University Of Wyoming Team Catalogs Quasars To Study Dark Energy, Black Holes

Sep 4, 2020

A team of University of Wyoming astronomy students have compiled the largest ever catalog of quasars. Wyoming Public Radio's Ashley Piccone spoke with graduate student Brad Lyke about what a quasar is and why they are important.

Brad Lyke: The short version is that they are the biggest, angriest engines in the universe. The slightly longer version is that every galaxy has a supermassive black hole at the center that we're aware of. But they aren't all drawing in material at the same time, and it's the actual process of drawing in the material which causes the whole thing to release a lot of light and that thing itself is the quasar. It's the black hole plus the material being sucked in, so it's a process more than an object.

Ashley Piccone: So not every black hole is a quasar?

BL: No, but every quasar has a supermassive black hole at the center.

AP: How do we look at quasars?

BL: We want spectra, instead of just a picture that you know you can see with your eyes. So for a spectrum, we spread the light out kind of like you do with a prism and then look at all the different colors and how much of each color there is.

AP: And what does that tell you?

BL: It tells us chemistry, processes, ages sometimes, and even distance from just the spectra.

AP: How do you tell a quasar spectrum from any other kind of spectrum?

BL: That's a big part of what this research is. The easiest way of course is for somebody to look at it and there will be a certain type of feature called a broad emission line. In a squiggly spectrum, you'll see some spike, a big and tall spike, that shows up. That's a broad emission line as long as it's pointing up. Quasars are pretty much the only object that have those. It can take a while to look at a full spectra especially if it's a really far away object. It can take human beings a little while, so you need to train a computer to do it in those numbers.

AP: So how many quasars are in your catalog?

BL: We have about 1.5 million things they thought was a quasar originally and we have to go back through and say yes or no. And then it ends up half, 750,000.

AP: And so why is identifying all of these quasars important?

BL: The primary project is studying dark energy, the expansion of space and time and you need quasars because they are very, very bright, the angriest engines in space, so you can see them far away. So, we can look at a whole swath of space and a whole swath of history, a whole swath of time to see how dark energy affected things over time.

AP: How does looking farther away let you look at longer periods of time?

BL: So that comes down to the speed of light. It travels at a certain speed and if something is far enough away it takes light time to get to us. So, by the time a distant object gets to us, what we saw was the light from could be millions, or even billions years ago. So, what you're seeing is the past. I described it one place as the childhood photo album of the universe, that's what telescopes give us.

The expansion part only looks at where a quasar is in space because that's all we need to know is 'where is it?'. But there's a lot of people who want to know what they are because we don't really understand them very well. So being able to provide them with a very large catalog of quasars of all strengths, all over space, all ages, lets them study the physics of quasars so we can finally understand what's happening.

Have a question about this story? Contact the reporter, Ashley Piccone, at