Primordial Black Hole contribution to the stochastic background of Gravitational Waves

The amplitude of the detected stochastic gravitational wave background measured by pulsar timing arrays and the discovery of early and over-massive central black holes at high redshift by the James Webb Space Telescope challenge current. The new analysis still awaits peer review, but it already lays out the central claim clearly.

It matters because astrophysics becomes persuasive only when an observed signal can be tied to a physically defensible explanation. Compact objects such as neutron stars and black holes are natural laboratories for extreme physics, but the distance and complexity of these systems make interpretation difficult without multi-wavelength coverage and careful modeling. A detection without a mechanism is only half a result. the other half comes from showing that the signal fits quantitatively inside a coherent physical picture rather than merely being consistent with a broad family of models. The amplitude of the detected stochastic gravitational wave background (SGWB) measured by pulsar timing arrays (PTAs) and the discovery of early and over-massive central black. We study if halos containing a significant population of primordial black holes (PBHs) would increase the amplitude of the PTA signal.

PBHs add an iso-curvature component to the matter power spectrum, accelerating the formation and merger of dark matter halos at all redshifts. We propose that black holes in the halo sink to the center via dynamical friction.

The central black hole grows through hierarchical merging in addition to the gas accretion channel. We computed the resulting GW amplitude and performed a Bayesian inference analysis using the NANOGrav 15-year dataset.

We show that the predicted amplitude of the gravitational wave background agrees with the observations. The PBH model that explains the JWST new found populations of SMBHs also explain the amplitude of the stochastic background of gravitational waves.

The broader interest lies in turning an observational clue into something that can be weighed against competing models of the underlying physics. Astrophysics does not have the luxury of controlled experiments; everything is inferred from radiation that traveled across cosmic distances under conditions that cannot be reproduced in a terrestrial laboratory. This makes the interpretation chain longer and more uncertain than in bench science, but it also means that a well-constrained measurement of an extreme object carries theoretical information that no earthbound experiment can provide.

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Because this is still a preprint, the result should be read with genuine interest and proportionate caution. Peer review is not a guarantee of correctness, but it is a process that forces authors to respond to technical criticism from specialists who have no stake in a particular outcome. Preprints that survive that process, often with substantive revisions, emerge with a stronger evidential base than the version that first appeared. Until that stage is complete, the responsible reading keeps uncertainty explicitly visible rather than treating the claims as established findings.

The next step is to see whether independent datasets and physical modeling converge on the same interpretation. Multi-wavelength follow-up, combining X-ray, radio and optical data where possible, is typically what separates a compelling detection from a robust physical characterization. In high-energy astrophysics, results that initially looked definitive have been revised when data from a second messenger arrived; the current result should be read with that history in mind. Until peer review and independent follow-up address those open questions, skepticism is not a failure of appreciation for the work; it is part of how science decides what to keep.

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