For the first time, astronomers have obtained visual evidence of the existence of a star that was destroyed by not one, but two supernova explosions. The discovery plays an important role in understanding how one of the most important processes in the Universe takes place.
A supernova explosion is one of the most powerful events in the Universe, releasing as much energy as the Sun produces during its entire lifetime. Most of them originate from supermassive stars that collapse at the end of their life cycle.
However, there is another mechanism for the formation of supernovae — the thermonuclear explosion of a white dwarf whose mass exceeds the Chandrasekhar limit (approximately 1.4 times the mass of the Sun). This can occur as a result of its merger with another white dwarf or during the accretion of matter from a companion star, causing its mass to exceed the critical threshold. Such supernovae are classified as type Ia.
Type Ia supernovae play an important role in astronomy. Scientists use them as standard candles to determine distances in the Universe. They are also the main source of iron on Earth, including the iron in our blood. However, despite their importance, the long-standing mystery of the exact mechanism that causes them to explode remains unsolved.
Until recently, Type Ia supernova explosions were considered to be a single event. However, recent studies have shown that at least some of them can be better explained by a double explosion caused before the star reached critical mass. In this alternative model, the white dwarf forms a layer of helium “stolen” from another star around itself, which can become unstable and ignite. This first explosion generates a shock wave that propagates around the white dwarf and inside it, causing a second detonation in the core, ultimately creating a supernova.
Modeling showed that this process would create a distinctive pattern or imprint in the still-glowing remnants of the supernova, visible for a long time after the initial explosion. The remnants of such a supernova should contain two separate calcium shells.
Until now, there has been no clear visual evidence of a double detonation of a white dwarf. But now astronomers have found it in the form of SNR 0509-67.5: a supernova remnant located in the Large Magellanic Cloud. During observations carried out with the Multi Unit Spectroscopic Explorer (MUSE) mounted on ESO’s Very Large Telescope, they managed to detect traces of calcium (marked in blue in the published image). This is compelling evidence that a Type Ia supernova can explode before the white dwarf reaches critical mass.
According to ESO
