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HD 265435 is a binary system with an orbital period of about 100 min which consists of a white dwarf and a hot sub-dwarf star.
Artist’s impression of HD 265435, a binary system located approximately 1,500 light years away in the constellation Gemini. Image credit: Mark Garlick / University of Warwick.
Type Ia supernovae are important to cosmology as “standard candles”.
Their luminosity is constant and of a specific type of light, which means that astronomers can compare the luminosity they should be with what we observe on Earth, and from this, determine their distance with a good degree of precision.
By observing these supernovae in distant galaxies, astronomers combine what they know about a galaxy’s travel speed with our distance from the supernova and calculate the expansion of the Universe.
It is generally believed that a Type Ia supernova occurs when the nucleus of a white dwarf reignites, resulting in a thermonuclear explosion.
There are two scenarios where this can happen. In the first scenario, the white dwarf gains enough mass to reach 1.4 times the mass of our Sun, known as the Chandrasekhar limit.
The HD 265435 system falls under the second scenario, in which the total mass of a near binary is near or above this limit.
“We don’t know exactly how these supernovae explode, but we do know that it must be happening because we are seeing it happening elsewhere in the Universe,” said Dr Ingrid Pelisoli, astronomer in the physics department at the University of Warwick and the Institut für Physik und Astronomie at the Universität Potsdam.
“One way is that if the white dwarf accumulates enough mass from the hot sub-dwarf, so that the two orbit and come together, matter will start to escape from the hot sub-dwarf and fall onto the white dwarf. “
“Another way is that because they lose energy from the emission of gravitational waves, they will come closer until they merge.”
“Once the white dwarf gains enough mass with either method, it will become a supernova.”
Dr Pelisoli and his colleagues analyzed the light curve obtained by NASA’s Transiting Exoplanet Survey (TESS) satellite as well as data from the Palomar Observatory and the WM Keck Observatory to characterize the HD 265435 system and determine the masses of its components.
They discovered that the hidden white dwarf is as heavy as our Sun, but just slightly smaller than the radius of the Earth.
Combined with the mass of the hot sub-dwarf, which is just over 0.6 times the mass of our Sun, the two stars have the mass necessary to cause a Type Ia supernova.
Since the two stars are already close enough to begin to move closer, the white dwarf will inevitably become a supernova in about 70 million years.
Theoretical models predict that the hot sub-dwarf will contract to also become a white dwarf star before merging with its mate.
“The more we understand how supernovae work, the better we can calibrate our standard candles,” said Dr Pelisoli.
“This is very important at the moment because there is a gap between what we get from this type of standard candle and what we get by other methods.”
An article on the results has been published in the journal Nature astronomy.
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I. Pelisoli et al. An ancestor of the hot subnain-white dwarf supernova candidate Ia supernova. Nat Astron, published online July 12, 2021; doi: 10.1038 / s41550-021-01413-0
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