Tree rings reveal ancient supernovae

When a star explodes, it sends radiation, energy, and physical material into space.

Some of what it sends out into space — extremely fast-moving protons or atomic nuclei — can collide with other planets, like Earth.

When cosmic rays hit Earth’s atmosphere, they can create an isotope of carbon called radiocarbon, which ends up mixed into Earth’s natural carbon cycle.

Radiocarbon isn’t uncommon in living things like trees (which use carbon dioxide and water to make their food), but sometimes in tree rings, scientists have seen unusually high amounts of radiocarbon.

“These are extreme events, and their potential effects seem to match tree ring records,” author Robert Brakenridge, a senior researcher at the University of Colorado, Boulder, says in a statement.

He found spikes in radiocarbon in tree rings associated with supernova events — like a supernova in the Vela constellation, 815 lightyears away.

This star exploded 13,000 years ago, and Brakenridge found a spike in radiocarbon in the tree-ring record not long after.

But the correlation warrants further investigation, especially because supernovae within our galaxy could be harmful to Earth.