Davide Gerosa

University of Birmingham

Winter visitors

Two close collaborators will be visiting my group this winter.

Vijay Varma, postdoc at Caltech and expert of numerical relativity surrogate models, will be here on October 7-11. Get ready for his talk “Binary black hole simulations: from supercomputers to your laptop”.

Giovanni Rosotti, Veni fellow in Leiden, will be here on November 4-15. He will also give a talk: “The observational era of planet formation”. Wait a minute, what does planets have to do with black holes? Well, turns out their evolution is set by the same key equations. We have a lot to learn from each other! Giovanni’s visit is supported by the GWverse COST Action (thanks EU!).

Amplification of superkicks in black-hole binaries through orbital eccentricity

Today’s paper is about superkicks. These are extreme configurations of black hole binaries which receive a large recoil. Black hole recoils work much like those of, say, a cannon. As the cannonball flies, the cannon recoils backwards. Here the binary is shooting gravitational waves: as they are emitted, the system recoils in the opposite direction. Here we show kicks might be up to 25% larger if the binary is mildly eccentric. This means it’s a bit easier to kick black holes out of stellar clusters and galaxies.

Ulrich Sperhake, Roxana Rosca-Mead, Davide Gerosa, Emanuele Berti.
arXiv:1910.01598 [gr-qc].

Machine-learning interpolation of population-synthesis simulations to interpret gravitational-wave observations: a case study

Gravitational-wave astronomy is, seems obvious to say, about doing astronomy with gravitational waves. One has gravitational-wave observations (thanks LIGO and Virgo!) on hand and astrophysical models on the other hand. The more closely these two sides interact, the more we can hope to use gravitational-wave data to learn about the astrophysics of the sources. Today’s paper with JHU student Kaze Wong tries to further stimulate this dialog. And, well, one needs to throw some artificial intelligence in the game. There are three players now (astrophysics, gravitational waves, and machine learning) and things get even more interesting.

Kaze W.K. Wong, Davide Gerosa.
arXiv:1909.06373 [astro-ph.HE].

Black holes in the low mass gap: Implications for gravitational wave observations

What’s in between neutron stars and black holes? It looks like neutron stars have a maximum mass of about 2 solar masses while black holes have a minimum mass of about 5. So what’s in between? That’s the popular issue of the ‘low mass gap’. Actually, now we know something must be in there. LIGO and Virgo have seen GW170817, a merger of two neutron stars, which merged in to a black hole with the right mass to populate the gap. Can this population be seen directly with (future) gravitational-wave detectors? That’s today’s paper.

Anuradha Gupta, Davide Gerosa, K. G. Arun, Emanuele Berti, B. S. Sathyaprakash
arXiv:1909.05804 [gr-qc].

Summer research fun

This summer I’ll be working with two undergraduate research students. Luca Reali is finishing his master at my alma mater (University of Milan, Italy) and is visiting Birmingham with a scholarship from the HPC Europa 3 cluster. Daria Gangardt just finished her 3rd year in Birmingham. Their projects concentrate on spin effects in black hole binaries and the properties of merger remnants. Welcome Daria and Luca, hope you’ll have a very rewarding summer!

Escape speed of stellar clusters from multiple-generation black-hole mergers in the upper mass gap

Funny things happen in supernova explosions. Funny and complicated. If the star is too massive, the explosion is unstable. The black hole it formed it not as massive as it could have been. In gravitational-wave astronomy, this means that we should not observe black holes heavier than about 50 solar masses. This does not apply, of course, to black holes that are not formed from stars, but from other black holes (yes! more black holes!). If black holes resulting from older gravitational wave events somehow stick around, they could be recycled in other generations of mergers. We point out that this can work only if their astrophysical environment is dense enough. Can we measure the escape speed of black holes “nurseries” using gravitational-wave events that should not be there because of supernova instabilities?

Davide Gerosa, Emanuele Berti.
Physical Review D Rapid Communications 100 (2019) 041301R.
arXiv:1906.05295 [astro-ph.HE].
Press release: Birmingham.
Other press coverage: interestingengineeringmetro.co.ukMedia INAF (Italian), Great Lakes Ledgersciencealert.