New research by the US Department of Energy’s Lawrence Berkeley National Laboratory theoretical physicist suggests that never-before-seen particles called axions could be the source of unexplained high-energy X-rays surrounding clusters of neutron stars.
X-rays around the Magnificent Seven may be traces of the target particle. The researchers say they may have found evidence for putative axions and possibly dark matter around a cluster of neutron stars.
Axions are expected to form in the cores of stars and transform into particles of light called photons in the presence of a magnetic field, first appearing in the 1970s as part of a solution to the problem of fundamental particle physics.
Axions can also make up dark matter – a mysterious material that is estimated to account for 85% of the total mass of the universe, but so far we have only seen its gravitational effects on ordinary matter. Even if it turns out that the excess X-ray radiation is not associated with axions or dark matter, it can still open up new physics.
The collection of neutron stars known as the Magnificent Seven has served as an excellent test bed for the possible presence of axions, as these stars have strong magnetic fields, are relatively close – within hundreds of light years – and are expected to produce only low energy X-rays. and ultraviolet light.
If neutron stars were pulsars, they would have an active surface emitting radiation at different wavelengths. This radiation will appear across the entire electromagnetic spectrum and could drown out this X-ray signature that the researchers have found, or it will produce radio frequency signals. But the Magnificent Seven are not pulsars, and no such radio signal has been detected. Other common astrophysical explanations do not seem to match observations either.
If the excess X-rays found around the Magnificent Seven are generated by an object or objects lurking behind neutron stars, it would likely show up in the datasets that researchers use from two space satellites.
The new non-axion theory explains the observed excess of X-ray radiation, although they still hope that such an explanation will lie outside the standard model of particle physics and this new basis, and space experiments will confirm the origin of the high-energy X-ray signal.
If axions exist, you can expect them to behave in the same way as neutrinos in a star, since both have very low masses and very rarely and weakly interact with other matter. They could be produced in abundance within the stars. Uncharged particles called neutrons travel within neutron stars, sometimes interacting, scattering away from each other and releasing a neutrino or possibly an axion. The process of emitting neutrinos is the main way neutron stars cool over time.
Like neutrinos, axions can travel outside the star. The incredibly strong magnetic field surrounding the stars of the Magnificent Seven – billions of times stronger than the magnetic fields that could be created on Earth – could cause existing axions to transform into light.
As the next step in this study, white dwarfs will be the best places to look for axions because they also have very strong magnetic fields and are expected to be “X-ray-free environments.”
Axions have gained more attention because a number of experiments have revealed no signs of WIMP (weakly interacting massive particle), another promising dark matter candidate.
There may be hundreds of axion-like particles or ALPs that make up dark matter, and string theory – a candidate theory for describing the forces of the universe – opens up the possibility of many types of ALPs.