A New Measurement of the Hubble Constant Using Lensed Supernovae Requiem and Encore ✛ ✦
Context
The Hubble constant characterizes the expansion rate of the Universe, but current measurements from the early and late Universe diverge by nearly 5σ — this is the so-called Hubble tension. Edwin Hubble discovered the expansion, and Hubble's law relates redshift to distance. Gravitational lensing, predicted by Einstein in general relativity and developed by Fritz Zwicky, allows an alternative measurement of H0 based on time delays between lensed images of variable sources. Gravitational lenses in galaxy clusters offer a unique opportunity: time delays on the order of years, which reduces the relative measurement error.
Methods
The scientists used data from the Hubble and JWST telescopes, along with MUSE spectroscopy, to identify 23 multiple images from 8 background sources with known redshifts in the MACS J0138 cluster. Lens mass modeling was performed using the Gravity.jl package, parameterizing dark matter with a NIE profile and galaxies with scaling relations. Dark energy was incorporated via the ΛCDM cosmology. Time delays for the supernovae were measured from light curves with an accuracy of a few days.
Results
The best model reproduces image positions with an rms deviation of 0.24″. Predicted delays: for SN Encore, Δt1b,1a = −38+3−3 days (consistent with observations), the long-delayed image 1d will appear after Δt1d,1a = 3177+78−59 days. For SN Requiem, the deferred image 2d is expected after Δt2d,2a = 3938+90−77 days (≈2027). Joint analysis of the delays yielded a measurement of the Hubble constant: H0 = 67.0+9.3−7.8 km/s/Mpc. This value matches estimates from the early Universe and confirms the tension with local measurements.
Implications
This result strengthens the Hubble tension, showing that the independent gravitational lensing method gives an H0 value close to the cosmological one, not the local one. The model confirms the predictability of lensed supernovae as standardizable candles, allowing new image appearances to be predicted with high accuracy. Incorporating delays into a joint Bayesian mass+H0 analysis lays the foundation for time-delay cosmography with galaxy clusters.
Future development
Future observations require long-term monitoring of the expected images. Adding the surface brightness of arcs to the lens model will refine the potential near the images and reduce systematics. With the advent of the JWST and Rubin observatories, the statistics of lensed supernovae will dramatically increase, turning the method into a routine cosmological tool.
Impact
Resolving the Hubble tension and testing ΛCDM. The method is applicable for testing dark matter and dark energy models, as well as calibrating supernovae as standard candles.
Next steps
Await the reappearance of the SN Requiem image in 2027 and measure its delay with ~1% accuracy. Implement full modeling of arc surface brightness in Gravity.jl.
Key open problems
The work directly addresses the Hubble tension — the discrepancy between the H0 value from the early Universe (CMB, BAO) and local supernovae. It also touches on the nature of dark matter through cluster profiles and dark energy, which determines the global geometry.
The knowledge machine's view
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The authors performed Bayesian mass modeling of the cluster MACS J0138.0-2155, combining the positions of 23 multiple images and the time delays of two lensed supernovae, SN Requiem and SN Encore. They obtained H0 = 67.0+9.3-7.8 km/s/Mpc, consistent with early-Universe estimates.
Where its strength is
The strength of the work lies in the joint analysis of image positions and time delays, which simultaneously constrained the cluster mass profile and the Hubble constant. The prediction of future supernova images opens the way for further refinement.
Where it could go next
- It might be interesting to compare the obtained H0 value with gravitational-wave measurements: nearby in the archive is a work where dark sirens provide an independent estimate of the expansion rate.based on: One Night to a Percent: Dark Sirens Reveal the Universe's Speed arXiv:2607.17284v1
- There is also an approach using radio bursts: there the Hubble tension is explored through dispersion measure, which could provide an additional cross-check for cosmological models.based on: In the Rhythm of the Universe: Radio Bursts vs. Hubble Tension arXiv:2606.22390
- One could look at how authors of another work combine Type Ia supernova data with other distance indicators to reduce systematic errors in determining H0.based on: Universe's expansion rate refined using supernova 'twins' arXiv:2512.02391
Worth trying
- Test incorporating dispersion measure data from fast radio bursts to jointly constrain H0 and baryon density.
- Investigate how accounting for microlensing effects in the cluster might affect supernova light curves and, consequently, the measured delays.
- Use the predicted appearances of new images to plan targeted observations and obtain more precise time delays.
Why this may matter
Refining the Hubble constant with an independent method is important for understanding the nature of the Hubble tension and possible new physics beyond ΛCDM.
Nearby works in our archive
- Cosmic Detective: Two Independent Clues Against the Main Cosmological Debatesimilarity 0.68
- Gravitational waves measure the expansion rate of the universesimilarity 0.66
- Universe's expansion rate refined using supernova 'twins'similarity 0.66
- Cosmic Clocks Diverge: A New Mystery of the Universe's Expansionsimilarity 0.65
- The Cosmic Tuning Fork: Why the Universe Plays Two Different Notessimilarity 0.65
- Gravitational waves refine cosmic expansion ratesimilarity 0.64
- In the Rhythm of the Universe: Radio Bursts vs. Hubble Tensionsimilarity 0.62
- One Night to a Percent: Dark Sirens Reveal the Universe's Speedsimilarity 0.61
The closest work in the archive sits at 0.68 by meaning — the usual level for our corpus.
Original abstract
as written by the authors arXiv:2606.25205
We present a strong-lensing (SL) analysis of the galaxy cluster MACS J0138.0-2155 (z=0.336), the first known lens cluster discovered to host two distinct multiply imaged Type Ia supernovae (SNe): SN Requiem and SN Encore. Both SNe are located in the massive, multiply imaged red galaxy MRG-M0138 at z=1.949. The projected total mass of this cluster has been investigated with several independent lens models (Suyu+26; Pierel+26), using a sample of 23 spectroscopically confirmed multiple images from 8 background sources (0.767
Fun fact: SN Requiem was discovered in 2016 in archival images, and its 'twin' — SN Encore — appeared in 2023, confirming lensing predictions. Two different supernovae in the same distant galaxy — a very rare occurrence.
Key numbers
- Measured Hubble constant: 67.0+9.3/-7.8 km/s/Mpc
- Expected delay of SN Requiem: ≈3938 days (~11 years)
- Current relative delay error: >10%
- Projected H0 accuracy after 2027: ~3-5%
- RMS position deviation: 0.24″