Observing dark matter, the unseen stuff that makes up most of the universe, takes some ingenuity. Mike Gladders has a few creative suggestions. This mysterious matter is called "dark" because it doesn't interact with light. But you can observe its giant fingerprints across the cosmos - in the form of distortions it causes as gravity from huge clusters of galaxies and dark matter bend nearby light on its way toward Earth. Gladders will take a new tack by seeking answers among the most massive objects in the universe, galaxy clusters. The huge tug of gravity from any immense distant object can become a sort of lens, altering light waves like a pair of reading glasses. Gladders' research focuses on that effect, called gravitational lensing. If you know what to expect without the distortion, you can calculate whatever was making it happen. "Gravity almost acts like an optic, or a lens, would," said Gladders, an assistant professor of astronomy at the University of Chicago. "The gravity in this case is caused by the mass of huge clusters of galaxies, which are mostly dark matter." Dark matter has baffled physicists and astronomers since the 1930s, when its presence was inferred by calculations to explain the motions of the galaxies within galaxy clusters. While no one yet understands dark matter, there are plenty of competing theories, and Gladders plans to help sort them out. "We will ask how the lens acts to distort the background images in the sky," he said. "Then we can say, ‘This is what you'd expect given this amount of dark matter.' At a minimum you eliminate some of the competing models, and perhaps one will come to the fore." Imagine you were an optometrist and someone asked you to calculate the strength of a certain pair of glasses. You could test them and calculate the prescription. "That's what we do with these gravitational lenses," Gladders said. The goal is to find just the right kind of clusters. "Clusters are rare," Gladders said. "And those that exhibit lensing are even rarer, and really hard to find." To search for galaxy clusters that act as gravitational lenses, you have to start by finding a large number of galaxy clusters. Gladders does this by an analysis of large galaxy catalogs, searching for sometimes subtle overdensities in the galaxy distribution that mark the clusters. The largest such source catalog is the noted Sloan Digital Sky Survey, which contains information on some 250 million objects. The second largest such catalog is Gladders' own Red-Sequence Cluster Survey, comprising roughly 150 million objects, some of them more than a million times fainter than the faintest objects that your eye can see. Gladders will start with such a list of individual galaxies, and reduce this to 50,000 or so really promising galaxy clusters. From there, the task is to generate a list of the few hundred gravitational lenses lurking in this vast data set. "These are visually spectacular objects," Gladders said. "They have a real discovery aspect to them." Gladders is a regular at the world's top observatories. He has visited the Magellan telescopes at Las Campañas Observatory, in the remote Andean foothills of Chile, more than 30 times. Getting there is a privilege and a feat, taking months of preparation. So when his last visit overlapped his teaching of the "Astronomy and Astrophysics of Stars" class at Chicago, Gladders simply lectured from Chile by an Internet hookup. He was able to share with students the joy of doing astronomy 18 hours a day, on three or four hours of sleep and lots of coffee, running the telescope, taking data, modifying the program. "When it's cloudy one night, you have to figure how to get two nights of work done the next night," he said. "I still enjoy it, the fascinating moments on a mountaintop, in a control room, with banks of computers. There's a mystical quality to the experience, staring at the night sky, figuring out deep questions you've been asking for years. As I prioritize things, that ranks above almost anything else." Gladders was born in Southampton, England, and studied briefly at Canada's University of Victoria before he was thrown out for poor grades. "This can teach students that sometimes you can fall down and get back up," he said. He worked at geophysics for the oil industry in Calgary until he was readmitted to college. He moved on to a Ph.D. at the University of Toronto, and became a fellow at The Carnegie Observatories in Pasadena, California, and then joined the University of Chicago. Astronomers need big samples for robust tests of their models. "A few years ago the total known sample of lenses was just a few handfuls of objects," he said. "We are now finding hundreds of these objects." As to direct measurement, Gladders said, some astronomers have high hopes for the Large Hadron Collider, the new accelerator under the Swiss-French border. "The LHC may reveal the dark matter particle". "If not," he added, "then maybe astronomical tests are the only way."
Michael Gladders' Teaching Plans
Gladders plans to use emerging technologies in public outreach projects as part of the teaching component made possible by his Cottrell Award. He will deliver results from the huge Red-Sequence Cluster Survey (RCS), a catalogue of the largest search for distant galaxy clusters ever, to two popular "desktop planetarium" programs, along with background on how to try your own hand at cosmology, and perhaps make your own scientific discovery with the data. In the United States and beyond, Gladders says, one of the biggest challenges to scientists is how to engage the public as a whole in science. "We often work with a few people as teachers, mentors, instructors. We in astronomy can tell powerful stories, how stars are born, evolve, die, how the universe has a beginning point and evolution, and that can be visually fascinating. But we need to go beyond simple story telling and bring some hard science to more than the few people at a lecture." To do that he plans to use GoogleSky and Microsoft's Worldwide Telescope, programs that let users vicariously ride into space using their computers. Gladders plans to make the Red-Sequence Cluster Survey navigable by the public and students. His effort will build on ideas first explored by others in Galaxy Zoo, a web project that invites the participation of volunteers in searching images in a large database. Volunteers will log on, receive their assigned images and after taking a tutorial will perform classification of images, contributing some significant analysis. Gladders is particularly interested in having volunteers help look through the millions of images to search for the strong "lenses" at the center of his research. It will help with the actual research effort and, Gladders adds, "It will teach them some interesting physics." The non-science students he teaches, Gladders says, can make significant contributions to this effort. "They have a very interesting skill set," Gladders said. "They are artists, public policy students, English majors. We hope to engage these students as research assistants and bring their skills to bear on the research and outreach questions."