What the study found
The study found that reanalyzing GW170817, a binary neutron star merger, produced tighter constraints on the jet viewing geometry and on Hubble’s constant (H0, the cosmic expansion rate). Using a fixed cosmology, the authors report a viewing angle of 18.3°–20.3°; when fitting distance and H0 directly, they report 16.8°–19.2°, D_L = 44.0 ± 1.6 Mpc, and H0 = 65.5 ± 4.4 km s−1 Mpc−1.
Why the authors say this matters
The authors say this matters because the accuracy of the standard siren measurement of H0 from GW170817 depends strongly on how well the merger inclination angle is constrained. They also note that their H0 result is close to the early-Universe Planck value and less close to the late-Universe SH0ES measurement, in the context of the current Hubble constant discrepancy.
What the researchers tested
The researchers tested a Bayesian visibility-plane model-fitting framework that included all relevant very long baseline interferometry (VLBI; high-resolution radio interferometry) data, handled systematic uncertainties, and sampled the model parameter space rigorously. They fit new hydrodynamical afterglow models with a continuum of jet geometries, and then extended the framework to fit for luminosity distance and H0 directly while marginalizing over plausible peculiar velocity corrections.
What worked and what didn't
Including all relevant VLBI data and systematic uncertainties allowed the authors to obtain more informed and robust measurements of the viewing geometry and H0. The fit with a fixed cosmology gave a viewing-angle range of 18.3°–20.3°, and the direct fit gave 16.8°–19.2° with D_L = 44.0 ± 1.6 Mpc and H0 = 65.5 ± 4.4 km s−1 Mpc−1. The abstract does not report any failed test case or comparison showing a method that did not work.
What to keep in mind
The abstract notes potential caveats, but it does not list them in detail. The reported H0 result depends on the modeling choices, the included VLBI data, and the treatment of peculiar velocity corrections, and the fixed-cosmology viewing-angle estimate uses D_L = 40.7 Mpc as in most previous analyses.
Key points
- GW170817 was reanalyzed to constrain jet geometry and H0 more precisely.
- The authors used a Bayesian visibility-plane model with VLBI data and systematic uncertainties.
- With fixed cosmology, they report a viewing angle of 18.3°–20.3°.
- With distance and H0 fitted directly, they report D_L = 44.0 ± 1.6 Mpc and H0 = 65.5 ± 4.4 km s−1 Mpc−1.
- The peak H0 value is within 0.5 sigma of Planck and 1.7 sigma from SH0ES, according to the abstract.
Disclosure
- Research title:
- GW170817 analysis gives tighter constraints on viewing angle and H0
- Authors:
- K. Gourdji, Adam T. Deller, Chris Flynn, Taya Govreen-Segal, Cullan Howlett, K. P. Mooley, Ehud Nakar
- Institutions:
- ARC Centre of Excellence for Gravitational Wave Discovery, ARC Centre of Excellence for Gravitational Wave Discovery, ARC Centre of Excellence for Gravitational Wave Discovery, California Institute of Technology, Commonwealth Scientific and Industrial Research Organisation, Indian Institute of Technology Kanpur, Swinburne University of Technology, Swinburne University of Technology, Swinburne University of Technology, Tel Aviv University, Tel Aviv University, The University of Queensland
- Publication date:
- 2026-06-29
- OpenAlex record:
- View
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