Zwicky Transient Facility’s 772 Type Ia supernovae yield H0 ≈ 72 km/s/Mpc, reinforcing local measurements

A new arXiv preprint reports that 772 nearby Type Ia supernovae observed by the Zwicky Transient Facility yield a local Hubble constant of about 72 kilometers per second per megaparsec, reinforcing the higher, late-universe side of the long-running Hubble-tension debate.

The result stands out less for the number itself than for the dataset behind it. Supernova-based measurements of the universe’s expansion rate have often stitched together observations from multiple surveys and instruments, leaving room for concerns about calibration differences and selection effects. In the new paper, posted Oct. 26 as “ECH0EZ: Estimating the Hubble constant with ZTF SN Ia DR2,” researchers use what they describe as the first preliminary cosmological analysis of 772 Type Ia supernovae from the second data release of the Zwicky Transient Facility, a wide-field sky survey. Because the sample comes from a single, untargeted survey, and because its volume-limited subset at redshift below 0.06 is designed to avoid overrepresenting intrinsically brighter objects at larger distances, the study is meant to reduce some of those longstanding concerns.

The authors — Konstantin Karchev, Marco Giunta, Raul Jimenez, Roberto Trotta and Licia Verde — anchored their distance scale using 42 supernova host galaxies previously calibrated by the SH0ES team with Cepheid variable stars, which brighten and dim in a way that reveals distance. Their main result is H0 = 71.6 ± 1.5 km/s/Mpc after allowing for uncertainty in cosmic deceleration. In an alternate analysis that applies a matter-density prior from the Pantheon+ supernova compilation, they find H0 = 72.3 ± 1.1 km/s/Mpc. The paper says the uncertainty is driven mainly by the limited number of calibrators, not by the size of the ZTF supernova sample in the Hubble flow, the more distant set used to trace cosmic expansion.

That places the new estimate much closer to recent local distance-ladder measurements than to the value inferred from the early universe. The European Space Agency’s Planck mission, which mapped the cosmic microwave background and inferred the present-day expansion rate under the standard cosmological model, found about 67.4 ± 0.5 km/s/Mpc. By contrast, the SH0ES collaboration reported 73.04 ± 1.04 km/s/Mpc in 2022. The mismatch between those approaches is known as the Hubble tension: early-universe data point to a slower present-day expansion rate than local, late-universe methods such as Cepheids plus Type Ia supernovae. In the new preprint, the ZTF result differs from Planck by 2.7 sigma in the baseline case, or 4.1 sigma with the Pantheon+ prior.

The paper also says the finding is stable under several reasonable changes to the analysis, including the choice of supernova light-curve model and Milky Way dust model, as well as extensions that account for peculiar-velocity correlations, a host-mass step and two stretch populations. The team says it corrected the public ZTF data for known instrumental and calibration biases and adjusted redshifts for peculiar motions, the local gravitationally induced motions of galaxies on top of the overall cosmic expansion.

Still, the authors emphasize an important limitation. Their result does not yet come from a fully self-contained ZTF distance ladder, because ZTF-observed calibrator supernovae are not yet available. Instead, the analysis depends on cross-calibration between ZTF data and the Pan-STARRS/SH0ES system used for the calibrators. Any unaccounted-for offset there, they note, would shift the inferred value of H0.

Even so, the authors argue that their preliminary result points in a familiar direction. In the abstract, they write: “These results are in agreement with previous distance-ladder measurements and 2.7σ (4.1σ) away from the value obtained from Planck data, suggesting that the resolution of the Hubble tension lies outside of SNe Ia—or the distance ladder entirely.” For now, that remains the interpretation of a preprint, but one built on a more uniform nearby supernova sample than earlier studies.