As the story goes, galaxies in the early universe could form in all sizes through the collapse of massive clouds of gas. Over time, smaller galaxies would continue to form through the collapse of gas into stars, but new larger galaxies would only be formed through the merger of smaller systems. It’s a good story, but the question becomes, at what point does this breakdown? Just how small of a system can form through mergers? To find out, researchers examined the stellar population of the nearby Large Magellanic Cloud. 

This southern hemisphere sky object looks like a cloud reflecting backlight but is actually a dwarf irregular galaxy that is zipping past our galaxy. Using the Very Large Telescope and Magellan telescopes in Chile, researchers led by Alessio Mucciarelli studied the compositions of stars in this galaxy’s various globular clusters. 

When a galaxy merges with a galaxy, the resulting system contains the globular star clusters from both systems, and these clusters’ stars reflect the chemistry of where they formed. And one of their observed globular clusters did not form with the others. Designated NGC 2005, this system may be all that remains recognizable from a small dwarf galaxy the LMC merged with in the past. All other stars and gas from this former system have thoroughly mixed into the LMC, becoming indistinguishable from stars that formed in other parts of our universe.

More Information

NOVA press release

“A relic from a past merger event in the Large Magellanic Cloud,” A. Mucciarelli et al., 2021 October 18, Nature Astronomy