The “GRACE-BH” project (funded by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 101025436), aims to tackle the challenge of answering the question
“What are the best conditions under which an intermediate-mass black hole forms in a massive stellar system?”
The project, led by Manuel Arca Sedda, will follow the complex phases that undermine the possible development of intermediate-mass black holes (IMBHs) in star clusters. To reach this goal, he will develop the most refined numerical simulations of star clusters on the market, which will feature up to 1 million stars and will represent reliably the clusters that we can admire in our skies.
The DRAGON-II simulations Intermediate-mass black holes in dense star clusters with up to 1 million stars
Press releases
(see original press release here)
A Gran Sasso Science Institute study shows how elusive Intermediate-Mass Black Holes could form inside star clusters
A recent study led by Gran Sasso Science Institute researcher Manuel Arca Sedda and published in Monthly Notices of the Royal Astronomical Society journal (MNRAS), sheds light on the mechanisms that lead to the formation of mysterious Intermediate-Mass Black Holes (IMBHs). These are objects with masses between a few hundred and tens of thousands of solar masses, which could represent the link between their smaller relatives, stellar black holes, and the supermassive giants that populate the centres of galaxies.
Indeed, there are different types of black holes: although they share such high densities that even light cannot escape their gravitational pull, the mass of these celestial bodies can vary over a very wide range and discriminate their formation mechanism. We can identify three macro-categories of astronomical interest: stellar, intermediate, and supermassive. The former, as the name suggests, are formed when a star of sufficiently large mass (i.e., at least twenty times more massive than our sun) exhausts its fuel and succumbs to the force of gravity by collapsing in on itself: they represent the lightest type of black hole, and we have a clear theoretical picture about the process leading to their formation. At the opposite extreme are the immense supermassive black holes, with masses millions or billions of times greater than our star. Every galaxy is believed to host one at its centre and in 2019, thanks to the Event Horizon Telescope, it was possible to obtain the first direct image of one of them. Despite this formidable achievement, the formation and accretion of these objects still represent a fascinating mystery to modern astronomy, mainly due to the lack of a definitive smoking gun supporting the very existence of Intermediate-Mass Black Holes. And that is precisely the subject of Arca Sedda’s study, the first of two others currently under review.
“Intermediate-Mass Black Holes are difficult to observe”, explains the GSSI researcher, “the current observational limits do not allow us to say anything about the population of IMBHs with masses between 1,000 and 10,000 solar masses, and they also represent a headache for scientists in terms of the possible mechanisms that lead to their formation”.
One of the goals of the research was precisely to try to understand how these black holes form. “We have carried out new computer models that can simulate the formation of these mysterious objects, and we have found that such IMBHs can form in star clusters through a complex combination of three factors: mergers between stars much larger than our sun, accretion of stellar material onto stellar black holes, and, finally, mergers between stellar black holes. The latter is a process that results in the possibility to “see” these phenomena through the detection of gravitational waves”, Arca Sedda explains. The study also hypothesises what happens after intermediate black holes are born: they are thrown off their own clusters through complex gravitational interactions or due to a process known as relativistic recoil, thus preventing their further growth. “Our models show that although IMBH seeds form naturally from energetic stellar interactions in star clusters, they are unlikely to become heavier than a few hundred solar masses unless the parent cluster is extremely dense or massive”, the GSSI researcher says.
However, an important scientific mystery is yet to be answered: whether intermediate black holes represent the link between stellar and supermassive black holes. It is an open question, but the study gives space for some speculation. “We need two ingredients for a better clarification”, Arca Sedda explains, “one or more processes capable of forming black holes within the mass range of IMBHs, and the possibility of retaining such IMBHs in the host environment. Our study places stringent constraints on the first ingredient, giving us a clear overview of which processes may contribute to the formation of IMBHs. Considering more massive clusters containing more binaries (systems composed of two stars orbiting each other) in the future could be the key to obtaining the second ingredient as well. But this will require enormous efforts from a technological and computational point of view”.
DOI: 10.1093/mnras/stad2292 “The Dragon-II simulations — II. Formation mechanisms, mass, and spin of intermediate-mass black holes in star clusters with up to 1 million stars”
Institutes involved: Gran Sasso Science Institute, Università degli Studi di Padova, Astronomisches Rechen Institute (Zentrum fur Astronomie der Universitat Heidelberg), Max Planck Institut fur Astronomie (MPIA, Heidelberg), Max Planck Institute for Astrophysics (MPA, Garching), National Astronomical Observatories and Key Laboratory of Computational Astrophysics (Chinese Academy of Science, Beijing), Kavli Institute for Astronomy and Astrophysics (Peking University), Nicolaus Copernicus Astronomical Centre (CAMK, Warsaw), Konkoly Observatory (Eotvos University, Budapest), Main Astronomical Observatory (National Academy of Science of Ukraine, Kiev), INFN-Padova, INAF-Padova, INAF-Osservatorio Astronomico di Capodimonte.
