Galactic Nuclei as Nurseries for Gravitational Wave Sources
Lead Research Organisation:
University of Surrey
Department Name: Physics
Abstract
We are in a similar position as Galileo when he first peered through a telescope: mankind has developed a new way to study the Universe, we can now see gravitational waves! Advance LIGO has provided unique access to the properties of space-time in the strong field of gravity together with a direct confirmation of the existence of black holes and in particular of binary black holes that merge within the age of the Universe. The Advanced LIGO detections have not only confirmed the existence of gravitational waves but have also ushered astrophysics into a new era of observing cosmic events that were previously invisible. This new set of eyes on the Universe is expected to provide important clues to the properties of black holes and to the environments in which they form. But a proper theoretical understanding of the astrophysical processes leading to black hole coalescence is required to make sense of the large amount (hundreds to thousands) of new detections expected in the next few years from Advanced LIGO and other interferometers on the ground.
In this project I will study the formation and dynamical evolution of black hole binaries that are likely to merge and become gravitational waves sources. It has long been recognised that dense star clusters are a preferred site for the formation of compact objects binaries. Of particular relevance among star clusters are the so called nuclear clusters, massive stellar systems that are observed at the centre of most nearby galaxies, including our own. Nuclear clusters have similar sizes to galactic globular clusters but are much more massive, and as such represent the densest systems observed in the local Universe - they contain between 1 to 100 million stars within the same distance that separates our Sun from its closest star, alpha Centauri. Due to these extreme densities, close dynamical encounters involving black holes, stars, and binaries are common and lead to the formation of black hole binaries. It is likely that many, or perhaps even most, of the gravitational waves sources detectable by Advanced LIGO are binary black holes produced dynamically in nuclear clusters. Therefore, nuclear star clusters are ideal nurseries for binaries of compact objects and high frequency gravitational waves sources.
The main objective of this proposal is to make detailed predictions for the properties (e.g. mass, eccentricity, spin distributions) of black hole binaries in nuclear star clusters and of their merger rate. I will characterize how such properties can be related to the global properties of the host cluster, opening the door to more quantitative comparisons between theoretical models and observations. The method will include a combination of analytical calculations and state-of-the-art numerical simulations, including high accuracy simulations of nuclear star clusters with realistic stellar and binary populations.
My goals go beyond a characterization of the gravitational wave sources. I will build hundreds to thousands of cluster models that I will make publicly available to the community. These will represent the most detailed theoretical framework for the interpretation of a variety of interesting additional phenomena, including stellar collisions and blue stragglers, radio pulsars, planetary systems in star clusters, and the dynamical formation of stellar triples.
In this project I will study the formation and dynamical evolution of black hole binaries that are likely to merge and become gravitational waves sources. It has long been recognised that dense star clusters are a preferred site for the formation of compact objects binaries. Of particular relevance among star clusters are the so called nuclear clusters, massive stellar systems that are observed at the centre of most nearby galaxies, including our own. Nuclear clusters have similar sizes to galactic globular clusters but are much more massive, and as such represent the densest systems observed in the local Universe - they contain between 1 to 100 million stars within the same distance that separates our Sun from its closest star, alpha Centauri. Due to these extreme densities, close dynamical encounters involving black holes, stars, and binaries are common and lead to the formation of black hole binaries. It is likely that many, or perhaps even most, of the gravitational waves sources detectable by Advanced LIGO are binary black holes produced dynamically in nuclear clusters. Therefore, nuclear star clusters are ideal nurseries for binaries of compact objects and high frequency gravitational waves sources.
The main objective of this proposal is to make detailed predictions for the properties (e.g. mass, eccentricity, spin distributions) of black hole binaries in nuclear star clusters and of their merger rate. I will characterize how such properties can be related to the global properties of the host cluster, opening the door to more quantitative comparisons between theoretical models and observations. The method will include a combination of analytical calculations and state-of-the-art numerical simulations, including high accuracy simulations of nuclear star clusters with realistic stellar and binary populations.
