Research for Axions From Close by Star Betelgeuse Comes Up Empty
Success significantly slender the range of doable locations to discover the hypothetical dim subject particles.
The elusive axion particle is numerous periods lighter than an electron, with properties that barely make an perception on ordinary issue. As these kinds of, the ghost-like particle is a primary contender as a ingredient of dark matter — a hypothetical, invisible variety of make a difference that is believed to make up 85 p.c of the mass in the universe.
Axions have so significantly evaded detection. Physicists forecast that if they do exist, they ought to be created within extreme environments, these types of as the cores of stars at the precipice of a supernova. When these stars spew axions out into the universe, the particles, on encountering any bordering magnetic fields, really should briefly morph into photons and most likely reveal on their own.
Now, MIT physicists have searched for axions in Betelgeuse, a close by star that is anticipated to burn out as a supernova quickly, at minimum on astrophysical timescales. Presented its imminent demise, Betelgeuse should really be a natural manufacturing unit of axions, frequently churning out the particles as the star burns away.
Even so, when the workforce looked for envisioned signatures of axions, in the form of photons in the X-ray band, their research arrived up vacant. Their results rule out the existence of ultralight axions that can interact with photons more than a large range of energies. The findings established new constraints on the particle’s homes that are a few situations stronger than any prior laboratory-primarily based axion-detecting experiments.
“What our benefits say is, if you want to look for these definitely light particles, which we looked for, they’re not likely to converse extremely significantly to photons,” says Kerstin Perez, assistant professor of physics at MIT. “We’re basically making everyone’s life more durable since we’re declaring, ‘you’re going to have to assume of anything else that would give you an axion sign.’”
Perez and her colleagues have posted their success in Actual physical Evaluation Letters. Her MIT co-authors include things like lead author Mengjiao Xiao, Brandon Roach, and Melania Nynka, alongside with Maurizio Giannotti of Barry University, 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
Several of the present-day experiments that lookup for axions are developed to appear for them as a products of the Primakoff impact, a process that describes a theoretical “coupling” involving axions and photons. Axions are not generally thought to interact with photons — that’s why their probability of getting dim make any difference. Nonetheless, the Primakoff result predicts that, when photons are subjected to powerful magnetic fields, such as in stellar cores, they could morph into axions. The heart of quite a few stars should really consequently be all-natural axion factories.
When a star explodes in a supernova, it should churn the axions out into the universe. If the invisible particles run into a magnetic field, for occasion concerning the star and Earth, they should flip again into photons, presumably with some detectable electrical power. Experts are hunting for axions via this approach, for occasion from our individual sunshine.
“But the solar also has flares and offers off X-rays all the time, and it is difficult to understand,” says Perez.
She and her colleagues in its place seemed for axions from Betelgeuse, a star that ordinarily does not emit X-rays. The star is amongst those closest to Earth that are predicted to explode soon.
“Betelgeuse is at a temperature and lifestage where you never expect to see X-rays coming out of it, by means of regular stellar astrophysics,” Perez explains. “But if axions do exist, and are coming out, we could possibly see an X-ray signature. So that’s why this star is a nice item: If you see X-rays, it is a cigarette smoking gun signal that it is got to be axions.”
“Data are data”
The scientists appeared for X-ray signatures of axions from Betelgeuse, making use of info taken by NuSTAR, NASA’s area-based mostly telescope that focuses substantial-electricity X-rays from astrophysical sources. The workforce obtained 50 kiloseconds of knowledge from NuSTAR throughout the time the telescope was trained on Betelgeuse.
The researchers then modeled a selection of X-ray emissions that they might see from Betelgeuse if the star was spewing out axions. They considered a variety of masses that an axion might be, as very well as a assortment of likelihoods that the axions would “couple” to and reconvert into a photon, relying on the magnetic field power in between the star and Earth.
“Out of all that modeling, you get a variety of what your X-ray sign of axions could possibly seem like,” Perez states.
When they searched for these signals in NuSTAR’s details, however, they located nothing at all previously mentioned their expected history or outdoors of any standard astrophysical sources of X-rays.
“Betelgeuse is likely in the late levels of evolution and in that case ought to have a massive likelihood of converting into axions,” Xiao claims. “But data are data.”
Presented the variety of ailments they considered, the team’s null result procedures out a huge area of prospects and sets an higher limit that is 3 occasions much better than prior limitations, from laboratory-centered searches, for what an axion should be. In essence, this means that if axions are ultralight in mass, the team’s benefits show that the particles must be at minimum a few occasions much less likely to pair to photons and emit any detectable X-rays.
“If axions have ultralight masses, we can unquestionably convey to you their coupling has to be very little, usually we would have witnessed it,” Perez suggests.
Ultimately, this suggests that researchers may have to glimpse to other, considerably less detectable electrical power bands for axion signals. Even so, Perez states the research for axions from Betelgeuse is not over.
“What would be fascinating would be if we see a supernova, which would ignite a substantial quantity of axions that wouldn’t be in X-rays, but in gamma rays,” Perez states. “If a star explodes and we really do not see axions, then we’ll get actually stringent constraints on an axion’s coupling to photons. So everyone’s crossing their fingers for Betelgeuse to go off.”
Reference: “Constraints on Axionlike Particles from a Tough X-Ray Observation of Betelgeuse” by Mengjiao Xiao, Kerstin M. Perez, Maurizio Giannotti, Oscar Straniero, Alessandro Mirizzi, Brian W. Grefenstette, Brandon M. Roach and Melania Nynka, 21 January 2021, Bodily Assessment Letters.
This exploration was supported, in component, by NASA.