White dwarf is turning into a giant 'diamond'

Astronomers have discovered a white dwarf star made mostly of carbon and oxygen in the process of crystallizing just 104 light years from Earth.

Simulation of a white dwarf core crystallizing into a diamond. Photo: Harvard-Smithsonian Center for Astrophysics

The star’s temperature and mass suggest that its core is transforming into a solid cosmic diamond. The research results will be published in the journal Monthly Notices of the Royal Astronomical Society and are available on the arXiv database, Science Alert reported on June 11.

The matter in white dwarfs is tightly compressed but does not collapse into their cores because of electron degeneracy pressure. Although they are very dim, they still glow with residual heat. Over time, they cool and will evolve into black dwarfs when they lose all their heat, turning into crystalline carbon. Estimates indicate that this process is very long, about a quadrillion years, while the universe is only 13.8 billion years old. Therefore, scientists can only determine that the crystallization signs begin in the core of the white dwarf.

During crystallization, the carbon and oxygen atoms inside the white dwarf stop moving freely and form bonds, arranging themselves into a crystal lattice. The energy released from the process dissipates as heat, slowing the white dwarf's cooling, making it appear "younger" than it actually is.

An international team of astronomers led by Alexander Venner of the University of Southern Queensland, Australia, used data from the Gaia observatory to search for multiple star systems. They discovered a white dwarf star that was being gravitationally influenced by a triple star system called HD 190412. The HD 190412 system was renamed 190412 C and became a quadruple star system. The white dwarf's characteristics indicate that it is undergoing crystallization. The star's density is more than one million kilograms per cubic meter, while the density of diamonds is 3,500 kilograms per cubic meter.

The other three stars in the system allowed the team to determine the age of the white dwarf. The star system is about 7.3 billion years old and the white dwarf is 4.2 billion years old. The age difference of 3.1 billion years suggests that the crystallization rate has delayed the cooling of the white dwarf by a billion years. Its proximity to Earth suggests that there may be many such systems in the universe.

An Khang (According to Science Alert )

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