Flaring of tidally compressed dark-matter clumps

TL;DR

This paper investigates how tidal compression events of dark-matter clumps by supermassive black holes can produce observable signals such as gamma-ray flares, synchrotron radiation, and gravitational waves, offering new ways to study dark matter.

Contribution

It provides an analytic framework for understanding the physical processes and observational signatures of DMCs undergoing tidal compression near SMBHs, including novel predictions of multi-messenger signals.

Findings

Tidal compression significantly increases dark-matter density and velocity dispersion.

TCEs can produce detectable gamma-ray flares via dark-matter annihilation.

TCEs generate unique gravitational wave signatures.

Abstract

We explore the physics and observational consequences of tidal compression events (TCEs) of dark-matter clumps (DMCs) by supermassive black holes (SMBHs). Our analytic calculations show that a DMC approaching a SMBH much closer than the tidal radius undergoes significant compression along the axis perpendicular to the orbital plane, shortly after pericenter passage. For DMCs composed of self-annihilating dark-matter particles, we find that the boosted DMC density and velocity dispersion lead to a flaring of the annihilation rate, most pronounced for a velocity- dependent annihilation cross section. If the end products of the annihilation are photons, this results in a gamma-ray flare, detectable (and possibly already detected) by the Fermi telescope for a range of model parameters. If the end products of dark-matter annihilation are relativistic electrons and positrons and the local magnetic field is large enough, TCEs of DMCs can lead to flares of synchrotron radiation. Finally, TCEs of DMCs lead to a burst of gravitational waves, in addition to the ones radiated by the orbital motion alone, and with a different frequency spectrum. These transient phenomena provide interesting new avenues to explore the properties of dark matter.