Earth is bathed in droves of neutrinos spewed by the Milky Way’s stars

The Milky Way could be called “the Neutrino Way.” Its stars produce vast numbers of the subatomic particles. Now, scientists have calculated how many of them should be streaming down onto Earth from all the stars within our galaxy. And they have an idea of how to detect them.

Neutrinos born in stars in the galaxy — other than the sun — pass harmlessly through your thumbnail at a rate of about 1,000 a second, researchers report January 7 in Physical Review D. That may seem like a lot, but neutrinos from the sun are about 100 million times as prevalent, thanks to its proximity.

The sun is a well-understood source of neutrinos, lightweight subatomic particles that are produced in a variety of processes in the universe, including the reactions that take place within stars’ cores. Scientists first detected solar neutrinos in the 1960s, and today, they have isolated different classes of neutrinos from the various nuclear reactions that take place within Earth’s home star. But we’ve yet to detect the rarer neutrinos from other stars in our galaxy, although scientists are confident they must be out there.

To calculate how many to expect, researchers used data on the Milky Way’s multitude of stars from the European Space Agency’s Gaia spacecraft coupled with information about how the galaxy formed and evolved. Combined with calculations of how stars of different masses emit neutrinos as they age, this information revealed the neutrinos’ numbers.

Many of these galactic stellar neutrinos, the researchers found, come from the center of the galaxy, which is crowded with stars. That means these neutrinos could potentially be detected by considering where they came from. They could be separated from the much more plentiful solar neutrinos by using a neutrino detector that can determine the direction of incoming particles, says physicist Pablo Martínez-Miravé of the University of Copenhagen, an author of the study. Scientists could look for neutrinos that came from the direction of the galactic center, not from the direction of the sun.

Detecting galactic stellar neutrinos would allow scientists to test multiple physics concepts at once, Martínez-Miravé says. That includes details of how stars live and die, how neutrinos behave and theories of how our galaxy came to be. “It’s proving that we understand our galaxy, the stars in our galaxy —things we see in the sky every night.”