Black Holes
No TL;DR found
Abstract
Who says you can't get anything out of a black hole? In the past two years, astronomers have taken unprecedented aim at the first black hole ever found, Cygnus X-1. Using a vast armada of instruments, they have pinpointed Cygnus X-1's distance, which has let them measure the black hole's mass and even determine how fast it spins. These feats have then motivated two other astronomical teams to decipher the black hole's past and forecast its future. The flurry of recent activity concerning an object astronomers discovered nearly half a century ago has one simple cause: for the first time, we know its distance. " The distance was the breakthrough, " says Jerome Orosz, an astronomer at San Diego State University in California. To a non-astronomer, the distance to a celestial object may seem trivial, just another arcane statistic about a far-off body. In fact, distances are as vital as they are difficult to obtain. If you do not know how far away a star is, you do not know how much light it emits, which makes estimating its mass more difficult. A star that is twice as far away as you had thought is also four times as powerful. Furthermore, in the case of Cygnus X-1, this distance held the key to whether it really was a black hole at all. Most dead stars – dark objects that no longer shine – are not black holes. But dark objects that are at least three times as massive as the Sun must be black holes, because they are so heavy that nothing can stop them from collapsing into one. For Cygnus X-1, a 2009 paper gave such an enormous range of distances – from 3600 to 8200 light-years The swan's dark heart Astronomers discovered what they thought was the first black hole more than 40 years ago but have only recently verified its identity by establishing its distance, mass and spin. These fascinating observations are yielding new insights into Cygnus X-1's past and future, as Ken Croswell explains Ken Croswell is an astronomer and