What Do Quasars Reveal about the Early Universe?

An artistic look at what an early distant quasar might look like. ESO/M. Kornmesser

Quasars are incredibly bright objects that exist because of activity by some of the most mysterious and dark things around: supermassive black holes at the hearts of galaxies. The name "quasar" comes from the term "quasi-stellar radio source" because they were first seen by their strong radio emissions. However, they also give off other light waves. 

Quasars exist throughout cosmic history, but astronomers are especially interested in studying the ones that were around when the universe was a mere infant, perhaps around a billion years old. That's when the cosmos was entering its toddler-hood. Until 2016, astronomers knew of only a handful of these distant beacons of light in the early universe. Although they are very bright, distance dims their brightness, so finding the most distant ones is like searching for a flashlight flickering at the edge of our solar system. In other words, like looking for a needle in a very distant haystack. Astronomers have found more early quasars, which will give them more insight into the goings-on in the universe during its first billion years.

Finding New, Distant Quasars Illuminates the Early Universe

Why should we care about the early universe? Have you ever looked at your own baby pictures? Or pictures of your parents and earlier ancestors? If you have, you probably noticed some interesting things about your appearance and how similar it might be to your great-grandfather or a great-aunt. Just looking at your own baby pictures shows you what you once looked like and how that little tot grew up to be you.

Take a look at images of your town 100 years ago, or your home 35 years ago, or the arrangement of Earth's continents from millions of years ago. You notice that things change over time. Yet, some things remain fairly similar. Perhaps the main building in your town is still there after 200 years. Its façade may be different, but the shape is the same. The continents may have drifted apart, but rocks remain the same.

The universe is no different. Its early objects — the stars — for example, look similar to stars we see today. When astronomers study those stars, they might notice that the earliest stars were much more massive than even some of the most massive stars today. But, they're still stars.

Go back early enough, and the universe is more of a "soup" of particles that eventually cooled enough to make clouds of hydrogen and helium gas. Those were the birthplaces of the first stars and galaxies. However, there wasn't a lot of light in the very early universe, so it's difficult to study. The births of the first stars and the earliest giant galaxies within the first few hundred million years of the universe gave rise to the supermassive black holes that sat at their hearts. And, when those black holes "went active" and became quasars, they lit up the infant universe. Along with the role of dark matter, the toddlerhood of the universe remains one of the great unstudied eras of the cosmos. Quasars will help with that study.

How Do Quasars Help?

You might wonder how the light from a quasar can help us "see" into the nurseries of stars and galaxies. Quasars are active galaxy cores. The supermassive black holes that power them form huge jets of superheated material that stream across space. They are bright in x-rays, radio, ultraviolet, and even visible light. 

All that light they emit travels across space and space is not empty. In its own neighborhood, the light from a quasar encounters clouds of gas and dust. As it travels through, some of the light is absorbed by those clouds. That leaves a very distinct "fingerprint" in the light that we receive here on Earth. 

Astronomers can use that fingerprint to tell how much gas there is, how it is moving, and where it is, which gives them useful insight into what conditions were like at that time in cosmic history.  It can provide insight into what's happening in and around the black hole.The intensity of the light (which may be visible, ultraviolet, radio or even gamma-rays), tells them something about the conditions right at the center of the home galaxy. The quasar's emissions also heat up material surrounding the black hole, and that gives off light as well. So, there's a lot of information to be gleaned from a quasar's light. Plus, the fact that they exist so early in the universe also tells astronomers something about conditions in the galaxies at that time, plus some more information about the formation and existence of black holes.

There is still a lot about this era when the universe’s lights were turned back on that science doesn’t understand. But having more examples of ancient quasars will help astronomers figure out what happened in those first billion years after the Big Bang.