Before you can get Fast Radio Bursts, you need to build a galaxy. We try to understand how that occurs from two different directions – by observing our galaxy and by looking for galaxies forming in the early universe.

From our position inside the Milky Way, we can study our system’s individual stars to get a sense of the generations and their chemical genetics. Stars generally form in clusters, with all the stars in the cluster having the same chemical composition. Particularly small galaxies may even form all their stars in a single burst, where the tiny galaxy is essentially a single large star cluster.

Most larger galaxies form through the merger of small systems, and our own Milky Way is included in that most. As projects like the Sloan Digital Sky Survey and the Gaia mission measure the colors and positions of stars, they identify streams of same-composition, same-age stars that became part of our Milky Way when their small home galaxy merged into our galaxy. Remarkably, though, for as many streams of colliding objects we find, it still looks like most of our galaxy was already in place ten billion years ago, with what we see now only merging later. 

The earliest major merger to be identified was the collision of what is being called the Gaia Sausage galaxy. The Gaia spacecraft discovered a family of stars that are all of the same composition and that are orbiting at a weird angle to the rest of the disk of the Milky Way. Those stars were slightly younger than the Milky Way’s native stars. This means the bulk of our stars are older, and our disk was mostly formed before the Milky Way and Sausage galaxies collided and even before the Sausage galaxy was made. Our galaxy put simply is really old and was already pretty big early in the history of the universe.

One of the major rules of science is that we start from the belief that we don’t occupy a special place in the universe. This means that whatever we see shouldn’t be too different from what we’d see from somewhere else, and whatever got us here should have also happened elsewhere. Using the Atacama Large Millimeter/submillimeter Array (ALMA), researchers were able to find galaxies showing vague spiral structures more than twelve billion years ago.  

These earliest systems were a little weird, were compact, and their structure is most likely driven by interactions with invisible companions. How the galaxy evolved from these weird early systems to the universe we see today isn’t well understood, but it looks like we can thank galaxy interactions both for forming spiral structures and building up large galaxies over time. While ALMA creates shockingly good images, the JWST was actually designed to tell us how galaxies formed. It looks like JWST’s launch is going to be delayed again, this time due to the rocket, so the answers on how galaxies evolved from what ALMA sees to what we see locally… we’re going to have to wait a bit longer.

More Information

The Ohio State University press release

The Milky Way may have grown up faster than astronomers suspected (Science News)

“Chronologically dating the early assembly of the Milky Way,” Josefina Montalbán et al., 2021 May 17, Nature Astronomy

ALMA press release

“Spiral morphology in an intensely star-forming disk galaxy more than 12 billion years ago,” Takafumi Tsukui and Satoru Iguchi, 2021 May 20, Science