Davide Gerosa

University of Birmingham

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.

Multiband gravitational-wave event rates and stellar physics

The prospect of multiband gravitational-wave astronomy is so so so exciting (I mean, really!). So exciting that we want to make sure once again it’s true; and this is today’s paper. Multiband means seeing the same black hole binary with both LIGO at high frequencies and LISA at low frequencies. LISA observations can serve as precursors for the LIGO mergers, and you can a whole lot of new science (astrophysics, tests of GR, smart data analysis, cosmology, etc). Here we have a new semi-analytic way to estimate the rate (i.e. how many) of multiband events, and we also explore some of the stellar physics one could constraint with them. Enjoy!

Davide Gerosa, Sizheng Ma, Kaze W.K. Wong, Emanuele Berti, Richard O’Shaughnessy, Yanbei Chen, Krzysztof Belczynski
Physical Review D 99 (2019) 103004.
arXiv:1902.00021 [astro-ph.HE].
Supporting material available here.

Frequency-domain waveform approximants capturing Doppler shifts

We all know Doppler shifts, right? That’s like the biibouuubiiiiboouuuuuu of an ambulance. That happens to gravitational waves as well. Suppose you have a merging binary which is emitting gravitational waves (bibooou). If that binary is going somewhere (say it’s falling into the gravitational potential of a third body), much like the ambulance, the emitted signal will be Doppler shifted. This paper shows a very nice calculation to incorporate Doppler shifts into gravitational waves.

ps. This started out as Katie’s undergraduate summer project at Caltech. Congrats Katie!

Katie Chamberlain, Christopher J. Moore, Davide Gerosa, Nicolas Yunes.
Physical Review D 99 (2019) 024025.
arXiv:1809.04799 [gr-qc].

Spin orientations of merging black holes formed from the evolution of stellar binaries

Today’s paper celebrates the wedding of startrack and precession (the nickname for this project was pretrack 😉 ). We use population synthesis evolution from startrack to predict the parameters of spinning black-hole binaries observed by LIGO. The spin distribution is then propagated from formation to detection using post-Newtonian evolutions from my precession code. The bottom line is that spin measurements can be used to truly reconstruct the binary formation channels, and some specific mechanisms (like mass transfers, tides, natal kicks, supernova’s instabilities etc.). Our database is publicly available (play with it!), as well as a little code to compute gravitational-wave detectabilities.

Update: this is my 25th published paper! That’s silver, right?

Davide Gerosa, Emanuele Berti, Richard O’Shaughnessy, Krzysztof Belczynski, Michael Kesden, Daniel Wysocki, Wojciech Gladysz.
Physical Review D 98 (2018) 084036.
arXiv:1808.02491 [astro-ph.HE].
Supporting material available here.

Mining gravitational-wave catalogs to understand binary stellar evolution: a new hierarchical bayesian framework.

Gravitational-wave astronomy is moving. Quickly. In a few years we are going to have large catalogs of many detections, and a whole lot of information to extract from them. Instead of focussing on parameters (masses, spins, redshifts) of single sources, we will want to extract hyperparameters describing physical features of the population (metallicity, natal kicks, common envelope, stellar winds, etc). Here we show how to do this in practice: read our new paper for an amazing journey through hyperlateral cubes, Gaussian process emulators, selection biases, hierarchical modeling and more.

Our tools are publicly available! Here is Steve’s Webpage and our public code.

Stephen R. Taylor, Davide Gerosa.
Physical Review D 98 (2018) 083017.
arXiv:1806.08365 [astro-ph.HE].
Editor’s coverage in APS’s Kaleidoscope.

Gravitational-wave astrophysics with effective-spin measurements: asymmetries and selection biases

LIGO can measure spins. Well, effective spins actually. These are special combinations of the two spins (magnitude and direction) and the binary mass ratio. There’s a ton of astrophysics that can be done just with this quantity, but one should always be careful. Today’s paper points out a few important shortcomings when dealing with effective spin measurements. Want to know more about asymmetries and selection biases?

ps. You can hardly find a better day to post a paper on the arxiv than May 4th

Ken K. Y. Ng, Salvatore Vitale, Aaron Zimmerman, Katerina Chatziioannou, Davide Gerosa, Carl-Johan Haster.
Physical Review D 98 (2018) 083007.
arXiv:1805.03046 [gr-qc].

Black-hole kicks from numerical-relativity surrogate models

Surrogate models are fancy interpolation schemes developed to provide accurate (well, really accurate) waveforms directly from numerical relativity simulations. The first surrogate able to model fully precessing systems came up recently (and it’s really an amazing work!). Here we exploit these advances to explore how linear momentum is emitted in generic black-hole mergers, and well as its back-reaction. Black holes get kicked!

