[LINK] "Dark Matter May Be Building Up Inside the Sun"

[rfmcdonald]

Readers of science fiction writer Stephen Baxter's Xeelee Sequence novels would remember that one major theme was the fact that dark matter--the term for an unknown substance known only through its very weak interactions with the normal matter that makes up the visible universe--was contaminating the stars, influencing their energy cycles and ultimately their very lifetimes. According to Wired Science's Lisa Grossman, that may actually be true: dear old Sol may have absorbed more than enough dark matter over its lifetime to influence its evolution.

In a paper in the July 2 Physical Review Letters, [astrophysicist Subir] Sarkar and Oxford colleague Mads Frandsen suggest another way to find light dark matter: Look to the sun.

Because lightweight dark matter particles wouldn’t vaporize each other when they meet, the sun should collect the particles the way snowballs collect more snow.

“The sun has been whizzing around the galaxy for 5 billion years, sweeping up all the dark matter as it goes,” Sarkar said.

The buildup of dark matter could solve a pressing problem in solar physics, called the solar composition problem. Sensitive observations of waves on the sun’s surface have revealed that the sun has a much easier time transporting heat from its interior to its surface than standard models predict it should.

Dark matter particles that interact only with each other could make up the difference. Photons and particles of regular matter bounce off each other on their way from the sun’s interior to its surface, so light and heat can take billions of years to escape. But because dark matter particles ignore all the regular matter inside the sun, they have less stuff in their way and can transport heat more efficiently.

“When we do the calculation, to our amazement, it turns out this is true,” Sarkar said. “They can transport enough heat to solve the solar composition problem.”

Next, Sarkar and Frandsen calculated how being full of dark matter would affect the number of neutrinos the sun gives off. They found that the neutrino flux would change by a few percent. That’s not much, Sarkar said, but it’s just enough to be detected by two different neutrino experiments — one in Italy called Borexino and one in Canada called SNO+ — that are soon to get under way.

“It’s a speculative idea, but it’s testable,” Sarkar said. “And the tools to test it are coming on line pretty fast. We don’t have to wait 20 years.”

Grossman suggests that some preliminary data collected by separate groups support Sarkar and Frandsen's hypothesis.