Rare Stellar Explosion Gives Astronomers a Front-Row Seat to a Massive Star's Death
Today astronomers have announced that they caught a massive star’s death from the first explosive moment. The supernova may represent a new way for stars to end their lives. Press releases based on two papers just published in The Astrophysical Journal Letters describe the extensive set of observatories they used to study the supernova, including NOIRLab telescopes, NASA’s Chandra X-ray Observatory and the National Radio Astronomy Observatory’s Very Large Array. In particular, a press release from Carnegie Mellon University (CMU) highlights work by Brendan O’Connor who led one of these papers. We are delighted to welcome Brendan as a guest blogger to describe Chandra’s important role in this work.
Brendan O'Connor (Credit: Brendan O'Connor)
O’Connor is a McWilliams Fellow in the McWilliams Center for Cosmology and Astrophysics at CMU, where he studies cosmic explosions. His research concentrates on time-domain and transient astrophysics with a focus on the formation and evolution of high-energy transients and their progenitors. He uses a range of optical, infrared, and X-ray observatories to investigate these phenomena across the electromagnetic spectrum and is an avid user of NASA’s Chandra X-ray Observatory. He received his PhD from The George Washington University in 2023 under the supervision of Dr. Chryssa Kouveliotou, Dr. Eleonora Troja, and Dr. Brad Cenko. He will soon move to the Joint Space-Science Institute at the University of Maryland, College Park and NASA Goddard Space Flight Center as a Neil Gehrels Prize Postdoctoral Fellow.
Chandra Probes the Aftermath of a Rare X-ray Flash
Brendan O’Connor
On March 21, 2026, China’s Einstein Probe X-ray satellite detected a brief flash of X-rays from a galaxy about 500 million light-years away. Multiple groups of astronomers, including one that I was privileged to lead, have interpreted the flash, designated EP260321a, as a “shock breakout”. This type of flash is produced by the moment when the shock wave — similar to a supersonic plane’s sonic boom — from an exploding star reaches the star’s surface, and releases the supernova’s first observable burst of light. Astronomers kept observing this supernova (now called SN 2026gzf) and watched as it continued to get brighter., They now think SN 2026gzf belongs to the “broad-lined Type Ic” class of supernovas (“broad lined” references the width in the light spectrum and indicates material is moving very fast, at almost 10% of the speed of light) . These energetic explosions arise from massive stars that have lost their outer hydrogen and helium layers, and they are the same class of supernova seen accompanying many gamma-ray bursts (GRBs) that last longer than two seconds.
Caption: An image taken on March 25th, 2026 of supernova SN 2026gzf, which appears as a bright blue point source in the upper right corner of the host galaxy. The image was taken with the Dark Energy Camera (DECam), mounted on the NSF Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory in Chile.
Credit: CTIO/NOIRLab/DOE/NSF/AURA; Image Processing: D. de Martin & M. Zamani (NSF NOIRLab)
The resemblance raised a crucial question: had the stellar explosion producing SN 2026gzf launched a powerful jet even though astronomers didn’t detect a GRB ? A GRB occurs when a narrow jet of material moving at relativistic speeds — that is, close to the speed of light — successfully escapes the collapsing star. Astronomers may miss the very first gamma rays if the burst is faint or if the jet is not pointed toward Earth, but the jet should continue to reveal itself through a longer-lived afterglow. This afterglow is produced as the jet collides with particles surrounding the star, generating radiation that can remain visible in X-rays for days, weeks or even months depending on the density of the environment and the total energy of the jet.
NASA’s Chandra X-ray Observatory provided the critical test of whether such a jet had escaped. I initiated Chandra observations of SN 2026gzf to search for the predicted fading X-ray afterglow that is expected from a successful jet. Chandra’s exceptional sensitivity and sharp imaging allowed the team to search for very faint X-ray emission precisely at the location of the supernova. Although we did not detect an X-ray source, as reported in the newly published paper I led, we learned valuable information about the explosion. Due to the relatively close proximity of the explosion to Earth, the observations were sensitive enough that they would have detected nearly every known GRB X-ray afterglow.
The Chandra data therefore ruled out the typical bright X-ray afterglow produced by a successful GRB jet. The data also placed strong constraints on jets that might have been weaker or directed away from Earth, essentially ruling out those options. Instead, our results show that SN 2026gzf did not produce a normal, powerful relativistic jet. Rather, the star may have launched a weaker outflow that stalled inside the star before it could break free. EP260321a/SN 2026gzf is the first high-energy flash associated with a broad-lined Type Ic supernova that did not have a relativistic outflow, showing that stripped stars can explode in more ways than previously thought.