Search for Compact Binary Coalescences with Sub-solar Mass Components in Data from the Second Part of LIGO-Virgo-KAGRA's Fourth Observing Run

arXiv:2610.20276 · gr-qc, astro-ph.HE · Submitted 2026-10-14 · Read on arXiv

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Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: We're looking at the paper: "Search for Compact Binary Coalescences with Sub-solar Mass Components in Data from the Second Part of LIGO-Virgo-KAGRA's Fourth Observing Run".

Jocelyn: Here's the gist of the paper. Detailed Research Summary: Gravitational Wave Search for Compact Binary Coalescences with Sub-solar Mass Components This research presents a comprehensive analysis of gravitational wave data collected during the second part of the fourth observing run (O4b) of the LIGO–Virgo–KAGRA Collaboration, specifically focusing on searches for compact binary coalescences containing at least one sub-solar mass component.

Vera: The study builds upon previous work (Abac et al.

Jocelyn: 2026a) by providing the most exhaustive results to date for searches involving systems with at least one Sub-Solar Mass (SSM) compact object across the LVK network.

Vera: Search Scope and Methodology The analysis targets compact binary coalescences with a primary mass range between 0.2 M and 10 M, a secondary mass range between 0.2 M and 1 M, and component mass ratios restricted to lie between 0.1 and 1.

Paper summary: Vera: We start by looking at this paper "Search for Compact Binary Coalescences with Sub-solar Mass Components in Data from the Second Part of LIGO-Virgo-KAGRA's Fourth Observing Run". It focuses on searching for compact binary mergers where the secondary mass is between zero point two solar masses and one solar mass, and the primary mass is between zero point two and ten solar masses <ref:2610.20276#pg1>.

Jocelyn: The thesis here is that they’re using data from the second part of the fourth observing run—April ten two thousand twenty-four to January twenty-eight two thousand twenty-five—to search for these specific sub-solar mass systems <ref:2610.20276#pg1,the second part of the fourth observing run>. They found two outlier candidates that were flagged by individual pipelines like GstLAL and MBTA.

Vera: The importance is that they are providing upper limits on merger rates for different combinations of component masses. They report merger rate limits ranging from fifty Gpc to ten solar masses per year up to five thousand Gpc to one solar mass per year depending on the mass combinations they are looking at.

Jocelyn: So, in this segment, we covered the scope and the key findings of this paper, showing how these archival searches lead directly into new constraints on dark matter candidates <ref:2610.20276#pg1>.

Subrahmanyan: We established that even though no definitive detection was made yet, the search actually sets limits on how often these weird sub-solar systems might be merging.

Conclusion: Vera: So, we’ve been looking at the paper "Search for Compact Binary Coalescences with Sub-solar Mass Components in Data from the Second Part of LIGO-Virgo-KAGRA's Fourth Observing Run" and its authors, the LIGO Scientific Collaboration, Virgo Collaboration, and KAGRA Collaboration.

Jocelyn: That was a lot of searching across all three pipelines: GstLAL, MBTA, and PyCBC.

Subrahmanyan: And what we found is that while we didn't get a direct detection yet, the search actually sets limits on how often these weird sub-solar systems might be merging.

Vera: Exactly. The paper uses those merger rate limits to test some models for dark matter, specifically primordial black holes and dark black holes.

Jocelyn: It’s about using null results to constrain particle physics candidates, which is a big thing for us as radio astronomers looking at time-domain events.

Subrahmanyan: The constraints they put on the fraction of dark matter in primordial black holes are quite specific based on the mass distribution they assumed.

Vera: And for those dark black holes forming in a dissipative model, the upper limit on their density is extremely low, around one point ten to one point one times ten to the negative five.

Jocelyn: So, what this means for us listening right now is that even though we didn't see a signal yet, we’re getting tighter restrictions on how many of these objects can exist in the universe.

Subrahmanyan: It tells us that if dark matter is made of primordial black holes or dark black holes, they have to be quite rare in certain mass ranges.

Vera: And future searches need more data, like from run O4c, to get those merger rates even tighter and rule out more possibilities.

Jocelyn: That’s right, because those tighter constraints are what we need to really push the understanding of both compact objects and dark matter candidates.