Davide Gerosa, François Hébert, Leo C. Stein.
Physical Review D 97 (2018) 104049.
arXiv:1802.04276 [gr-qc].
Open-source code: homepagerepository.

Explaining LIGO’s observations via isolated binary evolution with natal kicks

Natal kicks imparted to neutron stars and black holes at birth can be constrained using LIGO data. Kicks cause misalignments between the spins and the orbital angular momentum. Here we compare large banks of population synthesis simulations to LIGO data using hierarchical Bayesian statistics and show that (already with 4 events!) natal kicks are constrained from both above and below. Simulated binaries are produced merging Startrack evolutions to my precession code. More on this very soon…

Update: here it is!

Daniel Wysocki, Davide Gerosa, Richard O’Shaughnessy, Krzysztof Belczynski, Wojciech Gladysz, Emanuele Berti, Michael Kesden, Daniel Holz.
Physical Review D 97 (2018) 043014.
arXiv:1709.01943 [astro-ph.HE].

Nutational resonances, transitional precession, and precession-averaged evolution in binary black-hole systems

Part of our series of spin precession papers, here we study nutational resonances. Those are configurations where the precession of L about J, and that of the two spins are in resonance with each other. These configurations are very generic (virtually every binary will go through resonances), but their effect on the dynamics seems to be small, unless… unless you end up in transitional precession! Transitional precession (great paper!) turns out to be a very special nutational resonance.

Xinyu Zhao, Michael Kesden, Davide Gerosa.
Physical Review D 96 (2017) 024007.
arXiv:1705.02369 [gr-qc].

Are merging black holes born from stellar collapse or previous mergers?

What if the black holes LIGO sees are the results of a merger? I mean, we see mergers, but maybe those are second-generation ones, and the two merging black holes come from first-generation mergers. Or (more likely…) stellar mass black holes form from stars and only merge once…

Davide Gerosa, Emanuele Berti.
Physical Review D 95 (2017) 124046.
arXiv:1703.06223 [gr-qc].
Selected as PRD Editors’ Suggestion.
Other press coverage: Ars Technica.

PRECESSION: Dynamics of spinning black-hole binaries with python

Here we present my numerical code precession, which implements our multi-timescale way to look at spinning black-hole binaries. The paper has a detailed description of the various functions as well as lots of examples.

Update: typos in Eq. (36-37) have been fixed in v3 on the arXiv.

Davide Gerosa, Michael Kesden.
Physical Review D 93 (2016) 124066.
arXiv:1605.01067 [astro-ph.HE].
Open-source code: homepage, repository, documentation.

Distinguishing black-hole spin-orbit resonances by their gravitational wave signatures. II: Full parameter estimation

This is a follow up of arXiv:1403.7147, just done better. Instead of overlaps, we do real injections in LIGO parameter-estimation codes to show that spin-orbit resonances are indeed detectable.

Daniele Trifirò, Richard O’Shaughnessy, Davide Gerosa, Emanuele Berti, Michael Kesden, Tyson Littenberg, Ulrich Sperhake.
Physical Review D 93 (2016) 044071.
arXiv:1507.05587 [gr-qc].

Multi-timescale analysis of phase transitions in precessing black-hole binaries

Detailed analysis of 2PN black-hole binary spin precession using multi-timescale methods. Follow-up of the Letter arXiv:1411.0674, this paper contains the full calculation and the description of the underlying phenomenology.

Davide Gerosa, Michael Kesden, Ulrich Sperhake, Emanuele Berti, Richard O’Shaughnessy.
Physical Review D 92 (2015) 064016.
arXiv:1506.03492 [gr-qc].
Supporting material available here.

Distinguishing black-hole spin-orbit resonances by their gravitational-wave signatures

Spinning black-hole binaries might belong to two spin-orbit resonances, or families. Can you tell them apart using gravitational-wave observations? Spoiler: yes!

Bonus note: check out the title in v1 on the arxiv…

Davide Gerosa, Richard O’Shaughnessy, Michael Kesden, Emanuele Berti, Ulrich Sperhake.
Physical Review D 89 (2014) 124025.
arXiv:1403.7147 [gr-qc].

Resonant-plane locking and spin alignment in stellar-mass black-hole binaries: a diagnostic of compact-binary formation

Spin precession in stellar-mass black hole binaries encodes information on specific formation mechanisms like tides and mass transfers. My first paper on spin precession…

Davide Gerosa, Michael Kesden, Emanuele Berti, Richard O’Shaughnessy, Ulrich Sperhake.
Physical Review D 87 (2013) 10, 104028.
arXiv:1302.4442 [gr-qc].