Davide Gerosa

University of Birmingham

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.

COST comes to California!

The COST action GWverse is an impressive network of European researchers and institutions tackling gravitational waves, black holes, etc (i.e. the things I like… sweet!). Together with conferences and outreach, they support collaborative visits between the network members, so here we come. Hey wait a minute, Caltech is kind of far from Europe isn’t it? Here’s the news: Caltech is now an international partner of GWverse, and we’re very happy to host European researchers who want to collaborate with us in sunny southern California.

We’re having our first visitors. Serguei Ossokine from the AEI, is here to work with me on a black-hole binary spin project. Yann Bouffanais from University of Padova (Italy) is coming to collaborate on formation channels.  Welcome Serguei and Yann, and thanks to COST for supporting our science!


The binary black hole explorer: on-the-fly visualizations of precessing binary black holes

As you can imagine, I’m kind of obsessed with black hole binaries. So easy (let’s face it, a black hole is easy! Just mass and spin), but at the same time so terribly complicated… Happy to present our attempt to see the binary dynamics in real time. Technical blah blah: we attach a visualization tool to a numerical relativity surrogate model. Are you ready to be a binary black hole explorer?


ps. Kids can have fun with black holes too! From mikesmathpage.

Vijay Varma, Leo C. Stein, Davide Gerosa.
Classical and Quantum Gravity 36 (2019) 9, 095007.
arXiv:1811.06552 [astro-ph.HE].
Supporting material available here.

Wide nutation: binary black-hole spins repeatedly oscillating from full alignment to full anti-alignment

Latest in the series of our spin-precession papers, here we found a thing that was worthy of a new name: wide nutation (we had wide precession before, but this is better). These are black-hole binary configurations where the angle between any of the two spins and the orbital angular momentum changes a lot. Can’t change more actually: spins goes from full alignment to full anti-alignment. And they do it many times.

ps. We found this wide precession during Alicia’s SURF undergraduate summer project at Caltech. Jackpot!

Davide Gerosa, Alicia Lima, Emanuele Berti, Ulrich Sperhake, Michael Kesden, Richard O’Shaughnessy.
Classical and Quantum Gravity 36 (2019) 10, 105003.
arXiv:1811.05979 [gr-qc].
Supporting material available here.

High-accuracy mass, spin, and recoil predictions of generic black-hole merger remnants

Black hole mergers are like a scattering problem. Two black holes come in, and one black hole comes out. The difference is a bunch of gravitational waves. Those are nice, of course, but the remnant black hole is important too! Here we provide accurate predictions of the mass, spin and kick of this remnant given the properties of the two merging black holes. If you need those numbers (want to build a waveform family? or test GR perhaps?) just use our python module surfinBH!


Bonus note. What if you collide ducks instead of black holes? 

Vijay Varma, Davide Gerosa, François Hébert, Leo C. Stein, Hao Zhang.
Physical Review Letters 122 (2019) 011101.
arXiv:1809.09125 [gr-qc]
Press release: CaltechOle Miss.
Other press coverage: Space Dailyphys.orglongroomtasnimeuropapress (Spanish), Media INAF (video in Italian).

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.

Optimizing LIGO with LISA forewarnings to improve black-hole spectroscopy

LISA is going to be amazing: supermassive black-holes, galactic white dwarfs, EMRIs… Besides all of that, LISA can help us doing LIGO’s science better. Some LIGO sources (notably, things like GW150914) will show up in LISA years in advance. LISA is going to tell us when (in time) and where (in frequency) LIGO will see these sources. In this paper, we explore the idea of adapting the LIGO noise curve if one knows that a source is coming in (because LISA told us). We apply this idea to ringdown tests of GR, and show how powerful they become.

Rhondale Tso, Davide Gerosa, Yanbei Chen.
Physical Review D 99 (2019) 124043.
arXiv:1807.00075 [gr-qc].
Other press coverage: astrobites.

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.

Black holes, gravitational waves and fundamental physics: a roadmap

This is a massive review born out of the European COST Action CA16104 Gravitational waves, black holes and fundamental physics (GWverse). We summarize the status of the field of gravitational-wave astronomy and lie down a roadmap for the immediate future.

Leor Barack, et al. (199 authors incl. Davide Gerosa).
Classical and Quantum Gravity 36 (2019) 14, 143001.
arXiv:1806.05195 [gr-qc].
Editor’s coverage in physicsworld.com.

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.

Reanalysis of LIGO black-hole coalescences with alternative prior assumptions

These are proceedings of the IAU Symposium 338 “Gravitational Wave Astrophysics”, held in Baton Rouge LA on October 16-19, 2017. My contribution is based on arXiv:1707.04637, where we look at the first binary black hole data using different Bayesian priors. During that conference, we had the announcement of the first neutron start event, GW170817, and I was presenting black-hole science: so obsolete…

Davide Gerosa, Salvatore Vitale, Carl-Johan Haster, Katerina Chatziioannou, Aaron Zimmerman.
Proceedings of the International Astronomical Union, 13 (S338), 22-28.
arXiv:1712.06635 [astro-ph.HE].

