The seek for the universe’s darkish matter might finish tomorrow — given a close-by supernova and somewhat luck.
The character of darkish matter has eluded astronomers for 90 years, for the reason that realization that 85% of the matter within the universe isn’t seen by way of our telescopes. The most certainly darkish matter candidate in the present day is the axion, a light-weight particle that researchers around the globe are desperately looking for.
Astrophysicists on the College of California, Berkeley, now argue that the axion could possibly be found inside seconds of the detection of gamma rays from a close-by supernova explosion. Axions, in the event that they exist, can be produced in copious portions through the first 10 seconds after the core collapse of an enormous star right into a neutron star, and people axions would escape and be remodeled into high-energy gamma rays within the star’s intense magnetic subject.
Such a detection is feasible in the present day provided that the lone gamma-ray telescope in orbit, the Fermi Gamma-ray House Telescope, is pointing within the route of the supernova on the time it explodes. Given the telescope’s subject of view, that’s about one probability in 10.
But, a single detection of gamma rays would pinpoint the mass of the axion, specifically the so-called QCD axion, over an enormous vary of theoretical lots, together with mass ranges now being scoured in experiments on Earth. The shortage of a detection, nevertheless, would remove a wide variety of potential lots for the axion, and make most present darkish matter searches irrelevant.
The issue is that, for the gamma rays to be brilliant sufficient to detect, the supernova must be close by — inside our Milky Means galaxy or considered one of its satellite tv for pc galaxies — and close by stars explode solely on common each few a long time. The final close by supernova was in 1987 within the Giant Magellanic Cloud, one of many Milky Means’s satellites. On the time, a now defunct gamma-ray telescope, the Photo voltaic Most Mission, was pointing within the supernova’s route, nevertheless it wasn’t delicate sufficient to have the ability to detect the anticipated depth of gamma rays, in keeping with the UC Berkeley group’s evaluation.
“If we had been to see a supernova, like supernova 1987A, with a contemporary gamma-ray telescope, we might be capable to detect or rule out this QCD axion, this most attention-grabbing axion, throughout a lot of its parameter area — basically your complete parameter area that can not be probed within the laboratory, and far of the parameter area that may be probed within the laboratory, too,” mentioned Benjamin Safdi, a UC Berkeley affiliate professor of physics and senior creator of a paper that was printed on-line Nov. 19 within the journal Bodily Evaluate Letters. “And it will all occur inside 10 seconds.”
The researchers are anxious, nevertheless, that when the long-overdue supernova pops off within the close by universe, we cannot be able to see the gamma rays produced by axions. The scientists are actually speaking with colleagues who construct gamma-ray telescopes to evaluate the feasibility of launching one or a fleet of such telescopes to cowl 100% of the sky 24/7 and be assured of catching any gamma-ray burst. They’ve even proposed a reputation for his or her full-sky gamma-ray satellite tv for pc constellation — the GALactic AXion Instrument for Supernova, or GALAXIS.
“I feel all of us on this paper are confused about there being a subsequent supernova earlier than we’ve the suitable instrumentation,” Safdi mentioned. “It will be an actual disgrace if a supernova went off tomorrow and we missed a possibility to detect the axion — it won’t come again for one more 50 years.”
Safdi’s co-authors are graduate scholar Yujin Park and postdoctoral fellows Claudio Andrea Manzari and Inbar Savoray. All 4 are members of UC Berkeley’s physics division and the Theoretical Physics Group at Lawrence Berkeley Nationwide Laboratory.
QCD axions
Searches for darkish matter initially targeted on faint, huge compact halo objects (MACHOs) theoretically sprinkled all through our galaxy and the cosmos, however when these did not materialize, physicists started to search for elementary particles that theoretically are throughout us and needs to be detectable in Earth-bound labs. These weakly interacting huge particles (WIMPs) additionally failed to point out up. The present finest candidate for darkish matter is the axion, a particle that matches properly inside the usual mannequin of physics and solves a number of different excellent puzzles in particle physics. Axions additionally fall neatly out of string idea, a speculation concerning the underlying geometry of the universe, and may be capable to unify gravity, which explains interactions on cosmic scales, with the speculation of quantum mechanics, which describes the infinitesimal.
