How do they find black holes and how many are in the Milky Way?
March 31st, 2009 Josephine
To date, astronomers have found 19 confirmed black holes and an additional 18 potential black holes, for a total of 37. All but one of the 37 lie in binary (double star) systems, each in the range from 5 to 10 times the Sun’s mass. Astronomers have also identified a supermassive black hole at the galaxy’s center containing about 4 million times the Sun’s mass.
In binary systems, a black hole and a star orbit each other. The black hole’s powerful gravity strips gas from its companion. As the gas accelerates toward the black hole and heats to millions of degrees, it gives off X rays. Astronomers find the black holes by looking for their characteristic X-ray emissions.
To confirm the black hole’s existence, astronomers track the companion star’s orbital motions. Knowing the star’s orbital speed makes it possible to calculate the mass of the companion black hole.
Appeared in: May, 2009 issue of Astronomy Magazine
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