A fast-rising tidal disruption event from a candidate intermediate-mass black hole

Massive black holes (BHs) at the centres of massive galaxies are ubiquitous. The population of BHs within dwarf galaxies, on the other hand, is not yet known. Dwarf galaxies are thought to harbour BHs with proportionally small masses, including intermediate-mass BHs, with masses 10(2) < M-BH < 10(6) solar masses (M-circle dot). Identification of these systems has historically relied on the detection of light emitted from accreting gaseous disks close to the BHs. Without this light, they are difficult to detect. Tidal disruption events, the luminous flares produced when a star strays close to a BH and is shredded, are a direct way to probe massive BHs. The rise times of these flares theoretically correlate with the BH mass. Here we present AT 2020neh, a fast-rising tidal disruption event candidate, hosted by a dwarf galaxy. AT 2020neh can be described by the tidal disruption of a main sequence star by a 10(4.7)-10(5.9) M-circle dot BH. We find the observable rate of fast-rising nuclear transients like AT 2020neh to be low, at less than or similar to 2 x 10(-8) events Mpc(-3) yr(-1). Finding non-accreting BHs in dwarf galaxies is important to determine how prevalent BHs are within these galaxies, and to constrain models of BH formation. AT 2020neh-like events may provide a galaxy-independent method of measuring the masses of intermediate-mass BHs.

Automated summary

Massive black holes are commonly found in the centers of massive galaxies, but their presence in dwarf galaxies is not yet known. AT 2020neh is a fast-rising tidal disruption event candidate hosted by a dwarf galaxy, which provides a potential method of measuring the masses of intermediate-mass black holes. The observable rate of such events is found to be low, which highlights the importance of finding non-accreting black holes in dwarf galaxies and understanding their prevalence within these galaxies.