First Biological Evidence of a Supernova: Remains of Exploding Star Discovered in Bacteria

Evidence of an exploding star, known as a supernova, is usually found in space in the form of luminous bursts of radiation and clouds of interstellar gas. Yet now, researchers have found that fossil remains also hold clues to supernovas in the form of the remains of iron-loving bacteria. The findings are the first to show that there can be biological evidence of a supernova.

These iron-loving bacteria are called magnetotatic bacteria and live within the sediments of Earth's oceans, close to the water-sediment interface. There, they make hundreds of tiny crystals of magnetite within their cells. In order to obtain iron to create these crystals, the bacteria actually utilize atmospheric dust that enters the ocean. This unique property is what provided the evidence for a supernova.

During a core collapse supernova, a star ends its life in a gigantic starburst. It hurls most of its mass into space and creates the radioactive iron isotope, Fe-60. Because this isotope's half-life of 2.62 million years is short compared to the age of our solar system, no supernova iron should technically be present on Earth. Therefore, any discovery of Fe-60 would mean that a supernova occurred in our cosmic neighborhood.

The fact that these bacteria sop up iron means that when a supernova hurled its material toward Earth, the bacteria also absorbed Fe-60. The researchers actually examined a Pacific Ocean sediment core from the Ocean Drilling Program, dating between 1.7 and 3.3 million years ago. More specifically, they took sediment samples corresponding to intervals of about 100,000 years and then treated them chemically in order to extract any Fe-60 that they might contain.

In the end, the researchers discovered these isotopes occurring about 2.2 million years ago. This actually matches the expected time from a previous study.

"It seems reasonable to suppose that the apparent signal of Fe-60 could be remains of magnetite chains formed by bacteria on the sea floor as a starburst showered on them from the atmosphere," said Shawn Bishop, one of the researchers, in a news release.

The findings could allow scientists to better understand our galactic history. Currently, the researchers are preparing to analyze a second drill core, which may reveal more clues about this ancient supernova.

The findings are published in the journal Nature.