The X-ray emission coming off a set of neutron stars often known as the Magnificent Seven is so extreme that it may very well be coming from axions, a long-predicted type of particle, cast within the dense cores of those useless objects, scientists have demonstrated.
If their findings are confirmed, this discovery might assist unravel a few of the mysteries of the bodily Universe – together with the character of the mysterious darkish matter that holds all of it collectively.
“Discovering axions has been one of many main efforts in high-energy particle physics, each in idea and in experiments,” mentioned astronomer Raymond Co of the College of Minnesota.
“We expect axions might exist, however we’ve not found them but. You possibly can consider axions as ghost particles. They are often anyplace within the Universe, however they do not work together strongly with us so we have no observations of them but.”
Axions are hypothetical ultra-low-mass particles, first theorised within the Nineteen Seventies to resolve the query of why robust atomic forces comply with one thing referred to as charge-parity symmetry, when most fashions say they need not.
Axions are predicted by many fashions of string idea – a proposed resolution to the strain between normal relativity and quantum mechanics – and axions of a selected mass are additionally a robust darkish matter candidate. So scientists have various actually good causes to go searching for them.
In the event that they exist, axions are anticipated to be produced inside stars. These stellar axions aren’t the identical as darkish matter axions, however their existence would indicate the existence of different kinds of axions.
One strategy to seek for axions is by searching for extra radiation. Axions are anticipated to decay into pairs of photons within the presence of a magnetic subject – so if extra electromagnetic radiation than there needs to be is detected in a area the place this decay is predicted to happen, that would represent proof of axions.
On this case, extra laborious X-radiation is strictly what astronomers have discovered when trying on the Magnificent Seven.
These neutron stars – the collapsed cores of useless huge stars that died in a supernova – aren’t clustered in a bunch, however share various traits in widespread. They’re all remoted neutron stars of round middle-age, a couple of hundred thousand years since stellar dying.
They’re all cooling, emitting low-energy (smooth) X-rays as they achieve this. All of them have robust magnetic fields, trillions of instances stronger than Earth’s, highly effective sufficient to set off axion decay. And they’re all comparatively close by, inside 1,500 light-years from Earth.
This makes them a wonderful laboratory for searching for axions, and when a crew of researchers – led by senior writer and physicist Benjamin Safdi of the Lawrence Berkeley Nationwide Laboratory – studied the Magnificent Seven with a number of telescopes, they recognized high-energy (laborious) X-ray emission not anticipated for neutron stars of that sort.
In house, nonetheless, there are lots of processes that may produce radiation, so the crew needed to rigorously study different potential sources of the emission. Pulsars, as an example, emit laborious X-radiation; however the different kinds of radiation emitted by pulsars, resembling radio waves, aren’t current within the Magnificent Seven.
One other chance is that unresolved sources close to the neutron stars may very well be producing the laborious X-ray emission. However the datasets the crew used, from two totally different house X-ray observatories – XMM-Newton and Chandra – indicated that the emission is coming from the neutron stars. Nor, the crew discovered, is the sign more likely to be the results of a pile-up of soppy X-ray emission.
“We’re fairly assured this extra exists, and really assured there’s one thing new amongst this extra,” Safdi mentioned. “If we have been 100% positive that what we’re seeing is a brand new particle, that will be large. That may be revolutionary in physics.”
That is to not say that the surplus is a brand new particle. It may very well be a beforehand unknown astrophysical course of. Or it may very well be one thing so simple as an artefact from the telescopes or information processing.
“We’re not claiming that we have made the invention of the axion but, however we’re saying that the additional X-ray photons will be defined by axions,” Co mentioned. “It’s an thrilling discovery of the surplus within the X-ray photons, and it is an thrilling chance that is already in keeping with our interpretation of axions.”
The subsequent step might be to attempt to confirm the discovering. If the surplus is produced by axions, then a lot of the radiation needs to be emitted at larger energies than XMM-Newton and Chandra are able to detecting. The crew hopes to make use of a more moderen telescope, NASA’s NuSTAR, to watch the Magnificent Seven throughout a wider vary of wavelengths.
Magnetised white dwarf stars may very well be one other place to search for axion emission. Just like the Magnificent Seven, these objects have robust magnetic fields and aren’t anticipated to provide laborious X-ray emission.
“This begins to be fairly compelling that that is one thing past the Commonplace Mannequin if we see an X-ray extra there, too,” Safdi mentioned.
The analysis has been revealed in Bodily Evaluate Letters.