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White dwarf stars may be billions of years older than estimated

In the vast expanse of the universe, white dwarf stars have long been considered celestial timekeepers. Their cooling rates marked the passage of billions of years. It was believed that these “dead stars,” or stellar remnants, would predictably cool down after depleting their nuclear fuel.

However, a groundbreaking theory from international researchers challenges the established view on the cooling of white dwarf stars, solving a longstanding astronomical puzzle.

Beyond traditional theories of white dwarf stars

The study was a collaboration among experts from the Institute for Advanced Study, the University of Victoria, and the University of Warwick. The research offers a compelling explanation for the enigmatic behavior of a subset of white dwarf stars that seemingly defy the laws of physics by halting their cooling process for an astonishing ten billion years.

Traditionally, astronomy textbooks have taught that the cooling of white dwarf stars is a straightforward process. As stars deplete their nuclear heat, the freezing of their core’s dense plasma causes them to solidify from the inside out.

This classical picture was upended in 2019 when an analysis of data from the European Space Agency’s Gaia satellite revealed that some white dwarfs remained unexpectedly warm over extensive periods, challenging experts to rethink their understanding of stellar evolution.

Uncovering new processes

“In order for these white dwarfs to cease cooling down, they must somehow produce additional energy,” explained study co-author Sihao Cheng.

The mystery of how these stars maintained their warmth has now been unraveled. The researchers propose a revolutionary theory in which the internal dynamics of certain white dwarfs diverge significantly from the expected behavior.

Rather than a uniform process of freezing, the formation of solid crystals within these stars triggers a surprising physical reaction. The crystals, less dense than the surrounding liquid plasma, rise toward the surface, displacing the denser liquid downward. This movement generates enough gravitational energy to stall the cooling process for billions of years.

A new understanding of white dwarf stars

Cheng compares this to ice cubes floating in water, illustrating the complex physics in ancient stars on a cosmic scale. This discovery enriches our knowledge of white dwarf stars and prompts questions about influences like composition changes from progenitor star mergers.

Furthermore, the implications of this research are profound. White dwarf stars are integral to our understanding of the cosmic timeline, serving as indicators of age within the galaxy.

The discovery that some white dwarfs cool more slowly suggests these stars may be billions of years older than estimated. This finding requires new age-calculation methods for stars, possibly changing our understanding of the Milky Way’s history.

A gateway to new discoveries

As we continue to explore the cosmos, the study of white dwarf stars remains at the forefront of unraveling the complex processes that govern the life and death of stars. “Our work will necessitate updates to astronomy textbooks,” said Cheng, highlighting the impact of their findings on the field of astronomy.

The study not only challenges our existing knowledge but also opens the door to new discoveries that could reshape our understanding of the universe.

The research was supported by a host of prestigious institutions, including the National Sciences and Engineering Research Council of Canada (NSERC) and the European Research Council.

The study is published in the journal Nature.


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