to discover more examples.

 

Black holes can lose their galactic trappings in a few ways, says Avi Loeb of Harvard University. When two supermassive black holes merge, a gravitational wave can well up capable of hurling the merged black hole from the galaxy. Loeb and his colleagues claim to have seen one of these before.

 

And if three black holes spiral towards each other, one can get tossed out, undressed. “Just like with human beings, three-body systems are unstable,” Loeb says.

 

According to Loeb, the black hole that Condon’s group think they have identified probably had its galaxy shredded, because it held on to a few stars – if it had been in a black hole merger or a three-body scuffle, it would have lost everything. Loeb hopes to observe more naked black holes formed in the latter two ways. “These are the more exotic birds,” he says.

 

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