Davide Gerosa

University of Birmingham


On the equal-mass limit of precessing black-hole binaries

Equal-mass binaries correspond to a discontinuous limit in the spin precession equations. A new constant of motion pops up, which can be exploited to study the dynamics. This is a really neat calculation done with Jakub, a Cambridge undergraduate student. Also, my first paper at Caltech!

Davide Gerosa, Ulrich Sperhake, Jakub Vošmera.
Classical and Quantum Gravity 34 (2017) 6 ,064004.
arXiv:1612.05263 [gr-qc].


Black-hole kicks as new gravitational-wave observables

Black hole kicks are cool: powerful (up to thousands of km/s!) recoils that black holes receive following a merger. Here we show these events might leave an imprint on the emitted gravitational waves, which is potentially detectable by future interferometers.

Davide Gerosa, Christopher J. Moore.
Physical Review Letters 117 (2016) 011101.
arXiv:1606.04226 [gr-qc].
Selected as PRL Editors’ Suggestion.
Press releases: Cambridge UniversityCambridge Center for Theoretical Cosmology
Other press coverage: Daily Mailphys.org, Particle Bitesegno.gr (Greek), Daily Galaxy, RegisterMedia INAF (Italian), IneffableIsland, AstronomyNow, Accademia delle Stelle (Italian), noticiasdelaciencia (Portuguese). Blog posts on astrobites and particlebites. TV interview, aired on Cambridge TV.


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.


Numerical simulations of stellar collapse in scalar-tensor theories of gravity

Here we present 1+1 numerical-relativity simulation of stellar collapse in scalar-tensor theories, where gravity is mediated by the usual metric coupled to an additional scalar field. Bottom line: you can test General Relativity with supernovae explosions!

Davide Gerosa, Ulrich Sperhake, Christian D. Ott.
Classical and Quantum Gravity 33 (2016) 13 , 135002.
arXiv:1602.06952 [gr-qc].
Supporting material available here.


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].


The birth of an idea

I wrote a post for The Birth of an Idea, which is a really beautiful blog collecting insights on how scientists start their science. Thanks Vitor for the opportunity to contribute! Here is my post:

Bikes and Colorful Pieces

An idea, a good one at least, is like a gift. It’s something which is not yours (indeed, you didn’t have it before!) but comes to you, it’s given to you.

I bike to work, it’s kind of ten minutes from my place to the Cambridge Maths department, but those ten minutes can be more productive than ten hours or ten days in front of my computer’s screen. It’s morning, your mind should be clear (you should pay attention to cars while biking!), but it’s actually already getting full of what you have to do today. You get to the office, sit down, turn your computer on, and start looking at your problem. You write the equations down, try putting them in a computer, it doesn’t work, just nans coming out. You ask a collaborator who hopefully knows something, write the equations down again, it doesn’t work. You check in a paper if someone else did something similar, take a break, get annoyed (and here I typically open football websites…). Oh, and you write the same equations down again, it simply doesn’t work.

At some stage, it’s time to go home, and that moment is precious to me. You know your problem so well, those equations, that crashing piece of code, but you were looking too close. When I close my laptop and get on my way home, fresh air on my face, I can look at the problem from afar. It’s like looking at those beautiful ancient mosaics. If you look very close, you only see one colored piece, but you can’t see any meaning in it. Each piece is crucial to the final piece of art, but the value of each piece is its relation to the bigger picture. You can only appreciate a mosaic if you take one step back and look to the whole picture from afar. Wow. Biking home is my step back. You’ve been looking at all pieces for days, weeks, you know the color of each piece so well that you can finally grasp the relation which puts them together.

An idea, a good one at least, is like a gift you can say thanks for.


Precessional instability in binary black holes with aligned spins

Here we study the stability of black-hole binaries with spins (anti)aligned with the orbital angular momentum. Aligned configurations are points of equilibrium, but are they stable? If the heavier black-hole is aligned and the lighter one is anti-aligned, this turns out to be unstable! And the onset of this instability can be in the LIGO or LISA band!

Davide Gerosa, Michael Kesden, Richard O’Shaughnessy, Antoine Klein, Emanuele Berti, Ulrich Sperhake, Daniele Trifirò.
Physical Review Letters 115 (2015) 141102.
arXiv:1506.09116 [gr-qc].
Selected as PRL Editors’ Suggestion.
Supporting material available here.


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.


Tensor-multi-scalar theories: relativistic stars and 3+1 decomposition

What happens if you throw a scalar field into General Relativity? And if you throw more than one? Here is a paper on the phenomenology of neutron stars in theories with more than one scalar field coupled to gravity.

Michael Horbatsch, Hector O. Silva, Davide Gerosa, Paolo Pani, Emanuele Berti, Leonardo Gualtieri, Ulrich Sperhake.
Classical and Quantum Gravity 32 (2015) 20, 204001.
arXiv:1505.07462 [gr-qc].
Featured in CQG+. Selected as IOPselect.


Spin alignment and differential accretion in merging black hole binaries

Supermassive black holes in binaries and their accretion discs… Spins align on some timescale, but migration also takes place. Do gas discs have enough time to align the spins? Well, the secret is the mass ratio: light secondaries might prevent primaries from aligning. A great collaboration between gravitational-wave and planet researchers!

Davide Gerosa, Benedetta Veronesi, Giuseppe Lodato, Giovanni Rosotti.
Monthly Notices of the Royal Astronomical Society 451 (2015) 3941-3954.
arXiv:1503.06807 [astro-ph.GA].


Effective potentials and morphological transitions for binary black-hole spin precession

2PN black-hole binary spin precession works exactly like Kepler’s two-body problem. Not kidding: just define effective potentials and divide the phase space into morphologies. The only things you need are a few timescales to play with.

Michael Kesden, Davide Gerosa, Richard O’Shaughnessy, Emanuele Berti, Ulrich Sperhake.
Physical Review Letters 114 (2015) 081103.
arXiv:1411.0674 [gr-qc].
Press releases: Cambridge University, Cambridge Center for Theoretical Cosmology, Ole Miss, UT Dallas.
Other press coverage: Science Daily, phys.org, phys.org (2), Media INAF (Italian), Astroblogs (Dutch), RIA (Russian), Daily News, Science World Report, Tech Times, Tech Times (2)SpaceRef, Space Daily, ECN, R&D, Daily Galaxy, scitechdaily, nanowerk
Supporting material available here.


Rival families: waveforms from resonant black-hole binaries as probes of their astrophysical formation history

These are my proceedings of the 3rd Session of the Sant Cugat Forum on Astrophysics, held in beautiful Sant Cugat, near Barcelona on April 22-25, 2014. My contribution is this paper: have a look if you want to know more about rival families in spinning black-hole binaries.

Davide Gerosa. 
Astrophysics and Space Science Proceedings 40 (2015) 137-145.


Missing black holes in brightest cluster galaxies as evidence for the occurrence of superkicks in nature

Black-hole kicks are powerful. I mean, really powerful. They can even eject supermassive black holes from the heavier galaxies in our Universe. And then these galaxies are left “empty”…

Davide Gerosa, Alberto Sesana.
Monthly Notices of the Royal Astronomical Society 446 (2015) 38-55.
arXiv:1405.2072 [astro-ph.GA].


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].