The Search for Intermediate Mass Black Holes using White Dwarf Tidal Disruption Events

Intermediate mass black holes (IMBH) are proposed to be the link between stellar mass black holes and supermassive black holes. However, there is little direct observational evidence of their existence. One promising way to discover IMBHs is through the tidal disruption events of white dwarf stars. Tidal disruption events (TDEs) occur when a star passes within the tidal radius of a black hole and the tidal forces stretch and compress the star enough that it is disrupted and accreted by the black hole, allowing us to detect it—in cases where the star has not yet crossed the event horizon. Unlike larger stars, white dwarf stars can only be tidally disrupted by IMBHs. Previous theoretical works find that the main and unique observable of a white dwarf TDE is a thermonuclear runaway event similar to a Type Ia supernova (SNe) at the time of tidal compression of the white dwarf. Such an event is expected to be dimmer and faster evolving than a typical Type Ia SN. Additionally, the event most likely occurs in dwarf galaxies. We crossmatched Type Ia supernovae reported by the Zwicky Transient Facility (ZTF) to dwarf galaxy catalogs, and identified SNe Ia hosted in dwarf galaxy nuclei with lower peak absolute magnitude and faster rise times than a control sample of SNe Ia in more massive galaxies. By doing so in the g and r bands, we found probable candidates of a white dwarf TDE. Future research involves conducting follow-up studies of the candidates in the X-ray band, along with searching for systematic Doppler shifts of the SNe Ia spectrum, which has been predicted to be a signature of a white dwarf TDE. Establishing a method to efficiently find white dwarf TDEs can lead to strong candidates for IMBHs, providing definitive evidence of their existence, and allowing us to pinpoint the galaxy hosts in which they reside. This project was supported in part by the NSF REU grant AST-1757321 and by the Nantucket Maria Mitchell Association.