Astronomers catch massive star's death from the first explosive moment

In March 2026, the Einstein Probe observed a brief flash of soft X-rays originating from a galaxy located about 500 million light-years away. This flash, named EP260321a, prompted an immediate global observing campaign. Within an hour, ground-based telescopes started monitoring the source, uncovering a rapidly brightening supernova, later identified as SN 2026gzf.

Two research teams, led by Brendan O'Connor from Carnegie Mellon University and Jillian Rastinejad from the University of Maryland, independently studied the event using multiple NSF NOIRLab facilities. Both groups identified the initial burst of X-rays as a shock breakout, the moment when a powerful shock wave from a stellar explosion pierces through the star's surface and releases the first light of a supernova.

Shock breakouts are typically fleeting, lasting only seconds to hours, and have been observed only once previously, making EP260321a an exceptionally rare discovery. Both teams confirmed that the explosion was a broad-lined Type Ic supernova, characterized by jets of relativistic material and often associated with gamma-ray bursts.

However, SN 2026gzf exhibited unique traits: the initial shock breakout was the faintest ever recorded in an Ic-BL supernova, despite the explosion's strength, and no gamma-ray burst was detected following the supernova, contrary to expectations. The researchers propose that the jet might have been choked by the star's surface or surrounding material.

Observations with the Dark Energy Camera captured deep images of the supernova as it brightened, revealing clues about the progenitor system and its environment before the star's demise. The Vera C. Rubin Observatory's COSMOS Deep Drilling Field, where the event occurred, provided additional data that aided the tracking of the supernova's evolution.

The Dark Energy Spectroscopic Instrument (DESI) conducted multiple spectroscopic observations using spare fibers on DESI, enabling follow-up on the transient alert from Rubin. These observations confirmed SN 2026gzf's Ic-BL nature and monitored its spectrum as the explosion evolved. Observations from various telescopes, including NASA's Chandra X-ray Observatory, the Very Large Array, and multiple ground-based facilities, helped Rastinejad's team disprove the presence of relativistic jets and understand the star's structure and surroundings prior to collapse.

The combined efforts of these telescopes offered a comprehensive understanding of this rare supernova event.