Most galaxies harbor weakly- or non-active central super-massive black holes (BHs). Roughly once every 10^4 - 10^5 years in each galaxy, a star enters the BH's tidal disruption radius within which the tidal force of the BH exceeds the star's self gravity, and hence the star gets tidally disrupted. In these so-called tidal disruption events (TDEs), the stellar debris feeds a burst of super-Eddington accretion that generates a bright flare of electromagnetic radiation. In the recent ~ 10 years, several dozen such flares have been discovered by transient surveys in various wavelengths from gamma/X-ray to UV and optical, and ~ 10 of them have optical spectra. In addition, the discoveries of Sw J1644+57 and Sw J2058+05 showed that the TDE accretion disk can launch relativistic jets, and these events are called jetted TDEs.

TDEs offer a new window of studying many astrophysical puzzles, such as super-Eddington MHD accretion physics, population of non-active super-massive BHs in the universe, composition and radiation mechanism of relativistic jets, etc. I'll talk about a few ongoing works with my advisor and collaborators. (1) If a relativistic jet is launched from the accretion disk, the electrons in the jet will inverse-Compton scatter external photons from the disk. We calculated the inverse-Compton luminosity and found it consistent with the X-ray observations from the jetted TDE Sw J2058+05. (2) A typical TDE emits about 10^51 - 10^52 erg of UV/optical energy, which will most likely be absorbed by pc-scale dust at the galactic center. Dust grains will re-radiate this energy in the mid-IR at a luminosity of 10^42 - 10^43 erg/s. Observations and applications of this mid-IR component will be discussed. (3) From the ~ 10 TDE candidates with optical spectra, but we see a large diversity of emission and absorption lines. We study the line formation physics in these spectra and have drawn some general conclusions about the gas properties (e.g. density, temperature and mass).