By: Brayden Yin

On June 8th, a meeting of the American Astronomical Society reported that phosphorus was found far from the center of the galaxy, at the edge of the Milky Way.

Phosphorus is one of six essential elements for life, along with nitrogen, carbon, hydrogen, oxygen, and sulfur. Until recently, it was the only element of the six missing from the farthest reaches of the galaxy. Finding phosphorus that far out signifies that life is indeed possible, extending the galaxy’s “habitable zone” by 22,000 light-years.

The team of astronomers pointed two of their radio telescopes at a cool, dusty gas cloud floating around at the edge of the galaxy. The cloud is frigidly cold, at -248 degrees Celsius, which is only 25 degrees above absolute zero, the point where atoms stop moving. The cloud is also 74,000 light-years from the galactic core, triple the distance of the Earth’s system from the middle of the galaxy. The cloud has the distinct chemical signature of phosphorus monoxide and phosphorus mononitride.

The reason phosphorus is so scarce in the outer regions of the galaxy is because the element is only produced in supernovae, catastrophic explosions in which heavy elements are created. There is not a lot of material in the outer galaxy, meaning it is hard to build stars that have the capability to end their life in a supernova. Beyond 49,000 light-years from the center of the galaxy, there is only one known supernova remnant.

The only possible explanation for phosphorus this far out in the galaxy is the phenomenon of “galactic fountains”. To understand this explanation, one must imagine the Milky Way as a round disk, with a bulge at the center. As a supernova occurs, matter is thrown above or below the disk, and it settles near the edge of the galaxy.

The discovery of phosphorus will compel astronomers to further study possible life-sustaining planets at the galaxy’s edge.