My goals go beyond a characterization of the gravitational wave sources. I will build hundreds to thousands of cluster models that I will make publicly available to the community. These will represent the most detailed theoretical framework for the interpretation of a variety of interesting additional phenomena, including stellar collisions and blue stragglers, radio pulsars, planetary systems in star clusters, and the dynamical formation of stellar triples.
Publications
Amaro-Seoane Pau
(2022)
Astrophysics with the Laser Interferometer Space Antenna
in arXiv e-prints
Antonini F
(2019)
Black hole growth through hierarchical black hole mergers in dense star clusters: implications for gravitational wave detections
in Monthly Notices of the Royal Astronomical Society
Antonini F
(2018)
Precessional dynamics of black hole triples: binary mergers with near-zero effective spin
in Monthly Notices of the Royal Astronomical Society: Letters
Antonini F
(2020)
Merger rate of black hole binaries from globular clusters: Theoretical error bars and comparison to gravitational wave data from GWTC-2
in Physical Review D
Antonini F
(2020)
Population synthesis of black hole binary mergers from star clusters
in Monthly Notices of the Royal Astronomical Society
Antonini Fabio
(2018)
Black hole growth through hierarchical black hole mergers in dense star clusters: implications for gravitational wave detections
in arXiv e-prints
Erkal D
(2018)
A hypervelocity star with a Magellanic origin
Erkal D
(2019)
A hypervelocity star with a Magellanic origin
in Monthly Notices of the Royal Astronomical Society
Description | Many, if not most, stars form in dense star clusters and associations. Due to the high density of bound stellar systems such as globular clusters and nuclear star clusters, black holes that form from the evolution of massive stars are expected to pair efficiently through dynamical interactions. The black hole binaries formed by such dynamical interactions in dense clusters are thought to be one of the main sources of gravitational waves detected by LIGO and Virgo. During my ERF fellowship I have investigated the origin of the detected gravitational wave sources and addressed whether the black hole binaries that produce them can be formed in dense star clusters. I have reached several key conclusions from my study. The most important are: (i) globular clusters can contribute at most <20% of the sources detected by LIGO/Virgo; (ii) the nuclear clusters found at the centre of most galaxies have an even lower contribution; (iii) the sources produced in these systems have, however, unique properties (e.g., high eccentricities, large masses) that can be used to learn about the physics of black holes and star cluster formation; and (iv) I have developed a fast code for the evolution of star clusters with black holes and I have made this code available to the community. |
Exploitation Route | The outcomes of this funding will pave the way for the astrophysical interpretation of the large set of gravitational wave data to come next year through the O4 LIGO science run. It is expected that hundreds of gravitational wave detections will be made during next year, and my results will be key for their interpretation. |
Sectors | Education Other |
Description | During the fellowship I have engaged in several outreach activities, which include talks to the wider public, and public lectures on gravitational wave astrophysics. I have given interviews to magazines and tv channels (e.g., new scientist and BBC) that are directed to the wider audience, and podcasts. I have also give guest lecturer for the module dynamical astrophysics at the University of Surrey and for introduction to general relativity at Cardiff university. Directly related to my scientific achievement. I have discovered that the seeds of supermassive black holes can form through the hierarchical merger of stellar origin black holes in star clusters. My results have initiated a large interest in this topic in relation to the massive black hole binaries detected by LIGO. Several groups are now investigating this mechanism as a possible formation pathway to supermassive black holes. My research has also shown the importance of multiple star interactions in the evolution of massive stars. Most massive stars that lead to black holes form in triples and higher multiplicity systems. I have shown that the higher multiplicity (beyond binaries) of massive stars change their evolution in fundamental ways. This result has received much interest by the scientific community and several groups are now investigating the effect of multiplicity on the formation of black hole mergers formed in the field of galaxies. |
First Year Of Impact | 2020 |
Sector | Other |
Impact Types | Cultural Societal |
