For the first time, astronomers have found evidence that two massive stars in a binary system both exploded as supernovae, leaving behind a pair of visible remnants in the Milky Way. The discovery, published in the journal Nature Communications, was led by Miltiadis Michailidis, a postdoctoral researcher at Stanford University. The two remnants are IC 443, known as the Jellyfish Nebula, and a second, less famous remnant designated G189.6+3.3. Both lie about 6,000 light-years from Earth in the constellation Gemini.

According to Michailidis, the probability of finding two unrelated supernova remnants so close together by chance is about one in 1,000, indicating that they are a genuine pair from a binary system. The team believes the star that produced IC 443 was 15 to 25 times the mass of the Sun, while its companion, which formed G189.6+3.3, was at least 20 solar masses. During their lives, both stars were likely tens of thousands of times more luminous than the Sun. After exploding, each probably collapsed into a dense neutron star.

The two explosions did not occur simultaneously. The older star, associated with G189.6+3.3, exploded between 20,000 and 110,000 years ago. Its partner exploded later, forming IC 443 roughly 8,000 to 9,000 years ago. The researchers were guided by more than 16 years of observations from NASA’s Fermi Gamma-ray Space Telescope. Michailidis noted that while most massive stars are born in binary systems, no pair in which both stars had exploded and left observable remnants had previously been identified.

Michailidis said the system offers a rare opportunity to reconstruct the full evolutionary history of a massive binary, from birth and interaction through both supernova explosions to the remnants left behind. He added that until now, understanding of these final evolutionary stages relied almost entirely on theoretical models and numerical simulations. The discovery provides direct observational constraints on how the presence of a binary companion alters the evolution of massive stars, a key open question in stellar astrophysics.