Chandra X-ray Observatory Finds Supernova Remnants Flickering Unexpectedly in M83

For decades, the death of a massive star was thought to be a grand but predictable fade to black. After the initial supernova explosion, the leftover cloud of hot gas and debris—known as a supernova remnant—was expected to simply cool and dim over centuries. But a new 14-year survey of the nearby spiral galaxy Messier 83 (M83) is turning that assumption on its head.

Using data from NASA’s Chandra X-ray Observatory, researchers identified 22 X-ray sources linked to supernova remnants in M83. They found that roughly half of these remnants are not fading quietly. Instead, they are flickering—brightening and dimming dramatically over timescales of years .

"We know that individual X-ray sources can vary wildly, but finding that so many supernova remnants are doing this was a real surprise," said Andrea Prestwich, an astronomer at the Catholic University of America who led the study. "Something unusual is definitely happening inside these objects" . The findings were presented at a meeting of the American Astronomical Society and published in The Astrophysical Journal .

The mystery of the restless remnants

Supernova remnants are typically hundreds or thousands of years old. As the initial shockwave from the explosion runs out of energy, the hot gas should radiate away its X-rays and grow steadily dimmer. The population in M83, located about 15 million light-years from Earth, is not following the script .

Of the 22 X-ray-emitting remnants analyzed over the 14-year observation window (from 2000 to 2014), around half showed measurable changes in brightness. This was not a subtle flicker; the variations were significant enough to be obvious in the data, with some sources brightening and fading by substantial amounts over irregular intervals .

Only one of the variable remnants has a straightforward explanation. Designated SN 1957D, this remnant was observed ramming its high-speed debris into a dense region of surrounding gas. The collision is producing a burst of shock-heated material and extra X-ray emission, explaining its flares. For the other more than ten flickering remnants, the cause is less clear .

Stellar zombies: Binaries and fallback accretion

The research team has put forward two primary theories for the mysterious flickering, both of which suggest these are not simply "dead" stars but systems still actively consuming material.

Surviving companion star scenario: Many massive stars are born in binary pairs. When the more massive of the two explodes, it can leave behind a dense compact object—a neutron star or black hole—while its companion remains intact. The remnant's gravity can then pull stellar material away from the surviving companion. As this gas spirals in, it heats up to millions of degrees, creating a powerful X-ray binary system. The unpredictable rate of this material transfer could cause the observed flickering .

Fallback accretion: Instead of a donor star, the newly formed black hole or neutron star might be recapturing a portion of the debris that was blasted outward in the original supernova. This "cosmic recycling," where some material fails to escape the gravitational pull and falls back onto the central object, would likewise produce variable X-ray emissions .

These explanations are not mutually exclusive, and it is possible that both processes are at work among the different remnants in the sample. The evidence for the binary-star theory is strengthened by the locations of the flickering remnants—they are found in pockets of M83 that have higher concentrations of massive young stars, exactly where high-mass X-ray binaries would be expected .

A similar surprise in another galaxy

M83 is not an isolated case. A follow-up study of the Whirlpool Galaxy (M51) has revealed a comparable population of variable X-ray sources associated with supernova remnants. The discovery of this pattern in a second star-forming galaxy suggests that flickering remnants may be a common, previously overlooked phase of stellar afterlife in the universe .

Bonus discovery: A supernova next door to a black hole

In an unrelated but equally fascinating finding, Chandra and the European Space Agency’s XMM-Newton satellite uncovered evidence for a supernova remnant in one of the most extreme environments imaginable. The wreckage was found near Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, some 26,000 light-years from Earth .

The astronomers estimate that the star that created this debris exploded a relatively recent 1,700 years ago. The resulting remnant, located near a region called Sagittarius C, is expanding at roughly 2 million miles per hour. If the identification is confirmed, this would be the closest supernova remnant ever discovered to our galaxy’s central black hole .

The discovery, also published in The Astrophysical Journal, places a stellar explosion in a violent neighborhood dominated by extreme gravity, dense magnetic fields, and clouds of gas being whipped around at high speeds. Studying a remnant in this environment gives astronomers a unique laboratory for understanding how matter behaves in the most powerful gravitational fields in the universe .