LIGO Scientific Collaboration · Virgo Collaboration · KAGRA Collaboration

gr-qc, astro-ph.HE

Submitted: 2026-10-14

Updated: 2026-10-14

License: http://creativecommons.org/licenses/by/4.0/

Importance score: 79/100

The gist: Detailed Research Summary: Gravitational Wave Search for Compact Binary Coalescences with Sub-solar Mass Components This research presents a comprehensive analysis of gravitational wave data

Key concepts

Sub-Solar Mass (SSM) Population: This refers to compact objects like black holes or neutron stars with masses between 0.2 solar masses ($M_{\odot}$) and 1 solar mass ($M_{\odot}$). The search specifically looks for binary systems where at least one of the components falls within this mass range, which is a key focus of this study.
Merger Rate Upper Limits: Since no events were definitively found, the researchers calculated 'upper limits' on how frequently these specific binary systems could be merging based on the sensitivity of their search pipelines. These limits show that the rate is constrained to be below certain values (e.g., $50 ext{ Gpc}^{-3} ext{ yr}^{-1}$ for some black hole combinations).
Primordial Black Holes (PBHs): PBHs are hypothetical black holes formed in the early universe, potentially from fluctuations in the very early cosmos. The study uses merger rate limits to constrain how much dark matter could be composed of these PBHs, finding that their fraction is limited depending on whether they form early or late.
Dark Black Holes (DBHs): This scenario involves black holes made from dark matter rather than normal baryonic matter. The analysis constrains the fraction of total dark matter that could be in these DBHs, finding extremely low limits for minimum masses, suggesting they are unlikely to constitute all of the dark matter.

Summary

Detailed Research Summary: Gravitational Wave Search for Compact Binary Coalescences with Sub-solar Mass Components

This research presents a comprehensive analysis of gravitational wave data collected during the second part of the fourth observing run (O4b) of the LIGO–Virgo–KAGRA Collaboration, specifically focusing on searches for compact binary coalescences containing at least one sub-solar mass component. The study builds upon previous work (Abac et al. 2026a) by providing the most exhaustive results to date for searches involving systems with at least one Sub-Solar Mass (SSM) compact object across the LVK network.

Search Scope and Methodology

The analysis targets compact binary coalescences with a primary mass range between 0.2 M and 10 M, a secondary mass range between 0.2 M and 1 M, and component mass ratios restricted to lie between 0.1 and 1. The search utilizes data from the LIGO, Virgo, and KAGRA detectors spanning April 10, 2024, to January 28, 2025 (O4b). The analysis employed three distinct search pipelines: GstLAL, MBTA (Massive Binary Tidal Analysis), and PyCBC.

Key Findings on Candidate Detection

The overall search using the combined pipelines did not yield any statistically significant gravitational wave candidates for SSM searches. The observed number of candidates was entirely consistent with the expected Poisson statistical distribution, with the exception of two specific outlier events identified by individual pipelines:

GstLAL Outlier (S240422ed): Identified by the GstLAL pipeline on April 22, 2024, at 21:35:13.42 UTC. This candidate was initially flagged by low-latency searches in both the GstLAL and PyCBC pipelines with False Alarm Rates (FARs) of 10-5 yr-1 and 10.3 yr-1, respectively. The candidate was consistent with a Neutron Star-Black Hole (NSBH) source binary, exhibiting a redshifted chirp mass of about 1.7 M and an effective inspiral spin (chi eff) greater than 0.75. Crucially, the MBTA pipeline did not detect this event.
MBTA Outlier (S241229bq): Identified by the MBTA pipeline on December 29, 13:52:36.83 UTC. This candidate was flagged by both the MBTA and GstLAL pipelines with FARs of 570 yr-1 and 100 yr-1, respectively. The PyCBC pipeline did not detect this specific candidate, as it does not incorporate a low-latency SSM search mode. The MBTA offline search identified this event with an FAR of 0.0043 yr-1, corresponding to a significance of 2.8 standard deviations (not including trials factors). GstLAL and PyCBC also identified this candidate, but with FARs consistent with noise (34 yr-1 and 7.7 yr-1, respectively).

Sensitivity and Merger Rate Constraints

The study quantifies the combined sensitivity of the LVK searches over O4b data for the target sub-solar mass black hole population, as well as for neutron star binaries containing one or more sub-solar components.

Merger Rate Upper Limits: The paper establishes stringent upper limits on merger rates based on different pipeline sensitivities:
For low-spin SSM Binary Black Holes (BBHs), the upper limits are 66.8 Gpc-3 yr-1 (GstLAL), 72.0 Gpc-3 yr-1 (MBTA), and 50.0 Gpc-3 yr-1 (PyCBC).
For SSM Binary Neutron Stars (BNS), assuming a simple, fixed population model consistent with previous literature, the upper limit is 249 Gpc-3 yr-1.

