The secret to neutrino interactions may lie in supernovae

In a novel study, scientists have conceived of a new framework that highlights how supernovae could be used to explain the interactions of neutrinos and their impact on the universe.

“Neutrinos only have very small rates of interaction with typical matter, so it’s difficult to detect them and test any of their properties,” said Po-Wen Chang, lead author of the study and a graduate student in physics at Ohio State. “That’s why we have to use astrophysics and cosmology to discover interesting phenomena about them.”

Neutrinos remain a mystery to scientists, despite much study. However, by evaluating how self-interactions would affect the neutrino signal from Supernova 1987A, the closest supernova spotted up to date, researchers found that “when neutrinos do interact with themselves, they form a tightly coupled fluid that expands under relativistic hydrodynamics.” Hydrodynamics is a branch of physics that deals with the motion of fluids and the forces acting on solid bodies immersed in fluids and in motion relative to them compare hydrostatics.

Complicated dynamics

“The dynamics of supernovae are complicated, but this result is promising because with relativistic hydrodynamics we know there’s a fork in the road in understanding how they work now,” said Chang. 

More work needs to be done before scientists can say for certain how neutrinos operate however the study is a an important milestone forward in figuring out the long-standing astrophysical issue of how neutrinos actually scatter when ejected from supernovae, said John Beacom, co-author of the study and a professor of physics and astronomy at Ohio State. 

“This problem has lain basically untouched for 35 years,” said Beacom. “So even though we were not able to completely solve how neutrinos affect supernovae, what we’re excited about is that we were able to make a substantial step forward.”

Now, the team hopes to further investigate neutrino self-interactions however since only about two or three supernovae happen per century in the Milky Way, it might be a very long time before the researchers can have all the data they need to prove their theories.

“We’re always praying for another galactic supernova to happen somewhere and soon, but the best we can do is try to build on what we know as much as possible before it happens,” said Chang. 

The study was published in Physical Review Letters.

Study abstract:

Neutrinos remain mysterious. As an example, enhanced self-interactions, which would have broad implications, are allowed. At the high neutrino densities within core-collapse supernovae, should be important, but robust observables have been lacking. We show that make neutrinos form a tightly coupled fluid that expands under relativistic hydrodynamics. The outflow becomes either a burst or a steady-state wind; which occurs here is uncertain. Though the diffusive environment where neutrinos are produced may make a wind more likely, further work is needed to determine when each case is realized. In the burst-outflow case, increase the duration of the neutrino signal, and even a simple analysis of SN 1987A data has powerful sensitivity. For the wind-outflow case, we outline several promising ideas that may lead to new observables. Combined, these results are important steps toward solving the 35-year-old puzzle of how affect supernovae.