Abstract
The tidal disruption of a star by a supermassive black hole (SMBH) is a highly energetic event with consequences dependent on the degree to which the star plunges inside the SMBH's tidal sphere. We introduce a new analytic model for tidal disruption events (TDEs) to analyze the dependence of these events on beta, the ratio of the tidal radius to the orbital pericenter. We find, contrary to most previous work, that the spread in debris energy for a TDE is largely constant for all beta. This result has important consequences for optical transient searches targeting TDEs, which we discuss. We quantify leading-order general relativistic corrections to this spread in energy and find that they are small. We also examine the role of stellar spin, and find that a combination of spin-orbit misalignment, rapid rotation, and high beta may increase the spread in debris energy. Finally, we quantify for the first time the gravitational wave emission due to the strong compression of a star in a high-beta TDE. Although this signal is unlikely to be detectable for disruptions of main sequence stars, the tidal disruption of a white dwarf by an intermediate mass black hole can produce a strong signal visible to Advanced LIGO at tens of megaparsecs.
Highlights
Stars which pass too close to supermassive black holes (SMBHs) are disrupted by the enormous gravitational gradients acting on them
The rate of tidal disruption events (TDEs) is highly uncertain, from both theoretical and observational perspectives. Uncertainties stem from both the low sample size and unclear sources of systematic error; observational estimates of the TDE rate per galaxy generally find N TDE ∼ 10−4 − 10−5 yr−1 (Donley et al 2002; Gezari et al 2008). This is in rough agreement with the wide range of theoretical predictions for the TDE rate, which invoke different ways to scatter stars into the SMBH “loss cone”
Much of the pioneering work on TDEs was done in the 1980s using the semi-analytic affine model (Carter & Luminet 1983, hereafter CL83), which treats the disrupting star as a set of concentric ellipsoidal shells evolving under the combined influences of self-gravity, pressure, and the SMBH tidal field (Carter & Luminet 1985; Luminet & Carter 1986)
Summary
Stars which pass too close to supermassive black holes (SMBHs) are disrupted by the enormous gravitational gradients acting on them. Much of the pioneering work on TDEs was done in the 1980s using the semi-analytic affine model (Carter & Luminet 1983, hereafter CL83), which treats the disrupting star as a set of concentric ellipsoidal shells evolving under the combined influences of self-gravity, pressure, and the SMBH tidal field (Carter & Luminet 1985; Luminet & Carter 1986) This model has found a wide range of uses, and has been generalized to include both thermonuclear reaction networks (Luminet & Pichon 1989) and general relativistic (GR) effects (Luminet & Marck 1985), its validity tends to break down at late times as the stellar debris exits the tidal sphere. We conclude with the observational implications of our work, which primarily involve the suppression of strongly super-Eddington TDEs (§8), and a general discussion (§9)
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