In school, they teach us that science is done by making a hypothesis, testing your hypothesis, and then revising your hypothesis as needed. Astronomy doesn’t really work that way. We generally start by looking at the universe, saying “Wow that’s weird,” finding a theorist to help us come up with a bunch of testable theories about what is going on, and then we test our theories to figure out what best matches reality and sometimes, along the way, our telescopes find new details that radically change what we thought we know. 

In general, when we look around the universe, we assume that while events like star formation may be more common at one point in time or another, the specific triggers for star formation were somewhat random, and different generations of stars have formed a bit randomly over time. At least, that was our thinking. 

A new set of observations of dwarf galaxies introduces confusion. In looking at 36 dwarf galaxies within about thirteen million light-years, astronomers found oddly synced star formation histories. For each system, they used two different methods to understand the ages of the stars and found that the present ages indicate there was a quiet period from about three to six billion years ago followed by a period of increased star formation enduring the past three billion years. 

It’s unclear if farther out galaxies also have this pattern of behavior. This work appears in The Astrophysical Journal and was led by Charlotte Olson, who said: The James Webb Space Telescope … will be the ideal way to add that new data to find out just how far outwards from the Milky Way this ‘baby boom’ extended.”

Beyond not knowing how far-reaching this pattern is, we also have no idea why this pattern is. According to coauthor Eric Gawiser: The full impact of the discovery is not yet known as it remains to be seen how much our current models of galaxy growth need to be modified to understand this surprise. If the result cannot be explained within our current understanding of cosmology, that would be a huge implication, but we have to give the theorists a chance to read our paper and respond with their own research advances.

It’s been a while since we encountered an acronym so bad we needed to take a moment to highlight its glory with a BABIES award (that’s Bad Acronyms & Backronyms in Everyday Science). This paper, folks, let me introduce you to ANGST: the ACS Nearby Galaxy Survey Treasury. ACS is the Advanced Camera for Surveys. So really, this is the  Advanced Camera for Surveys Nearby Galaxy Survey Treasury, which is a name that is giving me ANGST, so well done, namers. Well. Done.

More Information

Rutgers press release

“Star Formation Histories from Spectral Energy Distributions and Color–magnitude Diagrams Agree: Evidence for Synchronized Star Formation in Local Volume Dwarf Galaxies over the Past 3 Gyr,” Charlotte Olsen et al., 2021 May 24, The Astrophysical Journal