While we love to tell you what we know, let’s face it, sometimes it’s much more interesting to work through a “whodunnit?” mystery involving other galaxies than to try and make sense of any more terrestrial mysteries. 

In this story, we have the mystery of weird chemical ratios in a dwarf galaxy 430 million light-years away in the direction of the Hercules constellation. This little system is a leftover bit from the early universe that, like a bit of an unmixed splattered recipe, doesn’t contain all the ingredients or even the existing ingredients mixed as expected. 

This particular system is mostly made of the base hydrogen and helium our universe formed with, and it is enhanced by a touch of oxygen that was created in massive stars. Surprisingly, these systems also have an unexpectedly large dash of iron. Normally, we expect to see an iron-to-oxygen ratio that reflects the kinds of stars that create these elements under normal conditions. Iron comes from long-lived stars that explode as supernovae, and oxygen comes from smaller stars that exhale their materials into the space around them. The rarity of the supernova leads to typically less iron than oxygen, but that’s not what we see in this weird galaxy, and this is the second galaxy like this we’ve found. 

To explain these two galaxies, astronomers considered the differences between stars made today and made in the early universe and found that massive stars made prior to the creation of heavy elements could have formed both iron and oxygen, creating the chemical recipe we see in these systems. Because these galaxies are small, once those massive stars formed, nothing was really left to make more massive stars. If this theory is true, these systems should contain intermediate-sized black holes – black holes a hundred times the mass of the Sun. 

It’s unclear how we might observe such black holes in these systems, but it is still cool that we have a theory for what happened that has an observational test. And maybe someday we’ll find a way to see the effects of those possible black holes.

More Information

Science News article

“EMPRESS. II. Highly Fe-Enriched Metal-poor Galaxies with ∼1.0 (Fe/O)⊙ and 0.02 (O/H)⊙ : Possible Traces of Super Massive (>300M⊙) Stars in Early Galaxies,” Takashi Kojima et al., to be published in The Astrophysical Journal (preprint on arxiv.org)