June 8, 2023


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This spinning white dwarf is about to explode. It could revolutionize our understanding of supernovae

The answer to this question is: not necessarily. Imagine that this sun-like star is a component of a binary system in which two stars orbit a common center of mass. One of the stars passes into the white dwarf stage and is still in a system with the other main sequence star. Under the right conditions, when the second star becomes a red giant and its outer shell is less gravitationally bound to the star, the outer layer of gas can begin to fall onto the white dwarf’s surface.

Too heavy a white dwarf will explode. Always at the same moment

This situation causes the white dwarf’s mass to increase. The situation is stable until the dwarf’s mass reaches the equivalent of 1.44 solar masses. At this point, after crossing the so-called Chandrasekhar limit, conditions on the dwarf’s surface lead to the initiation of thermonuclear reactions and the explosion of a Type Ia supernova. So it turns out that the white dwarf may have another moment of amazing glow after the death of its star.

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A team of scientists from the Max Planck Institute in Garching, Germany, described V Latest scientific article A binary system consisting of a red giant and a white dwarf. This system emitted a surprising amount of ultra-soft X-rays. This radiation is emitted in the process of fusion on the surface of the white dwarf. What is unusual about this particular case is the gas that is burning on the surface of the white dwarf.

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ESO’s VISTA telescope reveals a remarkable image of the Large Magellanic Cloud, one of our closest neighboring galaxies. VISTA is surveying this galaxy and its sister galaxy, the Small Magellanic Cloud, as well as the regions around it, in unprecedented detail. This survey allows astronomers to observe a large number of stars, opening up new opportunities to study stellar evolution, galactic dynamics, and variable stars.

The white dwarf is burning helium, not hydrogen, on its surface. The system’s brightness indicates that the white dwarf’s mass is growing very slowly, in fact even slower than was thought.

At the end of the 20th century, with the help of the ROSAT satellite, astronomers discovered the first sources of soft X-rays, on the surface of which hydrogen was burned. Scientists then concluded that it is such systems that give rise to Type Ia supernova explosions. There was only one problem with this theory: While these systems burn hydrogen, there is no hydrogen in Type I supernovae.

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Therefore, an alternative from that time was binary systems, in which hydrogen falls on a white dwarf, and helium burns on its surface. Here, in turn, the problem was that there was no observational confirmation that such things ever existed. Now, however, that has changed.

The first white dwarf with a helium envelope

Interestingly, this object [HP99] 159 has been known to astronomers for decades. Over the years, the emitted X-rays have been monitored by the ROSAT, XMM-Newton, and now eROSITA satellites. Moreover, scientists have now succeeded in combining an X-ray source with its optical counterpart. It turned out to be a binary system located in the nearby dwarf galaxy – the Large Magellanic Cloud. But the most interesting thing is that the spectrum of this body is dominated by helium.

Are we dealing with a real object that will soon explode as a Type Ia supernova? The short answer to this question is: it’s complicated. Standard type Ia supernovae do not contain as much helium as in a theoretical system explosion [HP99] 159. However, astronomers also note that there is a small group of supernovae called Type Iax supernovae, which are slightly less exciting and spew less helium into space.

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