Cambridge

The disc migration issue: from protoplanets to supermassive black holes

Our workshop “The disc migration issue: from protoplanets to supermassive black holes” took place in May (2017) at the Cambridge Institute of Astronomy. Chaired by Cathie Clarke and co-organized by me, Giovanni Rosotti and a few other people, we tried to bring together people working on both planetary and black-hole physics, to understand what we have in common… Much like planets migrate in protoplanetary discs, supermassive black holes are also brought together by gas interactions. Same physics, different scales, right?

Here is the conference program (with some of the talk’s slides) and below is our beautiful logo (there are discs, waves, inspirals, and King’s College!). Thanks to the KAVLI and Templeton foundations for making this possible.

Migration Issue workshop




Cambridge TV interview

I was interviewed by our local Cambridge TV. It was a funny experience: they asked me about black holes, gravitational waves, and black hole kicks.


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.

D. Gerosa, C. J. Moore.
Physical Review Letters 117 (2016) 011101. arXiv:1606.04226 [gr-qc].
PRL Editors’ Suggestion. Covered by press release.

Press release : Cambridge University, Cambridge Center for Theoretical Cosmology
Other press coverage: astrobites, particlebites, Daily Mail, phys.org, Particle Bites, egno.gr, Daily Galaxy, Register, Media INAF, IneffableIsland, AstronomyNow, Accademia delle Stelle, noticiasdelaciencia, Cambridge TV.





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:

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!

D. Gerosa, M. Kesden, R. O’Shaughnessy, A. Klein, E. Berti, U. Sperhake, D. Trifiro’.
Physical Review Letters 115 (2015) 141102. arXiv:1506.09116 [gr-qc].
PRL Editors’ Suggestion.



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.

M. Horbatsch, H. O. Silva, D. Gerosa, P. Pani, E. Berti, L. Gualtieri, U. Sperhake.
Classical and Quantum Gravity 32 (2015) 204001. arXiv:1505.07462 [gr-qc].
IoP Editor’s choice (CQG++, 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!

D. Gerosa, B. Veronesi, G. Lodato, G. 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.

M. Kesden, D. Gerosa, R. O’Shaughnessy, E. Berti, U. Sperhake.
Physical Review Letters 114 (2015) 081103. arXiv:1411.0674 [gr-qc].
Covered by press release.

Press release : Cambridge University, Cambridge Center for Theoretical Cosmology, Ole Miss, UT Dallas.
Other press coverage: Science Daily, phys.org, phys.org (2), Media INAF, Astroblogs, RIA, Daily News, Science World Report, Tech Times, Tech Times (2), SpaceRef, Space Daily, ECN, R&D, Daily Galaxy, scitechdaily, nanowerk.