From agnosticism to astrophysics: a new approach to non-parametric methods to infer the astrophysical populations of binary black holes from gravitational waves

• Applicant: Stefano Rinaldi
• Subject Area: Astrophysics and Astronomy
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 546677095

The astrophysical graveyard is populated by black holes and neutron stars. These are the remains of the most massive stars, and studying them will teach us about the physics that governs the stars' lives and deaths. Gravitational wave observations are now revealing the population of black holes via the detection of binary black hole mergers, and the numbers are set to grow rapidly in the coming years. Currently, the characterisation and interpretation of this new data is mainly guided by astrophysical models which depend on the not well understood physics of massive binary evolution. The mass function and redshift distribution of binary black holes provide a key to interpret their formation channels, but current analysis still struggles to extract this information from the data. Moreover, the characterisation and interpretation of this new data is currently guided by astrophysical models which depend on the not-well-understood physics of massive binary evolution. The features in the black hole population, peculiar signature of astrophysical processes, have to come up from observations alone: therefore, my project DAMASCUS will use Bayesian non-parametric methods to study the black hole primary mass, mass ratio and redshift distribution, leveraging on the events observed during the ongoing fourth LIGO-Virgo-KAGRA observing run. I propose to connect the features I will discover to the astrophysical models in two parallel ways: the first is to join different astrophysical models and augment them using non-parametric methods to account for unforeseen channels. The second line of research develops a new statistical framework that will use the non-parametric reconstructions to compare different astrophysical models: with these two new methods, DAMASCUS will help shedding light on which processes give the main contribution in populating the black holes in our Universe.

• DFG Programme: WBP Position