杏吧原创

WE KNOW they are heavy, but how exactly do you weigh a black hole? The usual way to estimate the mass of black holes orbiting stars is to look at how the star wobbles under the influence of the black hole鈥檚 motion. But this method is imprecise, says Nikolai Shaposhnikov, an astrophysicist at NASA鈥檚 Goddard Space Flight Center in Greenbelt, Maryland.

Instead, Shaposhnikov and Lev Titarchuk, at George Mason University in Fairfax, Virginia, thought about the disc of material ripped from the companion star that forms around such black holes. As more matter falls in, the inner part of the disc becomes congested, 鈥渓ike when five lines of traffic have to merge into one鈥�, Shaposhnikov says. This clogged material oscillates, producing X-ray pulses at a rate that is related to the black hole鈥檚 mass, he says.

The pair measured such pulses using NASA鈥檚 Rossi X-ray Timing Explorer (RXTE) satellite and found the black hole Cygnus X-1 has 8.7 times the mass of our sun 鈥� reducing the estimated error of previous measurements tenfold. The work will appear in The Astrophysical Journal.