TDCOSMO preprint: strong-lensing and JWST kinematics measure H0 = 71.1 ±2.4 km/s/Mpc (3.3%)

A new preprint reports one of the sharper independent measurements yet of the Hubble constant, the rate at which the universe is expanding today, using strong gravitational lensing and stellar motions in distant galaxies. The TDCOSMO Collaboration said its blind analysis found H0 = 71.1^{+2.4}_{-2.3} kilometers per second per megaparsec, a 3.3% measurement that lands between the two main rival values in the long-running Hubble-tension debate.

The result, posted Oct. 29 in revised form on arXiv as “TDCOSMO 2026: A 3% measurement of the Hubble constant from strong lensing and stellar kinematics” and submitted to Physical Review D, does not settle that debate. But it strengthens a key third line of evidence: a late-universe method that is independent of both the traditional local distance ladder and the early-universe inference from the cosmic microwave background, the relic light from the Big Bang.

The team based its estimate on 11 strongly lensed quasars with measured time delays. In this method, known as time-delay cosmography, a foreground galaxy bends and splits the light from a variable background quasar into multiple images. Because the light paths differ in length and pass through different gravitational fields, brightness changes in the quasar appear at different times in each image. Combined with detailed modeling of the lensing galaxy and measurements of how its stars move, those delays give an absolute distance scale and, from that, an estimate of the Hubble constant.

The collaboration said the work was done as a blind analysis, meaning researchers finalized their methods before seeing the cosmology result. In the paper’s abstract, the team wrote: “We find H0 = 71.1^{+2.4}_{-2.3} km.s^{-1}.Mpc^{-1}, a 3.3% uncertainty that accounts for the mass-sheet degeneracy.”

That last point matters because the mass-sheet degeneracy is one of the biggest systematics in lensing-based H0 measurements. In plain terms, different distributions of matter in and around the lens can reproduce nearly the same image pattern while shifting the inferred expansion rate. The collaboration said its quoted uncertainty includes that effect.

The new analysis improves materially on the group’s 2025 milestone result, which found H0 = 72.1^{+4.0}_{-3.7} km/s/Mpc from eight lenses. This time, the sample grew to 11 systems. The researchers also added spatially resolved stellar kinematics for nine systems, including six observed with JWST’s Near-Infrared Spectrograph, or NIRSpec. In three lens models, JWST Near-Infrared Camera, or NIRCam, imaging replaced earlier Hubble Space Telescope data. The team also applied axisymmetric dynamical modeling directly to the resolved stellar-motion data and updated estimates of matter along the line of sight using Euclid Flagship simulations instead of the older Millennium Simulation.

In the wider Hubble-constant debate, that places TDCOSMO’s value between the two best-known benchmarks. The Planck satellite’s 2018 analysis of the cosmic microwave background, interpreted in standard flat Lambda-CDM cosmology, gave about 67.4 ± 0.5 km/s/Mpc. The H0DN, or Local Distance Network, reported 73.50 ± 0.81 km/s/Mpc in 2026 using late-universe distance-ladder methods. TDCOSMO’s number is therefore closer to the local measurements than to Planck’s, but does not fully match either one.

The paper also reports that adding outside lens-galaxy samples from SLACS and SL2S improves the precision to about 3.0%, with one table entry giving roughly 71.3^{+2.2}_{-2.1} km/s/Mpc. Swapping the matter-density prior from the DES-Dovekie supernova sample to DESI-DR2 baryon acoustic oscillation data produced a consistent answer, with one configuration yielding about 71.7^{+2.5}_{-2.3} km/s/Mpc. As the abstract puts it, “Using the DESI-DR2 baryon acoustic oscillations (BAO) likelihood instead of DES-Dovekie yields fully consistent results.”

For now, though, the finding is still a preprint, not a peer-reviewed paper. What it adds is not a verdict, but a more precise independent measurement from the late universe — one that narrows the range with new JWST-backed data and keeps pressure on both sides of one of cosmology’s biggest disagreements.