From the appearance of these stars, a supernova is inevitable

Sometimes loud explosions are easier to deal with when you know they’re coming. They are also easier to monitor. So when astronomers at the University of Warwick found a rare teardrop-shaped star known as HD265435, they knew they were looking at a potential new supernova waiting to happen. The only caveat – this might not happen for 70 million years.

It may be an absurdly long time in human terms, but in astronomical terms it is a blink of an eye. Fortunately, TESS, the telescope used to capture the data for the article describing the system, which was published in Nature Astronomy, doesn’t have to blink. Originally designed to capture the transits of exoplanets, TESS is particularly effective at quantifying slight drops in a star’s luminosity. Sometimes these dips are caused by planets moving in front of the star. But there are also other explanations for the drop in brightness.

Another explanation for the variation in brightness is if the star has been distorted. In the case of HD265435, it looks like a teardrop rather than the traditional spherical star fireball. So what would cause a star to warp into such a shape? The answer seems to be – another star. The star whose brightness visibly diminishes is known as the “hot sub-dwarf” – a type of star that is slightly less bright than the sun. Calculations that Dr Ingrid Pelisoli, the lead author of the article, carried out using radial velocity data from Palomar and the Keck Observatory, showed that the relatively bright hot subdwarf star was in fact probably hiding a much larger white dwarf. dark.

Considering how close the two stars are, it seems inevitable that they will end up falling into each other. They have already started to spiral around each other, spinning around each other every 100 minutes. But what makes this combination particularly interesting is the fact that one of the companions is a white dwarf.

White dwarfs are thought to cause Type 1a supernovae when their nucleus reignites, burning with a fire so bright and consistent that it helps astronomers determine how fast the universe is expanding. This can potentially occur when the total mass of the white dwarf and its surrounding stars has a total mass greater than the Chandrasekhar limit, or about 1.4 times the mass of the Sun. The combined mass of the hot sub-dwarf (about 0.6 times the mass of our Sun) and the white dwarf (similar to the mass of our Sun) exceeds this limit. As such, the system is expected to become a supernova when the mass is gravitationally crushed in the core of the white dwarf.

This system is one of the few to produce supernovae in the (relatively) near future. And this is the only one that contained a binary system of hot dwarfs and white dwarfs. Estimates of the total number of supernovae expected in a given area can be obtained both from methods of observing other galaxies and also from modeling stellar evolution. But given these estimates of how many supernovae researchers expect to occur in our own galaxy, there aren’t many candidate systems where we expect them to occur. This means that, despite the occasional discovery of systems where it’s clear this will happen, we could ultimately get some unexpected explosions.

Learn more:
University of Warwick – Star of Teardrop reveals supernova’s hidden fate
Astronomy of nature – An ancestor of the supernova Ia candidate hot dwarf white dwarf and super-Chandrasekhar
Live Science – Rare teardrop star and invisible partner doomed to explode in massive supernova
Sci-News – HD 265435 will explode as Type Ia supernova in 70 million years, astronomers say
UT – White Dwarf measured before exploding as a supernova

Main picture:
Artist’s representation of the teardrop shape of the HD265435 system.
Credit – University of Warwick / Mark Garlick