Small universe, big glass
Leading cosmologist Wendy Freedman trains a telescopic lens on the biggest questions in the universe.
Last September, observational cosmologist Wendy Freedman joined the Department of Astronomy and Astrophysics as a University Professor. Freedman’s appointment follows 30 years at the Carnegie Observatories in Pasadena, California, where she became the first woman on the observatories’ permanent scientific staff in 1987 and the Crawford H. Greenewalt Director in 2003. The Chicago-Carnegie connection puts her in good company with George Ellery Hale, founder of UChicago’s astronomy and astrophysics department, and Edwin Hubble, SB 1910, PhD 1917.
Freedman first rose to prominence leading the Hubble Space Telescope Key Project, which measured the universe’s current expansion rate—the Hubble constant—and thus determined the age of the universe more precisely. The project began in the mid-80s. In 2001 the team announced that the universe is 13.7 billion years old, with an uncertainty of 10 percent. Previously cosmologists could estimate only that the universe was between 10 and 20 billion years old.
Now she leads the Chicago Carnegie Hubble Project, which aims to reduce that uncertainty even further—to within 3 percent—using the Spitzer Space Telescope, the Hubble Space Telescope, and the Magellan telescopes. Freedman also is a cofounder of the Carnegie Supernova Project, which uses the 100-inch and Magellan telescopes at Las Campanas Observatory in Chile to study the universe’s acceleration—which in turn contributes to the study of dark energy, the hypothetical explanation for cosmic acceleration.
Freedman has served as chair of the board of directors of the Giant Magellan Telescope (GMT) Organization since its inception in 2003. This super giant earth-based telescope, which will start construction this year, also in Las Campanas, will have 10 times Hubble’s resolution. To function, it requires a minimum of four of its seven mirrors to be in place. Production of the fourth, which will take several years, begins in late March. Freedman expects the GMT to provide its first data by 2022, and that all mirrors will be in place by 2025.
The Magazine’s interview with Freedman is edited and adapted below.
Women in science then and now
I notice a big difference from when I was a graduate student at the University of Toronto. The number of women entering into graduate classes and getting positions as professors at major universities across the United States now has increased. And the opportunities for women to become directors of major observatories—those were opportunities that didn’t exist just a few decades ago. I always felt I was born at the right time. A lot of women before me, it was their efforts that allowed a younger generation to succeed.
I’ve seen a lot of change, but that isn’t to say there aren’t still issues and difficulties. We need to start early in encouraging girls to pursue careers in science and technical fields. It’s still unusual. It’s not something that many girls even think about. I had my share of teachers who were very encouraging and others who weren’t. I had a physics teacher once who would say, “The girls don’t have to listen to this.” That’s when I was growing up. I feel really pleased at all the progress, but watching my own daughter and hearing some of the comments that were made in her science classes, I still think there is a ways to go.
Art of science
Science isn’t a textbook where you just read and memorize things. Science is a way of looking at the world and first and foremost testing ideas. It’s a human enterprise. Parts of it are fascinating, parts are beautiful and elegant, parts are mysterious and complex, and you see the whole range of human effort and creativity. Part of what makes us human is our curiosity and learning about the world. I think as a field sometimes we let people down in not being able to communicate the excitement of science.
Window on the past
Cosmology asks questions on the big scale of what is our universe, what’s it made of, how’s it behaving, how’s it changing with time, and those are questions that fascinate me. We can make measurements and actually learn something about the universe. We can peer back in time; because light has a finite speed, as you look farther back in distance you’re also looking further back in time. It’s an incredible opportunity that you don’t have in many sciences.
Measuring distances within our galaxy ...
You look up in the sky with a telescope at the direction of the star. Then as Earth is going through its annual motion around the sun, if you look six months later from the opposite side of its orbit, you end up with a triangle with the diameter of Earth’s orbit as its base. Then it’s just high school geometry, ordinary Euclidean geometry; you can solve for the distance. That anchors what we call the zero point, and then you can measure relative distance.
... and beyond
You need to know how bright objects actually are, as opposed to how bright they appear. Something can appear faint because it’s far away, or that might be the nature of the object. You have to be able to determine what the brightness of an object is to calibrate its absolute distance. So we use pulsating stars called Cepheid variables to do that.
The upper atmosphere of a Cepheid variable is moving in and out, which changes the star’s brightness, and the rate at which it’s changing is directly related to how bright the star is. That’s called a period luminosity relation, which was discovered by an astronomer named Henrietta Leavitt. She worked at the Harvard College Observatory in the early 1900s, and she discovered this relationship, which we’re now calling the Leavitt relation. She received very little recognition for her work, but all of modern cosmology rests on that relationship. That is the pillar for our ability to measure distances.
So we use these Cepheid variables, and when they become too faint as they’re too far away, we use supernovae, these really bright explosions of stars at the end of their lifetime. In that way we can chart the distance scale of the universe.
The GMT is comprised of seven 8.4-meter mirrors, six in a circle and one in the center. The mirrors take four years apiece from the beginning of the casting; they have to be cooled very slowly over a period of several months. Then they’re taken out and the back sides and front sides are polished. They have to be tested, so they move between a polishing machine and a test tower. Each phase in that process is about a year. One of the big decisions I made early on as chair of the board was to go ahead with the first mirror, even though we had only a small fraction of the funding, because I knew if we didn’t demonstrate technically that it was feasible, we would never be in a position to build the project. Without knowing that you could solve the technical challenges, you wouldn’t begin construction of this billion-dollar project. The first mirror took seven years.
What we might see
If someone were on the moon and lit a candle, we’d see it. The GMT is sensitive enough to detect that. The power is quite extraordinary. In terms of resolution, the example I like to give is, you look at the surface of a dime and you can hold it up and see the detail and read the writing. With the GMT you can go 200 miles away and see that kind of detail.
What we might find
A real niche for the GMT will be the ability to study planets outside of our solar system. Because of this high resolution and sensitivity, it will be possible to measure masses and densities, and so characterize the properties of planets that are as low-mass as Earth. Right now it’s possible to do that for planets that are many times the mass of Earth, and certainly for the Jupiters and Saturns and Neptunes.
If there are nearby planets that have life in a form similar to what we’re familiar with, we would be able to take spectra of the atmospheres of those planets and actually look for the biological signatures, as opposed to chemical signatures in the atmospheres.
Since Galileo turned a telescope to the sky in 1609, every time there’s been a jump in capabilities or that next generation of telescopes, we’ve made discoveries, without exception. So it’s that possibility for discovery that’s really exciting—what we can’t anticipate at all.
You can help ensure UChicago astronomers’ continued access to “big glass,” including the Giant Magellan Telescope, and the discoveries it makes possible. Visit campaign.uchicago.edu/priorities/psd.