Astronomers find phosphorus at galaxy’s edge

Astronomers peering toward the outermost reaches of the Milky Way have found phosphorus, a critical element for life, where none was believed to exist (Nature, 2023, DOI: 10.1038/s41586-023-06616-1).

Using telescopes at the Arizona Radio Observatory and the Institute of Millimetric Radio Astronomy, a team from the University of Arizona (UA) detected signals emitted by electrons transitioning from one energy level to another in molecules of phosphorus monoxide and phosphorus mononitride. The signals came from a molecular cloud nearly 74,000 light years from the center of the galaxy. By comparison, Earth is about 26,000 light years from the center.

Phosphorus is believed to be created solely by supernovae, but in that part of the galaxy, matter is spread too thin to form stars big enough to create such massive explosions.

“There’s just no supernovae out in this part of the galaxy, so where’s the phosphorus coming from?” asks Lucy Ziurys, an astrochemist at UA, who led the study proposed by two of her graduate students.

Their observations suggest that lower mass stars may also produce phosphorus, which would help explain discrepancies in the amount of the element found in nearby regions of space. They also raise the possibility that habitable planets exist far beyond the area where astronomers have discovered them thus far. Biomolecules containing phosphorus, such as DNA, are more complex, but the discovery of simpler molecules mean that the element is available, raising the possibly that life could arise even at great distances from Earth.

“The galaxy’s a big place, and there might be nice, habitable solar systems at the edge, which people didn’t think would ever occur,” Ziurys says.