Search for Sub-Solar Mass Binaries in the First and Second Part of LIGO's Fourth Observing Run O4a-O4b
Abstract
The observation of sub-solar mass neutron stars and black holes would signify a new class of astrophysical objects since these systems are not expected to form via standard stellar evolution. We present the first sub-solar mass search for binaries consisting of neutron star or black holes that uses the data from both the second part (O4b) and first part (O4a) of the fourth observing run of the Advanced LIGO detectors. The search covers primary masses 0.1 to 2 M⊙ and secondary masses 0.1 to 1 M⊙. Tidal effects up to 7×105 are accounted for in extremely low-mass neutron stars. No statistically significant candidates are identified. We place a 90% confidence upper limit on the merger rate ℛ90 for sub-solar mass black holes and neutron stars to be < 5.2×102 Gpc−3 yr−1 for a chirp mass of 0.5 M⊙, a factor 2.2 × lower compared to previous O1-O4a searches. We constrain the effective local dark matter fraction to be f̃PBH<0.6% for MPBH=0.8 M⊙, approximately $1.5$ factor improvement to previous O1-O4a constraints. Given our model assumptions, our local dark matter fraction constraints are 2−7 times lower than the OGLE microlensing survey for MPBH≥0.6 M⊙.
Related
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- In Search of the Gravitational Wave of Fast X-Ray Transient in the Second Part of the LIGO-Virgo-KAGRA Fourth Observing Run
- Constraints on ultralight bosons from merging binary and remnant black holes observed during the second and third parts of the fourth LIGO-Virgo-KAGRA observing run
- Open Data from LIGO, Virgo, and KAGRA through the Second Part of the Fourth Observing Run
BibTeX
@misc{kacanja2026search,
title = {{Search for Sub-Solar Mass Binaries in the First and Second Part of LIGO's Fourth Observing Run O4a-O4b}},
author = {Keisi Kacanja and Kanchan Soni and Alexander H. Nitz},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.19329},
eprint = {2610.19329},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.19329},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Search for Sub-Solar Mass Binaries in the First and Second Part of LIGO's Fourth Observing Run O4a-O4b
AU - Keisi Kacanja
AU - Kanchan Soni
AU - Alexander H. Nitz
PY - 2026
DA - 2026/10/14
PB - arXiv
DO - 10.48550/arxiv.2610.19329
UR - https://arxiv.org/abs/2610.19329
AB - The observation of sub-solar mass neutron stars and black holes would signify a new class of astrophysical objects since these systems are not expected to form via standard stellar evolution. We present the first sub-solar mass search for binaries consisting of neutron star or black holes that uses the data from both the second part (O4b) and first part (O4a) of the fourth observing run of the Advanced LIGO detectors. The search covers primary masses 0.1 to 2 M_⊙ and secondary masses 0.1 to 1 M_⊙. Tidal effects up to 7×10^5 are accounted for in extremely low-mass neutron stars. No statistically significant candidates are identified. We place a 90% confidence upper limit on the merger rate ℛ_90 for sub-solar mass black holes and neutron stars to be < 5.2×10^2 Gpc^−3 yr^−1 for a chirp mass of 0.5 M_⊙, a factor 2.2 × lower compared to previous O1-O4a searches. We constrain the effective local dark matter fraction to be f̃_PBH<0.6% for M_PBH=0.8 M_⊙, approximately $1.5$ factor improvement to previous O1-O4a constraints. Given our model assumptions, our local dark matter fraction constraints are 2−7 times lower than the OGLE microlensing survey for M_PBH≥0.6 M_⊙.
ER -