The sun and other not too large stars end their lives, turning into white dwarfs. They are gradually cooling down, but so slowly that this process can take trillions of years until the former star cools down to the state of a black dwarf. The Universe itself is too young for this, and it is possible that no such object has yet appeared in it. Recently, however, Australian astronomers spotted a white dwarf in transition, fueled by the crystallization of cooling matter. Their paper has been accepted publications In the magazine Monthly Notices of the Royal Astronomical Society.
When the resources for fusion run out, the star dies. Its further fate depends on the mass; medium-sized stars become white dwarfs. They shed their outer shells, and the core, which no longer supports the internal pressure of thermonuclear reactions, collapses. The resulting compact and superdense object is saturated with relatively heavy elements such as carbon, which were formed during the past life of the star.
By stellar standards, white dwarfs are dim, but they continue to radiate, gradually dissipating heat, until they turn into black dwarfs. No such object is yet known: theory predicts that the process takes an incredible amount of time, perhaps up to hundreds of billions and trillions of years. However, signs of such a transition were recently discovered by Alexander Venner (Alexander Venner) and his colleagues from the University of South Queensland, and relatively close to Earth.
The cooling of a white dwarf must be accompanied by the crystallization of its matter. Carbon and oxygen atoms cease to flow freely and are laid out in an ordered lattice, in a state with less energy. This process proceeds with the release of heat, additionally slowing down the cooling of the white dwarf. As a result, his temperature should not correspond to his real age. A few years ago, a massive survey of white dwarfs confirmed that many of them are much hotter than they should be.
A similar picture was observed by astronomers in the HD 190412 system, located at a distance of just over a hundred light years from us. It was known to include three “ordinary” stars main sequence, but new observations have shown that a white dwarf, gravitationally associated with them, also rotates right there. Scientists estimate the age of the system itself at 7.3 billion years, and the temperature of the dwarf corresponds to the age of 4.2 billion years.
These estimates are rather approximate, but whatever the difference, it indicates the processes of crystallization of matter taking place in the depths of the dwarf. Moreover, the fact that it was found so close to the Sun may indicate that such objects must be quite numerous. It is possible that soon new white dwarfs will be found, gradually turning into black ones.
