Postdoc Spotlight: Eduardo Bañados

What excites you about your research?
 
I like to look into the distant past to understand how we got here. When we look very, very far away, we are looking into a snapshot into the universe’s past. What I am doing is to look as far back as when the first objects in the universe formed, which is a key component to tell us why our universe is the way it is now and what happened in between.
 
It’s like astronomical archaeology. Archaeologists dig into the Earth to see the layers and reconstruct the history of our planet. Likewise, in astronomy, we have layers and layers of the universe, and astronomers try to put them together to make sense of it.
 
 
How do you look so far into the early universe?
 
It’s difficult! Objects that are far away are also generally very faint. Eventually we’ll have 30-meter class telescopes, like the Giant Magellan Telescope (GMT), which will be better able to observe faint and distant objects. But I’m impatient. My approach is to use current, large telescopes like the twin Magellans at Las Campanas Observatory to look at extremely bright objects that are also far away.
 
Quasars are the most-luminous objects known, so we can study them even when they are far away. They are supermassive black holes at the center of massive galaxies—a billion times the mass of our Sun—that have material actively falling into it. There is a swirling disk of material around the black hole, which heats up creating an extreme amount of light. Light from a quasar can be a thousand times brighter than the light from the entire galaxy. Not every galaxy has a quasar, so they are exciting when we find them.
 
 
 
One of the amazing things you’ve done is play a key role in discovering more quasars than has ever been known before, especially very distant quasars. How did you accomplish this?
 
When I started at Carnegie three years ago, there were only about 60 very distant quasars known. Today we have about 250 known, most of which I’ve helped discover. The trick is to go farther and deeper with your telescopes, which is a high-risk, high-reward project. Carnegie is one of the few places that gives you access to telescopes and the freedom to try outrageous projects.
 
The challenging part in quasar hunting is to identify where we should look. I start by data mining the large astronomical surveys, such as Pan-STARRS, WISE, UKIDSS, and others. I write algorithms to find the needle in a haystack, which is most of my daily work.
 
Then we need to confirm that they are indeed distant quasars, and not, say, a nearby brown dwarf. Brown dwarfs and quasars look remarkably similar in some images. Brown dwarfs are intrinsically faint and red, while the quasars I study also look faint and red, but because they are extremely far away. So we use large telescopes to get more data from an individual candidate to characterize better each candidate’s color and other properties. At the end of the day, we take spectra of the most promising candidates and only then we can be sure that what we are looking at is a supermassive black hole accreting material in the center of a galaxy. The spectrum is like a fingerprint that can tell you the chemical composition of an object. 
 
 
 
Your work has made worldwide headlines since starting your fellowship at Carnegie three years ago. Which three discoveries stand out to you?
 
First, with my international team of collaborators, we doubled the number of known quasars, tripling those known in the Southern Hemisphere—that was two years ago and this number keeps increasing! Now we can study this population with lots of great telescopes in different wavelengths of light. Having a big atlas of quasars with data allows us to move from studying individual objects to characterizing the whole population. (Read the story here.)
 
Second, my colleagues and I started a program using the Atacama Large Millimeter Array, or ALMA, to study the host galaxies where quasars live. At the long wavelengths that ALMA uses, we can see the galaxies through the dust and gas. The program was a success. We were able to see some of the first massive galaxies that formed in the universe within less than 10 minutes of observation. But an even bigger surprise was that the observations revealed that a quarter of the quasars had another massive galaxy very nearby. Perhaps we are seeing the mechanisms to form these extreme objects or perhaps we are seeing the formation of the first large-scale structures in the universe. This finding was published in the renowned journal Nature. (Read the story here.)

Third, I found the most-distant quasar ever observed (also published in Nature)—it is from when the universe was only about 5 percent of its current age, and the black hole is about 800 million times the mass of the Sun. I was able to recognize what I had as soon as I saw the spectrum from the Magellan telescope when I was observing. It was really exciting, and an example of that high-risk needle- in-a-haystack search that paid off. (Read the story here.)
 
With all of these, there’s so much more work to do and unknown questions to continue to investigate.

 
What was your path to becoming an astronomer?
 
I grew up in Chile, which is home to a huge number of the best telescopes in the world.
 
I was always a curious kid and was very interested in science. When I was in high school, my family went on a vacation to La Serena where we went to a tourist telescope in the mountains. This was the first time I saw the Milky Way, looked at planets, and realized that you could get paid to look at the stars.
 
Then, in my junior year of high school, I took a six-week summer astronomy class at the University of Chile. I got to meet professional astronomers and find out what they do, which made my career path clear.
 
I went to Pontificia Universidad Católica de Chile as an undergrad, majoring in astronomy. There, I worked with Leopoldo Infante who is now the director of Carnegie’s Las Campanas Observatory. I received my Ph.D. from the Max Planck Institute for Astronomy (MPIA) in Germany, which is where I’m headed for a scientific staff position in 2019. It’s like there are two circles in my professional career that keep intersecting.
 
 

What has the Carnegie Princeton fellowship meant to you?

This has been a unique opportunity—Carnegie gives me all the resources that I need to do what I want to do. I get unparalleled access to some of the most powerful telescopes, freedom to pursue my own research, and an amazing group of colleagues who teach me and push me to do new things. For example, I like to call myself a multiwavelength astronomer, but it was at Carnegie where I wrote my first X-ray proposal. It’s great having these experts in-house.
 
At Carnegie, I proved that I can lead an international team of astronomers, and at my new position at MPIA I’ll be building a group. Right now, I have more data than I can handle, so my group will help me push the projects forward. And this is just the beginning.
 
This is an exciting time to be an astronomer—we’re the first generation who are finding objects at the edge of the universe. I’m really looking forward to using the next generation of telescopes—from space-based missions like the James Webb Space Telescope to the next generation of large ground-based telescopes like the Large Synoptic Survey Telescope and the GMT.  All of these will revolutionize our view of the universe, and it is exciting to be part of these projects from the beginning. We’re in a cool epoch of astronomy, but it’s just going to get more interesting.