The assembly of massive black holes in the early universe remains a poorly constrained open question
in astrophysics. The merger and accretion of light seeds (remnants of Population III stars with mass
below ∼ 1000 M ) or heavy seeds (in the mass range 104−106 M ) could both explain the formation of
massive black holes, but the abundance of seeds and their merging mechanism are highly uncertain. In
the next decades, the gravitational-wave observatories coming online are expected to observe very highredshift mergers, shedding light on the seeding of the first black holes. In this Letter we explore the
potential and limitations for LISA, Cosmic Explorer and Einstein Telescope to constrain the mixture
ratio of light and heavy seeds as well as the probability that central black holes in merging galaxies
merge as well. Since the third generation ground-based gravitational-wave detectors will only observe
light seed mergers, we demonstrate two scenarios in which the inference of the seed mixture ratio
and merging probability can be limited. The synergy of multi-band gravitational-wave observations
and electromagnetic observations will likely be necessary in order to fully characterize the process of
high-redshift black hole formation.
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Constraining High-redshift Stellar-mass Primordial Black Holes with Next-generation Ground-based Gravitational-wave Detectors
Abstract The possible existence of primordial black holes in the stellar-mass window has received considerable attention because their mergers may contribute to current and future gravitational-wave detections. Primordial black hole mergers, together with mergers of black holes originating from Population III stars, are expected to dominate at high redshifts ( z ≳ 10). However, the primordial black hole merger rate density is expected to rise monotonically with redshift, while Population III mergers can only occur after the birth of the first stars. Next-generation gravitational-wave detectors such as the Cosmic Explorer (CE) and Einstein Telescope (ET) can access this distinctive feature in the merger rates as functions of redshift, allowing for direct measurement of the abundance of the two populations and hence for robust constraints on the abundance of primordial black holes. We simulate four months’ worth of data observed by a CE-ET detector network and perform hierarchical Bayesian analysis to recover the merger rate densities. We find that if the universe has no primordial black holes with masses of ( 10 M ⊙ ) , the projected upper limit on their abundance f PBH as a fraction of dark matter energy density may be as low as f PBH ∼ ( 10 − 5 ) , about two orders of magnitude lower than the current upper limits in this mass range. If instead f PBH ≳ 10 −4 , future gravitational-wave observations would exclude f PBH = 0 at the 95% credible interval.
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- Award ID(s):
- 2006538
- NSF-PAR ID:
- 10340479
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 933
- Issue:
- 2
- ISSN:
- 2041-8205
- Page Range / eLocation ID:
- L41
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/2041-8213/ac7aae
