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Astrophysicists from the University of California, Berkeley, have proposed a novel method to confirm the existence of axions, a leading candidate for dark matter, upon the detection of gamma rays from a nearby supernova. Following the collapse of a massive star into a neutron star, it produces axions in immense quantities within the first 10 seconds. These axions could then be converted into detectable gamma rays in the star's intense magnetic field.

Today, such an event could be observed by the Fermi Gamma-ray Space Telescope, provided it is directed towards the supernova at the time of the explosion—a one in ten chance according to current estimates. The prompt detection of gamma rays would not only confirm the existence of axions but could also determine their mass, sweeping across a vast range of theoretical masses. Conversely, the absence of detection would constrain the parameter space for these elusive particles.

A significant challenge lies in the rarity of nearby supernovae—the last one occurred in 1987 in the Milky Way's satellite, the Large Magellanic Cloud. During that event, the existing Solar Maximum Mission gamma-ray telescope wasn’t sensitive enough to detect the predicted gamma-ray intensity. Benjamin Safdi, UC Berkeley associate professor of physics, emphasized that a modern gamma-ray telescope would significantly improve the chance of detection, given that even a single 10-second observation period could be revolutionary for axion research.

To avoid missing such opportunities, UC Berkeley researchers are advocating for the deployment of a constellation of gamma-ray telescopes, capable of covering 100% of the sky continuously. They’ve proposed calling this full-sky array the GALactic AXion Instrument for Supernovae (GALAXIS), ensuring that any supernova event could be captured.

Axions interact weakly with matter through gravity, electromagnetism, the strong force, and the weak force, setting them apart from neutrinos, which only interact via gravity and the weak force. Axions should occasionally convert into photons in strong magnetic fields, making neutron stars—the strongest known magnetic fields in the universe—optimal for detecting axion signals.

UC Berkeley’s ongoing efforts include lab-based experiments, but a supernova detection remains a tantalizing prospect. Safdi and his team have already put stringent limits on axion masses using cooling rates of neutron stars. A real-time gamma-ray observation would refine these constraints further. Detecting such a burst would not only identify the axion’s mass but also determine its interaction strength, providing vital, previously inaccessible data about these prospective dark matter particles.