We’re back to predicting the excitation amplitude of black hole merger ringdowns. We already looked into the simpler case of binaries with aligned spins, and now tried to study the full problem of binaries with misaligned (i.e. processing) spins. Well, this is a hard problem! It’s not even clear which mode is the stronger one anymore, and finding suitable coordinates is not at all trivial. While this is just a first exploration, there’s so much interesting phenomenology here! Do it yourself with the postmerger package.
Francesco Nobili, Swetha Bhagwat, Costantino Pacilio, Davide Gerosa. arXiv:2504.17021 [gr-qc].
The 2017 paper “Are merging black holes born from stellar collapse or previous mergers?” that I wrote with Emanuele Berti was selected 2025 Frontiers of Science Award. These prizes are awarded by the International Congress of Basic Science (ICBS), sponsored by the City of Beijing and the Yanqi Lake Beijing Institute of Mathematical Sciences and Application (BIMSA). Every year, they select influential recent papers in Physics, Maths, and Computer Science.
The complete list of Physics papers selected for awards is available here. Ours is one of only three papers that were selected in the category Astrophysics and Cosmology – Theory. We’ll collect the award in July at the Great Hall of the People of China in Beijing.
I’m so happy to see how a seemingly simple idea we had (“What if LIGO’s black holes merge multiple times?”) went so far! Our paper was published in Physical Review D in 2017, selected as an Editor’s Suggestion back then… and now got an award!
Great paper led by our former MSc student Alessandro today! This is about combining the distributions of gravitational waves and galaxies to do cosmology. These two probes measure different things (distance and redshift, respectively), so their distributions will “match” only if the cosmological model is right. You can actually use this to measure the cosmological model itself. Short answer: putting together 3G detectors and Euclid is a great idea.
Four BSc+MSc students just graduated with projects in our group!
Alessandro Malfasi completed his BSc project with Pippa Cole on combining PTA data and primordial black holes (a believer!).
Nicole Grillo got her MSc degree in Astrophysics with a project, also with Pippa Cole, on EMRIs and environmental effects.
Olga Pietrosanti also got her Astrophysics MSc today, and she works in collaboration with Alessandro Trani (Copenhagen), Evgeni Grishin (Monash, Australia), and Clement Bonnerot (Birmingham, UK) on black holes migrating in AGN disks.
Giovanni Giarda (…”my name is Giovanni Giarda“) completed his MSc project with Arianna Renzini and Costantino Pacilio on a deep learning pipeline to speed up the computation of GW stochastic backgrounds.
If you’re looking for a PhD in gravitational-wave physics, our 2025 call for PhD scholarships is now available. The procedure is described here (Session 1):
For instructions, start from the file “Guide to filling in the online application.” There’s a key step on page 10 where candidates can express interest in some themed scholarships. If you’re interested in working with my group, I encourage you to select PROG.1 and PROG.3.
You will need to submit your research proposal/statement. These are usually 2-3 pages long. It should provide some context about your work in gravitational-wave astronomy (or astrophysics more in general), what you want to do next, your key interests, what you would like to work on here with us, why you want to work with us, and more in general how you plan to integrate with our activities. It should be forward-looking and not just about what you’ve done already. Hope this helps!
For any questions, please do not hesitate to contact me: [email protected]
Happy to share this postdoc opportunity from the Cariplo Foundation, which is a private trust that operates in the Milan area. It’s an independent fellowship for early career researchers, with a duration of 3 years and a total budget of 200k EUR.
I’m on the hook for teaching this semester (can’t complain really with such fun classes!). I’m down for “Astrostatistics and Machine Learning” for our MSc degree in Astrophysics and “Machine Learning for Physics and Astronomy” for our BSc degree in Artificial Intelligence. Here is my material for both, and thanks to all the students who will be engaging with this!
The Italian Society of General Relativity and Gravitation (SIGRAV) announces the 26th SIGRAV Conference, hosted by the University of Milano-Bicocca, to be held in Milan, Italy, from September 8-12, 2025.
The conference will cover various aspects of classical and quantum gravity, including tests of General Relativity, cosmology, gravity experiments, and gravitational waves from experimental, theoretical, and data-analysis perspectives.
