Tidal Disruption Events: A New Black Hole Census

Massive black holes (MBHs) are key players in high energy astrophysics, galaxy formation and evolution, and astroparticle physics. Despite their centrality to astronomy, we still cannot answer basic questions about MBHs. What are their origins? How have they grown over cosmic time? What are their current demographics?

To answer these questions, the project will turn tidal disruption events (TDEs) from curiosities into reliable probes of MBH parameters. A TDE occurs when an unlucky star passes too close to a MBH and is ripped apart by tidal forces. The ensuing fallback of debris powers a highly luminous, potentially multimessenger flare.

TDEs are, in principle, ideal probes of MBH properties.

Unlike standard techniques for measuring MBHs, TDEs (i) happen in all galaxies, (ii) are visible to cosmological distances, and (iii) involve very few free parameters.

But the theoretical picture of TDEs remains confused, as the large dynamic range of TDEs has prevented ab initio simulations to determine how tidal debris evolves and radiates.

At present, there is no consensus on the geometry or even the power source of observed TDE flares, making robust parameter estimation impossible.

I will solve these open theoretical questions, capitalizing on my recent pilot study that for the first time ever simulated a typical, first-principles TDE.This project will deliver (a) first-principles simulations of the evolution and emission of TDEs; (b) idealized but accurate models of TDE light curves and spectra suitable for parameter estimation; (c) a first-ever sample of MBH parameters derived from fitting ab initio models to TDE observations.

I will use these results to sidestep the limitations of other MBH measurement techniques and to place unique constraints on the formation and growth history of the smallest MBHs.

This work is urgently needed in light of upcoming all-sky surveys such as ULTRASAT and LSST, which will expand the TDE sample from dozens to thousands in the mid-2020s.