Two Stars Orbited Each Other, Then Both Exploded. Astronomers Just Found the Wreckage Side by Side.

Astronomers have found what appears to be the first known case of a binary star system in which both stars exploded as supernovae, leaving two remnants sitting next to each other in the same patch of the Milky Way.

One of them is famous. IC 443, the Jellyfish Nebula, is a tangle of glowing filaments in the constellation Gemini about 6,000 light-years from Earth, and it has been photographed by amateur and professional observatories for decades. The other, G189.6+3.3, is faint, sprawling and easy to miss — it overlaps the Jellyfish on the sky and has generally been treated as an unrelated object that happens to lie along the same line of sight.

A team led by Miltiadis Michailidis at the W.W. Hansen Experimental Physics Laboratory argues that the two are related by birth. The work, published July 21 in Nature Communications under the title "Shared cloud interactions unveil a candidate binary-system supernova pair with no known analogue," combines 16 years of observations from the Fermi Large Area Telescope with X-ray data from eROSITA and a stack of complementary multiwavelength measurements.

The decisive move was to stop looking in radio light, where the two remnants blur into each other, and look in gamma rays instead. Supernova remnants glow in gamma rays where their expanding shock fronts slam into dense interstellar gas. Both IC 443 and G189.6+3.3 show that signature, and critically, they show it against the same molecular cloud. Two remnants plowing into the same body of gas have to be at the same distance from Earth and physically adjacent, not merely aligned by chance.

The team also worked out the sequence. The star that produced G189.6+3.3 blew up somewhere between 20,000 and 100,000 years before the one that produced IC 443 — a gap that fits comfortably within the lifetimes of two massive stars born together but with slightly different masses. The heavier star burns through its fuel first and dies first; its companion follows tens of thousands of years later.

To test whether the arrangement could be coincidence, the researchers simulated a million binary systems and ran a statistical comparison against the observed geometry. The odds of a chance alignment came out below one in 1,000.

Massive stars are overwhelmingly born in pairs or larger groups, so double supernovae from a single system should be common in principle. The reason none has been identified before is practical: the first remnant typically fades below detectability long before the second star explodes, and even when both survive, telling them apart requires exactly the kind of multi-instrument evidence assembled here. The Jellyfish and its sibling give astronomers a template for finding others.