Tidal effect on scalar cloud

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Maths. Dept. Room Sousa Pinto
Taishi Ikeda (IST-Lisbon)
The existence of light, fundamental bosonic fields is an attractive possibility that can be tested via black hole observations. 
We study the effect of a tidal field -- caused by a companion star or black hole -- on the evolution of superradiant scalar-field states around spinning black holes. For small tidal fields, the superradiant ``cloud'' puffs up by transitioning to excited states and acquires a new spatial distribution through transitions to higher multipoles, establishing new equilibrium configurations. For large tidal fields the scalar condensates are disrupted; we determine numerically the critical tidal moments for this to happen and find good agreement with Newtonian estimates. We show that the impact of tides can be relevant for known black-hole systems such as the one at the center of our galaxy or the Cygnus X-1 system. The companion of Cygnus X-1, for example, will disrupt possible scalar structures around the BH
for gravitational couplings as large as $M\mu\sim 2\times 10^{-3}$.