Astronomy Colloquium

Tidal disruption events (TDEs) are luminous bursts of electromagnetic radiation emitted from galactic nuclei when stars are ripped apart by supermassive black holes.  In the last decade, dozens of candidate flares have been seen by time-domain efforts such as Pan-STARRS, PTF, ASASSN, ROSAT, and the XMM-Newton Slew Survey.  Although the locations, energetics, and durations of these flares are generally compatible with theoretical expectations, many surprises have emerged from our growing observational sample.  I will focus on two in particular.  First, the observed TDE sample is preferentially concentrated in a very rare galaxy subtype.  Post-starburst, or E+A, galaxies make up ~0.2% of all low redshift galaxies but host an order unity fraction of optically-selected tidal disruption flares.  I will present preliminary observational evidence that this preference is due to centrally concentrated star formation during the starburst, and the creation of an overdense galactic nucleus.  Second, it is increasingly clear that only a small fraction of TDEs launch collimated relativistic jets (Swift J1644+57 being the most famous example of this).  I will present recent theoretical work translating nondetections of radio afterglows around thermally-selected TDEs into upper limits on the energetics of off-axis relativistic jets.  We found that <10% of all TDEs launch jets comparable to those of Swift J1644+57, and I will discuss possible theoretical explanations for this, which connect to open questions in jet launching physics.