Stochastic gravitational-wave background from subsolar neutron stars in collapsar disks
Abstract
The fragmentation of the neutrino-cooled accretion disks that surround the black holes formed in collapsars has recently been proposed as an astrophysical channel for the production of neutron stars with masses well below the standard core-collapse floor. These disk-born objects merge either with one another or with the central black hole, and the superposition of all such mergers across cosmic history sources a stochastic gravitational-wave background. In this work we compute the energy density of this background for both merger channels, adopting a formation history tied to the observed rate of long gamma-ray bursts. We find that the merger of a subsolar neutron star with the central black hole is the loudest channel, already constrained by current data and within reach of next-generation observatories, while the binary neutron-star channel is at most two orders of magnitude fainter, with its widest binaries remaining accessible to next-generation detectors. Confronting these predictions with the fourth observing run of the LIGO--Virgo--KAGRA Collaboration, we derive two upper bounds on the fraction of collapsars whose disks produce such mergers: a robust one from the non-detection of an isotropic background, and a tighter one that could be achieved by a dedicated search for resolvable subsolar events in current data. Gravitational waves from non-axisymmetric deformations of the collapsar disk itself would provide an additional independent signature for the collapsar scenario, enabling cross-correlation studies with future deci-Hz detectors. Overall, the background computed here provides a population-level probe of disk-born subsolar neutron stars, which next-generation detectors could bring firmly into view.
Related
- Gravitational wave signatures of subsolar neutron star formation in collapsar disks
- Correcting for Evidence Uncertainty in the Templated Background Search for the Stochastic Gravitational-Wave Background
- Polarized Anisotropic Stochastic Gravitational Wave Background Search with Ground-Based Detector Networks
- A Delayed Rejection Reversible Jump Markov Chain Monte Carlo Method for Multi-Resolution Maps of the Stochastic Gravitational Wave Background with Pulsar Timing Array Data
- Thermalization of the Primordial Stochastic Gravitational-Wave Background
BibTeX
@misc{luca2026stochastic,
title = {{Stochastic gravitational-wave background from subsolar neutron stars in collapsar disks}},
author = {Valerio De Luca and Loris Del Grosso and Emanuele Berti},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.36005},
eprint = {2609.36005},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.36005},
}
RIS
TY - UNPB
TI - Stochastic gravitational-wave background from subsolar neutron stars in collapsar disks
AU - Valerio De Luca
AU - Loris Del Grosso
AU - Emanuele Berti
PY - 2026
DA - 2026/09/28
PB - arXiv
DO - 10.48550/arxiv.2609.36005
UR - https://arxiv.org/abs/2609.36005
AB - The fragmentation of the neutrino-cooled accretion disks that surround the black holes formed in collapsars has recently been proposed as an astrophysical channel for the production of neutron stars with masses well below the standard core-collapse floor. These disk-born objects merge either with one another or with the central black hole, and the superposition of all such mergers across cosmic history sources a stochastic gravitational-wave background. In this work we compute the energy density of this background for both merger channels, adopting a formation history tied to the observed rate of long gamma-ray bursts. We find that the merger of a subsolar neutron star with the central black hole is the loudest channel, already constrained by current data and within reach of next-generation observatories, while the binary neutron-star channel is at most two orders of magnitude fainter, with its widest binaries remaining accessible to next-generation detectors. Confronting these predictions with the fourth observing run of the LIGO--Virgo--KAGRA Collaboration, we derive two upper bounds on the fraction of collapsars whose disks produce such mergers: a robust one from the non-detection of an isotropic background, and a tighter one that could be achieved by a dedicated search for resolvable subsolar events in current data. Gravitational waves from non-axisymmetric deformations of the collapsar disk itself would provide an additional independent signature for the collapsar scenario, enabling cross-correlation studies with future deci-Hz detectors. Overall, the background computed here provides a population-level probe of disk-born subsolar neutron stars, which next-generation detectors could bring firmly into view.
ER -