Volume XXVII Number 1
The 36-inch WIYN telescope dome slit opens at sunset in preparation for viewing.
Photo by Karen Masters
Liese van Zee
Photo © Tyagan Miller
If you think your schedule is hectic, note how Liese van Zee spent a full semester last year: On Tuesdays and Thursdays, she taught a brand-new class. Then, each Friday, she left town for Arizona, where she logged time collecting data from a pair of big telescopes, returning on Monday in time to teach again.
It's exhausting for a listener to contemplate, but van Zee doesn't sound the least bit aggrieved. She barely sounds harried. She seems to regard her trips to the telescopes the way some of us might look forward to a weekend at the beach: "It's fun! Not practical, exactly, in terms of your personal life. But it's very fun."
Liese van Zee is an assistant professor of astronomy at Indiana University Bloomington, her office tucked away in a remote and obscure hallway in Swain Hall West that can only be found using a star map, a wormhole, and a little luck. Anyone overly concerned about her personal life--or her jet lag--can rest easy: this year has been less hectic, even as she's continued to log weeks of telescope time for just one of her several projects.
That project is called the Systematic Multiwavelength Unbiased catalog of Dwarf Galaxies and Evolution of Structure survey. The project's acronym--SMUDGES--is convenient but does little to convey the breadth or import of its research. Dwarf galaxies are very low-mass galaxies, about 10 to 100 times smaller--hence the name--than our Milky Way.
"Dwarf galaxies come in a couple of different flavors," van Zee explains. "Some are essentially dead, what we call dwarf ellipticals. Others still have some gas, they're still forming stars. This category includes some really oddball galaxies, called starbursts. Relative to their mass, they're forming huge amounts of stars. This makes them become really luminous and, thus, easy to find."
Because starburst galaxies are so visible and easy to locate, it's relatively easy to observe and collect data on them. But "if you just look for the bright things," van Zee declares, "you won't know anything about what's going on in the universe." That's where SMUDGES comes in: unlike past studies, the project samples a wide range of different dwarf galaxies, regardless of luminosity--that's where the "unbiased" in the acronym comes from.
"We're looking to find out this: is what's going on in starbursts, which we like because they're so visible, typical for all dwarf galaxies?" van Zee says. "You have to start with a sample where you know how it was derived." SMUDGES creates a sample that includes even those dwarf galaxies whose contrast against the darkness of the night sky is minimal.
Of course, for those samples to be valuable, they have to be large enough to allow van Zee and her team to detect a sufficiently large number of dwarfs. And then, having located those dwarfs, they have to be able to determine how far away they are. This is where IU's remarkable resources come into play. "The complement of telescopes available in Arizona is what makes this project possible," says van Zee. The WIYN consortium telescopes in Arizona enable SMUDGES to exist.
Contrary to what the average layperson might think, van Zee's trips to these telescopes don't involve peering through eyepieces. Her work doesn't need old-school stargazing. "Instead of using our eye, which isn't a very sensitive receptor, we use a camera that collects data," she says. The camera, attached to the back of WIYN's smaller .9- meter telescope, handles the imaging chore, while spectroscopy is accomplished with the consortium's larger 3.5-meter telescope. "The purpose of the imaging is to identify likely (galaxy) candidates," van Zee explains. "If you can see the object through the small telescope, you're likely to be able to get spectra on it in a large one."
The spectroscopy pinpoints the dwarf's distance by identifying the redshift of the galaxy. "Hydrogen, for instance, emits light at certain wavelengths," van Zee notes. "If your object is moving, those wavelengths get shifted." Spectroscopy detects shifts to determine how fast the object is moving away from us--because the universe is expanding--and therefore how far away it is.
SMUDGES relies on large samples, so this is a big job. The .9 meter telescope has a camera that can observe a full square degree at a time, which is a significant area of the sky. But if van Zee needs to cover 134 square degrees, that requires 134 individual pointings. That's a lot of imaging.
"There are thousands of galaxies, I mean, galaxies are everywhere," van Zee says. "But on average, any given square degree has only one galaxy that's interesting (for the survey)."
Last year, van Zee spent an aggregate of about a month on imaging, and about a week on spectroscopy; now, as the imaging nears completion, that ratio is on the verge of switching. "So that's where all my time goes!" she says, laughing.
