Collaborative Research: Tidal Disruption of Stars by Massive Black Holes

The disruption and subsequent accretion of stars by super-massive black holes (SMBHs) has been linked to many luminous flares observed in the nuclei of nearby galaxies. Our theoretical understanding of these tidal disruption events (TDEs), however, remains incomplete. A research collaboration between the University of California Santa Cruz, the University of California Berkeley, and Northwestern University will bring together experts in different fields of physics: hydrodynamics, general relatively and radiative transfer to address important gaps in our understanding of TDEs.

This understanding requires a multi-pronged approach that attempts to resolve the underlying physics at a wide range of physical and temporal scales. The phenomena of TDEs provide an exciting opportunity to study the size of SMBHs in quiescent galaxies, the stellar populations and dynamics in galactic nuclei, and the physics of black hole accretion under well-defined conditions.

Whereas active galactic nuclei may be supplied by a steady stream of fuel for thousands of years, TDEs offer a unique opportunity to study a single SMBH when the mass accretion rates and feeding timescales change over days or months. The project will also include an education and public outreach program which aims to cross-fertilize the training of computational scientists and students in the visual arts and digital media using state-of-art simulations as common ground in a group environment that significantly increases the number of under-represented students trained in computational astrophysics.

To do this, the astronomers will partner with university arts and education programs and with local schools.

Wide-field transient surveys are currently delivering more and better data on TDEs. Fully three-dimensional simulations of accretion disks are computationally expensive, and as a result there is trade-off between running a simulation with significant resolution that only resolves a fraction of the disk and global simulations at moderate resolution that resolve the full structure.

For TDEs the trade-offs are even more pronounced and require a large range of scales to be resolved simultaneously. As a consequence, running a single simulation of the full problem incorporating all of the aforementioned effects would not only be prohibitive, but also difficult to interpret because of the complexity of the interplay between the various physical mechanisms at different scales.

As an alternative, the investigators will aim to answer these questions via a series of numerical experiments that isolate the key processes that regulate the disruption itself, the formation of the debris disk, the production of jets and the generation of the emanating radiation. In addition to being computationally feasible, this approach will enable a thorough understanding of each of the processes, which are likely highly reminiscent of the well-studied phenomenology of steadily-accreting AGN.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.