An artist's illustration depicts what astronomers think is happening within the Cygnus X-1 system. Cygnus X-1 is a so-called stellar-mass black hole, a class of black holes that comes from the collapse of a massive star. New studies with data from Chandra and several other telescopes have determined the black hole's spin, mass, and distance with unprecedented accuracy. (Image: NASA/CXC/M.Weiss)
I remember, as a kid, reading about Cygnus X-1, which was discovered in 1964 and is the first black hole ever discovered. What made Cygnus X-1 so cool to my fevered childhood imagination is that it orbits a companion star, at a distance only about 20% of the distance from the Earth to the Sun. That means that stellar material is constantly being torn from the star and drawn towards the black hole. The thought of that both fascinated and terrified me then, and frankly, still does a little bit now.
Cygnus X-1 is one of the most studied objects in the night sky, as you might imagine. (It was also the source of a famous bet. In the 1970s, Stephen Hawking bet Kip Thorne that X-1 wasn't a black hole. In 1990, Hawking conceded he was wrong and ponied up.) And now some new research has given us substantially more information about how the black hole works. The Harvard-Smithsonian Center for Astrophysics, working in conjunction with the Chandra X-Ray Observatory and several other telescopes, have announced that they have a virtually complete description of the black hole, including its mass, spin, and approximate age.
From their telescope data, scientists have determined that the black hole is about 6,070 light years from Earth, and it's mass is almost 15 times that of the Sun's. The Event Horizon of the Black Hole - which is the point where nothing, not even light, can escape, is spinning at about 800 revolutions per second. The team was also able to determine that Cygnus X-1 is not the result of a supernova - the proposed cause for some black holes - but rather the collapse of a star that at one point was most likely 100 times the mass of the Sun. From all of this data, the scientists were able to determine that the black hole itself is about 6 million years old - just a baby, in stellar terms.
Kip Thorne, who had won the bet with Hawking about Cygnus X-1's black hole status, surprisingly admitted until this point, he actually hasn't been convinced that X-1 was a black hole. "For forty years, Cygnus X-1 has been the iconic example of a black hole. However, despite Hawking's concession, I have never been completely convinced that it really does contain a black hole -- until now," said Thorne. "The data and modeling described in these three papers at last provide a completely definitive description of this binary system."
