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…
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.
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).
Yann Bouffanais, Michela Mapelli, Davide Gerosa, Ugo N. Di Carlo, Nicola Giacobbo, Emanuele Berti, Vishal Baibhav.
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.
Vijay Varma, Scott E. Field, Mark A. Scheel, Jonathan Blackman, Davide Gerosa, Leo C. Stein, Lawrence E. Kidder, Harald P. Pfeiffer.
We moved (back) to the UK. I’m now a lecturer at the University of Birmingham (which is equivalent to assistant professor in the US). Really excited to start this new adventure!
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.
Supporting material available here.
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!