Physicists Spot Attainable Breeding Grounds for Darkish Matter

A hypothetical particle that might make up the universe’s darkish matter could also be produced by and hold round neutron stars, a number of the densest objects within the universe, in accordance with a workforce of physicists.

The particles are axions, considered one of a number of proposed candidates for so-called dark matter, the enigmatic stuff that makes up over 1 / 4 of the universe’s matter. A workforce of researchers from the colleges of Amsterdam, Princeton, and Oxford now posit that axions might kind clouds round neutron stars, that are the incredibly dense, collapsed remnants of dead stars. The discovering provides a brand new area the place researchers can focus astrophysical searches for darkish matter, whereas highlighting the potential utility of a radio telescope in house.

Attainable darkish matter factories

The workforce means that some axions produced inside neutron stars might convert into photons and escape into house. However many of those particles would stay trapped by the star’s gravity, forming an axionic cloud across the neutron star. The group’s analysis describing the concept was just lately published in Bodily Overview X and follows up on an earlier work by the workforce that explored axions that might escape the gravitational fields of the neutron stars that produce them.

“After we see one thing, what is going on is that electromagnetic waves (gentle) bounce off an object and hit our eyes. The way in which we ‘see’ axions is just a little completely different,” mentioned Anirudh Prabhu, a analysis scientist on the Princeton Heart for Theoretical Science and co-author of the paper, in an e mail to Gizmodo. “Whereas gentle can ‘bounce’ off of axions, this course of is extraordinarily uncommon. The extra widespread approach to detect axions is thru the Primakoff impact, which permits axions to transform into gentle (and vice versa) within the presence of a powerful magnetic subject.”

Some neutron stars will be among the many most magnetic objects within the universe, and subsequently are given a particular label: magnetars. This extraordinarily magnetized atmosphere is fertile breeding grounds for axions’ conversion into gentle, Prabhu mentioned, which then might be detectable by space-based telescopes.

Darkish matter and axion waves within the universe

Darkish matter is the catch-all title for the 27% of stuff within the universe that scientists can not straight observe as a result of it doesn’t emit gentle and solely seems to work together with atypical matter by means of gravitational interactions. Different candidates embrace Weakly Interacting Large Particles (or WIMPs), dark photons, and primordial black holes, to call a couple of. Axions have been initially proposed as an answer to an issue in particle physics: Principally, a number of the predicted traits of the neutron aren’t noticed in nature. Therefore their title—axions—which comes from a cleansing product model. In any case, the axion was proposed as a approach to clear up a number of the nasty conundrums that arose across the Normal Mannequin of particle physics. Final yr, a distinct workforce of researchers studied Einstein rings—areas of house the place gentle has been bent strongly by gravity, forming a visual “ring” in house—and located evidence boosting axions as a candidate for darkish matter.

The electromagnetic waves (i.e., gentle) produced by changing axions might have wavelengths a fraction of an inch as much as greater than half a mile (one kilometer) lengthy, Prabhu famous. However Earth’s ionosphere blocks very lengthy wavelengths from Earth-based telescopes, so space-based observatories is perhaps our greatest guess for recognizing proof of axions.

Neutron stars and axions have a historical past

“It’s nicely established within the subject of axion physics that when you’ve got giant, time-varying electrical fields parallel to magnetic fields you find yourself with best situations for producing axions,” mentioned Benjamin Safdi, a particle physicist at UC Berkeley who was not affiliated with the current paper, in an e mail to Gizmodo. “On reflection, it’s apparent and clear that if this course of occurs in pulsars a large fraction of the axions produced might be gravitationally certain as a result of sturdy gravity of the neutron star. The authors deserve loads of credit score for pointing this out.”

In 2021, Safdi co-authored a paper positing that axions could also be produced within the Magnificent Seven, a bunch of neutron stars in our personal galaxy. The Magnificent Seven produce high-frequency X-rays, and the workforce proposed that axions changing into photons might produce X-rays like these noticed by some telescopes. However lots of the axions produced on the cores of these neutron stars keep nearer to the supply, the current workforce mentioned, and construct up a big inhabitants over tons of of tens of millions—if not billions—of years.

“These axions accumulate over astrophysical timescales, thereby forming a dense ‘axion cloud’ across the star,” the workforce wrote within the paper. “Whereas a deeper understanding of the systematic uncertainties in these methods is required, our present estimates counsel that present radio telescopes might enhance sensitivity to the axion-photon coupling by greater than an order of magnitude.”

“There are loads of uncertainties, nevertheless, within the calculations introduced on this work — that is no fault of the authors; it’s merely a tough, dynamical drawback,” Safdi added. “I’d additionally wish to see extra thorough work on the detection prospects for this sign, together with a greater job modeling the neutron star inhabitants and estimating the sensitivity with present and upcoming devices.”

So how can we detect and determine darkish matter?

However the state-of-the-art telescopes in house are not radio telescopes. The Webb Space Telescope, launched in 2021, observes a number of the oldest gentle we are able to see at infrared and near-infrared wavelengths. ESA’s Euclid Space Telescope, launched final yr with the precise objective of bettering our understanding of the universe’s darkish matter, additionally sees the cosmos within the infrared. The truth is, one of the vital compelling choices for a radio-based observatory is the Lunar Crater Radio Telescope (LCRT), which is strictly what it seems like: an enormous radio telescope that might make a dish out of a lunar crater on the darkish aspect of the Moon.

“Axions are considered one of our greatest bets for brand new physics,” Safdi mentioned, although they’re “notoriously tough to probe given their feeble interactions with atypical matter.”

“These feeble interactions will be magnified in excessive astrophysical environments resembling these present in neutron star magnetospheres,” he added. “Work like this might thus simply open the pathway in direction of discovery.”

There are many radio telescopes doing fantastic work on Earth—MeerKAT, the Very Giant Telescope, and ALMA, to call a couple of—nevertheless it appears we might have a brand new space-based mission if we need to have an opportunity of seeing axionic waves. No strain, NASA coffers!