Tidal disruption of stars by supermassive black holes: Status of observations
Abstract
Stars in the immediate vicinity of supermassive black holes (SMBHs) can be ripped apart by the tidal forces of the black hole. The subsequent accretion of the stellar material causes a spectacular flare of electromagnetic radiation. Here, we provide a review of the observations of tidal disruption events (TDEs), with an emphasis on the important contributions of Swift to this field. TDEs represent a new probe of matter under strong gravity, and have opened up a new window into studying accretion physics under extreme conditions. The events probe relativistic effects, provide a new means of measuring black hole spin, and represent signposts of intermediate-mass BHs, binary BHs and recoiling BHs. Luminous, high-amplitude X-ray flares, matching key predictions of the tidal disruption scenario, have first been discovered with ROSAT, and more recently with other missions and in other wavebands. The Swift discovery of two γ-ray emitting, jetted TDEs, never seen before, has provided us with a unique probe of the early phases of jet formation and evolution, and Swift J1644+75 has the best covered lightcurve of any TDE to date. Further, Swift has made important contributions in providing well-covered lightcurves of TDEs discovered with other instruments, setting constraints on the physics that govern the TDE evolution, and including the discovery of the first candidate binary SMBH identified from a TDE lightcurve.
In X-rays, TDEs probe relativistic effects (via emission-line profiles or precession effects in the Kerr metric) and the extremes of accretion physics at high rates and near the last stable orbit, and provide us with a new means of measuring BH spin. Jetted TDEs provide new insight into the formation and early evolution of radio jets, and may shed new light on related issues like the cause of the radio-loud radio-quiet dichotomy of active galactic nuclei (AGN). TDEs, once detected in large numbers, will unveil the population of IMBHs in the universe. TDE rates depend on, and therefore trace, stellar dynamics in galaxy cores on spatial scales which cannot be resolved directly. TDEs are signposts of binary SMBHs and recoiling BHs, because their rates are strongly enhanced under these conditions, and TDEs will occur off-nuclear if the SMBH is recoiling. TDEs in gas-rich environments will illuminate the circum-nuclear material, so that the reprocessed emission lines and their temporal evolution provide us with an unparalleled opportunity of reverberation mapping the cores of quiescent galaxies. Here, we present an overview of the status of observations of TDEs, highlighting the important role plaid by the Swift mission (Gehrels et al., 2004; Gehrels and Cannizzo, in press). An accompanying review by Lodato (in press) will focus on theoretical aspects of tidal disruption.- Publication:
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Journal of High Energy Astrophysics
- Pub Date:
- September 2015
- DOI:
- 10.1016/j.jheap.2015.04.006
- arXiv:
- arXiv:1505.01093
- Bibcode:
- 2015JHEAp...7..148K
- Keywords:
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- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Review, 12 pages, to appear in Journal of High-Energy Astrophysics. Proceedings (review contributions) of "Swift: 10 years of discovery"