Abstract
In a binary system composed of a supermassive black hole and a star orbiting the hole in an equatorial, circular orbit, the stellar orbit will shrink due to the action of gravitational radiation, until the star fills its lobe outside the Innermost Stable Circular Orbit (ISCO) of the hole or plunges into the hole. In the former case, gas will flow through the inner Lagrange point (L1) to the hole. If this tidal stripping process happens on a time scale faster than the thermal time scale but slower than the dynamical time scale, the entropy as a function of the interior mass is conserved. The star will evolve adiabatically, and, in most cases, will recede from the hole while filling its lobe. We calculate how the stellar equilibrium properties change, which determines how the stellar orbital period and mass-transfer rate change through the Roche evolution for various types of stars in the relativistic regime. We envisage that the mass stream eventually hits the accretion disc, where it forms a hot spot orbiting the hole and may ultimately modulate the luminosity with the stellar orbital frequency. The ultimate goal is to probe the mass and spin of the hole and provide a test of general relativity in the strong-field regime from the resultant quasi-periodic signals. The observability of such a modulation is discussed along with a possible interpretation of an intermittent 1 hour period in the X-ray emission of RE J1034 + 396.
Highlights
When a star passes by a supermassive black hole (SMBH) closely, tidal effects can be induced
As the star is stripped on an adiabatic time scale, its entropy as a function of interior mass is conserved
A dwarf star or brown dwarf or red giant can produce emissions with such a periodicity when tidally stripped by a ∼106 −107 M SMBH, though the mass accretion rate under adiabatic condition and pure gravitational radiation torque is too low to produce the observed X-ray flux. 16 cycles of signals are insufficient to be confident of a stable period
Summary
When a star passes by a supermassive black hole (SMBH) closely, tidal effects can be induced. The first case is a tidal disruption event, to which most talks in the meeting were dedicated. Tidal disruption can happen when a star passes close by a black hole in an unbound orbit or a very eccentric orbit. As broadly discussed in the meeting, one convincing instance of a tidal disruption event is the recent luminous Sw J1644 + 57 X-ray observation ([2, 15]). We will only focus on the relativistic treatment of the problem as it is more intriguing. The details of Newtonian and relativistic calculations can be found in [4]
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