Some white dwarf stars point to possible dark matter

These stars are cooling “too fast” — unless some mystery particle is present to carry that energy away

White-dwarf stars (circled) cool as they become older. Scientists have found some that pulsate. And these variable white dwarfs are cooling faster than expected. One possible explanation: Hypothetical particles are ferrying some of their energy away.

H. RICHER/UBC ET AL., WFPC2, HST, NASA

CHICAGO, Illinois — Cooling stars could shine some light on the nature of dark matter. Scientists have argued that this unknown — and never seen — dark stuff must be what makes up most of the matter in our universe.

Certain types of stars are cooling faster than scientists had expected. This oddity hints at the presence of hypothetical particles known as axions. Such particles have also been proposed as a candidate for dark matter.

Researchers analyzed recent measurements for a certain type of small, white-hot star. These five white dwarfs periodically grow dimmer and brighter. The rate at which their brightness varies should relate to how fast those stars are cooling. And each of these stars appears to be cooling far more quickly than expected. Likewise, aging, red-giant stars also have shown excess cooling.

Each result on its own, “is not that interesting,” says Maurizio Giannotti. But taken together, the consistent pattern could indicate something funny is going on. Giannotti is a physicist at Barry University in Miami Shores, Fla. He reported his team’s conclusions on August 4, here, at the International Conference on High Energy Physics.

The team considered several possible explanations for the fast cooling of these stars. In the end, they find the axion explanation seems most likely. (That’s assuming, they add, that something simpler, like measurement error, is not to blame.) Axions produced within a star would stream outward, they say. As they left, those bits would take some energy with them. This would further cool the star.

It may be more likely that the seemingly fast cooling is simply a case of measurement error, Giannotti acknowledges. Still, he points out, it’s important to take note when something doesn’t add up. “We can’t ignore the small hints.” 

Physics writer Emily Conover studied physics at the University of Chicago. She loves physics for its ability to reveal the secret rules about how stuff works, from tiny atoms to the vast cosmos.

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