Prime suspect for dark matter could escape neutron stars

After axions were first theorized by physicists in the Chicago suburbs 45 years ago, they quickly became a robust candidate for explaining black matter. All the while, however, the ultra-small particles remained hypothetical. Now, a team of astrophysicists have proposed that axions could be responsible for excess x-ray emissions seen from a cluster of neutron stars in our galaxy.

The stars, nicknamed the “Magnificent Seven”, are neutron stars that emit low frequency X-rays from their surfaces. Neutron stars are extremely dense remnants of collapsed stars. They have strong magnetic fields and, as the name suggests, are made up largely of neutrons. The new research, published This week, in the journal Physical Review Letters, focuses on an as yet unexplained cluster of high-frequency x-rays emitted by the seven stars.

“It is possible that what we are seeing here is evidence of new physics, or evidence of axions, which would transform our understanding of nature in a really huge way, which is difficult to convey,” Benjamin Safdi, a particle physicist at the Lawrence Berkeley National Laboratory and lead author of the recent article, said during a phone call. “This discovery could come with this paper; it could come in 500 years. This is how science works, so there is no guarantee of instant gratification. “

The main uncertainty about axions revolve around their existence. In other words, there is a consensus among physicists about the properties that these theoretical particles would possess, if they existed. One of these properties is that axions would interact very weakly, and rarely, with ordinary matter. Instead of scattering matter throughout the star, the axions would simply escape. Another is that axions can turn into photons in the presence of magnetic fields – like those surrounding the seven neutron stars.

Researchers are comparing the possible behavior of axions to neutrinos, an equally small particle (even if it is proven) that rarely interacts with other matter. Neutrons in neutron stars are known to collide and emit neutrinos, which is the star’s primary way of cooling over time.

The team’s proposal is that axions could be created in the centers of neutron stars, where it is much hotter and more energetic than the star’s surface. Just as the neutrons inside this dense and very hot region produce neutrinos by their collisions, axions could also be produced. The difference is that in the presence of a magnetic field, the axion could convert into a photon. The sparkling energy of this photon would be detectable on the X-ray spectrum, specifically in the high frequency range. Previous data had been collected on these high-frequency waves, but only as a by-product of the main subject of investigation: low-frequency x-ray waves from the surface of stars.

“We are not claiming that we have made the discovery of the axion yet, but we are saying that the extra x-ray photons can be explained by axions,” said Raymond Co, astrophysicist at the University of Minnesota and a co -author of the article, in a press release. “This is an exciting discovery of excess X photons, and it’s an exciting possibility that is already consistent with our interpretation of axions.

Safdi’s hope is that future attention may be focused on a nearby white dwarf, a degenerate star that is less compact and with a much cooler surface temperature than a neutron star. Since white dwarfs do not emit low-frequency x-rays from their surface, no x-ray telescope has ever had much purpose. pointed at one.

“There is really nothing that should show up in any x-ray wavelength,” Safdi said. “If we see a signal, we can be much more sure that what we are seeing is coming from the axions.”