Tidal Disruption Events

Abstract

The concept of stars being tidally ripped apart and consumed by a massive black hole (MBH) lurking in the center of a galaxy first captivated theorists in the late 1970s. The observational evidence for these rare but illuminating phenomena for probing otherwise dormant MBHs first emerged in archival searches of the soft X-ray ROSAT All-Sky Survey in the 1990s, but has recently accelerated with the increasing survey power in the optical time domain, with tidal disruption events (TDEs) now regarded as a class of optical nuclear transients with distinct spectroscopic features. Multiwavelength observations of TDEs have revealed panchromatic emission, probing a wide range of scales, from the innermost regions of the accretion flow to the surrounding circumnuclear medium. I review the current census of 56 TDEs reported in the literature, and their observed properties can be summarized as follows: ▪ The optical light curves follow a power-law decline from peak that scales with the inferred central black hole mass as expected for the fallback rate of the stellar debris, but the rise time does not. ▪ The UV-optical and soft X-ray thermal emission come from different spatial scales, and their intensity ratio has a large dynamic range and is highly variable, providing important clues as to what is powering the two components. ▪ They can be grouped into three spectral classes, and those with Bowen fluorescence line emission show a preference for a hotter and more compact line-emitting region, whereas those with only Heii emission lines are the rarest class. Expected final online publication date for the Annual Review of Astronomy and Astrophysics, Volume 59 is August 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The bulge masses of TDE host galaxies and their scaling with black hole mass

“…approximately half of the disrupted material falls back onto the SMBH, likely forming an accretion disk, while the other half becomes unbound (Rees 1988;Lacy & Townes 1982). Both the circularization and ultimate accretion of the bound matter can cause a luminous flare, with characteristic luminosity of ∼ 10 44 erg s −1 (Rees 1988;Gezari 2021). However, if the tidal radius is smaller than the gravitational radius of the SMBH, the star's orbit will intersect the event horizon before disruption, and so it will be swallowed whole, without a visible flare (Hills 1975;MacLeod et al 2012).…”

Advancing the Landscape of Multimessenger Science in the Next Decade

“…The stellar debris is ultimately accreted onto the SMBH, and generates an accompanying electromagnetic flare. TDEs were first proposed to exist in 1988 [250], but in the subsequent two decades only eight candidates were found [251]. Fortunately, systematic searches for TDEs have been steadily increased the underlying TDE detection efficiency in recent years [e.g., 252], with a new TDE now discovered every 3-4 weeks.…”

Tidal Disruption Events and High-Energy Neutrinos

“…A Tidal Disruption Event (TDE) occurs when a star passes sufficiently close to a supermassive black hole (SMBH), such that the tidal forces exceed the self-gravity holding the star together [1]. The star then disintegrates and is partially accreted onto the SMBH, generating an electromagnetic flare that can then be detected on Earth [2]. TDEs have also been observed to launch relativistic jets [3] or outflows [4][5][6], but these signatures are not ubiquitous.…”