Description | Einstein Telescope |
Organisation | European Gravitational Observatory |
Country | Italy |
Sector | Public |
PI Contribution | Attend and contribute to monthly scientific meeting held online. |
Collaborator Contribution | Provide an overview of the progress in the planning and realisation of the third generation gravitational wave detector ``the Einstein telescope''. This is strongly related to my research and provides continuous stimulus to my work. |
Impact | Inspiration for new projects with students and postdocs at Cardiff where we look at the implications of our model predictions for 3-G detectors like the Einstein telescope. |
Start Year | 2021 |
Description | LISA consortium |
Organisation | European Space Agency |
Department | ESA Laboratories |
Country | European Union (EU) |
Sector | Public |
PI Contribution | My contribution is to provide the consortium with my expertise on the theoretical modelling and inference. |
Collaborator Contribution | N/A |
Impact | LRR article: https://arxiv.org/abs/2203.06016 |
Start Year | 2018 |
Description | Ligo scientific collaboration |
Organisation | LIGO Scientific Collaboration |
Country | United States |
Sector | Academic/University |
PI Contribution | From January 2020 I am a member of the Ligo scientific collaboration and GEO. I have actively engaged in the discussion of the astrophysical interpretation of the results from the O3 Ligo observing run. |
Collaborator Contribution | Provide data that I will compare to my models to establish how the detected sources have formed. |
Impact | At the moment, there are no outputs from this collaboration. |
Start Year | 2020 |
Title | Triple black hole dynamics |
Description | Code to evolve a systems containing three black holes in a hierarchical configuration, including relativistic corrections to the motion and spin-orbit dynamics |
Type Of Technology | Software |
Year Produced | 2018 |
Impact | First understanding of the evolution of spin-orbit alignment in black hole triples. Results published in Antonini, Rodriguez et al. (2018), and Rodriguez and Antonini (2018) |
URL | https://github.com/carlrodriguez/kozai |
Title | model for computing the evolution of dense star clusters |
Description | the software, clusterBH, is a fast code to evolve the properties of a dense star clusters. |
Type Of Technology | Software |
Year Produced | 2019 |
Open Source License? | Yes |
Impact | clusterBH has been used in Antonini and Gieles (2019, MNRAS) to determine how the formation of BH binary mergers is affected by the properties of their parent cluster and its time evolution. This code allows to evolve a cluster model in less than one sec. Other methods adopted in the previous literature would require more than one week. |
URL | https://github.com/mgieles/clusterbh |
Title | model for computing the formation and merger rate of BH binaries in dense star clusters |
Description | Determine the formation rate and properties of merging BH binaries from a given model of a star cluster. |
Type Of Technology | Software |
Year Produced | 2019 |
Open Source License? | Yes |
Impact | This software was used in Antonini and Gieles (2019, MNRAS) to compute how the merger rate and eccentricities of merging BH binaries depend on the properties of their parent cluster and its secular evolution. |
URL | https://github.com/antoninifabio/BHBdynamics |
Description | Colloquium at University of Birmingham. Title:"Nuclear clusters and (supermassive) black holes".Nov. 15 |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Other audiences |
Results and Impact | 1hr talk that which sparked a lengthy discussion with the research stuff members of the gravitational wave group at Birmingham. |
Year(s) Of Engagement Activity | 2018 |
URL | http://talks.bham.ac.uk/show/archive/281 |
Description | Invited (virtual) seminar at the TATA institute in India: ''Dense star clusters as nurseries of gravitational wave sources'' |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Study participants or study members |
Results and Impact | Seminar about recent publication Antonini and Gieles (2020, PRD). The seminar stimulated a number of questions and a discussion afterwards and I received useful feedback on my work from experts in the audience. |
Year(s) Of Engagement Activity | 2020 |
URL | https://indico.tifr.res.in/indico/conferenceDisplay.py?confId=7837 |
Description | Invited seminar at Imperial College, London. Feb 7. Title:"Nuclear clusters and (supermassive) black holes" |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Other audiences |
Results and Impact | Visit to astrophysics group at Imperial College London. This involved a 1 hour talk, followed by questions and discussions with students, and meetings with some of the staff members in the group. |
