With a little luck: Nearby supernova could end the search for dark matter
The particles that make up dark matter could be created right at the start of a supernova. However, we would need a bit of luck to observe them.
Artist's impression of a neutron star with an enormously strong magnetic field: Axions are likely to be produced during its formation.
(Image: Casey Reed, courtesy of Penn State)
The search for the mysterious dark matter could end at any time – with a comparatively close supernova and luck. A research team from the University of California, Berkeley has determined this and explained that in the first ten seconds of such a stellar explosion, so-called axions should be produced in sufficient quantities. These are considered to be the most promising candidates for the particles on which dark matter is based. If such a supernova occurs in the Milky Way or one of its satellite galaxies, NASA's Fermi Gamma-ray Space Telescope should be able to detect traces in the gamma radiation. But only if it happens to be looking in the right direction. The probability of this happening is around 1 in 10.
Could happen at any time
As the research group explains, observing a supernova like the one in 1987 with a modern gamma-ray telescope would be enough to either confirm or rule out one of the most interesting theories on the nature of dark matter. It is mainly about those properties that cannot be studied in the laboratory. The main issue here is the mass of the particle, which has so far only been described theoretically. Only a few seconds of observation data would suffice for this, but it would have to be the data immediately at the start of the explosion. That's why everyone in the team is quite nervous because we would need a lot of luck for such a supernova – and it could happen at any time.
"Everyone who worked on the study is worried that the next supernova could happen before we have the right instruments," says physicist Benjamin Safdi, who led the work. It would be really annoying if such a supernova were to occur tomorrow and we had no way of detecting it, he says. We might then have to wait another 50 years. That is why proposals have already been drawn up for a fleet of gamma-ray telescopes that would keep an eye on the entire sky around the clock. They would be called the "GALactic AXion Instrument for Supernova" or GALAXIS.
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One of the big questions
The question of the nature of dark matter is currently one of the most important in fundamental physics. Its existence was postulated based on astronomical observations, in which stellar movements were measured that could not be adequately explained by known matter and its gravity. In total, there should therefore be five times more dark matter in the cosmos than classical matter. Axions are considered to be the particles of which it is composed, and the German Electron Synchrotron (DESY) is also searching for them. With the research work now published in Physical Review Letters on detection using a supernova, the team from California wants to help ensure that a promising method is not overlooked.
In the research paper, the team not only describes how axions are likely to be produced immediately after the collapse of a star into a neutron star. From the lack of evidence of the resulting gamma rays in the closest supernova to Earth in recent centuries, the group has also been able to better determine which mass is not an option for the axions. This occurred in 1987 in the Large Magellanic Cloud. If the next one can be observed with the Fermi space telescope, much more precise values could be determined and with great reliability – "because no normal matter can trigger such an event," explains Safdi.
(mho)
