Cold, dead stars could help limit dark matter

Hunting for cold stellar corpses near the center of the galaxy or in star clusters could put new limits on the properties of dark matter.

“You can exclude a big class of theories that theexperiments cannot exclude just by observing the temperature of a neutron star,” said physicist Chris Kouvaris of the University of Southern Denmark, lead author of a paper in the Sept. 28 Physical Review D.“Maybe by observations, which come cheaper than expensive experiments, we might get some clues about dark matter.”

Dark matter is the irritatingly invisible stuff that makes up some 23 percent of theuniverse, but makes itself known only through its gravitational tug on ordinary matter.

There are several competing theories about what dark matter actually is, but one of the most widely pursuedis a hypothetical weakly interacting massive particle (WIMP). Physicists in search of WIMPs have placed experimental detectors deep underground in mines and mountains, and are waiting for a darkmatter particle to hit them.

Others have proposed looking for the buildup of dark matter in stars like the sun or white dwarfs. But both subterranean and stellar-detection strategies will light up onlyfor WIMPs larger than a certain size. That size is miniscule — about a trillionth of a quadrillionth of a square centimeter — but dark matter particles could be smaller still.

One way to rule outsuch diminutive particles is to look to neutron stars, suggest Kouvaris and co-author Peter Tinyakov of the Université Libre de Bruxelles in Belgium.

Neutron stars are the cold, dense remnants ofmassive stars that died in fiery supernova explosions. They tend to have masses similar to the sun, but in diameter they would barely stretch from one end of Manhattan to the other. This extreme densitymakes neutron stars exceptionally good nets for dark matter.

“For their size and their temperature, they have the best efficiency in capturing WIMPs,” Kouvaris said. Particles up to 100 times...