The HD265435 system is about 1,500 light-years away from us and contains two stars: a giant white dwarf and a very mild hot sub-dwarf. The two stars are gravitationally linked and astronomers predict that this binary will experience a dramatic evolution over a few tens of millions of years as the white dwarf explodes in a Type 1a supernova.
White dwarfs are not stars in the classical sense. They do not glow, but warm and cool very slowly over billions of years. These stars represent the final stages of the evolution of Sun-like mass stars that, after consuming all their fuel, inflate disproportionately and explode forming a planetary nebula. At the center of which would be the bare core of the ancient star, the white dwarf. These stars can “reign” and explode with tremendous energy to form a Type 1a supernova. These supernovae occur in binary systems when the white dwarf has a companion star that can siphon matter up to A mass limit, called the Chandrasekhar limit, is equal to 1.44 solar masses. In addition, the white dwarf becomes unstable and explodes. It would contain nothing but a giant bubble of particles heated to millions of degrees called a supernova slush. Another mechanism produces a similar effect: when two stars in a binary system are very close and eventually merge.
The scenario for the HD265435 system is not entirely clear, but it is almost certain that the white dwarf will end its life as a supernova 1a in about 70 million years. Indeed, astronomers were able to observe the hot sub-dwarf with the TESS space telescope and show that it had been deformed into a teardrop shape by a massive object, the white dwarf, which is too dim to be visible. Complementary measurements carried out with the Palomar Observatories in California and WM Keck in Hawaii determined that the hot sub-dwarf weighed more than 0.6 solar masses and the white dwarf was roughly the mass of the Sun. The estimated mass of the entire system is 1.65 solar masses which exceeds the limit of Chandrashekhar.
Standard candles and gravitational waves
So the two stars have the material needed to cause a Type 1a supernova. But the simulations done for this study, published in the journal nature astronomy, indicates that the hot sub-dwarf will turn into a white dwarf even earlier. Then the two stars must merge by emitting gravitational waves and then exploding in a supernova. It is also possible that the large white dwarf will build up enough mass to explode on its own before fusion. Observing this supernova ancestor will make it possible to better understand the mechanisms that lead to these explosions which are of great importance in cosmology.
Indeed, astronomers use them as “standard candles” to calculate distances in the universe. All white dwarfs of similar mass, before exploding in a supernova, make it possible to establish the difference between absolute brightness and apparent brightness and therefore use them as benchmarks. It was in order to calculate the slowdown in the expansion of the universe that the 2011 Nobel Prize winners in physics began extensive observations of type Ia supernovae, eventually finding the opposite: a mysterious dark energy would have accelerated the expansion of the universe. is.