Dead Stars Refuse to Fade: Chandra Reveals a Galaxy Full of Flickering Supernova Remnants

For decades, textbooks taught that the remnants of exploded stars slowly and predictably cool over thousands of years. But a painstaking new analysis of 14 years of archival data from NASA's Chandra X-ray Observatory reveals a far more chaotic reality. In the nearby spiral galaxy Messier 83 (M83), a population of supernova remnants is refusing to fade quietly, instead flickering dramatically in X-ray light over timescales of just a few years.

A Deep-Sea Fireworks Display in M83

To build a baseline of how supernova remnants evolve, astronomers turned Chandra toward M83, a spectacular face-on spiral galaxy located about 15 million light-years away, for observations spanning from 2000 to 2014 . The team tracked 22 X-ray sources previously identified as supernova remnants and made a startling discovery: approximately half of them showed significant and unexpected changes in their X-ray brightness .

"We know that individual X-ray sources can change dramatically, but to find that so many supernova remnants are doing this really surprised us," said Andrea Prestwich, an astronomer at the Catholic University of America and a co-author of the study published in The Astrophysical Journal .

This high proportion—roughly 11 out of 22—is what makes the finding so disruptive. It is not a single oddball object breaking the rules, but a widespread behavior that forces a re-examination of the standard evolutionary model for stellar remnants .

Why Are "Dead" Stars Still Flaring?

The team identified two leading, and potentially concurrent, mechanisms to explain the erratic X-ray flickering .

1. The Survivor Companion Star

The preferred explanation is that many of these supernova remnants host a survivor. Most massive stars exist in binary systems. When the more massive star goes supernova, it can leave behind a black hole or neutron star. If the companion star survives the cataclysm, it can become locked in a tight orbit around the new compact object. The intense gravity of the black hole or neutron star then begins pulling material from the companion's surface. This process, known as accretion, heats the infalling gas to millions of degrees, producing powerful and variable X-ray emissions that depend entirely on the rate of accretion .

2. Cosmic Recycling: Fallback Accretion

An alternative scenario flips the sourcing around. Rather than stealing gas from a companion, the central compact object may be "recycling" its own debris. Astronomer Roy Kilgard, a co-author of the study, described the possibility as debris from the explosion falling back onto the very object the supernova created . This "fallback accretion" could also produce the observed brightening and dimming as material recaptured by the black hole or neutron star is heated to X-ray-emitting temperatures.

At least one remnant in the sample, SN 1957D, has a simpler explanation. First observed nearly 70 years ago, its X-ray brightening is likely caused by its high-velocity ejecta slamming into the surrounding interstellar material, converting kinetic energy into heat .

This phenomenon of long-term remnant variability may not be unique to M83. Early follow-up observations of the Whirlpool Galaxy (M51) have revealed a similar population of variable remnants, suggesting that this behavior could be a common, and previously overlooked, feature of star-forming galaxies .

A New Firecracker Near the Milky Way's Black Hole

In a separate investigation, a different team of astronomers pointed both Chandra and ESA's XMM-Newton satellite toward the turbulent center of our own galaxy. Their target was Sagittarius C (Sgr C), a dense star-forming region located just 26,000 light-years from Earth—cosmologically speaking, right next door to the supermassive black hole Sagittarius A* .

Within Sgr C, they identified a distinct "blob" of X-ray emission nestled inside a larger bubble of ionized hydrogen that surrounds a young, massive star . If confirmed as a supernova remnant, it would be one of the closest such objects ever found to the Milky Way's central black hole . The data indicate that the ejected stellar material is expanding at a velocity of roughly two million miles per hour and that the original explosion occurred only about 1,700 years ago .

The discovery was made possible by combining the high-resolution X-ray vision of Chandra and XMM-Newton with complementary radio data from the MeerKAT telescope array in South Africa and optical data from the Pan-STARRS survey . The finding offers a rare opportunity to study the life cycle of stars in the most extreme environment in the galaxy.