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Astronomy: Possible binary supernova system *IMAGES*

The detection of what may be the remnants of a companion to the star that exploded to form IC 443 (also known as the Jellyfish nebula) is reported in Nature Communications. The findings, supported by multiple lines of evidence, indicate that this is the first known candidate binary star system in which both stars have undergone supernova events.

Supernova remnants are expanding clouds of debris left behind after supernova (stellar explosions). While hundreds of such remnants are known in our galaxy, identifying relationships between them is difficult, particularly in crowded regions of the Milky Way. One well-studied example is IC 443, a remnant located in the constellation Gemini approximately 6,000 light-years from Earth. It sits close to other astronomical structures and within a complex cloud of gas and dust, making its surrounding region difficult to study.

Miltiadis Michailidis and colleagues combined 16 years of observations from the Fermi Large Area Telescope gamma-ray observations with eROSITA X-ray and complementary multiwavelength data. Using this data, the authors are able to establish that the recently-discovered supernova remnant G189.6+3.3 occupies the same physical environment as IC 443, indicating that the two exist in close proximity and at approximately the same distance from Earth. The age estimates suggest that the parent star of G189.6+3.3 exploded between approximately 20-100,000 years before the explosion that created IC 443. Validation of these measurements using statistical analysis and simulations suggest that this configuration is highly unlikely to be a chance alignment, suggesting that the two stars that preceded these remnants were born together in a binary system.

This discovery has the potential to provide new insights into our understanding of both supernova and binary star systems.