Astronomers spotted a supernova named SN Ares using the James Webb Space Telescope in August 2025. Gravity from a massive galaxy cluster acts like a lens, bending light from the explosion. Experts said the SN Ares system has by far the highest predicted delays of any discovered lensed supernova system.
Thanks to the gravitational lensing caused by a massive galaxy cluster and high-resolution images from the James Webb Space Telescope (JWST), astronomers discovered an exploding star when the universe was 4.9 billion years old. The discovery paper, posted to the arXiv preprint server on Oct. 23, presents a prediction for when the rest of the distorted images of SN Ares will arrive.
Gravity bends light
When a massive galaxy cluster sits between us and a distant galaxy, the galaxy cluster's gravity acts like a natural lens, bending and magnifying the light coming from the background galaxy. This is called gravitational lensing, and it can result in the creation of multiple images of the same galaxy. When different light rays take slightly different paths, the images arrive at different times, sometimes hours apart and sometimes decades apart. Some of the famous examples of multiple-image lensing include Einstein Cross, Molten Ring and Smiley Face.
In this study, astronomers led by Conor Larison of the Space Telescope Science Institute report the discovery of a supernova that occurred around 8.8 billion years ago. They spotted SN Ares in August 2025 in the JWST's near-infrared images taken of the field of the galaxy cluster MACS J0308.9+2645.
JWST spectroscopy revealed helium and hydrogen features, which are telltale signs of a star losing most of its outer hydrogen layer before exploding—a category called the Type IIb supernova. Researchers say it is "the highest-redshift member of its class spectroscopically identified."
Two are yet to arrive
For now, astronomers are seeing only one magnified image of Ares. But their analysis using three lens models revealed that two more images of this supernova are yet to reach us. The predictions say that they will appear in about 73 and 76 years, respectively. At an assumed timeline of 70 years, "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.
The delay in the arrival of these images depends on the geometry of space. But space is also expanding, with galaxies moving away from us and light getting stretched. So measuring the delay between when the images arrive also helps pin down the Hubble constant, the universe's expansion rate.
"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," researchers explain.
If, in 70 years, astronomers can catch the return, the delay could be timed extremely precisely. That could give one of the most precise single measurements of the universe's expansion rate.
The team plans to conduct additional spectroscopic redshift measurements in early 2027. This will help researchers better understand the lens properties and improve delay predictions.
The study also offers a rare opportunity to watch gravitational lensing play out over generations. Researchers say that they cannot predict what the science of the universe will look like in 70 years, but are sure that the reappearance of SN Ares will be a scientifically rich event, worth looking forward to.