Meanwhile, imaging and spectroscopy are only two-thirds of the SMUDGES to-do list; once those are complete, the team will return to imaging again, this time with a different filter, to track the dwarf galaxies' star formation rates by tracing the brightness of the gases illuminated when massive stars ignite.
This may seem like an awful lot of work and frequent flyer miles just to attend to dwarf galaxies. But before categorizing her research as specialized arcana, it helps to know that van Zee isn't one to get wrapped up in the obscure, the marginal, or the intentionally incomprehensible. A chemistry major as an undergraduate, she was always drawn to astronomy. "Chemistry projects are interesting, but when they're described they're not very intuitive (to the non-specialist)," van Zee observes. "What I've always liked about astronomy is that its questions are fundamental and intuitive and approachable by everybody: How did the universe form? That's an interesting question."
She has a point. Listening to van Zee describe her research at a brisk conversational clip can be dizzying or occasionally intimidating, but it's never opaque. And while the papers and graphs tacked up by faculty and grad students along her Swain West hallway are initially indecipherable, a second look reveals those formal shapes and plotted points to be almost instinctively familiar--Oh, that's a supernova; hey, that kind of looks like a black hole. A picture that might be a comet fragment smashing into Jupiter is undeniably cool. Even a passerby with nary a day of astronomy training might glance at a random scattering of thumbtacks across an empty corkboard and find echoes of celestial patterns that resonate with early childhood gazings at stars, the sun, and the moon.
So if van Zee is committed to studying the big, intuitive, and consequential questions, then what's driving her SMUDGES research on star formation in dwarf galaxies? "The theme of my work is tied to the concept of what happened first. Dwarf galaxies are interesting fundamentally because they are the building blocks of the universe. Our Milky Way was built up through the accretion of little tiny things. In dwarf galaxies we can see the fundamental underpinnings of how all galaxies evolve."
There aren't many bigger questions than that.
On one level, van Zee admits, she studies galaxies that are close to us because she can. It would be nice to be able to examine galaxies further away to watch galaxy evolution in action, but technology limits that possibility. Here again, though, the particular properties of dwarf galaxies come to the rescue.
"Nearby dwarf galaxies actually mimic the early galaxies in many respects," van Zee says. "Like the early galaxies, nearby dwarf galaxies are also low-metallicity objects with little star formation activity." So the conditions of our own galaxy's infancy might reasonably be observed in neighboring dwarf galaxies.
That's worthwhile, and not just for nostalgic reasons. The question of how the first stars formed is a thorny and baffling one, sort of like trying to answer the chicken-and-the-egg conundrum after first getting rid of the chicken. And the egg.
"How do you form the first stars?" van Zee says. "You have to have a way to cool a cloud of gas, to get it to collapse. Most clouds of gas are somewhat stable as they are, so you need to remove the cloud's pressure support by cooling it down. In the universe today, that cooling is accomplished most efficiently by certain molecules. Any simple molecule like carbon monoxide could work. But in the early universe, which didn't yet have stars or metals, that cooling is unlikely to happen be-cause there weren't molecules to do it. It's all very perplexing."
There are theories about how these initial formations might have happened, including the idea that the kind of star that formed early on was a huge one that never fully collapsed. "That's an attractive notion," van Zee says. "When a massive star evolves, it does so in a spectacular fashion. Metals go ripping out into the intergalactic medium. If that happens, you'd expect there to be enriched material out there in the middle of nothing. And sure enough, when we do certain experiments, we see this enriched material way out in the middle of nothing." Such an initial reaction, then, could conceivably have generated the metals necessary to enable cooling and star formation in other, distant galaxies.
van Zee hasn't entirely subscribed to that view, though. "I have written papers that say starbursts are rare events," she says. "Theorists don't like that, because as a practical matter, a starbursting galaxy is more useful than a galaxy sitting around doing nothing. By comparison, dwarf galaxies are these small little pathetic objects."
Meanwhile, the SMUDGES project continues to explore the question van Zee posed earlier: is what's happening in the conveniently visible starbursts typical for all dwarf galaxies? It's way too early to tell. But as long as she has access to telescopes, van Zee will take her time finding out.
Eric Pfeffinger is a freelance writer in Toledo, Ohio.