A recurring theme here is “how did everything start?” Like, we know there was a Big Bang, things expanded and cooled for 400,000 years, and then stars and galaxies started doing their thing, and their light cleared out the universe. Where we get stuck is did those galaxies most responsible for clearing out the universe grow from the massive collapse of stuff into massive galaxies or through the formation of myriad tiny galaxies?

We know galaxies formed both ways. The universe is all about “yes and,” but in this particular whodunnit, we’re learning that while there were massive galaxies out there clearing out their surrounding gas and ionizing everything with ultraviolet starlight, it may have been the small galaxies, scattered everywhere, that actually did the bulk of the work.

Researchers led by Nathan Eggen and publishing in The Astrophysical Journal show that one tiny galaxy is clearly doing a lot to blow out the universe. This galaxy is POX 186. It’s a compact system with about 100,000 solar masses of massive stars. Where it’s located, just a couple of billion years after the formation of the universe, its light is ionizing the neutral gas all around it. Part of how it is doing this isn’t just the ultraviolet light. 

The stars, as they explode into supernovae, are pushing out the gas. Their ultraviolet light is breaking free of the galaxy, and all around it, the universe is becoming transparent. Now, little galaxies like this were the most common. Just like a single bonfire will do a really good job of lighting up one part of a field; if you fill that field with a hundred campfires, you can light so much more. And it looks like these little galaxies, like POX 186, lit not just “so much more” but everything. Thanks to them, we can look back to the earliest moments of the visibly transparent part of the universe a few billion years after it started. Once the JWST maybe launches, it will be able to see just what was forming.

More Information

University of Minnesota press release

“Blow-away in the Extreme Low-mass Starburst Galaxy Pox 186,” Nathan R. Eggen, Claudia Scarlata, Evan Skillman, and Anne Jaskot, 2021 April 29, The Astrophysical Journal