Astronomy often relies on extreme objects. It’s easier to get excited about "the best" or “the most”, and it's stories about exceptionality, not the norm, that usually grab headlines. But today, average galaxies can have the spotlight.
Astronomers have observed a faint and distant galaxy, which they believe is representative of the true average population of galaxies that formed so quickly after the Big Bang. Due to limitations in our instruments, the galaxies seen from this early time have been the brightest and biggest. But this object is definitely nothing special.
"Other most distant objects are extremely bright and probably rare compared to other galaxies," said lead author Austin Hoag, a UC Davis graduate student, in a statement. "We think this is much more representative of galaxies of the time."
As reported in Nature Astronomy, the light from MACS1423-z7p64 was emitted 13.1 billion years ago, just a few hundred million years after the beginning of the universe.
This galaxy comes from the mysterious period known as the epoch of reionization. At this time, the universe was full of neutral hydrogen, which blocked most light. The universe would have looked really foggy. But the light of the first stars ripped electrons away from the hydrogen (ionizing it again like after the Big Bang) and allowing the universe to become transparent.
It’s in this fog that the first galaxies and first stars formed, so if we want to understand how galaxies have evolved we need to understand reionization. And while the bigger and more luminous galaxies might be awe-inspiring, it’s the little guys like this one that did the bulk of it.
"We have a before and an after, but not exactly a when," Hoag added. Or a what, when it comes to what drove reionization. Was it mostly young galaxies, or did objects such as black holes and gamma ray bursts contribute as well?
The light of the galaxy is magnified by the nearby cluster and then it eventually reaches our observatories. NASA/Keck/Austin Hoag/Marusa Bradac
The discovery of MACS1423-z7p64 was possible because it was in the right location in the sky, just behind a very massive galaxy cluster. The gravity of the cluster is so high that it bends space-time creating a gravitational lens.
The cluster magnified the light of this faraway regular Joe and allowed astronomers to spot it. When the next generation of observatories come online, like the James Webb Space Telescope, they will see many more of these ‘average’ galaxies.