White Dwarf Crystallization: Discovery of a Cosmic Diamond

To us, the stars may be like cut gems, glinting coldly against the velvet darkness of the night sky. And for some of them, that may be true.

When a certain type of dead star cools, it gradually solidifies and crystallizes. Astronomers have discovered one of these in our cosmic backyard, a white dwarf composed mainly of metallic carbon and oxygen just 104 light years away, and its thermal mass profile shows that the star’s center is turning into a dense, dense “cosmic diamond”. “made of carbon and oxygen. amorphous.

These findings are detailed in the accepted paper Monthly Notices of the Royal Astronomical Society Pre-prints are available on the website arXiv.

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

“Through its association with this main sequence pair, it is the first crystallized white dwarf whose total lifetime can be limited externally, a fact we took advantage of by trying to experimentally measure the cooling delay caused by crystallization of white dwarf nuclei.”

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

For most stars — those with less than eight times the mass of the Sun, including the Sun — it’s a white dwarf.

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

The matter in white dwarfs is incredibly dense, but it’s kept from collapsing further by something called electron degeneracy pressure. No two electrons can occupy identical states, and this prevents white dwarfs from becoming more massive, as seen in neutron stars or black holes.

The white dwarf star is dim, but still glows with residual heat. Over time, they cool and are expected to evolve into so-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 one any time soon.

What we can do is identify signs of crystallization starting at the white dwarf nuclei that we see all around us.

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

This results in a kind of plateau or slow cooling of the white dwarf, which can be seen by the color and brightness of the star, making it appear smaller than it really is.

To accurately measure a star’s brightness, you have to know exactly how far it is, something that has become more possible in recent years thanks to the high-resolution star mapping performed by the Gaia mission.

This means that we can now recognize white dwarf crystallization with much more confidence.

Fenner and his colleagues have used Gaia data to search for several star systems, identifying stars whose relationships to others may be unclear.

And they found that the newly discovered white dwarf (remember this thing is very dim) is gravitationally bound to what is thought to be Three star systemlabeled HD 190412.

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

Either or not White dwarf diamond crystal Unknown The density of a white dwarf is about 1 million kilograms per cubic meter, while that of a diamond is about 3,500 kilograms per cubic meter. denser allotropes carbon present; On the other hand, there are lots of diamonds floating in the sky.

The three other stars in the system allowed the team to externally limit the age of the white dwarf — something that had never been done before for any known amorphous white dwarf.

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

By itself, dating isn’t enough to change our white dwarf crystallization models, but their discovery and proximity to Earth suggest that there may be many systems we can leverage to measure this amazing process.

“We argue that the discovery of this system at only 32 parsecs indicates that a Sirius-like system containing a crystallized white dwarf is most likely numerous. Future discoveries will allow testing of more robust white dwarf crystallization models.” the researchers wrote.

“We conclude that the discovery of the HD 190412 system has opened new avenues for understanding white dwarf crystallization.”

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