Surprises from the spins: astrophysics and relativity with detections of spinning black-hole mergers

These are my proceedings for the 12th Edoardo Amaldi Conference on Gravitational Waves (July 9-14, 2017, Pasadena CA). I summarize how to use black-hole spin dynamics to learn about the lives of stars using gravitational-wave data. There are surprises…

Before the talk, I was awarded the 2016 Stefano Braccini Thesis prize (here is Salvo’s tweet about it).

Davide Gerosa.
Journal of Physics: Conference Series 957 (2018) 1, 012014.
arXiv:1711.10038 [astro-ph.HE].

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].

Long-lived inverse chirp signals from core collapse in massive scalar-tensor gravity

Supernova can be used to test gravity! …and if there’s a massive scalar field around, things get terribly interesting. Here we generalize arXiv:1602.06952 to study stellar collapse in massive scalar-tensor theories of gravity (that is, the graviton is coupled to a massive scalar field) with numerical simulations. The scalar-field mass introduces a dispersion relation, and different GW frequencies travel at different speeds. It might even make sense to target historic supernovae: maybe the tail of the signal is still coming to us!

Ulrich Sperhake, Christopher J. Moore, Roxana Rosca, Michalis Agathos, Davide Gerosa, Christian D. Ott.
Physical Review Letters 119 (2017) 201103.
arXiv:1708.03651 [gr-qc].

Impact of Bayesian priors on the characterization of binary black hole coalescences

Bayesian statistics is really cool. It lets you specify clearly and openly all the assumptions that enter an analysis. What’s the effect of these prior assumptions on current inference with gravitational-wave data from black-hole binaries? Here we tackle this question head-on, and perform parameter estimation runs on LIGO data with many (astrophysically motivated!) prior assumptions. Some parameters (like chirp mass) do not suffer from prior choices but others (like the effective spin) do! Specifying the astrophysics as priors is a powerful tool to extract more science from GW data

Update: at the time of publication, this was the first independent reanalysis of any GW data! (There are many more now…). Also, use our data for your research!

Salvatore Vitale, Davide Gerosa, Carl-Johan Haster, Katerina Chatziioannou, Aaron Zimmerman.
Physical Review Letters 119 (2017) 251103.
arXiv:1707.04637 [gr-qc].
Posterior sample data release.

The evolutionary roads leading to low effective spins, high black hole masses, and O1/O2 rates of LIGO/Virgo binary black holes.

Looks like some of the LIGO black holes have low spins (better, low effective spins). In this paper we show these values can be accommodated with standard “field binaries”, i.e. formation channels where binary black holes form from binary stars.

Krzysztof Belczynski, Jakub Klencki, Carl E. Fields, Aleksandra Olejak, Emanuele Berti, Georges Meynet, Christopher L. Fryer, Daniel E. Holz, Richard O’Shaughnessy, Duncan A. Brown, Tomasz Bulik, Sching C. Leung, Ken’ichi Nomoto, Piero Madau, Raphael Hirschi, Samuel Jones, Samaresh Mondal, Martyna Chruslinska, Paweł Drozda, Davide Gerosa, Zoheyr Doctor, Mirek Giersz, Sylvia Ekström, Cyril Georgy, Abbas Askar, Daniel Wysocki, T. Natan, Will M. Farr, Grzegorz Wiktorowicz, M. Coleman Miller, Ben Farr, Jean-Pierre Lasota.
arXiv:1706.07053 [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].

Inferences about supernova physics from gravitational-wave measurements: GW151226 spin misalignment as an indicator of strong black-hole natal kicks

Black-hole data can be used to probe the lives of stars. That’s the promise of gravitational-wave astronomy, right? Here we give it a go. We present a (admittedly) very simple model showing that the misalignment of GW151226 can be easily explained with large natal kicks. I like simple things…

Richard O’Shaughnessy, Davide Gerosa, Daniel Wysocki.
Physical Review Letters 119 (2017) 011101.
arXiv:1704.03879 [astro-ph.HE].
Press release: Rochester Institute of Technology, Caltech’s tweet.
Editor’s coverage in physics.aps.org.
Other press coverage: IOP’s physicsworld.com, Science Daily, Phys.org, astronomy.com, sciencenews, iflscience.

filltex: Automatic queries to ADS and INSPIRE databases to fill LaTex bibliography

My little latex project to compile bibliographies in a smart way was published by JOSS. I really liked JOSS: it’s an innovative way to get recognition for your carefully crafted software, encouraging open science and good code practice. It’s really about publishing your code, not a paper that describes the code: they peer-review the repository, openly with pull requests.

Davide Gerosa, Michele Vallisneri.
The Journal of Open Source Software 2 (2017) 13.
Open-source code: homepagerepository.

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.

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].