Astronomers find rare white dwarf star crystallising into hard ‘cosmic diamond’

Findings suggest there may be star systems in the cosmos that could shed more light on white dwarf crystallisation

Astronomers have found a rare white dwarf star about 104 light-years away whose core appears to be transforming into an ultra-dense “cosmic diamond.”

When some stars, such as the Sun, near the end of their life, they become what is known as a white dwarf.

A white dwarf is very hot when it forms, but since it has no source of energy, it cools down, radiating energy, and some such stars may gradually harden and crystallise.

Astronomers, including those from the University of Southern Queensland in Australia, have now found one such white dwarf which has cooled down, and its core may be transforming into a “cosmic diamond.”

In a yet-to-be peer-reviewed study, posted in the arXiv preprint server, scientists describe a white dwarf star about 104 light years away, which is primarily made up of carbon and metallic oxygen.

“In this work, we present the discovery of a new Sirius-like quadruple system at 32 parsecs distance, composed of a crystallizing white dwarf companion to the previously known triple HD 190412,” scientists wrote in the study, accepted for publication in the Monthly Notices of the Royal Astronomical Society.

For comparison, 1 parsec is equal to 3.26 light-years or roughly 206,265 times the distance from Earth to the Sun.

When stars whose mass is less than eight times that of the Sun run out of fuel, their outer stellar material is no longer held together and is thrown out, leaving behind the star’s core which collapses onto itself into an ultradense object.

As white dwarfs shine with the residual heat of the core, they cool down over time and are expected to turn into black dwarfs made of crystallised carbon.

This crystalisation process is very slow, taking nearly a quadrillion years – or a million billion years – and we may not see one such completely crystallised star yet as the Universe is only about 13.8 billion years old.

However, researchers say we can spot signs of crystallisation starting in the cores of white dwarfs in the Universe.

In this process, carbon and oxygen atoms in the core of white dwarfs stop moving, form bonds, and arrange themselves into a crystal lattice structure.

But since the crystallisation process releases energy that dissipates as heat, scientists say it may lead to slowing in the cooling of white dwarf stars, which may make them appear younger than the dead star’s actual age.

With new-age telescope’s such as the European Space Agency’s Gaia, it has become easier to determine a star’s distance away from Earth, and based on that its actual brightness and age.

Using data from Gaia space telescopes, scientists discovered a white dwarf star gravitationally tied up with a system of three stars, named HD 190412.

New observations of the white dwarf suggest it is undergoing crystallisation, and based on the other stars in the system, scientists could estimate the white dwarf’s age.

Researchers suspect the star system is around 7.3 billion years old and the crystallising white dwarf’s age could be about 4.2 billion years.

The discovery of this system in such proximity to Earth, suggests there may be many similar star systems in the cosmos that could prove useful for benchmarking the crystallisation process, scientists say.

“We propose that the discovery of this system at only 32 parsecs suggests that similar Sirius-like systems containing crystallizing white dwarfs are likely to be numerous. Future discoveries may therefore allow for stronger tests of white dwarf crystallization models,” they wrote in the study.