Tidal-heating/viscous dissipation correspondence in black holes and viscous compact objects

TL;DR

This paper explores how viscosity in exotic compact objects (ECOs) affects energy absorption during binary inspirals, potentially mimicking black hole tidal heating and influencing gravitational wave signals.

Contribution

It establishes a connection between viscosity and energy dissipation in ECOs, highlighting how viscosity can alter GW waveforms and aid in distinguishing ECOs from black holes.

Findings

Viscosity in ECOs can significantly modify GW waveforms.

ECO absorption effects may be measurable with future GW observations.

Viscosity relates to the ECO reflection coefficient and entropy bounds.

Abstract

The effect of energy absorption during the binary evolution of Exotic-compact-objects (ECOs) is extensively studied. We review the underlying mechanism that provides the energy dissipation in material objects - tidal friction. We show that unlike typical astrophysical objects, where absorption due to viscosity is negligible, in ECOs, absorption could potentially mimic the analogous effect of black-holes (BHs) - tidal heating. We stand for their differences and similarities in the context of energy dissipation during the inspiral. Inspired by the membrane paradigm and recent studies, we demonstrate how viscosity is a defining feature that quantifies how close is the ECO absorption to that of a classical BH absorption. We show that for ECOs, viscosity can induce significant modifications to the GW waveform, which in some favorable scenarios of super-massive binaries of equal mass and spin, enables the measurement of the ECO absorption in the future precision gravitational-wave (GW) observations. Finally, we discuss the implications on the ECO reflection coefficient and the relation to the universal viscosity to volume entropy bound.