The axion, a particle that is elusive and difficult to detect, may soon be detected by scientists. This could happen with the aid of a supernova. The dark matter that makes up 85% of all the mass in our universe has been undetected since almost 90 years.
The researchers at UC Berkeley suggested that axions can be spotted soon after a supernova emits gamma rays. Fermi Gamma-ray Space Telescope has a one in 10 chance to observe the event. The axons are created during the first moments of the collapse of the star, and then they transform into high energy gamma-rays within the magnetic field.
One detection of gamma-rays coming from a supernova nearby could give crucial information on the QCD mass, allowing for a range of different axion masses. The ongoing research on dark matter would be greatly impacted by this.
If no gamma-rays were detected, many axion masses could be excluded, making some searches for dark matter obsolete. It is difficult to detect supernovae because they are rare and must be within the Milky Way galaxy or one of its satellite galaxies.
The last supernova that was close to us in 1987, however, is no longer. The gamma ray telescope at the time lacked the necessary sensitivity to detect the expected intensity of gamma rays.
Benjamin Safdi is a UC Berkeley Associate Professor of Physics and Senior Author of a Paper. If we could see supernovas like 1987A with a modern Gamma-Ray Telescope, we’d be able detect this QCD Axion — this most intriguing axion — across a large part of its parameter area. This includes the whole parameter range that is not accessible in the lab, as well as a good portion of that parameter range that is. It would happen in 10 seconds.”
Scientists are worried that they might not be able to detect gamma-rays from axions if the next supernova happens nearby. In order to address this issue, researchers are working with colleagues that design gamma ray telescopes in an effort to investigate the feasibility of launching telescopes that can continuously cover 100% of the sky. This will ensure they detect any gamma ray bursts.
For this, they have suggested a constellation of satellites named GALAXIS for Supernova (GALactic Xion Instrument). Safdi expressed concern that without proper equipment the ability to detect the axions of a supernova could be lost, potentially delaying this opportunity by decades.
Safdi is working on the project with graduate students Yujin park and Claudio Andrea Manzari, and Inbar Savoray from UC Berkeley.
The initial focus of the search for dark matter was MACHOs, or massive compact halo object. When they weren’t found, the focus shifted on weakly-interacting massive particles, which failed to appear. Dark matter is a leading candidate. The axion aligns well with standard particle models and solves many unresolved problems in particle physics.
The string theory also offers axion possibilities. It posits the fundamental structure of our universe, and it may be able to combine gravity (cosmic interaction) with quantum physics (micro level interactions).
Safdi said, It seems impossible that a theory of quantum mechanics and gravity could be consistent without axion particles.
The QCD axion, although weak, is the best candidate to interact with matter through gravity, electromagnetism and the strong force that holds together atoms, as well as the weak force which accounts for the breaking up of atoms.
Axions can sometimes transform into photons (electromagnetic waves) in a magnetic field. This is unlike neutrinos which interact only through the weak force, gravity, and do not respond to electromagnetic forces. Laboratory experiments such as ALPHA Consortium DMradio and ABRACADABRA, led by UC Berkeley scientists, use compact cavities which resonate like a tuned fork.
The cavities are used to amplify weak electromagnetic signals that occur when an axion of low mass transforms into a high-mass one in a magnetic field.
Astrophysicists previously concentrated on detecting photons that are formed when axons transform into gamma-rays within the magnetic fields galaxies. Safdi’s team found, however, that the process must be detected more efficiently from Earth. They instead investigated the axion generation in the magnetic fields that surround the neutron stars.
This process, according to supercomputer simulations, produces a burst gamma-rays that is highly dependent upon the mass of an axion. The burst is accompanied by a blast of neutrinos emitted from the newly formed neutron star.
The axion burst is only produced for about 10 seconds following the formation of the neutron stars, before it drops significantly. However, this occurs hours before the outer layer explodes.
Safdi said, This has made us think of neutron stars, as laboratories for the search for axions. They have many advantages. These are very hot objects. “They also have very strong magnetic fields.”
The strongest magnetic fields are around the neutron stars. These magnetars have fields that are tens and billions times more powerful than what we can create in the lab. This helps to convert the axions in these signals.
Safdi’s team and he set the upper limit of 16 million electron-volts for the QCD mass axion based on neutron star cooling rates. The UC Berkeley group has extended this research in their most recent work by analyzing gamma rays created during a core collapse of a star into a neutral star.
They provide the most accurate constraints on the mass for axion particles that do not interact via the strong force. The researchers predict that the QCD mass could be revealed by detecting gamma-rays if the axions exceed 50 microelectronvolts (meV) or one ten billionth of the mass an electron.
A supernova nearby or an accidental detection made by Fermi could be the catalyst for refocusing existing experiments.
Safdi said, The best case scenario is that Fermi captures a supernova. Just that it’s a small chance. We could still measure the mass if Fermi had seen it. We would be able measure the strength of its interaction. “We’d know everything about the axion, and be confident that the signal is accurate because nothing ordinary could produce such an event.”
Journal Reference
- Claudio Andrea Manzari. Yujin park, Benjamin R. Safdi and Inbar Savoray. Supernova Axions are converted to Gamma Rays by magnetic fields of progenitor stars. Physical Review Letters. DOI: 10.1103/PhysRevLett.133.211002
