Most supernovae are fiery finales for giant stars. But one powerful type, the Type Ia supernova, comes from a quiet leftover: a white dwarf, the burnt-out core of a sun-like star. When this tiny relic explodes, it leaves a huge cosmic impact. It helps astronomers measure how the universe is expanding. Also, it’s the reason we have iron on Earth, even the iron in your blood.
But here’s the twist: scientists still don’t know exactly what triggers these explosions, making white dwarfs one of space’s most mysterious spark plugs.
Usually, Type Ia supernovae happen when a white dwarf star slowly steals material from a nearby companion until it gets too heavy and explodes. But scientists have long suspected that some of these stars might explode twice, a smaller blast first, followed by a bigger one.
Now, they’ve captured the first visual proof: the ancient remnants of a supernova called SNR 0509-67.5 show signs of this “double-detonation.” Using the European Southern Observatory’s giant telescope, researchers discovered patterns confirming that the star exploded in two separate bursts.
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In this alternate supernova story, a white dwarf star snatches helium from its companion and wraps itself in a fiery blanket. When that helium gets unstable, it ignites in a first explosion, sending a shockwave that rushes around and dives inward. That shock sets off a second blast in the star’s core, causing a powerful double detonation, a cosmic chain reaction that ends in a supernova.
Astronomers had long suspected that some white dwarfs explode twice—once on the surface, then in the core. But until recently, there was no clear visual proof.
New predictions suggested this explosive duo would leave behind a unique fingerprint: two glowing shells of calcium lingering in the remains of the supernova, like cosmic echoes of each blast. Now, astronomers have spotted just that, offering the first real glimpse into the dramatic double-detonation of a dying star.
Astronomers have finally spotted the long-predicted “fingerprint” of a double-detonation supernova: two distinct calcium layers in the remains of SNR 0509-67.5. Using the powerful MUSE instrument on ESO’s Very Large Telescope, they confirmed that white dwarfs can indeed explode before reaching the Chandrasekhar limit, the mass once believed necessary for a Type Ia supernova.
This discovery shows that a white dwarf wrapped in helium can first ignite that helium, sending a shock inward that triggers a second explosion, proving the double-blast theory happens in nature.
Priyam Das, a PhD student at the University of New South Wales Canberra, Australia, who led the study on SNR 0509-67.5, said, “This tangible evidence of a double-detonation not only contributes towards solving a long-standing mystery but also offers a visual spectacle.”
Journal Reference:
- Das, P., Seitenzahl, I.R., Ruiter, A.J., et al. Calcium in a supernova remnant as a fingerprint of a sub-Chandrasekhar-mass explosion. Nat Astron (2025). DOI: 10.1038/s41550-025-02589-5
