Constraining compact binary formation with gravitational wave observations

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Black Holes and Neutron Stars are some of the strangest objects in the universe, containing moremass than the Sun packed into a sphere only a few kilometres across. They are formed from theremains of high mass stars, which burn their fuel quickly and end their lives in supernovaexplosions which can outshine a whole galaxy. There are different types of supernova for differenttypes of stars: their masses, spins and composition all play a role in determining their eventualfate, although the details are not fully understood yet.What is left over after the supernova is an object so dense that its gravitywarps the space-time around it: a neutron star is thought to contain the densest possiblematter, denser than an atomic nucleus, which is the only material strong enough to support the staragainst its own gravity. Even more extreme are black holes, which form when a star has even more mass,and neutron star matter cannot support its weight. When this happens the star collapses into a blackhole, becoming so dense that not even light can escape the gravitational pull. At this pointan event horizon forms, hiding its contents from the rest of the universe. Since black holes donot emit light, they are impossible for astronomers to find unless they are actively accreting materialfrom a companion star. But there is another way to detect them using a completely new astronomicaltool: gravitational waves.According to Einstein's theory of General Relativity, when black holes and neutron stars are foundtogether in a binary system, the movement of so much matter in such a concentrated space createsvibrations in space-time itself. These travel out across the universe at the speed of light, changingthe dimensions of everything they pass through, but invisible to the eye. Back on Earth, physicistshave long been searching for gravitational waves by making extremely precise distance measurementsusing gravitational wave detectors.So far no signs have been found, but soon the Advanced LIGO and Advanced Virgo detectors will becomeoperational with a sensitivity that ought to allow us to detect the gravitational waves from binary neutronstars within hundreds of millions of light years from Earth, and out to even greater distances for the heavierblack hole binaries. The detectors are so sensitive that the change they can measure is equivalent ofvarying the distance between the Sun and Saturn by a hair's breadth.Encoded in the gravitational waves is information about the sources that emitted them, which will let us learnabout the masses and spins of neutron stars and black holes. By measuring many signals, we will beable to piece together the physics that governs the evolution of massive stars, and how they end theirlives.