Great scientific discoveries often raise more questions than they answer. Just days after the announcement that gravitational waves from two merging black holes have been detected, astrophysicists are already pondering what this means for our understanding of stars. New studies are already being released and we can expect a flood of creative ideas in the near future.
One of the most surprising things about the discovery is the huge size of the black holes involved which is challenging our understanding of how they form. So how can we find out more? One way is by pinpointing the black holes on the sky so we can try to study them using regular telescopes.
Massive Mystery
LIGO, the observatory that detected the gravitational waves, is a so-called laser interferometer. It estimated that the two merging black holes would have masses of about 36 and 29 times that of the sun respectively (described as 36 and 29 “solar masses“), calculated from the frequency of the gravitational waves. But what’s so unusual about these masses?
Black holes form after huge supernovae explosions, which can only be produced by massive stars. The masses of the black holes in our own galaxy can be measured by looking at the speed of stars orbiting a black hole. The most massive black hole in a binary system (a black hole and a companion star orbiting a common center) in our galaxy is about 10-20 solar masses.
This is well explained by our knowledge of stars. The biggest stars are born at about 100 solar masses and end up at around only ten solar masses at their endpoints due to stellar winds blowing out material into space. This means they shouldn’t be able to produce the kind of huge black holes that LIGO detected. But there are still big uncertainties about the rate at which this occurs and the influence of a star’s spin, the existence of a second star orbiting a common center (binary stars), and its chemical composition.
