First visible evidence of a double explosion of a white dwarf star
According to a fairly new theory, white dwarfs can explode twice in a row in certain circumstances. For the first time, we now have visual proof.
The Supernova remnant SNR 0509-67.5
(Image: ESO/P. Das et al. Background stars (Hubble): K. Noll et al.)
An international research team has succeeded for the first time in providing visual proof that white dwarf stars can explode twice at their end. As the European Southern Observatory ESO writes, this was achieved using images of the supernova SNR 0509-67.5 taken with the Very Large Telescope (VLT). These show a pattern that can be explained by the fact that the star has experienced two detonations at its end. This also sheds new light on certain stellar explosions, which are of central importance for the study of the universe.
(Image:Â ESO/P. Das et al.)
First evidence for young theory
According to the ESO, these are so-called type Ia supernovae. According to the most widespread theory, these occur in binary star systems, in which one white dwarf star extracts matter from the second until it swells to a critical mass and dies in a single explosion. Recently, however, there have been indications that the white dwarf can also form a shell of helium around itself, which can become unstable and ignite. This explosion in turn creates a shock wave that triggers a detonation in the core of the white dwarf – together, in other words, a “double detonation mechanism”. However, there has been no evidence for this model so far. This has now changed.
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As the team explains, the models for the double detonations show that their remnants should have two separate shells of calcium. The researchers have discovered precisely this fingerprint in SNR 0509-67.5. This is a clear indication that white dwarfs can explode before they have reached the so-called Chandrasekhar mass limit – only then twice. And even if this is of great importance for astronomy, the observation is also valuable for another reason: it is a “visual spectacle” from a “beautifully layered structure”, says study leader Priyam Das from the University of New South Wales Canberra in Australia.
Type Ia supernovae are considered standard candles in astronomy. They behave very predictably, and their consistent brightness makes it possible to measure distances over particularly large distances. This is one of the reasons why it was discovered that the universe is expanding faster and faster. The better we understand their formation, the better we should be able to find out why they have this predictable brightness. The visual detection of the double detonation is now an important building block in this process. It will soon be presented in a scientific article in the journal Nature Astronomy.
(mho)
