Berkeley, California—Scientists at the University of California, Berkeley have proposed an intriguing solution to one of astronomy’s most elusive problems: the nature of dark matter. According to new research by the team, the detection of gamma rays from neutron stars following supernova explosions could potentially confirm the existence and properties of axions, hypothetical particles believed to be a primary component of dark matter.
For years, the composition of dark matter has puzzled scientists. Making up about 27% of the universe’s mass-energy composition, dark matter does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects. However, theoretical physicists have put forward the axion as a viable candidate, a particle so elusive that it has never been observed directly.
The Berkeley research group, led by associate professor Benjamin Safdi, pinpointed a potential natural phenomenon that could expose these ghostly particles: the explosive death of massive stars, or supernovae, within the Milky Way or its neighboring galaxies. These cataclysmic events are thought to be capable of producing axions that may convert into gamma rays under the extreme conditions present during the explosion.
Key to the detection of these gamma rays is their capture during the fleeting moments after a supernova detonates—within approximately 10 seconds of the event. For such an observation to be possible, existing space-based instruments like the Fermi Gamma-ray Space Telescope must be fortuitously positioned to observe the explosion. Given Fermi’s current field of view, the researchers estimate a 1 in 10 chance of successful alignment.
Safdi explains, “Observing gamma rays from a neutron star at the heart of a supernova could inform us not only about the presence of axions but also their mass.” This would provide critical data, as the mass of the so-called QCD axion, and its interaction strength, are derived from its reaction to high temperatures and strong magnetic fields.
Neutron stars, which are the extremely dense remnants of supernovae, naturally present some of the strongest magnetic fields known in the universe. Their unique environment makes them perfect laboratories for studying extreme states of matter and potentially, the peculiar properties of axions.
The significance of this discovery strategy extends further as it could bridge gaps in our understanding of fundamental physics. Axions are not only a candidate for dark matter but may also play a role in reconciling inconsistencies between quantum mechanics and Einstein’s theory of general relativity.
Despite the potential, there are formidable challenges to this method of detecting axions. The sporadic nature of supernovae—with the last nearby event occurring in 1987—and the narrow observational window present logistical hurdles. Moreover, the current capacity to monitor the sky for such gamma rays is limited.
In response, the Berkeley team has suggested an ambitious solution to increase these odds. They propose the development of the Galactic Axion Instrument for Supernova (GALAXIS), a satellite constellation that would monitor the entire sky continuously, thus ensuring that no supernova goes unobserved.
“Missing the opportunity to detect a supernova and thereby possibly identify the axion component of dark matter would be extremely disappointing,” Safdi remarked, highlighting both the potential and the challenges of this innovative approach to one of cosmology’s most profound mysteries. The team’s findings and proposals have been detailed in a recent publication in the journal Physical Review Letters, marking a hopeful step forward in the quest to unravel the dark sector of the universe.