Unraveling the Mystery of Dark Matter
For nearly a century, astronomers have been puzzled by the existence of dark matter, which makes up approximately 85% of the universe’s mass yet remains invisible to our telescopes. Researchers have proposed various theories to explain the nature of dark matter, but a conclusive proof has remained elusive. One promising approach involves detecting a supernova at the moment of explosion, which could provide valuable insights into the properties of dark matter.
The Axion Hypothesis
Among the various candidates for dark matter, the axion has emerged as a leading contender. This theoretical particle is characterized by its extremely small mass, which is compensated by its vast abundance. The QCD axion, favored by string physicists, interacts with the fundamental forces of nature, including gravity, electromagnetism, the strong force, and the weak force. Notably, the QCD axion has a maximum mass 32 times less than that of an electron.
Detecting Axions through Gamma Rays
Astrophysicists at the University of California, Berkeley, have proposed a novel approach to detect axions by observing gamma rays emitted from a nearby supernova explosion. According to their theory, axions would be produced in large quantities during the first 10 seconds after a massive star collapses into a neutron star. These axions would then escape and transform into high-energy gamma rays within the star’s intense magnetic field.
The Role of the Fermi Gamma Ray Space Telescope
The detection of gamma rays from supernova explosions is currently only possible if the Fermi gamma ray space telescope is pointing in the direction of the supernova at the time of its explosion. Given the telescope’s field of view, the likelihood of this occurring is approximately one in ten.
Implications of Detection or Non-Detection
A single gamma-ray detection would enable researchers to determine the mass of the axion, including the QCD axion, over a wide range of theoretical masses. Conversely, a lack of detection would eliminate a broad range of potential masses for the axion, rendering many current searches for dark matter irrelevant.
The Ongoing Search for Dark Matter
Initial searches for dark matter focused on compact, massive, and faint halo objects (MACHOs), which were theorized to be scattered throughout the galaxy and cosmos. When this approach yielded no results, physicists turned their attention to elementary particles that could be detectable in terrestrial laboratories. The weakly interacting massive particles (WIMPs) also failed to materialize.
The Axion: A Promising Candidate
In the quest to uncover the true nature of dark matter, the axion has emerged as a prime candidate. This particle fits well into the standard model of physics and resolves several outstanding problems in particle physics. Axions also arise naturally from string theory, which could help unify gravity and quantum mechanics.
Interactions between Axions and Matter
In theory, QCD axions interact weakly with all matter through the four fundamental forces: gravity, electromagnetism, the strong force, and the weak force. Researchers have proposed searching for axions produced inside neutron stars immediately after a core-collapse supernova, such as 1987A. Until now, they have primarily focused on detecting gamma rays from the slow transformation of these axions into photons in the magnetic fields of galaxies.