After axions were first theorized by physicists in the Chicago suburbs 45 years ago, they quickly became a robust candidate for explanation dark matter. But all along, the ultra-small particles have remained hypothetical. Now, a team of astrophysicists has proposed that axions may be responsible for excess X-rays emitted from a group of neutron stars in our galaxy.
The stars – called the “Magnificent Seven” – are neutron stars that emit low-frequency X-rays from their surface. Neutron stars are the extremely dense aftermath of collapsed stars. They have powerful magnetic fields and, as their name suggests, are made up largely of neutrons. The new research, published focuses this week in the journal Physical Review Letters on an as yet unexplained group of high-frequency X-rays emitted by the seven stars.
“It’s possible that what we’re seeing here is evidence for new physics, evidence for axions, which would change our understanding of nature in a very big way, which is difficult to convey,” said Benjamin Safdi, particle physicist at Lawrence Berkeley. National Laboratory and lead author of the recent paper, said in a phone call. That discovery could come with this document; it could come in 500 years. That’s how science works, so there is no guarantee of instant gratification. “
The main uncertainty about it axions is about their existence. In other words, there is consensus among physicists about the properties these theoretical particles would have if they existed. One of those properties is that axions would interact very faintly and rarely with ordinary matter. Rather than scattering the matter in the star, the axions would simply escape. Another is that axions can turn into photons in the presence of magnetic fields – such as those around the seven neutron stars.
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The researchers compare the possible behavior of the axions with neutrinos, a similar small particle (albeit with proven existence) that rarely interacts with other matter. Neutrons in neutron stars are known to collide and emit neutrinos, which is the main way the star cools over time.
The team’s contention is that axions can be created in the centers of neutron stars, where it is much hotter and more energetic than the surface of the star. Just as neutrons in that dense, super-hot region produce neutrinos through their collisions, so can axions. The difference is that in the presence of a magnetic field, the axion can be converted into a photon. The effervescent energy of that photon would be detectable on the X-ray spectrum, specifically in the high frequency range. Previous data had been collected from these high-frequency waves, but only as a byproduct of the main topic of research, the low-frequency X-ray waves coming from the surface of the stars.
“We are not claiming that we have already made the discovery of the axion, but we are saying that the extra X-ray photons can be explained by axions,” said Raymond Co, an astrophysicist at the University of Minnesota and a co-author of the paper. a press release. “It’s an exciting discovery of the excess X-ray photons, and it’s an exciting possibility that is already consistent with our interpretation of axions.”
Safdi hopes that future attention can be given to a nearby white dwarf, a degenerate star that is less dense and has a much cooler surface temperature than a neutron star. Since the white dwarfs don’t emit low-frequency X-rays from their surfaces, no X-ray telescope ever had much of a reason to do so. pointed to one.
“There is really nothing that should show up on an X-ray wavelength,” Safdi said. “When we see a signal, we can be much more confident that what we’re seeing is coming from axions.”