Exceptionally massive black hole discovered 3 mln light years from Earth

November 14th, 2007 - 2:28 am ICT by admin  
Lead author Jerome Orosz of San Diego State University said, with a mass 15.7 times that of the Sun, M33 X-7 is the most massive stellar black hole known till date.

A stellar black hole is formed from the collapse of the core of a massive star at the end of its life.

Orosz said their result has intriguing implications for the evolution and ultimate fate of massive stars.

“This discovery raises all sorts of questions about how such a big black hole could have been formed,” said Orosz.

M33 X-7 orbits a companion star that eclipses the black hole every three and a half days. The companion star also has an unusually large mass, 70 times that of the Sun, which makes it the most massive companion star in a binary system containing a black hole.

“This is a huge star that is partnered with a huge black hole. Eventually, the companion will also go supernova and then we’ll have a pair of black holes,” said co-author Jeffrey McClintock of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

He said conventional models for the evolution of massive stars fail to explain the properties of the M33 X-7 binary system.

He said the parent star for the black hole must have had a mass greater than the existing companion in order to form a black hole before the companion star.

He said such a massive star would have had a radius larger than the present separation between the stars, so the stars must have been brought closer while sharing a common outer atmosphere.

“Massive stars can be much less extravagant than people think by hanging onto a lot more of their mass toward the end of their lives. This can have a big effect on the black holes that these stellar time-bombs make,” said Orosz.

Co-researcher Wolfgang Pietsch said that Chandra observations had revealed M33 X-7 to be the first black hole in a binary system observed to undergo eclipses.

The eclipsing nature enabled unusually accurate estimates for the mass of the black hole and its companion, Pietsch said.

“Since it’s eclipsing and because it has such extreme properties, this black hole is an incredible test-bed for studying astrophysics,” said Pietsch.

The study appears in the October 18 issue of the journal Nature. (ANI)

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