Ohio State Modeled 700 Manganese Emission Lines and Turned a Supernova Leftover Into a Cosmic Clock

Astronomers have a persistent problem with time. There is no clock on a distant galaxy, and the light arriving from one is a blend of everything that has ever happened inside it. So they read the chemistry instead: elements heavier than helium are manufactured by stars, and their abundances build up in a rough sequence, which means the mix in a galaxy encodes how much stellar life it has been through.

A team at The Ohio State University has now added a new hand to that clock, and it is an element nobody was using: manganese.

Manganese is forged in supernovae, particularly the thermonuclear explosions of white dwarfs, and its abundance relative to iron climbs steadily as a galaxy ages. That makes it an unusually clean chronometer in principle. In practice it has been almost unusable, because reading an element's abundance from a spectrum requires knowing precisely what wavelengths its ions emit under specific temperatures and densities — and for doubly ionized manganese, written [Mn III] in the literature, that atomic data barely existed.

Anil Pradhan and Sultana Nahar, astrophysicists at Ohio State, set out to compute it. Working with Zher Samak of Al-Aqsa University in Gaza, the study's first author, they simulated how electrons scatter off manganese ions and generated more than 700 models of the resulting emission lines across the range of conditions found in supernova remnants and interstellar gas clouds. The point of running that many was to identify which lines stay bright and unambiguous under real astrophysical conditions, rather than merely existing on paper.

"If we understand the chemical composition of galaxies, we can learn more about the chemistry of stars and their elements," Pradhan said.

The findings were published in Monthly Notices of the Royal Astronomical Society on Aug. 31.

Atomic physics of this kind is invisible infrastructure. Nobody points a telescope at a manganese calculation, but every abundance measurement ever made depends on tables like these, and where the tables are thin the measurements inherit the uncertainty. Filling in [Mn III] means an element that was previously discarded from spectral fits can now be included, which tightens the age estimates that come out the other side.

The team plans to test the predictions against real observations using NASA's James Webb Space Telescope and ground-based observatories. Webb is particularly well matched to the problem: it can resolve individual emission lines in galaxies far enough away that their light left when the universe was a fraction of its current age, which is exactly where a chemical clock is most useful and where the existing ones are least reliable.

If the lines behave as modeled, manganese joins iron, oxygen and alpha-elements as a standard part of the toolkit for dating what astronomers are looking at.