Participation is open to SIGRAV members and non-members alike, both nationally and internationally. The program will feature a series of broad review talks on various aspects of gravitational physics, as well as contributed talks. The SIGRAV Amaldi medals, the SIGRAV prizes for young researchers, and the Giulio Rampa PhD thesis prize will be awarded during the conference. There will also be a public event dedicated to the 10-year anniversary of the first direct detection of gravitational waves, GW150914.
Abstracts for contributed talks should submitted by May 31, 2025. We aim to announce the full conference program by the end of June. Registrations will be accepted until July 15, 2025.
Milan is a beautiful, international city in the north of Italy and is served by three major airports with worldwide connections. The city is home to art, history, and great food; you can also explore nearby lakes or venture into the stunning Alps.
When inferring black holes from gravitational-wave data, we tend to do two things, one after the other. First, we consider each event individually and measure its parameters (masses, spins, etc). Then we consider all the events together and measure the population properties. This is what we do all the time, but, actually, if objects are now part of a population, those parameters should be looked at again in light of all the others. This full problem (all parameters of all the events plus the population parameters) is daunting, and in the past we used an indirect and somewhat convoluted approach. We got back to it now, and this time, we managed to do it head-on. Let me introduce this giant 500-dimensional sampling of the full population problem!
Long gravitational-was signals are, well, long. And long often means painful, as more data need to be stored and processed. Kind of intuitively, the solution might be that of cutting things into chunks, so that long becomes short. Here we apply this idea to the popular inner product entering all gravitational-wave pipelines; this is a key building block of everything we do. The answer is that using SFTs, “Short-time Fourier Transforms”, can make things faster by more than 3 orders of magnitudes, sometimes 5. We think this is the solution to future gravitational-wave data analysis problems (think LISA and 3G…).
General relativity has this beautiful property that coordinates are meaningless. You can change them at will, which means they don’t contain any physics. And, believe it or not, some of the popular formulations we use to write down the dynamics of eccentric binary black holes still have coordinates in them. They go away if you take an average of an orbit (Peters, the man!) but that’s killing some information. In this paper we go back to those old results and show how those gauges can actually be absorbed into the formulation itself. The paper is on the maths-heavy side of things, but the results are great. Peters, you were basically right, but not quite.
Giulia Fumagalli, Nicholas Loutrel, Davide Gerosa, Matteo Boschini. arXiv:2502.06952 [gr-qc].
We’re going to have quite a few visitors in the next few months. They will be giving amazing seminars, with lots of research ideas floating around: Stephen Green from Nottingham, Cecilia Sgalletta from Trieste, Francisco Duque from the AEI, Angela Borchers from the other AEI, Lorenzo Pompili also from AEI (!), Ilaria Caporali from Pisa, Aleksandra Olejak from the MPA at Garching, Pantelis Pnigouras from Alicante, Lucy McNeill from Kyoto, and James Alvey from Cambridge. Hope I didn’t forget anyone… This is going to be exciting 🙂
Quasar 3C 186 strikes back! Matteo and I got interested in this funny quasar last year (see this one). When our paper hit the arxiv, we got contacted by the real astronomers who take actual data, who told us they had even more beautiful data. We ended up contributing with our relativistic model and… well… everything seems to work. 3C 186 is indeed a recoiling black hole (it might be a rare one, but we’ve observed it nonetheless). The abstract says “decisive,” and this is indeed the right word.
Marco Chiaberge, Takahiro Morishita, Matteo Boschini, Stefano Bianchi, Alessandro Capetti, Gianluca Castignani, Davide Gerosa, Masahiro Konishi, Shuhei Koyama, Kosuke Kushibiki, Erini Lambrides, Eileen T. Meyer, Kentaro Motohara, Massimo Stiavelli, Hidenori Takahashi, Grant R. Tremblay, Colin Norman. arXiv:2501.18730 [astro-ph.GA].