Constraints on Dark Matter Scenarios

The derived merger rate limits are used to constrain two illustrative dark matter scenarios capable of forming sub-solar mass compact objects: primordial black holes (PBHs) and dark black holes (DBHs) arising from a dissipative dark matter model.

Primordial Black Holes (PBHs):
Assuming a monochromatic mass distribution, the fraction of dark matter in PBHs is constrained to be 0.018–0.032 at 1 M, and 0.10–0.18 at 0.35 M for early-forming binaries, or less than unity for masses above (44) times 10-2 M for late-forming binaries.
The most restrictive limit on the fraction of dark matter in PBHs, derived from EB formation models (Equation 12), constrains f PBH to be less than unity across the entire mass range explored.
Dissipative Dark Matter Model (Dark Black Holes):
For this scenario, assuming SSM DBHs form with a minimum possible mass, the most restrictive limit on the fraction of total dark matter density in DBHs, for a minimum mass of 0.65–(85) M, is extremely low: (1.0–(1.1)) times 10-5.
If dark black holes constitute all the dark matter, the minimum mass constraint excludes masses above ((4.2–4.4)) times 10-2 M.

Sensitivity in Hypervolume

The study also provides a measure of sensitivity in terms of hypervolume, finding that the typical sensitive hypervolume (V T) for populations of BNSs with at least one SSM neutron star is approximately about 10-3 Gpc cubed yr.

Conclusion and Outlook

The analysis confirms that while no definitive detection has been made, the search successfully constrained the merger rates for various SSM compact object populations. The continued operation of LIGO and Virgo in O4c, augmented by KAGRA data, is expected to increase overall search sensitivities. This enhanced sensitivity will lead to tighter constraints on the merger rates of SSM BBHs and BNSs, which holds profound implications for fundamental physics regarding the nature of compact objects and dark matter candidates.

Improvements for AI systems

The AI system can now constrain dark matter models by setting upper limits on their merger rates; specifically, it can constrain any model that predicts a non-negligible rate of binary mergers within the parameter space analysed by the search.
The system gains the ability to differentiate between formation scenarios for primordial black holes (PBHs) by constraining the fraction of dark matter in primordial black holes, assuming a monochromatic mass distribution, to be ≤ (0.018–0.032) at 1 M⊙ and similarly for other mass ranges.
The AI can constrain models involving dissipative dark matter by bounding the fraction of the total dark matter density in the Universe in DBHs; our most restrictive limit, for a minimum mass (0.65–0.85) M⊙, is (1.0–1.1) × 10−5.
The system can be used to probe the microphysics of dissipative dark matter by deriving bounds on the ratio of dark fermion masses to the Standard Model proton mass, specifically bounding µ Darkmχ/mp up to (16.5–16.6).

Abstract

We report on a gravitational wave search for compact binary coalescences with secondary mass between 0.2 M and 1 M and primary mass between 0.2 M and 10 M, restricting the component mass ratio to lie between 0.1 and 1. The analysis uses data collected by the LIGO and Virgo detectors between 2024 April 10 15:00:00 and 2025 January 28 17:00:00, the second part of the fourth observing run of the LIGO-Virgo-KAGRA Collaboration. Results from two out of three search pipelines show outlier candidates, but not at a sufficient level of significance to provide evidence for detection. We report the combined sensitivity of the current searches over the first and second parts of the observing run to the target sub-solar mass (SSM) black hole (BH) population, as well as to neutron star (NS) binaries with one or more sub-solar component. We place upper limits on the merger rate of SSM BHs, ranging from 50 Gpc-3 yr-1 to 5000 Gpc-3 yr-1 (90% confidence) for different component mass combinations. We use the merger rate limits to constrain two illustrative dark matter (DM) scenarios that can form SSM compact objects: primordial BHs, and dark BHs forming in a dissipative DM model. Our search limits the fraction of DM in primordial BHs, assuming a monochromatic mass distribution, to be at most (0.018-0.032) at 1 M, and at most (0.10-0.18) at 0.35 M for early-forming binaries; or to be less than 1 at masses above (0.62-0.74) M for late-forming binaries. For the dissipative model, we constrain the fraction of DM for a range of minimum dark black hole masses below 1,M to be as low as (1.0-1.1) x 10-5; we also exclude minimum masses above (0.62-0.74) M, if dark BHs constitute all of the DM. For binary NSs that include sub-solar mass components, assuming a simple, fixed population model we find a merger rate upper limit of 249 Gpc-3 yr-1.