Waves from the centre: probing PBH and other macroscopic dark matter with LISA

Florian Kühnel,Katherine Freese,Andrew Matas,Glenn D Starkman

doi:10.1140/epjc/s10052-020-8183-4

Abstract

A significant fraction of cosmological dark matter can be formed by very dense macroscopic objects, for example primordial black holes. Gravitational waves offer a promising way to probe these kinds of dark-matter candidates, in a parameter space region that is relatively untested by electromagnetic observations. In this work we consider an ensemble of macroscopic dark matter with masses in the range 10^{-13}–1 M_{odot } orbiting a super-massive black hole. While the strain produced by an individual dark-matter particle will be very small, gravitational waves emitted by a large number of such objects will add incoherently and produce a stochastic gravitational-wave background. We show that LISA can be a formidable machine for detecting the stochastic background of such objects orbiting the black hole in the centre of the Milky Way, Sgr mathrm{A}^{!*}, if a dark-matter spike of the type originally predicted by Gondolo and Silk forms near the central black hole.

Highlights

There are well-known limits on macros from microlensing of Milky Way and Magellanic Cloud stars [36,37,38,39] limiting the abundance of macros above approximately 4 × 1024 g
The Laser Interferometer Space Antenna (LISA) [56], is a space-based gravitational-wave detector which will operate in the 10−4–10−1 Hz band
The detectability of individual macros/objects orbiting Sgr A∗ with LISA has been discussed in Ref. [57]

Summary

Introduction

There are well-known limits on macros from microlensing of Milky Way and Magellanic Cloud stars [36,37,38,39] limiting the abundance of macros above approximately 4 × 1024 g. It has long-been recognized that there are viable dark-matter candidates of much greater mass, notably primordial black holes (PBH) [6,7] There has been significant attention to the possibility that multi-solar-mass black holes, such as those detected by Advanced LIGO, could be the dark matter [19,52,53,54,55].

Results

Conclusion