Famous black hole divulges its vital statistics

SOME black holes keep a tight hold on everything, even their own vital statistics. Now Cygnus X-1, the first black hole discovered, has divulged its distance from Earth and in turn its weight - and that it was born spinning.

Cygnus X-1 was identified as a likely black hole in 1972, but its distance from Earth has been maddeningly difficult to pin down. This in turn has made it hard to determine basic properties like its mass and spin.

Mark Reid of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and colleagues used the Very Long Baseline Array of radio telescopes spanning the US to measure the object's parallax - tiny shifts in its apparent position due to Earth's motion around the sun. Based on the size of the shifts, Cygnus X-1 is 6000 light years away, give or take a few hundred light years, the team reports (arxiv.org/abs/1106.3688).

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