NASA JWST Spots Oldest Supernova Ever Observed

Astronomers Spot Oldest Supernova Ever Observed

By Clara Moskowitz edited by Claire Cameron

The James Webb Space Telescope observed the oldest known supernova: the explosive death of a star that lived when the universe was only 730 million years old.

The ancient explosion occurred when the cosmos was only 5% of its current age, and light from the supernova has been traveling through space ever since. Astronomers were surprised to find that this primitive explosion strongly resembled today’s supernovae, which occur when massive stars run out of fuel for the nuclear fusion reactions that power them and then collapse under their own gravity.

Scientists suspected that the universe’s first supernovae might look different because they represent the death of some of the earliest stars. Compared to today’s stars, they formed in a smaller, denser cosmos and contained lighter elements, mainly hydrogen, helium and traces of lithium. And they were more massive than modern stars.

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Astronomers first spotted this primordial supernova in March, thanks to a 10-second high-energy flash of light called a gamma-ray burst. Such an explosion can be caused by a collision between a black hole and a dense object called a neutron star or, as in this case, by the death of a large star.

A telescope that looks for fleeting events in space, called the Space-Based Multi-Band Astronomical Variable Objects Monitor (SVOM), first detected the flash on March 14. This detection quickly sparked a chain of observations around the world, including by NASA’s Neil Gehrels Swift Observatory, which pinpointed the flash’s location in the sky, the Canary Islands Nordic Optical Telescope, which suggested it was very far away, and the European Southern Observatory’s Very Large. Telescope in Chile, which determined its age.

Because the object was so old, its light stretched as space expanded over time. As a result, the light from the initial supernova that caused the gamma-ray burst was expected to become brighter a few months after the gamma-ray burst was observed. The James Webb Space Telescope saw it in July, confirming that the flash was caused by a supernova, designated GRB 250314A. The powerful observatory was also able to spot the galaxy that housed the exploded star, although it only appeared as a small red spot.

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