On Thursday 22th, we have the pleasure to host the Belgian Gravitational Waves meeting. It starts at 2pm, seminar room E349. Our guest speaker is Chris Belczynski and our local speaker is Sébastien Clesse.
At 14:00, Chris Belczynski (Copernicus Center, Warsaw, Poland), will be talking about
Gravitational-wave Astrophysics: LIGO/Virgo BH-BH/BH-NS/NS-NS mergers
I will discuss the astrophysical importance of the recent LIGO/Virgo direct detections of gravitational-waves. Despite the fact that massive BH-BH dominance in gravitational-wave signal was predicted prior the detections, it is not at all clear which one of the several formation scenarios produces these massive mergers. This inhibits astrophysical information inference from LIGO/Virgo observations, as conclusions are different within each formation scenario. There is quite an opposite problem with the first detection of NS-NS merger in an old elliptical host galaxy, as none of the formation channels can easily recover rather high NS-NS merger rate estimated by LIGO/Virgo. The recent detection of BH-NS merger seems to indicate the existence of compact objects in the first mass gap. Additionally, all of the ten O1/O2 LIGO/Virgo BH-BH merger detections have low values for their effective spins. I will demonstrate how this can be naturally explained within framework of classical binary evolution scenario of the formation of BH-BH mergers. It appears that magnetic fields (Tayler-Spruit dynamo) play an important role in efficient transport of angular momentum and spin-down of massive stars that produce low-spinning black holes.
After a coffee break, at 15:30, Sébastien Clesse (CURL, UCLouvain) will talk about
Primordial black hole predictions for black hole merger detections in LIGO/Virgo
Soon after the first gravitational-wave detection, it has been suggested that the black hole merger progenitors might have a primordial origin, and eventually explain all or part of the Dark Matter in the Universe. Due to the known thermal history of the Universe, the primordial black hole (PBH) mass function have specific features that will be probed by the third observing run of LIGO/Virgo. The predictions for the mass distribution of black hole merger progenitors and their spins are distinguishable from the ones of stellar evolution scenarios, and the upcoming detections will be decisive to confirm or rule out the scenario. In addition to explain mergers around 30 solar masses, PBH predict a second peak around 2 solar mass, due to the boost of PBH formation at the QCD transition, and some mergers above 60 solar masses, in the mass gap, with low mass ratios, and involving one sub-solar black hole. These features are universal, whatever is the underlying PBH formation scenario and their abundance.