Cake Talk by Seppo Mattila
Intermediate-mass black holes (BHs) bridging the gap between stellar mass and supermassive BHs are still elusive. Here, we report the observations of a remarkable optical transient event 0.4" from the centre of a dwarf galaxy with a stellar mass log(M∗/M⊙) ~ 8.14 M⊙. Its bright and extremely fast-evolving light curves share many similarities with those of the rare, luminous, fast blue optical transients. Spectroscopically, its evolution is unprecedented. The spectra show blueshifted, broad hydrogen emission lines indicating velocities of up to 10% of the speed of light. We show that its observed properties can naturally be explained by the tidal disruption of a star by an intermediate-mass BH with M_BH = 10^3.6 M⊙. Further observations of similar events can pinpoint quiescent intermediate-mass BHs in low-redshift galaxies and constrain their masses, shedding light on the formation of massive BHs in the early Universe.