Cottrell Scholar Awards - 2009
University of Wisconsin, Madison
Rethinking the Stellar Soup: Nonstop Action between the Stars
For centuries, astronomers underestimated the vitality of the vast galactic soup between the stars. Now with new tools to observe the galaxies and new models of their behavior, we are getting a picture of a wild and unexplained scene filled with fountains of hot gases exploding and cooling down into clumps that may give birth to new stars.
Snezana Stanimirovic, an assistant professor of astronomy at the University of Wisconsin-Madison, is among the leaders in bridging the two main ways of studying the stuff between the billions of stars - direct observations and astrophysical models.
Using data from the Arecibo radio telescope, the world's largest, she is helping paint a richly detailed panorama of one of the liveliest components of space, the thin atmosphere called the interstellar medium, or ISM.
"What's interesting is that the interstellar medium makes stars, and then at end of their lives the stars return their matter and energy back into that medium," she said. "It's very dynamic. And it's essential for galaxies, for their evolution, and for how the galaxies behave and interact with their neighbors."
Stanimirovic studies how the galactic clouds form and morph into stars, in turn shaping the evolution of galaxies like our own Milky Way, and the next-door Small Magellanic Cloud, all of them alive with big gravitational forces and little understood turbulence.
"This turbulence is something we don't understand well," she said. "We know it affects many astrophysical processes, especially star formation. A lot of recent models using numbers and theoretical assumptions have simulated the interstellar medium. Some are starting to include information about turbulence. However, we still need to test how well the simulated spectra match the observations.
"By comparing observations and simulations we are trying to understand all the essential physics that needs to be included in the models. We are not there yet."
Stanimirovic, pronounced stani-MEE-ro-vitch, was born in Serbia, then Yugoslavia, and studied at Belgrade University and at the University of Western Sydney at Nepean, in Australia, and did postdoctoral work at the Arecibo Observatory, in Puerto Rico, and at the University of California, Berkeley.
Her initial focus was the Small Magellanic Cloud, a dwarf galaxy 200,000 light years away, but she expanded her study to include the Milky Way, taking a hard look at the substantial gravity interactions between the two neighbors.
Interstellar medium is quite different in the two galaxies, Stanimirovic said. "We are still trying to establish how this affects star formation," she said. "There is a lot of theory that cloud formation depends on galactic environments. The amount of metals in the atmosphere is important for how the clouds fragment. We are still trying to establish the links between cloud and star formation. The story is still evolving."
Her work takes spectra and images of atomic hydrogen and translates them into statistical functions that can be compared with predictions from numerical models.
"You compare what you measure using a radio telescope with what the models predict that ISM should look like. If the model doesn't match the observation, you may need to include one or more ingredients in the model," she said. "You keep going until you pin down what's going on."
From the start, Stanimirovic was thinking big. As a girl in a mountain town in Yugoslavia called Surdulica, she read books by Carl Sagan and whatever other astronomy she could find. At the end of high school, one big exam screened all the students in the country for just five places in astronomy at Belgrade University. If she failed, she recalled, she would settle for a less competitive subject - like theoretical math, numerical math or theoretical physics. At the three-hour exam in June in a large theater in Belgrade, she recalls, "I just went in and did well, and I got it." That October, her classes began.
A few years later, she was studying the ISM for her Ph.D. thesis at the Australia Telescope Compact Array, doing interferometry, a method that allows extremely fine detail images of the ISM, and working with the Parkes Observatory. Both are in New South Wales.
That theme has continued at Arecibo, where she has found that the ISM looks remarkably different in the Milky Way from what she found in the Small Magellanic Cloud. "It's amazing," she said. "You study a far away galaxy in the universe, and then step back into our own, and you are so limited in how to explain the complexity and diversity of what you see."
She believes the Small Magellanic Cloud can serve as a stepping stone to study of distant galaxies. But more powerful tools are needed, Stanimirovic says, and she looks forward to working with one in particular, the ASKAP. That stands for Australian Square Kilometer Array Pathfinder, a powerful radio telescope consisting of 36 antennas, expected to be able to pull in more information than any device in the history of astronomy, to be ready by 2013.
"Just imagine that," she said. "We will be one step closer to the future."
Snezana Stanimirovic's Teaching Plans
Stanimirovic's top goal is to bring experiences closely resembling actual research to upper-level undergraduate students as well as graduates, letting them make radio observations of several galaxies. She plans to build a small radio observatory for students using three radio telescopes, 2 meters in diameter, made from kits purchased from the Haystack Observatory at MIT. "With them we can observe hydrogen spectra from the Milky Way and use them in various undergrad classes. With a tiny radio dish, you can still get interesting images and study how our Milky Way rotates. We can do very simplified and well documented research with these telescopes for lower-level nonscience students as well who have had little connection with the science world," she said. "It will be really a cool thing for them. It will give a nice flavor of how astronomy works, how to obtain measurements, and what do with them."