Full Breakdown
Neutron-Star Merger Offers Fresh Measurement of the Hubble-Lemaître Constant
7/11/2026, 11:33:21 AM
New Measurement from a Cosmic Collision
An international team led by researchers at Swinburne University of Technology and Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) analyzed the aftermath of a binary neutron-star merger. By combining data from the High Sensitivity Array, Hubble Space Telescope astrometry, and gravitational-wave observations, the collaboration derived a new estimate of the Hubble-Lemaître Constant. The value aligns more closely with early-Universe measurements from the cosmic microwave background than with late-Universe supernova-based estimates, providing an additional data point in the ongoing “Hubble tension” debate.
Background: The Hubble Tension and the Cosmic Distance Ladder
Cosmologists determine the Universe’s expansion rate using a “Cosmic Distance Ladder.” The first two rungs rely on parallax and standard candles (Cepheid variables and Type Ia supernovae) to gauge distances up to tens of millions of light-years, yielding an expansion rate of about 252,000 km h?¹ Mpc?¹. The final rung uses redshift measurements of the Cosmic Microwave Background (CMB), with ESA’s Planck satellite producing an estimate near 244,000 km h?¹ Mpc?¹. These two approaches produce discrepant results—a discrepancy termed the Hubble tension.
Official Statements & Responses
CSIRO’s Dr Kelly Gourdji, lead author, explained that the team’s gravitational-wave method is a “late Universe” technique whose result “is more consistent with the early Universe value.” Swinburne Professor Adam Deller highlighted the observational challenge, noting that the merger’s jets “are launched for only a couple of seconds, but as they slam into the surrounding gas, they glow for months afterwards.”
Criticism & Limitations
The new measurement is less precise than established values and, while more accurate than prior gravitational-wave attempts, still carries sizable uncertainties. Some astronomers have suggested that both early- and late-Universe measurements could be correct if cosmological models are revised; the team’s result “argues quite strongly against that solution,” indicating that current physics may not require alteration.
Verbatim Quotes
- “CSIRO’s Dr Kelly Gourdji, the lead author on the paper, explained in a SUT press statement: One method uses data from the very early Universe -the cosmic microwave background radiation - to make the measurement, while the other uses measurements from relatively nearby supernovae, making it data from the late Universe.” — Dr Kelly Gourdji, CSIRO
- “Our independent measurement using gravitational waves is a late Universe method, but the result is more consistent with the early Universe value.” — Dr Kelly Gourdji, CSIRO
- “Said Swinburne Professor Adam Deller, who led the radio observations used in the research: These jets are launched for only a couple of seconds, but as they slam into the surrounding gas, they glow for months afterwards.” — Prof Adam Deller, Swinburne University
- “This would suggest that there is not something wrong with our understanding of cosmology, though we’ll need to examine more neutron star mergers like this one to be sure,” — Lead author, Dr Kelly Gourdji
- “For now, this result adds another data-point for cosmologists to consider in the lively Hubble tension debate.” — Dr Kelly Gourdji, CSIRO
