After the axions were first theorized by physicists in the suburbs of Chicago 45 years ago, they quickly became a robust candidate for explanations dark matter. However, during all this time, the ultra-small particles remained hypothetical. Now, a team of astrophysicists has proposed that the axes may be responsible for an excess of X-rays seen from a group of neutron stars in our galaxy.
The stars – nicknamed the “Magnificent Seven” – are neutron stars which emit low frequency X-rays from their surfaces. Neutron stars are the extremely dense later lives of collapsed stars. They possess strong magnetic fields and, as their name suggests, are largely neutrons. New research, published this week, in the journal Physical Review Letters, he focuses on a still inexplicable pile 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 actions, which would turn our understanding of nature into a really huge, hard-to-pass way,” said physicist Benjamin Safdi particle at Lawrence Berkeley National Laboratory and the lead author of the recent paper, said in a phone call. “This discovery could come with this work; it could come over 500 years from now. This is how science works, and therefore there is no guarantee of instant gratification. ”
The main uncertainty about the axes 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 such property is that axes would interact very weakly and rarely with ordinary matter. Instead of scattering matter in the star, the axles would simply escape. Another is that axes can turn into photons in the presence of magnetic fields – such as those surrounding the seven neutron stars.
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The researchers compare the possible behavior of the axes with neutrinos, an equally small particle (although one whose existence is proven) that rarely interacts with other matter. It is known that neutrons in neutron stars collide and emit neutrinos, which is a major way in which the star cools over time.
The team’s proposal is that the axes could be created in the centers of neutron stars, where it is much warmer and more energized than the surface of the star. Just as neutrons in that dense, super-hot region produce neutrinos through collisions, so axes could be produced. The difference is that in the presence of a magnetic field, the action could turn into a photon. The sparkling energy of the photon would be detectable on the X-ray spectrum, specifically in the high frequency range. Previous data were collected about these high-frequency waves, but only as a by-product of the main subject of the investigation: low-frequency X-rays coming from the surfaces of stars.
“We do not yet claim to have discovered the axion, but we say that additional X-ray photons can be explained by the axes,” Raymond Co., an astrophysicist at the University of Minnesota and a co-author of the paper, said in a press release. “It’s an interesting discovery of excess X-ray photons and it’s an interesting possibility, which is already consistent with our interpretation of the axes.”
Safdi’s hope is that future attention can be paid to a nearby white dwarf, a less compact degenerate star with a much colder surface temperature than a neutron star. Because white dwarfs do not emit low-frequency radiation from their surface, no X-ray telescope has ever had a reason to be pointed at one.
“There is nothing that should appear in any X-ray wavelength,” Safdi said. “If we see a signal, we can be much more sure that what we see is from the axes.”