This summer I’m having the honor to work with two incredible 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 graduated from Birmingham (congrats Daria!). 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
Davide Gerosa, Emanuele Berti.
arXiv:1906.05295 [astro-ph.HE].
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, if black holes are not formed from stars, but from other black holes (yes! more black holes!). If black holes 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?
Gravitational-wave detection rates for compact binaries formed in isolation: LIGO/Virgo O3 and beyond.
Vishal Baibhav, Emanuele Berti, Davide Gerosa, Michela Mapelli, Nicola Giacobbo, Yann Bouffanais, Ugo N. Di Carlo
arXiv:1906.04197 [gr-qc].
LIGO and Virgo are up and running like crazy. They started their third observing run (O3) and in just a few months doubled the catalogs of observing events. And there’s so much more coming! In this paper we try to work out “how much” using our astrophysical models. Figure 4 is kind of shocking: we’re talking about thousands of black holes in a few years, and millions of them in 20 years. Need to figure out what to do with them…
Are stellar-mass black-hole binaries too quiet for LISA?
Christopher J. Moore, Davide Gerosa, Antoine Klein.
Monthly Notices of the Royal Astronomical Society Letters 488 (2019) L94–L98.
arXiv:1905.11998 [astro-ph.HE].
Spoiler alert: this paper is a bit sad.
Stellar-mass black-hole binaries are now detected by LIGO on a weekly basis. It would be really cool if LISA (a future space mission targeting low-frequencies gravitational waves) could see them as well. We could do a lot of cool stuff, in both the astro and the theory side of things. In today’s paper, we try to figure out how easy or hard it will be to extract these signals from the LISA noise. Well, it’s hard. In terms of the minimum signal-to-noise ratio required, we find that this is as high as 15. The number of expected detection becomes discouragingly low unless the detector behaves a bit better at high frequencies or black holes with 100 solar masses start floating around.
Constraining the fraction of binary black holes formed in isolation and young star clusters with gravitational-wave data
Yann Bouffanais, Michela Mapelli, Davide Gerosa, Ugo N. Di Carlo, Nicola Giacobbo, Emanuele Berti, Vishal Baibhav.
arXiv:1905.11054 [astro-ph.HE].
Where do black holes come from? Sounds like a scify book title, but it’s real. These days, that’s actually the million dollar question in gravitational-wave astronomy. LIGO sees (lots of!) black holes in binaries, and those data encode information on how their stellar progenitors behave, what they like or did not like to do. This is paper is the latest attempt to understand if black holes formed alone (i.e. a single binary star forms a single binary black hole) or together (i.e. many stars exchange pairs in dense stellar environments).
Surrogate models for precessing binary black hole simulations with unequal masses
Vijay Varma, Scott E. Field, Mark A. Scheel, Jonathan Blackman, Davide Gerosa, Leo C. Stein, Lawrence E. Kidder, Harald P. Pfeiffer.
arXiv:1905.09300 [gr-qc].
Surrogate models are the best of both worlds. Numerical-relativity simulations are accurate but take forever. Waveform models have larger errors but can be computed cheaply, which means they can be used in the real world and compared with data. Surrogates are as fast as the approximate waform models, but as accurate as the numerical-relativity simulations they are trained on. Don’t believe me? I don’t blame you, this does sound impossible. Check out our new paper, where we pushed this effort to binaries with spins and more unequal masses.
Bham, here I come
We moved (back) to the UK. I’m now a lecturer at the University of Birmingham (that’s roughly equivalent to assistant professor in the US). Really excited to start this new adventure!
My group is part of the Birmingham Institute for Gravitational Wave Astronomy. If you’re interested in joining us, have a look at this page. And see you in the Midlands!