Year(s) Of Engagement Activity | 2018 |
URL | http://www.imperial.ac.uk/astrophysics/seminars-and-journal-club/astrophysics-seminars/ |
Description | Invited seminar at Warwick. Title: "Nuclear clusters and (supermassive) black holes". 26 Sep. |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Other audiences |
Results and Impact | Visit to University of Warwick involved a 1hr talk, which led to questions and discussions afterwards. The talk was also followed by a discussion with the postgraduate students in the group. |
Year(s) Of Engagement Activity | 2018 |
URL | https://warwick.ac.uk/fac/sci/physics/research/astro/seminars/ |
Description | Invited talk at EAS2021 |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Other audiences |
Results and Impact | Talk on supermassive black hole evolution at the Special Session (SS18) entitled "Shining Light on Quiescent Black Holes with Tidal Disruption Events" at the Leiden EAS2021. About 40 colleagues. students and postdocs attended the talk, which was followed by a Q&A section and a discussion afterwards. |
Year(s) Of Engagement Activity | 2021 |
URL | https://eas.unige.ch/EAS2021/ |
Description | Invited talk at Lorentz Center (Leiden) workshop "triple evolution and dynamics", September 10-14 |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Other audiences |
Results and Impact | 30 minutes talk describing my recent work on stellar triple evolution. The talk was followed by a lengthy work group discussion involving about 20 people, in which the results and implications of my work were discussed in more detail. |
Year(s) Of Engagement Activity | 2018 |
URL | https://www.lorentzcenter.nl/lc/web/2018/1016/info.php3?wsid=1016&venue=Oort |
Description | Invited talk at Princeton University during the conference ''Gravity Initiative: Exploring Supermassive Black Holes'' |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Study participants or study members |
Results and Impact | Presentation to the working group about the final parsec problem and the evolution of massive black hole binaries in galaxy mergers. The presentation sparked a wide discussion about dynamics in galactic nuclei virtually through zoom and slack, and I received useful feedback on my research activity and request for future collaborations. |
Year(s) Of Engagement Activity | 2020 |
URL | http://pcts.princeton.edu/programs/current/gravity-initiative-exploring-supermassive-black-holes/129 |
Description | Invited talk at University of Padova |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Postgraduate students |
Results and Impact | Invited talk at university of Padova on gravitational wave science. My talk focused on my work on the formation of black hole binary mergers in dynamical environments. About 30 people attended, including colleagues, postdocs and students. The talk sparked questions and discussion afterwards. The followingweeks I had several interactions with Michela Mapelli and her students. |
Year(s) Of Engagement Activity | 2021 |
Description | Invited talk at the 15th Marcel Grossmann Meeting in Rome, July 1-7 |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Other audiences |
Results and Impact | Invited talk at conference. About 50 researchers attended, which led o questions and discussions afterwards, especially with the students from the University of Rome La Sapienza. |
Year(s) Of Engagement Activity | 2018 |
URL | http://www.icra.it/mg/mg15/map.htm |
Description | Invited talk at workshop "The Central Arcsecond: Towards Testing General Relativity in the Galactic Center" at Castle Ringberg, October 28 - November 3, 2018 |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Other audiences |
Results and Impact | Participation to the workshop involved daily discussions about Galactic centre astrophysics. During the workshop I have given a 20 minutes presentation about my recent work, which led to a number of questions and discussions with colleagues. Possible collaborations with some of the observational astronomers attending the workshop were discussed. |
Year(s) Of Engagement Activity | 2018 |
URL | http://www.mpe.mpg.de/ir/meetings/ringberg2018 |
Description | Open day activities |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Undergraduate students |
Results and Impact | about 100 undergraduate students and parents attended the open day event. I gave two presentations of the work done by the gravitational wave group, including the work done by me as part of the ERF award. Several students engaged with me in discussions afterwards, expressing increased interest in the subject of gravitational wave astrophysics and black hole physics. |
Year(s) Of Engagement Activity | 2022,2023 |