Gravitational-wave population people talk all the time about parametric vs non-parametric methods. Parametric methods mean imposing our astrophysical knowledge on how we look at GW data. This is great, we do want to extract astrophysical knowledge, but what if we don’t know what to look for? The statisticians tell us to go non-parametric, which means using a flexible model that can fit whatever you want. That’s great, but what do we learn then? In other words, where’s the boundary between flexibility and interpretability? Today’s paper shows that one can conceptually separate these two processes and extract parametric results from non-parametric fits. I’m very proud of this piece of work, which was Cecilia Fabbri‘s MSc thesis project and was actually kickstarted by one of my previous students, Alessandro Santini. We even wrote a poem about this!
Cecilia Maria Fabbri, Davide Gerosa, Alessandro Santini, Matthew Mould, Alexandre Toubiana, Jonathan Gair. arXiv:2501.17233 [astro-ph.HE].
I’m so so proud to see my PhD student Viola De Renzis defending her PhD thesis today. Viola’s thesis is titled “Gravitational-wave astronomy at the crossroads: from current to future detectors, from single events to populations” and was examined by Maya Fishbach (Toronto), Laura Sberna (Nottingham) as external referees, as well as Walter Del Pozzo (Pisa), Stephen Green (Nottingham) and Alberto Sesana (Milano-Bicocca) as defense committee members. What should I say, from the first “off you go and learn Bilby” meeting we had, to all those discussions at the board, learning how to ski, those codes that did (not) work, and that distinctive laughter across the corridor. Our group will not be the same without Viola. You turned into a great scientist: now “spacca tutti” in Marseille!
Together with Ilya Mandel, last week I organized a workshop titled “Gravitational-wave snowballs, populations, and models” in Sexten (Italy). Both the science and the scenery were just stellar! We had almost zero talks, and the entire conference was made of brainstorming sessions on three topics “Parametrization”, “Correlation,” and “Falsification.” There are already several emails circulating with several paper ideas coming out of it. Huge thanks to all those who led and participated in the discussions. Here is the conference website…
Congrats to Alex Toubiana, postdoc with us, who was just awarded an independent fellowship from the Italian Research Ministry. The scheme is called Young Researcher 2024 and will fund Alex and his research for 3 years.
In 2024…. We welcomed Tristan, Chiara, Caroline, Rodrigo, Alex, Federico, and Zachos (group accretion at the Eddington limit). Michele started a faculty in Marseille, Daria graduated, Viola almost graduated and is fighting the paperwork in Marseille, Giulia went to Cambridge, Alice went to the AEI, Cecilia went to Nottingham, Costantino went to Novara. Ringdowns, EMRIs, stochastic backgrounds, p_det, catastrophes, SBI, and 3G detectors don’t have secrets for us. I think 13 BSc and 3 MSc students defended their projects with us, not sure. Arianna and Nick are two Giovani Talenti, Alex is a Young Researcher. We went to the lake together, got risotto together, and organized a conference named after Inter’s striker. If you don’t know what to eat for dinner, define a likelihood and sample it (Loutrel et al. 2024). Or put pins on google maps (Borhanian et al. 2024). You look at data, I look at the physics (Bruel et al. 2024).
FIS (“Fondo Italiano per la Scienza”) is an Italian grant opportunity which is conceptually similar to the ERC. The amount of these grants is >= 1M EUR and grant holders are offered a tenure-track or tenured position. The deadline for this year’s solicitation (FIS 3) is Mar 28, 2025. If you’re interested in applying with Milano-Bicocca as host institution please shoot me an email!
This semester I’m back teaching my “Scientific computing with Python” module to PhD students. It’s a really really fun class to teach (and it’s just 8 lectures, short and sweet!). If you’re curious:
Black holes on eccentric orbits… what does it even mean? The hard (but fun) thing is that we work in General Relativity, where coordinates don’t have a physics inside. One can always change the coordinates as they want, so they can’t be used to define observables. The eccentricity of an orbit has to do, indeed, with the shape of the orbit itself, and that can be transformed away with suitable coordinates. So, does it even sense to measure the orbital eccentricity of black-hole binaries? The one thing we are allowed to do is to find a coordinate-free estimator in General Relativity that reduces to the eccentricity we all know and love in the Newtonian limit. This is possible! The right mathematical framework for this is something called “catastrophe theory”, a funny name, but Nick likes it.