Figure caption (attached) and link to the video: In the picture, a simulation of a star cluster: in orange and yellow are the stars like the Sun, while in blue and light blue are those with a mass of 20 to 300 times that of the Sun. The large white ball above, represents a star with a mass of about 350 solar masses, which will shortly collapse to form a black hole of intermediate mass.
I buchi neri intermedi e le simulazioni
Interview with Dr Gianluigi Marsibilio for the podcast CO.Scienza, episode 184. Listen to it here (in Italian): https://www.spreaker.com/episode/i-buchi-neri-intermedi-e-le-simulazioni-puntata-centottantaquattro–57153519
Nel pensare ai buchi neri immaginiamo spesso stelle che hanno finito la loro vita o giganti super-massicci situati al centro delle galassie. Ci sono però diversi passi avanti che la ricerca sta facendo per identificare i buchi neri intermedi.
Nella puntata di oggi attraverso una chiacchierata con il dottor Manuel Arca Sedda (Gran Sasso Science Institute – Università di Padova) ragioneremo su possibilità e obiettivi raggiungibili nei prossimi anni.
La conoscenza di questi oggetti attualmente passa anche attraverso un miglioramento delle simulazioni computazionali e dei modelli che prevedono la formazione dei buchi neri intermedi.
Ecco lo studio al centro della chiacchierata. Per approfondire gli argomenti al centro della puntata, sulle fusioni e i buchi neri intermedi; il processo di crescita dei buchi neri intermedi.
Perché studiamo i buchi neri?
(See the original page of the project Science4All, promoted by the University of Padova, here)
Manuel Arca Sedda si occupa di buchi neri e la sua ricerca è incentrata sulla scoperta di una loro versione “intermedia”.
Come lavora? Che strumenti utilizza per svolgere la sua ricerca? Che conoscenze aggiuntive potrebbe portare alla comunità scientifica la scoperta di questi nuovi buchi neri? Nel video, il ricercatore risponde a queste ed altre interessanti domande dal mondo dell’astronomia.
Il Dott. Arca Sedda, dopo l’ottenimento del grant Marie Curie all’Università di Padova, è stato nominato assistant professor presso il GSSI – Gran Sasso Science Institute dell’Aquila.
Manuel Arca Sedda wins the MERAC Prize 2023
(See the press release here)
“The pioneering studies on black holes by Manuel Arca Sedda are milestones for interpreting the observations of the nascent astronomy of gravitational waves and for the science of future observatories on the ground and in space”, GSSI professor Marica Branchesi commented
Manuel Arca Sedda, Marie Curie fellow at the Department of Physics and Astronomy of the University of Padua, under the supervision of Professor Michela Mapelli, and recently adjoined as a researcher at the Gran Sasso Science Institute, has received the MERAC 2023 award for the Best Early Career Researcher in Theoretical Astrophysics. The European Astronomical Society (EAS) awarded the prize to a young European scientist who has achieved innovative results in his field.
The MERAC Foundation (Mobilising European Research in Astrophysics and Cosmology) is a non-profit foundation based in Switzerland and was born in 2012 to recognize and support young European astronomers. The EAS annually awards three MERAC prizes of 25,000 euros for Theoretical Astrophysics, Observational Astrophysics and New Technologies (Instrumental/Computational/Multi-Messenger).
The MERAC Prize for Theoretical Astrophysics is awarded to Manuel Arca Sedda “for pioneering research in the dynamics of binary compact objects as gravitational wave sources in galactic nuclei and dense star clusters”.
It is a result that fills me with pride and that I honestly did not expect – Arca Sedda said – the achievement of MERAC marks a new starting point for my future research on the nature of intermediate-mass black holes and their impact on populations of gravitational wave sources. I thank my family for their unconditional support, without which such a result would not have been possible. Finally, I want to thank all the collaborators and colleagues I worked with over the years: their contribution has been fundamental, and the merit of this award is theirs too.
Manuel Arca Sedda, recipient of MERAC Prize 2023
The importance of this type of award which testifies to the quality of the research carried out in the department. I like to remember that in 2015 the same prize had already been won by our teacher Michela Mapelli.
Flavio Seno, director of the Physics and Astronomy department
Manuel’s victory fills us with pride: the MERAC is one of the most prestigious awards in Europe in the field of astrophysics and it is a deserved recognition for the work on the dynamics of black holes that Manuel has conducted in recent years, opening up new perspectives on the study of gravitational wave sources. A note of color: this award returns to Padua after only 8 years, confirming the excellence of Paduan astrophysics.
Prof. Michela Mapelli
The pioneering studies on black holes by Manuel Arca Sedda are milestones for interpreting the observations of the nascent astronomy of gravitational waves and for the science of future observatories on the ground and in space, which they will go to investigate black hole coalescences of increasing mass. Furthermore, we are very proud that a brilliant new talent will soon arrive at GSSI: in L’Aquila, we will work together on wonderful discoveries with the Einstein telescope, the Luna Gravitational-Wave Antenna and LISA.
Prof Marica Branchesi
Manuel Arca Sedda 