JWST Spots Supernova That Will Explode Again—in 73 and 76 Years

JWST spectroscopy of SN Ares revealed helium and hydrogen features. Those are telltale signs of a star that shed most of its outer hydrogen layer before detonating — a category known as a Type IIb supernova.

Why will the same explosion arrive twice more?

Right now, astronomers see only one magnified image of Ares. But the team ran three separate lens models, and all of them point the same way: two additional images are still in transit, due to arrive in about 73 and 76 years respectively.

At an assumed 70-year timeline, "the SN Ares system has by far the highest predicted delays of any discovered lensed SN system so far," the team writes in its paper. For comparison, delays in known lensed supernova systems typically run from hours to a few decades — Ares roughly triples the record.

How could this measure the universe's expansion?

The arrival delays depend on the geometry of space itself. But space isn't static — it's expanding, with galaxies receding and light stretching as it travels. Measuring how far apart the images arrive therefore helps pin down the Hubble constant, the number that describes how fast the universe expands.

"Due to the direct relationship between these delays and geometric distance, a measurement of the offset in image arrival times leads to constraints on cosmological parameters such as the local expansion rate of the universe, H0," the researchers explain.

If astronomers in 70 years can catch the reappearance, they could time the delay extremely precisely. That timing, the team suggests, could yield one of the most precise single measurements of the universe's expansion rate ever made.

What happens next?

The team isn't waiting around. They plan additional spectroscopic redshift measurements in early 2027, which should clarify the lens cluster's properties and tighten the delay predictions.

The study also offers a rare chance to watch gravitational lensing play out across generations of scientists. The researchers admit they can't predict what cosmology will look like 70 years from now. But they're confident the return of SN Ares will be a scientifically rich event — one worth marking on a calendar, even if the calendar belongs to your grandchildren.

One caveat worth flagging: the paper is a preprint, posted to arXiv on Oct. 23, and has not yet completed peer review. The delay estimates also depend on lens models that the 2027 measurements could still refine. The headline numbers — 73 and 76 years — are predictions, not certainties.

The discovery is documented in Conor Larison et al., "SN Ares: A Strongly Lensed Type IIb Supernova at z=1.276 with a Predicted 70-Year Time Delay," arXiv (2026), DOI: 10.48550/arxiv.2610.33161.