Matteo Boschini, Nicholas Loutrel, Davide Gerosa, Giulia Fumagalli. Physical Review D 111 (2025) 024008. arXiv:2411.00098 [gr-qc].
Our “popfisher” paper is finally out! (and now Viola can submit her PhD thesis). This is about next-generation (aka 3G) gravitational wave detectors. Those beasts will measure millions of black holes… and with so many of them who cares about each source individually. The important thing will be the population of objects, i.e. how those black holes are distributed as a whole. Measuring populations is an interesting but convoluted statistical problem. Here we implement a quick shortcut (the Fisher matrix) and show that yes, 3G detectors will be amazing… but more amazing for some things than for others.
Viola De Renzis, Francesco Iacovelli, Davide Gerosa, Michele Mancarella, Costantino Pacilio. Physical Review D 111 (2025) 044048. arXiv:2410.17325 [astro-ph.HE].
Four BSc students and one MSc student defended their research project with us this month.
First, huge congrats to Federica Tettoni who got her MSc degree in astrophysics. She worked with Viola De Renzis and myself on labeling black holes in gravitational wave events. Such a fun problem (and we got confused so many times!), more here.
Giulia Foroni (BSc) worked with me on black-hole binary spin precession. The good old problem of the spin morphologies, but this time looking for two transitions at the same time.
Matilde Vergani (BSc) also worked with me; we looked at merger trees and their combinatorics problem (her presentation pictures of trees, I mean actual trees…).
Laura Tassoni (BSc) worked with Costantino Pacilio on ringdown data analysis.
Thanks all for spending some time in our research group!
Huge congrats to Arianna Renzini and Nick Loutrel who won two of this year’s “Giovani Talenti” (Young Talents) prizes from the University of Milano-Bicocca. These are internal grants for postdocs: there were four grants awarded in Physics in total and two of them are from our group! Let’s gooooooooooo
LISA will see a gazillion white dwarfs, but we won’t, or at least not individually. Those signals will actually pile up together in a mashed potato thing called foreground. But this mashed potato won’t be smooth (translate: the gravitational-wave signal won’t be stationary and Gaussian) and this structure can indeed be precious for extracting more information from LISA. But first, let’s taste this with today’s paper, i.e. characterize the foreground.
Riccardo Buscicchio, Antoine Klein, Valeriya Korol, Francesco Di Renzo, Christopher J. Moore, Davide Gerosa, Alessandro Carzaniga. arXiv:2410.08263 [astro-ph.HE].
ps. This started as the student project of Alessandro Carzaniga, great it’s finally out!
This is a fun IMBH story we worked out when Kostas and Luca were visiting last summer from JHU. What if (one day, who knows) we observe a highly spinning intermediate-mass black hole? If that happens, is going to be puzzling because IMBH that grow in clusters by mergers of smaller black holes tend to spin down, not up. This is a funny property of black holes, namely that extracting spins is easier than putting it in, so on average black holes slow down after they have merged many times. So if we see an IMBH with large spins, the spin must come from somewhere else. Where? Maybe gas. The argument then is that one can actually convert an IMBH spin measurement into the minimum amount of gas that must have been accreted to get that spin.
To Stars or to gas, that is the question. Whether ’tis nobler in the hardening to suffer The slings and arrows of passing stars, Or to dissipate against a sea of gas And by disk end them. To inspiral — to merge, No more; and by LISA to say we end The models and the thousand PE samples That gravity is heir to.
Alice Spadaro, Riccardo Buscicchio, David Izquierdo-Villalba, Davide Gerosa, Antoine Klein, Geraint Pratten. Physical Review D 111 (2025) 023004. arXiv:2409.13011 [astro-ph.HE].
