From Birth to Chirp – Astrophysics of Massive Stars as Gravitational Wave Progenitors.
Abstract: How did they form?’ is a question many asked when LIGO announced the first direct detection of gravitational waves originating from two surprisingly heavy stellar-mass black holes. With masses of about 30 solar masses each, they outweighed all of the known black holes known from X-ray binaries. Now, four years after the first detection, alerts of new triggers come in at a rate of almost one per week. The analysis of the first eleven events has been published and we learned that the first system was not exceptional: the majority of detected events involve heavy black holes. In parallel, classical telescopes have been revolutionizing our understanding of the properties of young massive stars.
One of the most remarkable findings is that the majority of massive stars have one or more companions so close that the exchange of mass between them in inevitable during their lifetime. Yet, only a very tiny fraction of these stellar couples are still with their companion after both ended their lives to leave behind a neutron star or black hole. What does it take for a `stellar marriage’ to be such that not even death can part them?
I will address some of the exciting new insights, but also the challenges and open questions that we are still facing. More generally I will argue that improving our understanding of massive stars is crucial for a variety of problems in astrophysics. This is because massive stars played a disproportionally large role in transforming the pristine Universe left after the Big Bang into the rich and diverse Universe in which we live today. The fact that we ourselves are largely made of the nuclear ashes of massive stars, makes the quest to understand their lives and deaths an integral part of our quest to understand our own cosmic origin.