“It appears nearly inconceivable to have a constant idea of gravity mixed with quantum mechanics that doesn’t have particles just like the axion,” Safdi mentioned.
The strongest candidate for an axion, known as a QCD axion — named after the reigning idea of the robust power, quantum chromodynamics — theoretically interacts with all matter, although weakly, by way of the 4 forces of nature: gravity, electromagnetism, the robust power, which holds atoms collectively, and the weak power, which explains the breakup of atoms. One consequence is that, in a robust magnetic subject, an axion ought to sometimes flip into an electromagnetic wave, or photon. The axion is distinctly completely different from one other light-weight, weakly-interacting particle, the neutrino, which solely interacts by way of gravity and the weak power and completely ignores the electromagnetic power.
Lab bench experiments — such because the ALPHA Consortium (Axion Longitudinal Plasma HAloscope), DMradio and ABRACADABRA, all of which contain UC Berkeley researchers — make use of compact cavities that, like a tuning fork, resonate with and amplify the faint electromagnetic subject or photon produced when a low-mass axion transforms within the presence of a robust magnetic subject.
Alternatively, astrophysicists have proposed on the lookout for axions produced inside neutron stars instantly after a core-collapse supernova, like 1987A. Till now, nevertheless, they’ve targeted totally on detecting gamma rays from these axions’ gradual transformation into photons within the magnetic fields of galaxies. Safdi and his colleagues realized that that course of isn’t very environment friendly at producing gamma rays, or a minimum of not sufficient to detect from Earth.
As a substitute, they explored the manufacturing of gamma rays by axions within the robust magnetic fields across the very star that generated the axions. That course of, supercomputer simulations confirmed, very effectively creates a burst of gamma rays that’s depending on the mass of the axion, and the burst ought to happen concurrently with a burst of neutrinos from inside the recent neutron star. That burst of axions, nevertheless, lasts a mere 10 seconds after the neutron star kinds — after that, the manufacturing fee drops dramatically — although hours earlier than the outer layers of the star explode.
“This has actually led us to serious about neutron stars as optimum targets for trying to find axions as axion laboratories,” Safdi mentioned. “Neutron stars have a whole lot of issues going for them. They’re extraordinarily sizzling objects. Additionally they host very robust magnetic fields. The strongest magnetic fields in our universe are discovered round neutron stars, corresponding to magnetars, which have magnetic fields tens of billions of instances stronger than something we will construct within the laboratory. That helps convert these axions into observable indicators.”
Two years in the past, Safdi and his colleagues put the most effective higher restrict on the mass of the QCD axion at about 16 million electron volts, or about 32 instances lower than the mass of the electron. This was primarily based on the cooling fee of neutron stars, which might cool quicker if axions had been produced together with neutrinos inside these sizzling, compact our bodies.
Within the present paper, the UC Berkeley group not solely describes the manufacturing of gamma rays following core collapse to a neutron star, but additionally makes use of the non-detection of gamma rays from the 1987A supernova to place the most effective constraints but on the mass of axion-like particles, which differ from QCD axions in that they don’t work together through the robust power.
They predict {that a} gamma ray detection would enable them to determine the QCD axion mass whether it is above 50 microelectron volts (micro-eV, or μeV), or about one 10-billionth the mass of the electron. A single detection might refocus present experiments to substantiate the mass of the axion, Safdi mentioned. Whereas a fleet of devoted gamma-ray telescopes is the best choice for detecting gamma rays from a close-by supernova, a fortunate break with Fermi can be even higher.
“The most effective-case situation for axions is Fermi catches a supernova. It is simply that the prospect of that’s small,” Safdi mentioned. “But when Fermi noticed it, we would be able to measure its mass. We would be able to measure its interplay power. We would be able to decide all the things we have to know concerning the axion, and we would be extremely assured within the sign as a result of there isn’t any atypical matter which might create such an occasion.”
The analysis was supported by funds from the U.S. Division of Vitality.