A Surprisingly Ancient Galaxy


Every once in a while, an astronomy paper comes out that makes me go, “Whoa. Whoa! Wait… really?” This is one of those papers.

Let me build the story for you. We’ll start with the Big Bang, which created the universe we know and love 13.75 billion years ago. From the near-uniform hydrogen and helium gas that pervaded the cosmos early on, we now live in a universe with clusters, galaxies, stars, black holes, planets, people, and so much more. So, one of the outstanding questions in astronomy today is: How did the universe get from point A to point B?

With bigger and more powerful telescopes, we’ve only recently been able to sample galaxies that are 12 to 13 billions light-years away. Galaxies so far appear as they did in the first billion years of the universe’s existence. Deep images that look far back in time, such as the Hubble Ultra Deep Field, show us that, on average, galaxies get smaller and more immature as you look back in time. Surely, outliers exist, such as the massive quasars that have helped astronomers probe this early epoch.

ANALYSIS: No Time Dilation for Distant Quasars?

The hunt is on to determine what the very first galaxies were like. Here is where the latest study blew my mind. Astronomers analyzed the light from an unnamed distant galaxy and determined that it formed just 200 million years after the Big Bang. That is really early to be making galaxies. That is just 1-2 percent of the universe’s current age.

As delighted as I was at reading this result, I have to reserve a bit of skepticism for this finding. After all, this is a really difficult measure to make for an object so far away, and thus so faint.

Astronomers were helped out by a cluster of galaxies that is “in the way” of our view of this very distant galaxy. The gravitational pull of the cluster actually bends the galaxy’s light as it passes, acting as a huge lens, allowing us to see the distant galaxy.

ANALYSIS: Mapping Dark Matter with a Cosmic Lens

The age of the galaxy at the time it is seen is determined by the spectrum of the combined light of all the stars in the galaxy. For this, you have to take an already faint light source and spread it out (sort of like a rainbow) and detect emissions and absorption lines. Then, the spectrum is fit with several models of various stellar populations of various ages. The best fit gives the 200 million year formation time, but it is a long process to get there.

I certainly hope that this particular study can be confirmed with further observations, or, if we’re lucky, more examples of such early galaxies. For now, we have a tantalizing hint that our universe was up and raring to go a bit earlier than expected. You go, universe!

Image: Most of what you see here is the galaxy cluster Abell 383. The arcs are other lensed objects further away. The two tiny dots that are circled? Yeah, THAT’S the galaxy in question. Credit: NASA, ESA, J. Richard (CRAL) and J.-P. Kneib (LAM). Acknowledgement: Marc Postman (STScI)

This research is to be published in the Monthly Notices of the Royal Astronomical Society, and a preprint is available at arxiv.org.

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