Rare double supernova discovered hidden in the Jellyfish Nebula

For decades, astrophysicists have wondered about a mystery hidden in plain sight: Most supernovae originate from the largest stars, and most of the largest stars in our galaxy are thought to be in multi-star systems. Yet no one had ever found two supernovae occurring in a single multi-star system – until now.

This newly discovered system is composed of one of the most studied supernova remnants in our galaxy, IC 443 (the Jellyfish Nebula), and a second, fainter remnant, called G189.6+3.3, hidden nearby. IC 443 shines so brightly that it obscures this second remnant, which only proved detectable thanks to reams of old data and new observations from new, extremely sensitive space telescopes.

Astronomers typically search for supernova remnants – neutron stars and occasional black holes, as well as their energy-ravaged surroundings – thanks to the shock waves left behind by their catastrophic birth. Such shock waves occur when the core of a massive star runs out of fuel, implodes, and blows the rest of the star to smithereens. To discover the shock waves from this supernova duo, astronomers relied on two subtle signatures: a spherical shell structure composed of debris and the glow of ejected stellar material projecting into the surrounding interstellar gas.

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In 2023, a team using eROSITA, an X-ray telescope launched in 2019, found evidence of a plasma shell structure heated to more than eight million degrees Celsius, but the telltale glow remained elusive. Glow commonly appears in radio signals; However, the G189.6+3.3 did not have a radio signal corresponding to the entire structure of the shell. The evidence was too ambiguous to constitute “compelling proof” of a second supernova remnant.

A breakthrough came when astronomers instead looked for the glow of gamma rays (a form of light with higher energy than radio waves). Using 16 years of data from NASA’s Fermi Gamma-ray Space Telescope, a team led by Miltiadis Michailidisa Stanford University astronomer and lead author of the study, discovered a complex gamma glow that traces the X-ray shell, indicating that G189.6+3.3 is, in fact, the remnant of a supernova. Details have been released In Natural communications.

But it’s not just any supernova remnant. Looking further into the gamma ray data, the team discovered that the northern part of the remains emitted a completely different signal than the rest of the region. This divergence, they say, indicates where two different types of particles release gamma rays within the expanding shock waves. And researchers say this idea provides powerful clues about how these double supernovae came to be.

It appears that most of G189.6+3.3 is in a relatively matter-poor volume of space, so the gamma-ray glow comes from electrons accelerated by the shock waves that permeate this region. The northern part of the remnant, however, is illuminated by gamma rays from accelerated protons, indicating that the shock interacts with a dense cloud of ionized hydrogen gas called the S249 H II region. This cloud turns out to be the same one that astronomers already knew interacted with the Jellyfish Nebula, strongly suggesting that these two remnants are true neighbors rather than separate, distant objects that simply appear close together in Earth’s sky.

In subsequent computer simulations, the team established a plausible sequence of events: the two objects began as a pair, each a short-lived massive star bound to the other by their respective gravity. When the first star exploded, the force of the explosion sent the second star flying into space. It traveled far enough that when the second star exploded, this second supernova did not combine with the remains of the first. Furthermore, “the two supernova explosions occurred on a reasonably short astronomical time scale” several thousand or tens of thousands of years apart, it is said. Mikako Matsuuraan astronomer at Cardiff University in Wales, who was not involved in the study.

By so conclusively linking these two supernovae, scientists can now measure the timing and distance between them and use them to directly calculate, for the first time, not only the energy of a supernova, but also how that energy propagates through its surroundings and sends stellar shrapnel zooming into deep space. This, in turn, can help refine our overall understanding of star and galaxy formation.

The study also has major implications for the study of binary star systems. “We only have theoretical models on the evolution of binaries and the different stages of the star’s evolution,” explains Michailidis. These models can now be verified against real physical observations.

Furthermore, these binary supernova remnants “could reproduce the conditions [that existed] “at an early age in the universe,” says Matsuura, when the cosmos was smaller and filled with more short-lived, constantly interacting massive stars. A closer look at this new system could therefore reveal more about the lives and deaths of these earlier, now-extinct stars.

As a next step, the team now plans to search for other binary supernova remnants. With more examples in hand, they hope to refine their theoretical models to better predict how and where these strange systems appear and evolve in the Milky Way and across the universe.