NIC Excellence Project 2024/2
Multi-Messenger Astrophysics Using Computer Simulations of Nuclear Star Clusters
John von Neumann Excellence Project 2024/2
Prof. Rainer Spurzem (University Heidelberg and Chinese Academy of Science Beijing, and guest scientist at Frankfurt Institute for Advanced Study)
Galaxies like our own Milky Way harbor a supermassive central black hole (few million to few billion solar masses) in their centers. There is evidence for the presence of such central massive or supermassive black holes from the earliest times in our universe, shortly after the formation of first stars and galaxies. This has been confirmed by both deep astrophysical observations e.g. with the recent James Webb Space telescope (JWST) as well as from theoretical grounds (computer models of structure and galaxy formation in the universe). How do the massive black holes in galactic centers grow to their observed sizes, and from what mass range are their progenitors drawn? We are examining this in our project, by following the formation and the growth of stellar-mass seed black holes through direct N-body simulations of nuclear star clusters. The black holes grow through direct hyperbolic encounters with stars (tidal disruption or direct capture) or through relativistic energy loss in strongly bound binaries. Our computer models consist of a generally Newtonian N-body simulation for a large number of stars (up to few million, which is the record particle number for this type of numerical models of dense, gravothermal star clusters); this is complemented by a detailed account of how the stars in our models evolve, changing their mass and radius with time, finally becoming a compact remnant (white dwarf, neutron star, stellar mass black hole); relativistic dynamics (in high order Post-Newtonian form) is used to follow the evolution of binaries of compact obects and their final coalescence under gravitational wave emission. We predict gravitational wave signals from these mergers, which would be measured by LIGO/Virgo/KAGRA. Our model simulations also show a possible pathway for intermediate mass black hole (IMBH) formation, a subject of hot debate whether they exist in our nearby universe.
We have published key results recently in three papers in Monthly Notices of the Royal Astronomical Society (Arca Sedda, Manuel, et al., MNRAS 2024, Vol. 528, p. 5140 and p. 5119, MNRAS 2023, Vol. 526, p. 429). The models are called DRAGON-II simulations, in recognition of a close collaboration with China; there are several other collaboration partners involved including MPA in Garching, MPIA in Heidelberg, the Nicolaus Copernicus Astronomical Center in Warsaw, and the Main Astronomical Observatory in Kyjiv, Ukraine. A press release of MPIA describes the results, which have been published last year: https://www.mpia.de/aktuelles/wissenschaft/2023-13-imbh-dragon-ii.
In the current computing time period we are modelling ultra-compact young star clusters in a universe which is only a few 100 million years old - as they have been recently detected by JWST (Adamo et al. 2024, Nature Vol. 632).
There is also a youtube movie available about our work: https://www.youtube.com/watch?v=8_74BRTI11Y&authuser=0
The movie is a zoom-in/out of a single snapshot in the simulation in which a very massive star with mass larger than 350 solar masses forms, the big white spot is the VMS, the blue stars with a bright halo are those with mass > 100 Msun; the blue stars without halo have masses 20 < m/Msun < 100; red and yellow stars are less massive than 20 Msun. The first author of our 2023/2024 publications (Manuel Arca Sedda) has been an Alexander-von-Humboldt fellow hosted by our Heidelberg team, who is now professor at the Gran Sasso Science Institute (GSSI) in L'Aquila near Rome.
