Seek for axions from close by star Betelgeuse comes up empty | MIT Information


The elusive axion particle is many instances lighter than an electron, with properties that hardly make an impression on peculiar matter. As such, the ghost-like particle is a number one contender as a part of darkish matter — a hypothetical, invisible sort of matter that’s thought to make up 85 p.c of the mass within the universe.

Axions have thus far evaded detection. Physicists predict that in the event that they do exist, they have to be produced inside excessive environments, such because the cores of stars on the precipice of a supernova. When these stars spew axions out into the universe, the particles, on encountering any surrounding magnetic fields, ought to briefly morph into photons and probably reveal themselves.

Now, MIT physicists have looked for axions in Betelgeuse, a close-by star that’s anticipated to burn out as a supernova quickly, not less than on astrophysical timescales. Given its imminent demise, Betelgeuse must be a pure manufacturing unit of axions, continually churning out the particles because the star burns away.

Nonetheless, when the crew appeared for anticipated signatures of axions, within the type of photons within the X-ray band, their search got here up empty. Their outcomes rule out the existence of ultralight axions that may work together with photons over a variety of energies. The findings set new constraints on the particle’s properties which can be 3 times stronger than any earlier laboratory-based axion-detecting experiments.

“What our outcomes say is, if you wish to search for these actually gentle particles, which we appeared for, they’re not going to speak very a lot to photons,” says Kerstin Perez, assistant professor of physics at MIT. “We’re principally making everybody’s lives tougher as a result of we’re saying, ‘you’re going to have to consider one thing else that will provide you with an axion sign.’”

Perez and her colleagues have revealed their outcomes immediately in Bodily Evaluate Letters. Her MIT co-authors embody lead creator Mengjiao Xiao, Brandon Roach, and Melania Nynka, together with Maurizio Giannotti of Barry College, Oscar Straniero of the Abruzzo Astronomical Observatory, Alessandro Mirizzi of the Nationwide Institute for Nuclear Physics in Italy, and Brian Grefenstette of Caltech.

A hunt for coupling

Most of the present experiments that seek for axions are designed to search for them as a product of the Primakoff impact, a course of that describes a theoretical “coupling” between axions and photons. Axions will not be usually thought to work together with photons — therefore their probability of being darkish matter. Nonetheless, the Primakoff impact predicts that, when photons are subjected to intense magnetic fields, corresponding to in stellar cores, they may morph into axions. The middle of many stars ought to due to this fact be pure axion factories.

When a star explodes in a supernova, it ought to churn the axions out into the universe. If the invisible particles run right into a magnetic subject, as an illustration between the star and Earth, they need to flip again into photons, presumably with some detectable vitality. Scientists are looking for axions by way of this course of, as an illustration from our personal solar.

“However the solar additionally has flares and provides off X-rays on a regular basis, and it’s exhausting to grasp,” says Perez.

She and her colleagues as an alternative appeared for axions from Betelgeuse, a star that usually doesn’t emit X-rays. The star is amongst these nearest to Earth which can be anticipated to blow up quickly.

“Betelgeuse is at a temperature and lifestage the place you don’t anticipate to see X-rays popping out of it, by way of commonplace stellar astrophysics,” Perez explains. “But when axions do exist, and are popping out, we would see an X-ray signature. In order that’s why this star is a pleasant object: If you happen to see X-rays, it’s a smoking gun sign that it’s received to be axions.”

“Knowledge are knowledge”

The researchers appeared for X-ray signatures of axions from Betelgeuse, utilizing knowledge taken by NuSTAR, NASA’s space-based telescope that focuses high-energy X-rays from astrophysical sources. The crew obtained 50 kiloseconds of information from NuSTAR in the course of the time the telescope was skilled on Betelgeuse.

The researchers then modeled a spread of X-ray emissions that they may see from Betelgeuse if the star was spewing out axions. They thought-about a spread of lots that an axion is likely to be, in addition to a spread of likelihoods that the axions would “couple” to and reconvert right into a photon, relying on the magnetic subject energy between the star and Earth.

“Out of all that modeling, you get a spread of what your X-ray sign of axions may presumably appear like,” Perez says.

After they looked for these indicators in NuSTAR’s knowledge, nevertheless, they discovered nothing above their anticipated background or exterior of any peculiar astrophysical sources of X-rays.

“Betelgeuse might be within the late levels of evolution and in that case ought to have a giant chance of changing into axions,” Xiao says. “However knowledge are knowledge.”

Given the vary of situations they thought-about, the crew’s null outcome guidelines out a big house of potentialities and units an higher restrict that’s 3 times stronger than earlier limits, from laboratory-based searches, for what an axion have to be. In essence, which means that if axions are ultralight in mass, the crew’s outcomes present that the particles have to be not less than 3 times much less prone to couple to photons and emit any detectable X-rays.

“If axions have ultralight lots, we will positively inform you their coupling must be very small, in any other case we’d have seen it,” Perez says.

Finally, which means that scientists might need to look to different, much less detectable vitality bands for axion indicators. Nonetheless, Perez says the seek for axions from Betelgeuse just isn’t over.

“What could be thrilling could be if we see a supernova, which might ignite an enormous quantity of axions that wouldn’t be in X-rays, however in gamma rays,” Perez says. “If a star explodes and we don’t see axions, then we’ll get actually stringent constraints on an axion’s coupling to photons. So everybody’s crossing their fingers for Betelgeuse to go off.”

This analysis was supported, partially, by NASA.

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