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.”
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axion A never-seen particle that some cosmologists argue could be the basis of dark matter — the unseen matter that must make up the majority of matter in the universe.
dark matter Physical objects or particles that emit no detectable radiation of their own. They are believed to exist because of unexplained gravitational forces that they appear to exert on other, visible astronomical objects.
hypothetical An adjective used to describe a proposal or idea based upon a hypothesis (which is itself a proposed explanation for something).
physics The scientific study of the nature and properties of matter and energy. A scientist who works in that field is known as a physicist.
red giant A large star that has cooled (hence its red color) that develops after helium-fueled fusion reactions in its core have shut down.
star The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become dense enough to sustain nuclear-fusion reactions, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.
white dwarf A small, very dense star that is typically the size of a planet. It is what is left when a star with a mass about the same as our sun’s has exhausted its nuclear fuel of hydrogen, and collapsed.