Description | Organisation of the Surrey astro seminars |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Other audiences |
Results and Impact | I have led the organisation of the Weekly astro seminars at University of Surrey. This has been very important for the professional development of our students at Surrey, |
Year(s) Of Engagement Activity | 2018 |
Description | Outreach presentation for the series ''meet the expert'' |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Public/other audiences |
Results and Impact | A presentation about my research activity was made to general audience. This led to a number of questions and a interesting discussion with the public about LIGO and the future role of gravitational wave detections in astrophysics. |
Year(s) Of Engagement Activity | 2021 |
URL | https://www.youtube.com/watch?v=81bWzOUA4Dg |
Description | Physics World interview |
Form Of Engagement Activity | A press release, press conference or response to a media enquiry/interview |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Media (as a channel to the public) |
Results and Impact | interview for Physics World Weekly podcast. The interview focused on the LIGO population results recently released. The interviewer reported to us that he received feedback from the audience and that the interview sparked interest among the audience. |
Year(s) Of Engagement Activity | 2022 |
URL | https://physicsworld.com/ |
Description | Public talk at University of Surrey "astronomy evenings", March 21 |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | Public talk of 1hr about gravitational wave astrophysics, which led to a number of discussions and questions afterwards with members of the public. |
Year(s) Of Engagement Activity | 2018 |
URL | https://www.surrey.ac.uk/events/20180321-astronomy-evening |
Description | Review talk at ESO conference: "One in a Million" |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Study participants or study members |
Results and Impact | 100 participants attended the talk. This led to numerous questions and a discussion afterwards. This led to a reported increased interest in the area of gravitational wave astronomy. |
Year(s) Of Engagement Activity | 2023 |
Description | Review talk at NAM23 |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Postgraduate students |
Results and Impact | Review talk. about 50 people attended the conference session and talk. This sparked many questions and interests by the participants and a panel debate at the end of the session, which I led. |
Year(s) Of Engagement Activity | 2023 |
Description | Seminar at Cardiff University |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Postgraduate students |
Results and Impact | Talk given to the gravitational physics group at Cardiff University. About 50 people attended the talk, leading to questions and discussion afterwards. |
Year(s) Of Engagement Activity | 2019 |
Description | Seminar at Max Planck Institute for gravitational physics |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Postgraduate students |
Results and Impact | 1 hour talk on formation scenarios for BH mergers. The talk was followed by discussion and questions with students and staff. |
Year(s) Of Engagement Activity | 2019 |
Description | Seminar at University of Manchester |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Postgraduate students |
Results and Impact | 1 hour colloquium at University of Manchester on BH mergers in nuclear clusters. This was followed by a number of discussions with the students and faculty. |
Year(s) Of Engagement Activity | 2019 |
Description | Talk at La Sapienza, University of Rome |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Postgraduate students |
Results and Impact | about 10 students attended the talk. This was followed by questions and a discussion. A new collaboration was initiated with a student. |
Year(s) Of Engagement Activity | 2022 |
Description | Talk at University of Cambridge Institute of astronomy. Title: "Merging black holes in nuclear star clusters". May 11. |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Other audiences |
Results and Impact | Visit to University of Cambridge Institute of Astronomy, which involved a 1hr seminar in the Galaxies Discussion Group. During the visit I discussed possible collaborations with members of the Institute of astronomy, whom include E. Vasiliev and W. Evans. |
Year(s) Of Engagement Activity | 2018 |
URL | https://www.ast.cam.ac.uk/people/staff |
Description | talk at LJM university |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Postgraduate students |
Results and Impact | about 50 people among students, postdocs and faculty attended the talk. This sparked question and interest afterwards and through the visit |
Year(s) Of Engagement Activity | 2023 |