Four students just graduated with projects in our group…
First, huge congrats to Cecilia Fabbri who got her MSc in Astrophysics. Cecilia (you might remember her) worked on an exciting applied statistics problem (which has already ended up in a poem, but soon in a paper). Her problem got like 10 more people hooked beside us, so we really have to finish it now! From my side, it’s always amazing to see scientists like her growing so much. Cecilia be moving on with a PhD in Nottingham (UK) with Steve Green (and when you come back to visit you’ll tell me everything I don’t understand about simulation-based inference!). Good luck!
We also supervised three BSc students who defended their short projects:
Matteo Pagani worked with Ssohrab Borhanian on testing Fisher Matrix codes (spoiler, it’s tricky).
William Toscani worked with Giulia Fumagalli on eccentric binary black holes, revisiting the old “isotropic stays isotropic” problem in PN dynamics.
Francesca Rattegni worked with Matteo “Bormio” Bonetti on how the Galaxy can cause Kozai-Lidov oscillations on wide binaries.
Congrats all, Spritz time now.
Here’s Cecilia (wearing Laurel crowns is a very Italian thing to do when graduating!)
All right I think this is great (but it took me a long time to convince myself and the others that’s the case!) In gravitational-wave astronomy we measure binaries, that is, pairs of two objects. Our signals have information about the pair as a whole. At the same time, we care very much about separating those two objects and measuring the properties of individual black holes and neutron stars. We always do that operation without thinking twice, just say that for each posterior sample object “1” is that with the larger mass and object “2” is that with the lower mass. But is that ok? Surely it’s a choice, but is it the best one? What does it even mean to pick the “best” labels? I think machine learning can help us here and that this problem can be framed using the language of semi-supervised clustering. The results? Well, they seem very significant. Measurements of the black-hole spins are more accurate, you can tell more easily if that’s a black hole or a neutron star, and overall the posterior distributions just look nicer (go away nasty multimodalities and non-Gaussianities!).
The ringdown is the final bit of a gravitational-wave signal, after the two black holes have merged. It’s nice because it’s clean; GR is so powerful that all that comes out after a black hole merger has specific frequencies, the fantastic “quasi-normal modes.” While the frequencies only depend on that final BH (thanks Kerr!), the excitations of those frequencies depend on all that happened before, i.e. the merger process itself. In this summer paper by Costantino and the rest of us, we present a new accurate approximant to those amplitudes. Now go home and test GR.
Costantino Pacilio, Swetha Bhagwat, Francesco Nobili, Davide Gerosa. Physical Review D 110 (2024) 103037. arXiv:2408.05276 [gr-qc].
Usually my students graduate in Physics, but not this time… Together with Matteo Boschini, I had the pleasure of supervising a student majoring in Computer Science. Alessandro Crespi got his BSc degree with a project on Simulation Design, which is really a computing thing but has lots of physics applications. That was so much fun! It is truly true that putting different expertise/approaches/ideas makes things better.
We’re having a few visitors this summer, with lots of science going around. Welcome Jam Sadiq from SISSA (Italy), Rossella Gamba from Berkeley (USA), Abhishek Chowdhuri from IIT Gandhinagar (India), Luca Reali from JHU (USA), and Kostas Kritos also from JHU (USA), thanks for joining us for a bit.
Daria Gangardt has just defended her PhD thesis at the University of Birmingham. The thesis is called “Black-hole dynamics and their environments” and jumps from black-hole spins all the way to AGN discs. Daria, it has been a true pleasure working with you, all the way since your very first summer project and through your supervisor changing countries. I’m both honored and proud that you completed your PhD with me, all the best with everything. Time for drinks now! Go Dr. Daria!
The workshop “Challenges and future perspectives in gravitational-wave astronomy: O4 and beyond” will take place at the Lorentz Center (Leiden, Netherlands) from October 14th to October 18th, 2024.
Our goal is to foster an interdisciplinary discussion (with astrophysicists, data analysts, and machine learners) about how current and future observations of gravitational and electromagnetic waves can be used to shed light on the physics of compact-object formation and evolution.
