To us, the stars may look like faceted gemstones that gleam coldly in the velvety darkness of the night sky. And for some, that may be true. A certain type of dead star slowly hardens and crystallizes as it cools. Astronomers have found that just 104 light-years away in our cosmic backyard, a white dwarf composed mostly of carbon and metallic oxygen, whose temperature-mass profile suggests the center of the star has turned into a dense, solid, cosmic diamond, does just that. “It consists of crystallized carbon and oxygen.

Details of the discovery are described in an accepted article. Monthly Notices of the Royal Astronomical Society and available on the arXiv preprint website.

“In this paper, we present the discovery of a new Sirius-like quadruple system at a distance of 32 parsecs, consisting of the crystallized white dwarf satellite of the previously known triple HD 190412,” writes an international team of astronomers led by the university. Alexander Wenner. South Queensland in Australia.

“Because of its association with these main sequence moons, this is the first crystallizing white dwarf whose total age can be externally limited, and we use this fact to try to empirically measure the cooling delay caused by crystallization of the white dwarf’s core.”

Everything in the universe has to change. Every star hanging in the sky, shining with the light created by atomic fusion, will one day run out of fuel for its fire and turn into something new. For the vast majority of stars—those with about eight times the mass of the Sun, including the Sun—that thing is a white dwarf.

When the fuel runs out, the star’s outer material is ejected into the surrounding space, and the remaining core, no longer supported by the external pressure created by fusion, will collapse into a superdense object the size of the Earth (or Moon). ). !), but has the same mass as the 1.4 Sun.

Matter in white dwarf stars is highly compressed, but its further collapse is hindered by something called electron degeneracy pressure. No two electrons can occupy the same states, and this prevents the white dwarf from becoming even denser, as in a neutron star or black hole.

White dwarf stars are dim, but continue to glow with residual heat. They cool over time and are expected to turn into something called a black dwarf when they lose all their heat and become a cold chunk of crystallized carbon.

Calculations show that this process took a very long time, about a quadrillion years (that’s a million billion years); Since the universe is only about 13.8 billion years old, we don’t expect to find it anytime soon. What we can do is detect signs of crystallization starting in the nuclei of the white dwarfs we see around us.

During crystallization, the carbon and oxygen atoms inside the white dwarf stop moving freely and form bonds, arranging themselves in a crystal lattice. During this process, energy is released, which is dissipated in the form of heat.

This creates a certain plateau or cooling slowdown that can be seen in the color and brightness of the star in white dwarfs, making it appear younger than it actually is. To accurately estimate the brightness of a star, you need to know exactly how far away it is, which has become much more possible in recent years thanks to the high-precision mapping of stars by the Gaia mission. This means we can now identify crystallized white dwarfs with much greater confidence.

Wenner and his colleagues used the Gaia data to search for several star systems and identified stars with unclear connections to others. And they discovered that a newly discovered white dwarf star (remember, these things are very faint) is gravitationally bound to something thought to be a triple star system called HD 190412. The discovery of the white dwarf, now called HD 190412 C, turned the trio into four, but something else was happening. Its properties indicate that it has undergone a crystallization process.

It is unknown whether the white dwarf crystal is a diamond; White dwarfs have a density of about 1 million kilograms per cubic meter, while diamond has a density of about 3,500 kilograms per cubic meter. There are denser carbon allotropes; On the other hand, there are a lot of diamonds floating in space.

The other three stars in the system allowed the team to constrain the white dwarf’s age externally; this was something that had not been done before for a known crystallizing white dwarf. The age of the system is about 7.3 billion years. The age of the white dwarf is about 4.2 billion years. The researchers suggested that the discrepancy was 3.1 billion years, and that the rate of crystallization slowed the cooling rate of the white dwarf by about 1 billion years.

Dating alone isn’t enough to change our models of white dwarf crystallization, but the discovery and its proximity to Earth suggest that there may be many more similar systems we can use to compare this fascinating process.

“We propose that the detection of this system at just 32 parsecs suggests that similar Sirius-like systems containing crystallizing white dwarfs may be numerous. Therefore, future discoveries may allow for more robust tests of white dwarf crystallization patterns,” the researchers write.

“We conclude that the discovery of the HD 190412 system opens up a new avenue for understanding crystallizing white dwarfs.” Source