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First theorized in the 1970s, axions are hypothetical particles that have been proposed to preserve a temporal inversion symmetry of the nuclear force. These particles can constitute dark matter and can be produced thermally inside the nuclei of neutron stars, escape from stars due to their weak interactions with matter, and then convert to X-rays in fields. magnets surrounding the stars. In a newspaper article Physical examination letters, astrophysicists show that a recently discovered excess of hard X-rays from a nearby cluster of isolated neutron stars, known as the Magnificent Seven, could be explained by this emission mechanism.
An artist’s impression of a neutron star. Image credit: Sci-News.com.
The Magnificent Seven is a group of faint x-ray neutron stars isolated at a distance of 400 to 2,160 light years from Earth.
These stars have strong magnetic fields and were only supposed to produce low energy X-rays and ultraviolet rays.
“They’re known to be very ‘boring’, and in this case that’s a good thing,” said Dr. Benjamin Safdi, theoretical physicist at the US Department of Energy’s Lawrence Berkeley National Laboratory.
If axions do exist, they are expected to behave a bit like neutrinos on a star, as both are said to have very slight masses and only very rarely and weakly interact with other matter. They could be produced in abundance inside the stars.
Uncharged particles called neutrons move through neutron stars, occasionally interacting by scattering over each other and releasing a neutrino or possibly an axion. The neutrino-emitting process is the primary way that neutron stars cool down over time.
Like neutrinos, axions could travel outside the star. The incredibly strong magnetic field surrounding the seven stars of Magnificent could cause the outgoing axions to convert into light.
“The axion was first proposed in the late 1970s to solve a problem called the strong CP problem, which means that the negative and positive electric charge distributions inside the neutron are centered around the same point, ”said Christopher Dessert, graduate student at the University. from Michigan.
“Over the next decade, it was discovered that if the axion existed, it could also be dark matter.
In 2019, astrophysicists observed a mysterious and inexplicable increase in X-rays emitted by the Magnificent Seven.
Dr Safdi, Dessert and their colleagues propose that these extra x-rays are caused by axions produced in the nuclei of neutron stars.
If the excess x-rays are generated by an object or objects hidden behind neutron stars, it would likely have manifested in the datasets that researchers are using from two space satellites: the XMM-Newton telescopes of the ‘ESA and Chandra from NASA. .
“It is still quite possible that a new non-axial explanation will arise for the observed excess X-rays, although we remain hopeful that such an explanation will lie outside the Standard Model of particle physics. , and this new ground and space. Technology-based experiments will confirm the origin of the high energy x-ray signal, ”said Dr Safdi.
“We’re pretty confident that this excess exists, and very confident that there is something new about this excess.”
“If we were 100% sure that what we are seeing is a new particle, that would be huge. It would be revolutionary in physics.
“Even if the discovery turns out not to be associated with a new particle or dark matter. It would tell us so much more about our universe and there would be a lot to learn.
“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 Dr. Raymond Co, postdoctoral researcher at the University of Minnesota .
“This is an exciting discovery of the excess of X photons, and it’s an exciting possibility that is already consistent with our interpretation of axions.
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Painted bushman et al. 2021. Axion’s emission may explain a new excess of hard X-rays from nearby isolated neutron stars. Phys. Rev. Lett 126 (2): 021102; doi: 10.1103 / PhysRevLett.126.021102
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