Lorentz Workshops@Oort are scientific meetings for small groups of up to 55 participants, including both senior and junior scientists. We will dedicate a considerable amount of time to discussion sessions, thus stimulating an interactive atmosphere and encouraging collaboration between participants. The venue Lorentz Center@Oort is located at the Faculty of Science campus of Leiden University, the Netherlands. The Lorentz Center provides each participant with office space as well as various practical services such as arranging accommodations at the nearby hotel Van der Valk Hotel Leiden/Tulip Inn Leiden at a special rate, visa assistance, and bike rental. For more information see: www.lorentzcenter.nl
SOC: Fabio Antonini (chair), Maya Fishbach, Davide Gerosa, Laura Nuttall, Rosalba Perna, Simon Portegies Zwart.
Three fits for the non-parametric under data sky, Seven for the astrophysicists in their clusters of stars, Nine for powerlaw+peaks doomed to die, One for the sampler on his python throne In the land of LIGO where the data lie. One population fit to rule them all One population fit to find them features One population fit to Bayes them all, and in the stats bind them. In the land of LIGO where the data lie.
The orbits of binary black holes could be eccentric, but in practice they’re not. At least when we observe them, and that’s because of a relativistic effect that circularizes the orbit. Even if astrophysics formed black holes eccentric, relativity makes them circular when we observe them with gravitational-wave interferometers. But we’re interested in the astrophysics back then! What we find here is that the tiny residual eccentricity at detection can be crucial. Even eccentricities that are so small that we cannot tell them apart from circular can mess up the astrophysical inference. Unfortunately, this is a new systematic error that needs to be taken into account: inferring the “formation channel” of binary black holes might be even harder than we thought.
Giulia Fumagalli, Isobel Romero-Shaw, Davide Gerosa, Viola De Renzis, Konstantinos Kritos, Aleksandra Olejak. Physical Review D 110 (2024) 063012. arXiv:2405.14945 [astro-ph.HE].
We are organizing “Gravitational-wave snowballs, populations, and models” — a workshop to be held in Sexten, in the Dolomites region of Italy, January 20-24, 2025: https://sites.google.com/unimib.it/gwsnowballs
Our goal is to bring together researchers at the forefront of both forward astrophysical modeling of compact object binary formation and gravitational-wave data analysis in preparation for the upcoming O4 data release of LIGO/Virgo, for discussions focused on population-level modeling and inference.
The meeting will be held at Bad Moos Hotel right next to the ski slopes and the conference program will have appropriate breaks for snow activities; more details are available at https://sites.google.com/unimib.it/gwsnowballs/logistics
We hope you will consider applying to participate. Space is limited to 40 people. Please apply online at https://sites.google.com/unimib.it/gwsnowballs/registration by July 15, 2024. We plan to notify accepted participants by the end of July.
… and we’re back to selection effects. That means modeling what you cannot see. The black holes that gravitational-wave detectors observe are not representative of those that are out there in the Universe. Some are easier to see, some are harder. Quantifying how much easier and harder is crucial to properly understand the underlying astrophysics. In this paper (which came out of a BSc student project!), we go back to the basics and work out gravitational-wave selection effects one step after the other, using and refining the most common approximation. Two things to remember: including noise fluctuations is easy, and a signal-to-noise ratio threshold of 11 is probably ok.
This is part of a PRIN grant we have together (thanks Italy) with support from other grants as well (thanks Europe). The meeting has the best title ever (that was actually my idea…), the best logo ever (that was Giulia’s idea), and the best organization ever (huge thanks Costantino and Sara!).
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.
Filippo Santoliquido, Ulyana Dupletsa, Jacopo Tissino, Marica Branchesi, Francesco Iacovelli, Giuliano Iorio, Michela Mapelli, Davide Gerosa, Jan Harms, Mario Pasquato. Astronomy & Astrophysics 690 (2024) A362. arXiv:2404.10048 [astro-ph.HE].
The University of Milano-Bicocca welcomes applications for PhD scholarships. This year’s application deadline is May 14th, 2024 (noon CEST) for positions starting in the Fall of 2024:
In particular, we are looking for highly motivated candidates to join our activities in black-hole binary dynamics and gravitational-wave data exploitation. Milano-Bicocca hosts a large group in gravitational-wave physics, covering activities ranging from astrophysical/numerical modeling to data analysis. The group counts 7 faculty members (Bortolas, Colpi, Dotti, Gerosa, Giacomazzo, Sesana, and an upcoming new hire) together with several postdocs (of which two prize fellows) and PhD students. Candidates will also have ample opportunities to work with and visit external collaborators.
