May 28, 2019 written by Elizabeth Howell
Our universe is a whopping 13.7 billion years old, and we still understand very little about how it all began. Sometimes, even what we thought we knew turns out to be off the mark: Researchers just learned that the most ancient galaxies — those that were around before the universe hit its one billionth birthday — are much brighter than they expected them to be. As researchers strive to learn more, their work is illuminating the secrets of the early universe.
It Started With a Bang
The universe (as we know it) formed in an event known as the Big Bang, when the universe expanded from an infinitesimally small point. At first, all the matter in the universe was nothing more than tiny particles such as neutrinos, electrons, and protons.01:0901:13
But if you could time-travel to that moment in history, you couldn’t have seen a thing. That’s because the electrons scattered photons of light in the same way sunlight scatters from cloud water droplets on Earth today, according to NASA. Light couldn’t move freely, which made the universe opaque. The universe eventually cooled down enough to allow atoms to form, which in turn allowed light to shine through. The first stars emerged around the universe’s 100 millionth or 200 millionth birthday, and soon afterward came the first galaxies.
Roughly 12.7 billion years ago, the universe looked a lot like the universe we have today, filled with stars and galaxies — although, of course, these galaxies were pretty young. At that point, the universe passed through a key milestone known as the epoch of reionization.
In this new universe, the atom hydrogen now existed in a new form — an ionized form, meaning that it was electrically charged instead of neutral. Why does that matter? It’s because the neutral atoms that existed before stopped all the shorter wavelengths of light, like X-rays, ultraviolet light, and gamma rays. The new ionized atoms allowed these wavelengths to shine through, which gives us a more complete view of how the universe works. Black holes tend to shine in X-rays, for example, while ultraviolet light helps us learn more about the temperatures of young stars.
What This Means for Old Galaxies
Here’s where our ancient galaxies become important. As announced in a new studyled by Stephane De Barros, a postdoctoral researcher at the University of Geneva in Switzerland, researchers used NASA’s Spitzer Space Telescope to examine 135 galaxies from the beginning of the universe. The team discovered that these early galaxies shine very brightly in infrared (heat-emitting) light. This heat comes from ionized radiation hitting gases of hydrogen and oxygen inside the galaxies. This, in turn, shows us more about how old galaxies were made.
“This implies that these galaxies were dominated by young, massive stars composed mostly of hydrogen and helium,” NASA said in a statement. “They contain very small amounts of ‘heavy’ elements (like nitrogen, carbon, and oxygen) compared to stars found in average modern galaxies.”
Here’s the more interesting thing this tells us: The first galaxies did not contain the first stars. The very first stars in the universe were made up of only hydrogen and helium and went supernova early in the universe’s lifetime. Over time, their explosions fueled more generations of stars. Those early “next generations” are contained in the ancient galaxies.
We still know very little about the epoch of reionization. Awesome as Spitzer is, it has a small mirror (only as large as a hula hoop, NASA says). To learn more, we need another observatory that can collect more light. Luckily, NASA’s James Webb Space Telescope is expected to launch in 2021 and can study many of the same light wavelengths as Spitzer. Webb’s mirror is a massive 21 feet (6.5 meters), which allows it to see even more detail in these ancient galaxies. What new wonders might lie in store?