Physicists Spot Possible Breeding Grounds for Dark Matter

A hypothetical particle that would make up the universe’s darkish matter could also be produced by and grasp round neutron stars, a few of the densest objects within the universe, in line with a group of physicists.

The particles are axions, one in every of a number of proposed candidates for so-called darkish matter, the enigmatic stuff that makes up over 1 / 4 of the universe’s matter. A group of researchers from the colleges of Amsterdam, Princeton, and Oxford now posit that axions might kind clouds round neutron stars, that are the extremely dense, collapsed remnants of useless stars. The discovering affords 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 group 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 thought was not too long ago revealed in Bodily Overview X and follows up on an earlier work by the group that explored axions that would escape the gravitational fields of the neutron stars that produce them.

“After we see one thing, what is occurring is that electromagnetic waves (mild) bounce off an object and hit our eyes. The way in which we ‘see’ axions is just a little completely different,” stated Anirudh Prabhu, a analysis scientist on the Princeton Middle for Theoretical Science and co-author of the paper, in an e-mail to Gizmodo. “Whereas mild 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 mild (and vice versa) within the presence of a powerful magnetic area.”

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 setting is fertile breeding grounds for axions’ conversion into mild, Prabhu stated, which then may very well 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 mild and solely seems to work together with strange matter by way of gravitational interactions. Different candidates embrace Weakly Interacting Large Particles (or WIMPs), darkish photons, and primordial black holes, to call a couple of. Axions have been initially proposed as an answer to an issue in particle physics: Mainly, a few of the predicted traits of the neutron aren’t noticed in nature. Therefore their title—axions—which comes from a cleansing product model. In spite of everything, the axion was proposed as a approach to clear up a few of the nasty conundrums that arose across the Normal Mannequin of particle physics. Final 12 months, a special group of researchers studied Einstein rings—areas of house the place mild has been bent strongly by gravity, forming a visual “ring” in house—and located proof boosting axions as a candidate for darkish matter.

The electromagnetic waves (i.e., mild) 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 may be our greatest guess for recognizing proof of axions.

Neutron stars and axions have a historical past

“It’s nicely established within the area of axion physics that if in case you have massive, time-varying electrical fields parallel to magnetic fields you find yourself with superb situations for producing axions,” stated 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 may very well be gravitationally sure because of the robust gravity of the neutron star. The authors deserve numerous 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 group 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 group stated, and construct up a big inhabitants over tons of of hundreds of thousands—if not billions—of years.

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

“There are numerous uncertainties, nonetheless, within the calculations introduced on this work — that is no fault of the authors; it’s merely a tough, dynamical downside,” Safdi added. “I’d additionally prefer 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 current and upcoming devices.”

So how can we detect and establish darkish matter?

However the state-of-the-art telescopes in house usually are not radio telescopes. The Webb Area Telescope, launched in 2021, observes a few of the oldest mild we will see at infrared and near-infrared wavelengths. ESA’s Euclid Area Telescope, launched final 12 months with the precise purpose of enhancing our understanding of the universe’s darkish matter, additionally sees the cosmos within the infrared. Actually, one of the compelling choices for a radio-based observatory is the Lunar Crater Radio Telescope (LCRT), which is strictly what it feels like: an enormous radio telescope that might make a dish out of a lunar crater on the darkish aspect of the Moon.

“Axions are one in every of our greatest bets for brand spanking new physics,” Safdi stated, although they’re “notoriously tough to probe given their feeble interactions with strange matter.”

“These feeble interactions will be magnified in excessive astrophysical environments similar to 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 implausible 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!