Tour: NASA's Chandra Finds Unexpected Fireworks in Aftermath of Stellar Explosions

The aftermath of a stellar explosion should be a slowly fading cloud of hot gas. So when astronomers pointed NASA's Chandra X-ray Observatory at the nearby galaxy M83, the last thing they expected to find was a population of supernova remnants appearing to dramatically change in brightness.

The new results were made possible by analyzing Chandra data of the galaxy Messier 83, or M83, that span 14 years from 2000 to 2014. Stars are forming at a high rate in M83 and the galaxy is about 15 million light-years from Earth.

Using this extensive set of data, the researchers caught surprising variations in the X-ray brightness of sources previously identified as supernova remnants, the debris from supernova explosions. Supernova remnants older than a century or so will fade gradually in X-rays, but they should not dramatically change in brightness.

The team found that roughly half of the X-ray sources associated with supernova remnants in their sample showed changes in X-ray brightness over the 14-year span of observations — a result that was completely unexpected.

While researchers knew that individual X-ray sources could vary dramatically, it was surprising to find that so many supernova remnants were behaving this way. Pinpointing the cause remains a challenge, however, since M83's distance limits the detail astronomers can observe.

The most likely explanation is that the team has uncovered a population of stellar survivors — stars that lived through their partner's destruction in a supernova explosion. In this scenario, each variable X-ray source began as a pair of massive stars orbiting each other. The more massive star collapsed and exploded as a supernova, leaving behind a black hole or ultra-dense neutron star. Its companion survived.

These results are not unique to M83. A follow-up study of the nearby star-forming galaxy Messier 51 has uncovered a similar population of variable X-ray sources associated with supernova remnants, suggesting that such systems may be a feature of galaxies undergoing vigorous star formation. Astronomers will continue to look at these and other galaxies to investigate these sources further.