Periodic Reporting for period 1 - TESIFA (Tracking the Evolution and dynamicS of Intermediate-mass black holes to Forecast their upcoming observAtions)
Reporting period: 2023-11-01 to 2025-10-31
Observational evidence suggests that massive black holes – with masses from about a hundred thousands to ten billion times the mass of the sun – inhabit the centre of many massive galaxies across the cosmic times. However, there is still poor understanding on how these objects grew and reached such high masses. In this framework, it is important to study the so-called intermediate mass black holes, with masses from hundreds to roughly hundred thousands the mass of the sun. These may inhabit the centre of less massive stellar systems and be more common at large distances from us, but they are much harder to observe via standard, electromagnetic telescopes. Yet, building a better knowledge on the population of intermediate mass black holes can inform us on what are the properties of the original seeds from which supermassive black holes have grown, and their growth history.
Supermassive black holes can not only grow by eating up gas in their vicinity, but also, they can disrupt and cannibalize stars passing too close to them; this phenomenon is called ‘tidal disruption event’. This latter growth channel has been poorly investigated in the scientific community, especially for intermediate mass black holes. These lighter objects can also grow through tidal disruption events, but most of the theory developed to study this accretion channel is only valid for the supermassive counterparts. TESIFA aims to investigate how efficiently intermediate mass black holes can grow through tidal disruption events. This will help us understand how long black holes last in the intermediate-mass category, and make predictions for future observatories able to detect tidal disruptions, such as Vera Rubin.
Furthermore, the knowledge developed in the project will be fundamental to foresee the events observed by future gravitational wave detectors, such as LISA and the Einstein Telescope; those will detect the merger between intermediate mass black holes, observing them directly for the first time.
Supermassive black holes can not only grow by eating up gas in their vicinity, but also, they can disrupt and cannibalize stars passing too close to them; this phenomenon is called ‘tidal disruption event’. This latter growth channel has been poorly investigated in the scientific community, especially for intermediate mass black holes. These lighter objects can also grow through tidal disruption events, but most of the theory developed to study this accretion channel is only valid for the supermassive counterparts. TESIFA aims to investigate how efficiently intermediate mass black holes can grow through tidal disruption events. This will help us understand how long black holes last in the intermediate-mass category, and make predictions for future observatories able to detect tidal disruptions, such as Vera Rubin.
Furthermore, the knowledge developed in the project will be fundamental to foresee the events observed by future gravitational wave detectors, such as LISA and the Einstein Telescope; those will detect the merger between intermediate mass black holes, observing them directly for the first time.
I have focussed on the study of tidal disruptions in different frameworks, together with my collaborators.
- Regarding the themes of the fellowship, I have set up a series of n-body simulations and of Fokker Planck integrations to study the rates of tidal disruption events that are occurring using both approaches. The simulations are running and we only have preliminary results. The objective is to compare the rates given by both and see why and by how much they differ. A comparison of the tidal disruption event rates as a function of time is shown in the attached image.
- We have studied the bulk rate of tidal disruption events within galaxies across all cosmic times and all galaxy types across cosmic epochs through a state-of-the-art semi-analytical code evolving galaxies and massive black holes across the cosmic time. In particular, we have included tidal disruption event rates in this model as a growth channel for massive black holes. We found good agreement between the observed and modelled rates of tidal disruption events. We also found out that tidal disruptions are not effective in significantly enhancing the mass of intermediate mass black holes, as gas accretion is more important.
- We have built a semi-analytical model that can model the occurrence of repeated partial disruption events. In these events, the black hole does not completely disrupt the star as it first gets close to the massive object. Instead, the star get disrupted through repeated, regular passages that strip only part of the stellar mass at each time. Our results help reconciling the observed with the theoretically predicted rates of tidal disruption events.
- Regarding the themes of the fellowship, I have set up a series of n-body simulations and of Fokker Planck integrations to study the rates of tidal disruption events that are occurring using both approaches. The simulations are running and we only have preliminary results. The objective is to compare the rates given by both and see why and by how much they differ. A comparison of the tidal disruption event rates as a function of time is shown in the attached image.
- We have studied the bulk rate of tidal disruption events within galaxies across all cosmic times and all galaxy types across cosmic epochs through a state-of-the-art semi-analytical code evolving galaxies and massive black holes across the cosmic time. In particular, we have included tidal disruption event rates in this model as a growth channel for massive black holes. We found good agreement between the observed and modelled rates of tidal disruption events. We also found out that tidal disruptions are not effective in significantly enhancing the mass of intermediate mass black holes, as gas accretion is more important.
- We have built a semi-analytical model that can model the occurrence of repeated partial disruption events. In these events, the black hole does not completely disrupt the star as it first gets close to the massive object. Instead, the star get disrupted through repeated, regular passages that strip only part of the stellar mass at each time. Our results help reconciling the observed with the theoretically predicted rates of tidal disruption events.
We have modelled for the first time the rate of tidal disruptions across the cosmic times and all galaxy types, including realistic event rates. The fact that predictions and observations agree well is a major achievement, and implies our work is fundamental to interpret the observations of tidal disruptions.
Furthermore, our work on partial disruption events is the first of its kind and considers an otherwise neglected accretion method, that helps interpreting some of the newest observations of tidal disruptions, that show evidence of repeated flares. Our results are thus very timely and fundamental to interpret current (and upcoming) observations.
Furthermore, our work on partial disruption events is the first of its kind and considers an otherwise neglected accretion method, that helps interpreting some of the newest observations of tidal disruptions, that show evidence of repeated flares. Our results are thus very timely and fundamental to interpret current (and upcoming) observations.