A supernova explosion (SN1987A) discovered within the Large Magellanic Cloud on February 24, 1987. The picture shows the ring around SN1987A and the ring from the supernova explosion at its center. (Public domain)
A study by a team at Northwestern University (USA) found that all three neutrino flavor electrons, muons, and τons (tau) should be taken into account to get a fuller picture of the supernova explosion process.
Many previous studies have tended to study neutrinos by simplifying them into two categories: electron neutrinos and non-electron neutrinos (i.e., including muon neutrinos and τ neutrinos), which this study finds is not a good approach.
“Our study shows that they (all three flavor states) are important, and ignoring muons is not a good strategy.” Manibrata Sen, lead author of the study, said, “Previous studies have been incomplete, and we see dramatically different results when we include all three flavor states for consideration.”
A supernova is a form of star that ends its life with an explosion. Ninety-nine percent of that energy is contained within neutrinos. Emitted from deep within the star’s core, outward at nearly the speed of light and largely without interacting with any other matter, these neutrinos are the first messengers to reach Earth in the event of a supernova explosion. Therefore, scientists are now focused on probing the supernova explosion process from neutrinos.
Starting from the 1950s, particle physicists and astrophysicists have made important progress in this area. However, in order to simplify the research models, most of them only consider neutrinos in two main categories: electron neutrinos and non-electron neutrinos, which means that different types of non-electron neutrinos are considered to behave the same during supernova explosions.
Manibulata Sen said the complexity of neutrino studies is that they interact with each other in flavor state transitions under conditions as highly compact as those inside the star, which leads to the fact that whenever one of the flavor states is affected, the overall neutrino properties will also change significantly.
“In a highly compact environment, the neutrino density is very high, so they interact with each other. You can’t simulate the interaction of neutrinos in different flavor states in the Earth’s environment.”
Neutrino oscillations occur during the departure of large numbers of neutrinos from a star, and the conversion of flavor states will affect the various characteristics of the oscillations.
In this study, the researchers set up a nonlinear simulation system to simulate the rapid transition interaction of flavor states during neutrino departure from supernovae, including three flavor states. It turns out that this interaction process has a significant impact on various properties of neutrino oscillations.
The researchers say that even with the inclusion of the three flavor states, there is still a degree of simplification in their model, for example, the team hopes to expand the consideration of the spatial dimension based on the angular momentum and time modules in the next step.
The study was published Dec. 16 in Physical Review Letters.
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