Astronomers have proposed a new theory to explain why a mysterious population of white dwarfs has stopped cooling for at least 8 billion years.
White dwarfs are the remains of stars without a nuclear energy source that gradually cool over billions of years, eventually freezing from the inside out to a solid state.
Recently, it was discovered that a population of frozen white dwarfs maintains a constant brightness for a period comparable to the age of the universe, indicating the existence of an unknown, powerful energy source that inhibits cooling.
“We find that the classical picture that all white dwarfs are dead stars is incomplete,” said astronomer Dr Simon Bruin from the University of Victoria.
“To stop these white dwarfs from cooling, we need some way to generate additional energy.”
“We didn’t know how this happened, but now we have an explanation for this phenomenon.”
The researchers say that in some white dwarfs, the dense plasma inside them doesn’t just freeze from the inside out.
Instead, the solid crystals that form when frozen tend to float because they are less dense than the liquid.
As the crystals float upwards, the heavier liquid moves downwards.
As heavy material is transported toward the star’s center, gravitational energy is released, and this energy is enough to interrupt the star’s cooling process for billions of years.
Dr Antoine Bedard, an astronomer at the University of Warwick, said: “This is the first time this transport mechanism has been observed in any type of star, and it’s very interesting because it’s not every day that a completely new astrophysical phenomenon is discovered.”
“We don’t know why this happens in some stars and not others, but it’s probably due to the star’s composition.”
“Some white dwarfs are formed by the merger of two different stars,” Dr Bruin said.
“When these stars collide to form white dwarfs, the star’s composition changes, allowing the formation of floating crystals.”
White dwarfs are routinely used as an indicator of age, and the cooler a white dwarf is, the older it is considered to be.
However, the extra delay in cooling seen in some white dwarfs means that some stars at certain temperatures may be billions of years older than previously thought.
“This new discovery will not only require a revision of astronomy textbooks, but will also require a reexamination of the processes astronomers use to determine the age of stellar populations,” Dr. Blouin said.
of the team paper Published in today’s diary Nature.
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A. Bedard other. Buoyant crystals stop the white dwarf from cooling. Nature, published online March 6, 2024. doi: 10.1038/s41586-024-07102-y
Source: www.sci.news
