A&A

Population 3 stars are like “the original” stars. Those formed with material that comes straight from the Big Bang. It would be very (like, a lot!) cool to see them with gravitational-wave detectors. But can we tell them apart? Or do they look like all the other stars? Here is an attempt with a fancy machine-learning classifier.

F. Santoliquido, U. Dupletsa, J. Tissino, M. Branchesi, F. Iacovelli, G. Iorio, M. Mapelli, D. Gerosa, J. Harms, M. Pasquato.
Astronomy & Astrophysics 690 (2024) A362. arXiv:2404.10048 [astro-ph.HE].

Not sure what happened here, how the hell did I end up writing a paper with actual radio data that needed to be reduced … Call me an ambulance.

The guy here is 3C186 which is not a postcode but a quasar. A funny one because it’s not centered on the galaxy (it’s a bit off) and it’s also going at another velocity (ciao ciao). One of the leading explanations is that 3C186 is a recoiling black hole, the remnant of black-hole merger is being kicked away (yeah these things can happen). 3C186 also has a radio jet, and that should point in the direction of the black-hole spin. The funny thing is that spin and the kick appear perpendicular to each other, and this is fun because theory says they should actually be parallel. We looked into this a bit carefully and discovered it’s all a lie! The spin and the kick both point along the line of sight and appear perpendicular only because of a super strong projection effect. If this is true, the radio jet should also point straight to us! We then tried to test this with whatever ratio data we could grab (where is that ambulance) and found that… mmh, well, it’s a maybe.

M. Boschini, D. Gerosa, O. S. Salafia, M. Dotti.
Astronomy & Astrophysics 686 (2024) A245. arXiv:2402.08740 [astro-ph.GA].

The Milky Way, our own Galaxy, is not alone. We’re part of a galaxy cluster, but closer in we have some satellites. The bigger ones are the Large and Small Magellanic Clouds (which unfortunately I’ve never seen because they are in the southern hemisphere) but also other smaller ones: faint groups of stars in the outskirts of the Milky Way. Much like all galaxies, these faint satellites will have white dwarfs, those white dwarf will form binaries, which will be observable by LISA. There’s a new population of gravitational-wave sources there waiting to be discovered!

ps. The second half of the story is here.

V. Korol, S. Toonen, A. Klein, V. Belokurov, F. Vincenzo, R. Buscicchio, D. Gerosa, C. J. Moore, E. Roebber, E. M. Rossi, A. Vecchio.
Astronomy & Astrophysics 638 (2020) A153. arXiv:2002.10462 [astro-ph.GA].

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.

K. Belczynski, J. Klencki, C. E. Fields, A. Olejak, E. Berti, G. Meynet, C. L. Fryer, D. E. Holz, R. O’Shaughnessy, D. A. Brown, T. Bulik, S. C. Leung, K. Nomoto, P. Madau, R, Hirschi, E. Kaiser, S. Jones, S. Mondal, M. Chruslinska, P. Drozda, D. Gerosa, Z. Doctor, M. Giersz, S. Ekstr:om, C. Georgy, A. Askar, V. Baibhav, D. Wysocki, T. Natan, W. M. Farr, G. Wiktorowicz, M. C. Miller, B. Farr, J.-P. Lasota.
Astronomy & Astrophysics 636 (2020) A104. arXiv:1706.07053 [astro-ph.HE].