Searching for primordial black holes with stochastic gravitational-wave background in the space-based detector frequency band

TL;DR

This paper explores the potential of space-based gravitational-wave detectors to identify primordial black holes through their unique stochastic background signatures, which could confirm their role in dark matter or constrain their abundance.

Contribution

It introduces a method to distinguish primordial black hole signals in the gravitational-wave background, focusing on spectral features from galactic and extragalactic sources.

Findings

Different spectral features for galactic and extragalactic sources.

Potential to detect primordial black holes via gravitational-wave background.

Constraints on primordial black hole abundance if no signal is found.

Abstract

Assuming that primordial black holes compose a fraction of dark matter, some of them may accumulate at the center of galaxy and perform a prograde or retrograde orbit against the gravity pointing towards the center exerted by the central massive black hole. If the mass of primordial black holes is of the order of stellar mass or smaller, such extreme mass ratio inspirals can emit gravitational waves and form a background due to incoherent superposition of all the contributions of the Universe. We investigate the stochastic gravitational-wave background energy density spectra from the directional source, the primordial black holes surrounding Sagittarius A$^\ast$ of the Milky Way, and the isotropic extragalactic total contribution, respectively. As will be shown, the resultant stochastic gravitational-wave background energy density shows different spectrum features such as the peak positions in the frequency domain for the above two kinds of sources. Detection of stochastic gravitational-wave background with such a feature may provide evidence for the existence of primordial black holes. Conversely, a null searching result can put constraints on the abundance of primordial black holes in dark matter.