While it’s been understood pretty much as long as we’ve understood stellar metallicities that globular clusters are low in metal content, we thought there was a floor to just how low that metallicity could go in large globular clusters. Essentially, when the raw material of the universe formed the first few generations of stars, it didn’t form those stars into globular clusters, and the dynamics associated with forming globular clusters only occurring after a minor amount of processing had occurred.
Well, apparently, the universe decided it “didn’t need no stinking” metal-enrichment to form at least some super metal-poor large globular clusters. And by some, I mean we have found one.
Astronomers using the High-Resolution Echelle Spectrometer (HIRES) spectrometer on the Keck Telescope had a couple of hours of time remaining after completing their planned observations and took a look at the Andromeda galaxy’s globular cluster RBVC EXT8. They found that it is three times less metal-rich than normal globular clusters, 800 times less metal-rich than our Sun. This accidental discovery is published in the journal Science with lead author Soren Larsen.
This is yet another example of our universe not letting us get too comfortable in our understanding of how things work. It is unclear if this is a random pocket of unprocessed gas that got shocked into forming a globular cluster without forming heavy metal producing stars that enriched it to normal levels or if this is some other rare situation we haven’t anticipated.
Whatever is happening, when we finally get the observations needed to explain the weirdness of what’s going on, we’ll bring them to you here.
“An Extremely Metal-Deficient Globular Cluster in the Andromeda Galaxy,” Soren S. Larsen, Aaron J. Romanowsky, Jean P. Brodie & Asher Wasserman, 2020
Oct. 16, Science