Webb is an Amazing Supernova Hunter

The James Webb Space Telescope (JWST) has just increased the number of known distant supernovae by tenfold. This rapid expansion of astronomers’ catalog of supernovae is extremely valuable, not least because it improves the reliability of measurements for the expansion of the universe.

“Webb is a supernova discovery machine,” said Christa DeCoursey of the Steward Observatory and the University of Arizona at a press conference earlier this week. “The sheer number of detections plus the great distances to these supernovae are the two most exciting outcomes from our survey.”

JWST’s advantage over previous surveys is its specialty in infrared wavelengths. As the universe expands, the light coming from distant objects gets stretched, “redshifting” the light to longer wavelengths. Most of the light from the early universe, therefore, reaches us in infrared.

That has allowed the telescope to discover a host of new supernovae in distant galaxies, some of which are the furthest ever seen. Supernovas are transient objects – they’re exploding stars that change and fade over time – so catching them happening at such great distances is exciting.

Previously, the most distant supernova fell about the redshift 2 mark (3.3 billion years into the Universe’s life). The new record holder just discovered by JWST has a redshift of 3.6, meaning it exploded just 1.8 billion years after the Big Bang.

Closeups of three out of the 80 transients discovered by JWST, where a change of brightness was observed between 2022 and 2023. NASA, ESA, CSA, STScI, Christa DeCoursey (University of Arizona), JADES Collaboration

Of the 80 new objects discovered, several were type 1a supernovae. These are of particular interest to scientists, because they are known to explode with a standard brightness, making it possible to take accurate distance measurements for the objects.

At least, that’s true for nearby supernovae. This new survey will allow researchers to see if that pattern remains true in the distant universe too, or if they behaved differently under the conditions of the early universe. At that time, there were fewer heavy elements in the cores of stars. Finding out if this changes their behavior is essential to measuring the expansion of spacetime itself, and could help resolve the crisis in cosmology, in which measurements using type 1a supernovae don’t align with those using the Cosmic Microwave Background.

“This is really our first sample of what the high-redshift universe looks like for transient science,” said Justin Pierel, a NASA Einstein Fellow at the Space Telescope Science Institute. “We are trying to identify whether distant supernovae are fundamentally different from or very much like what we see in the nearby universe.”

Pierel carried out a preliminary examination of one of the new supernovae, found at redshift 2.9. It seems to show no difference from the expected brightness, which is good news for astronomers’ confidence in their distance measurements to date. Further analysis of other supernovae in the data will be forthcoming.

Other outcomes of this research include a better understanding of star formation and the mechanisms behind supernova explosions in the early universe.

“We’re essentially opening a new window on the transient universe,” said STScI Fellow Matthew Siebert. “Historically, whenever we’ve done that, we’ve found extremely exciting things — things that we didn’t expect.”

Learn more:

NASA’s Webb Opens New Window on Supernova Science.” JWST.