If you want to understand a part of Earth’s galactic history—whether it passed near a supernova during its path around our galaxy, for example—you may be able to find the answer in the crystal structure of a rock, according to a University of Michigan study.

The study outlines a method using paleo-detectors, an idea inspired by work from the 1960s, which used ancient minerals to search for new physics. The idea is this: The Earth is constantly showered with cosmic rays. Cosmic rays are particles produced by an energetic universe, one in which stars explode in supernovae, supermassive black holes at the centers of galaxies accelerate particles to near the speed of light, and neutron stars collide and produce bright flashes of gamma rays and other energetic particles.

“There are energetic particles produced in cosmic events all the time: neutron star mergers and black holes and active galactic nuclei,” said lead author Joshua Spitz, a particle physicist and the Norman M. Leff Assistant Professor of Physics at U-M. “Some of those energetic particles reach the Earth and interact with the atmosphere, producing showers of particles which rain down on us all the time.”

Some of these particles are neutrinos, which are fundamental particles that only interact with matter very weakly. As a result, these atmospheric neutrinos can pass through the Earth without interacting, allowing them to reach ancient minerals deep in the Earth.

Occasionally, one of these neutrinos will interact with an atomic nucleus in the ancient mineral, leaving a trace within the rock’s crystalline structure. By examining these traces in excavated rocks, scientists can study the flux of cosmic radiation on Earth over time. The researchers’ method is published in Physical Review Letters.

“About a hundred billion neutrinos from the sun pass through the tip of your finger every second, but almost none of them interact. The same applies to atmospheric neutrinos, which rarely interact. However, every once in a while, one of these atmospheric neutrinos will hit a nucleus,” said co-author and U-M graduate student Johnathon Jordan. “And when they do, they give the nucleus a kick.”

You may find the rest of the article written by Morgan Sherburne on the U-M News website.

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