Our PhD admission program includes several “open” scholarships, covering all research activities in the department (including ours!). All candidates are considered for those by default. In addition, we are advertising an additional “project” scholarship titled “Gravitational-wave source modeling” which will be supervised by Prof. Davide Gerosa. Candidates wishing to be considered for this opportunity should indicate it explicitly when applying (the number of this position FIS.8). For more information on Gerosa’s group see www.davidegerosa.com/group
We strive to build an inclusive group and welcome applications from all interested candidates. For informal inquiries, expressions of interest, and application tips please do not hesitate to contact [email protected]
Three more students graduated in March with research projects completed in our group!
Alessandro Pedrotti defended his MSc thesis working with Michele Mancarella on gravitational-wave cosmology going from crazy calculations to fun correlations and all the way to Einstein Telescope! Alessandro is now moving on with his career with a research placement at the University of Aix-Marseille. Congrats!
Annalisa Amigoni completed a BSc project with Ssohrab: more fun with 3g detectors…
Alice Palladino also completed a BSc project; she worked with Viola and me on a strange and mind-twisting “ordering” problem using the LIGO posterior (how many times did we get confused on this!)
On top of “astrostats” for the MSc degree in Astrophysics, this semester I’m excited to start teaching for the new BSc degree in Artificial Intelligence. This course is delivered jointly by the University of Milano-Bicocca (my place), the University of Milano-Statale (“the other” uni in town), and the University of Pavia (south of here…). My class is actually a lab, the full (too long) title is “Laboratory of Machine Learning Applied to Physical Systems.” The class material is available here:
The teaching semester is back and I’ll be delivering my “Astrostatistics and Machine Learning” class once more. This is designed for our MSc program in Astrophysics.
And the second paper on the arxiv today is Daria’s masterpiece! pAGN (which Daria says you should read “pagan”) is a brand new, super cool code that implements the hydrodynamics of AGN disks, at least in their most popular one-dimensional fashion. Those solutions have been around for a long time but their details were, well, let’s say unclear. Daria went through everything from beginning to end, coming up with the “one-stop solution for your AGN disc needs” (that was actually the working title of the paper…). So pip install pAGN and have fun.
Daria Gangardt, Alessandro Alberto Trani, Clément Bonnerot, Davide Gerosa. Monthly Notices of the Royal Astronomical Society, 530 (2024) 3986–3997. arXiv:2403.00060 [astro-ph.HE].
This is the first of two papers on the arxiv today: it’s fun when two long, very different projects by different people just happen to be done on the same day! This paper is by my former colleague Nate Steinle (now a postdoc in Manitoba, Canada). Here we connect the dynamics of jets in AGN disks to the spin of black holes observable by LISA. And show the latter is a diagnostic of the former! And it’s nice to see my disk-binary code being used for something I didn’t think of when I wrote it.
Nathan Steinle, Davide Gerosa, Martin G. H. Krause. Physical Review D 110 (2024) 123034. arXiv:2403.00066 [astro-ph.HE].
Our student Lisa Merlo defended her BSc 3rd year project today! Lisa worked with Pippa Cole and me on computing rates for mergers of primordial black holes, also considering a new detector prototype that the experimental group here is developing (nickname BAUSCIA, from the Milan dialect). Short answer: the rate is low but now is more accurately low. Lisa’s presentation was amazing and working with her has been a real pleasure. Stay tuned for her future astro career!
Huge huge congrats to Zacharias Roupas who was awarded a Marie Curie Fellowship with us! Zachos is currently based at the British University in Egypt and will be joining my group in Milan in the Fall of 2024. The Marie Curie Fellowship program is a prestigious postdoctoral scheme operating at the EU level and, together with Arianna, we’ll now have two Marie Curie grantees in the group. Zachos’ winning proposal is titled “Black hole spin and mass function in gaseous proto-clusters” (nickname: protoBH).
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.
