Abstract
ABSTRACT A star approaching a supermassive black hole (SMBH) can be torn apart in a tidal disruption event (TDE). We examine ultra-deep TDEs, a new regime in which the disrupted debris approaches close to the black hole’s Schwarzschild radius, and the leading part intersects the trailing part at the first pericentre passage. We calculate the range of penetration factors β versus SMBH masses M that produce these prompt self-intersections using a Newtonian analytic estimate and a general relativistic (GR) geodesic model. We find that significant self-intersection of Solar-type stars requires β ∼ 50–127 for M/M⊙ = 104, down to β ∼ 5.6–5.9 forM/M⊙ = 106. We run smoothed particle hydrodynamic (SPH) simulations to corroborate our calculations and find close agreement, with a slightly shallower dependence on M. We predict that the shock from the collision emits an X-ray flare lasting t ∼ 2 s with L ∼ 1047 erg s−1 at E ∼ 2 keV, and the debris has a prompt accretion episode lasting t ∼ several minutes. The events are rare and occur with a rate $\dot{N} \lesssim 10^{-7}$ Mpc−3 yr−1. Ultra-deep TDEs can probe the strong gravity and demographics of low-mass SMBHs.
Highlights
Stars can be destroyed by the gravitational field of a supermassive black hole (SMBH) if they reach its tidal radius rt R∗(M/M∗)1/3, where the SMBH has mass M and the star has mass M∗ and radius R∗
The tidal gravity of the SMBH exceeds the self-gravity of the star, and the star is stretched into a stream of debris (Kochanek 1994; Coughlin et al 2016)
Evans et al (2015) examine disruptions of main sequence stars in deep encounters (β = 10, 15) with SMBHs of mass M = 105 M. Their simulations exhibit an early accretion burst followed by a flat accretion rate at later times; strong general relativistic (GR) effects modify the M ∼ t−5/3 late-time accretion rate expected of canonical tidal disruption event (TDE)
Summary
Stars can be destroyed by the gravitational field of a supermassive black hole (SMBH) if they reach its tidal radius rt R∗(M/M∗)1/3, where the SMBH has mass M and the star has mass M∗ and radius R∗. Evans et al (2015) examine disruptions of main sequence stars in deep encounters (β = 10, 15) with SMBHs of mass M = 105 M Their simulations exhibit an early accretion burst followed by a flat accretion rate at later times; strong GR effects modify the M ∼ t−5/3 late-time accretion rate expected of canonical TDEs. There has been greater focus on deep encounters of white dwarfs (WDs) on stellar and intermediate-mass BHs (Luminet & Pichon 1989b; Frolov et al 1994; Rosswog et al 2009; Haas et al 2012; MacLeod et al 2016; Tanikawa et al 2017; Kawana et al 2018; Anninos et al 2018), since these are more promising as sites of nuclear ignition near pericenter and as sources for gravitational wave (GW) emission.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
