Discovery validates white dwarf cooling theory

A study published in Nature challenges this theory. The University of Victoria (UVic) and its partners are using data from the European Space Agency’s Gaia satellite to uncover why a population of white dwarfs stopped cooling after more than 8 billion years. “We find that the classic picture that all white dwarfs are dead stars is incomplete,” said Simon Bruin, co-principal investigator and national research scientist at UVic’s Canadian Institute for Theoretical Astrophysics. says. “For these white dwarfs to stop cooling, they need a way to generate additional energy. We didn’t know how this happened, but now we have an explanation for this phenomenon. ” Understanding the age and other aspects of white dwarfs can help scientists reconstruct the formation of the Milky Way. Blouin made the discovery in collaboration with Antoine Bedard of the University of Warwick and researcher Shihao Chen of the Institute for Advanced Study, using 2019 Gaia data. More than 97 percent of the stars in the Milky Way eventually become white dwarfs. Scientists have long believed that these stars are reaching the end of their lives. Once the nuclear energy sources are exhausted, they stop producing heat and the dense plasma inside freezes into a solid state, cooling the star from the inside out. This cooling process can take billions of years. In some white dwarfs, the dense plasma inside them doesn’t just freeze from the inside, according to a new paper. 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 heavier material is transported to the star’s core, gravitational energy is released, and this energy is enough to interrupt the star’s cooling process for billions of years. “This is the first time that this transport mechanism has been observed in any type of star. It’s very interesting because it’s not every day that a completely new astrophysical phenomenon is discovered,” said Bedard, a researcher at the University of Warwick. . It’s unclear why this happens in some stars and not others, but Blouin thinks it’s probably due to the star’s composition. “Some white dwarfs are formed by the merger of two different stars. When these stars collide to form a white dwarf, the star’s composition changes and floating crystals can form.” says Mr. Blouin. White dwarfs are routinely used as an indicator of age, and the cooler a white dwarf is, the older it is considered to be. But some white dwarfs cool down even more slowly, so some stars at certain temperatures could be billions of years older than previously thought. “This new discovery will not only require a revision of astronomy textbooks, but will also require astronomers to rethink the process they use to determine the age of stellar populations,” Blouin added. Ta. This research is supported by the National Science and Engineering Research Council of Canada (NSERC), the Banting Postdoctoral Fellowship Program, the European Research Council, and the Canadian Institute for Theoretical Astrophysics (CITA).

source: http://dx.doi.org/10.1038/s41586-024-07102-y