A new rare type of supernovae: hypervelocity stellar collisions at galactic centres

Abstract

When a binary star system is tidally disrupted by a supermassive black hole at a galactic nucleus, one star is ejected at a high speed while the other remains in a tightly bound orbit around the black hole. The cluster of tightly bound stars builds over time, eventually creating a steady state in which the rate of collisions between these stars is similar to the rate of capturing new stars. A large fraction of the collisions occur near the periapsis of the orbits around the black hole, where the kinetic energies are sufficient to generate an explosive disruption of the two stars involved. The typical flare brightens for several days, with a peak luminosity that is comparable to the lower luminosity end of known supernovae. The explosion light curve is followed by a longer flare due to accretion of ejected matter on to the black hole. Dedicated searches in the near universe could observe several such 'collisional supernovae' per year.