One of the stars in the HD 190412 quadruple system, about 100 light-years distant from Earth, is turning to diamond. It is the smallest of the four stars in the group, a white dwarf composed mainly of carbon and metallic oxygen and inside which a nuclear fusion furnace no longer burns. For this reason, and as it cools, the core of the small star hardens and crystallizes, transforming itself into a dense and hard ‘cosmic diamond’. The extraordinary finding, which will soon be published in the Monthly Notices of the Royal Astronomical Society, can now be consulted on the prepublication server axXiv.
“In this work – write the scientists, led by Alexander Venner of the University of Southern Queensland in Australia – we present the discovery of a new Sirius-like quadruple system, 32 parsecs away, composed of a crystallizing white dwarf. which is a companion to the previously known HD 190412 triple system.”
When most stars (all those with less than eight solar masses, including our Sun) run out of fuel, they tend to eject their outer layers into space while their core, already quenched and thus unable to withstand the pressure of gravity collapses into a very small object (the size of the Moon or the Earth), but of enormous density. It is what is known as a ‘white dwarf’.
The matter that white dwarfs are made of, then, is extraordinarily compressed, although there is something called ‘radiation pressure’ that prevents them from being compressed even more. Two electrons, in fact, cannot occupy the same orbit around an atomic nucleus, and this prevents the white dwarf from degenerating into something even smaller and denser, like a neutron star or a black hole.
Thus, in that state, still hot and sporting a dim afterglow that fades with time, like an ember that is getting colder, white dwarfs can endure for untold billions of years. Eventually, when they lose all their heat, they will become ‘black dwarfs’, cold objects made of crystallized carbon. Something that, by the way, no one has yet seen for the simple reason that the Universe is not old enough. In other words, not enough time has elapsed for something like this to happen. The most recent calculations, in fact, suggest that black dwarfs will not come into existence for about a million trillion years (a trillion years), which is infinitely more than the current age of the Universe (13.7 billion years). .
The only thing we can do for now, therefore, is to identify the signs of crystallization in the cores of the white dwarfs around us.
During crystallization, the carbon and oxygen atoms of white dwarfs stop moving freely and form bonds, organizing themselves into a crystal lattice. The energy released during this process is dissipated in the form of heat, which causes a kind of ‘slowdown’ or slowdown in the cooling of these stars, observable in their color brightness, which makes them appear younger than they really are.
an unexpected find
Venner and his team were using data from the Gaia mission to study multiple star systems when they noticed the existence of a white dwarf gravitationally bound to the triple star system called HD 190412. The discovery of the white dwarf, now named HD 190412 C, suddenly turned the triple system into a quadruple one.
But there was more. The new star showed a series of properties that suggested that it was in the process of crystallization. For now it is unknown if this crystal is diamond or not, since the density of white dwarfs is around 1 million kilograms per cubic meter, while the density of diamond remains at about 3,500 kilograms per cubic meter. But there are allotropes of carbon denser than that, and many diamonds have already been observed floating in space.
The study of the other three stars in the system allowed the researchers to calculate the age of the white dwarf, something that had never been done with a star of this type in the process of crystallizing and which turned out to be about 4,200 million years, much less to the age of the entire system, estimated at about 7.3 billion years. The discrepancy, of 3.1 billion years, indicates that the rate of crystallization has slowed the rate of cooling of the white dwarf by about 1 billion years, the researchers say.
The discovery and its proximity to Earth suggest that there could be many more such systems for astronomers to explore to better understand this fascinating process. That is to say, that in the very distant future, if the Earth still exists, there will be numerous ‘diamond stars’ in the surroundings. Although none of us will be here to see them.
