A white dwarf star enters an age of crystallization and turns into a ‘cosmic diamond’: ScienceAlert

To us, the stars may be like cut jewels, shimmering coldly against the velvety darkness of the night sky. And for some of them, that might be kind of true.

When a certain type of dead star cools, it gradually solidifies and crystallizes. Astronomers have found one doing just that in our cosmic backyard, a white dwarf made primarily of carbon and the metallic oxygen just 104 light-years away, and its thermal mass profile indicates that the star’s center turns into a dense, solid, “cosmic diamond” made of carbon and oxygen. amorphous.

The discovery is detailed in an accepted paper Monthly Notices of the Royal Astronomical Society Pre-print is available on the website arXiv.

“In this work, we report the discovery of a new Sirius-like quadruple system at a distance of 32 parsecs, consisting of a crystallized white dwarf companion to previously known Triple HD 190412,” Type an international team of astronomers Led by Alexander Fenner of the University of Southern Queensland in Australia.

“By its association with these main sequence companions, this is the first crystallized white dwarf whose total lifetime can be constrained externally, a fact we take advantage of by trying to experimentally measure the cooling delay caused by crystallization of the white dwarf’s core.”

All things in the universe must change. Every star hanging in the sky, sparkling with light generated by atomic fusion, will one day run out of fuel for its fire and evolve into something new.

For the vast majority of stars — those less than eight times the mass of the Sun, including the Sun — that thing is a white dwarf star.

When the fuel runs out, the star’s outer matter is propelled into the surrounding space, and the remaining core, no longer supported by the outward pressure provided by fusion, collapses into a super-dense body, about the size of Earth (or the Moon!), but at a mass of 1.4 suns.

The matter in white dwarf stars is highly compressed, but it is kept from collapsing further by something called electron degeneracy pressure. No two electrons can occupy identical states, and this prevents the white dwarf from becoming more massive, as seen in a neutron star or black hole.

White dwarf stars are dim, but they still shine with residual heat. Over time, they cool and are expected to evolve into what are called black dwarf stars when they lose all their heat and become a cold mass of crystallized carbon.

Calculations show that this process takes almost too long quadrillion years (that’s a million billion years ago); Since the universe is only 13.8 billion years old, we don’t expect to find it any time soon.

What we can do is identify signs of crystallization that start in the cores 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 into a crystal lattice. Energy is released during this process, which is dissipated in the form of heat.

This results in a kind of plateau or slowdown in the cooling of white dwarf stars, which can be seen in the star’s color and brightness, making it appear smaller than it actually is.

In order to accurately measure a star’s brightness, you must know precisely how far away it is, something that has become more possible in recent years due to the high-resolution stellar mapping conducted by the Gaia mission.

This means that we can now more confidently recognize the crystallization of white dwarfs.

Fenner and his colleagues have been using Gaia data to search for multiple star systems, by identifying stars whose association with others may be unclear.

And they found that a recently discovered white dwarf star (remember this stuff is very dim) was gravitationally bound to what was thought to be Three star systemlabeled HD 190412.

The discovery of the white dwarf, now named HD 190412 C, made the triplet a quadruple, but there was more going on. Its properties indicate that it undergoes a crystallization process.

Be it or not White dwarf diamond crystal Unknown The density of white dwarfs is about 1 million kilograms per cubic meter, while the density of diamonds is about 3500 kilograms per cubic meter. more dense allotropes of carbon are present; On the other hand, there are a lot of diamonds floating around in space.

The other three stars in the system allowed the team to externally constrain the white dwarf’s age — something that had not been done before for a known amorphous white dwarf.

The age of the system is about 7.3 billion years. The age of the white dwarf appears to be about 4.2 billion years. The researchers say the discrepancy is 3.1 billion years, which indicates that the crystallization rate has slowed the white dwarf’s cooling rate by about a billion years.

By itself, dating isn’t enough to change our models of a white dwarf’s crystallization, but the discovery and its proximity to Earth suggest there may be many such systems that we can exploit to measure this fascinating process.

“We suggest that the discovery of this system at only 32 parsecs indicates that Sirius-like systems containing crystallized white dwarfs are likely to be numerous. Future discoveries may thus allow stronger tests of white dwarf crystallization models,” write the researchers.

“We conclude that the discovery of the HD 190412 system has opened a new avenue for understanding the crystallization of white dwarfs.”

Search accepted Monthly Notices of the Royal Astronomical Societyand is available at arXiv.