On the Tail of a Giant, Cosmic Collision of Galaxies

By Cathy Rainone

Charles Liu

Charles Liu

FOR ALL THE YEARS he’s been an astronomer, Charles Liu has examined thousands upon thousands of galaxies — 80,000 alone in a recent project, some as far as 7 billion light-years from Earth. He’s measured how quickly galaxies form stars and determined their age and luminosity. But one galaxy has captivated him more than all the others: J152426.55+080907, or as it’s more commonly known, Flagellan.

Flagellan, he says, is likely the best example of a nearly completed collision of two Milky Way-size galaxies in the nearby universe, or less than 1.5 billion light-years from Earth. “By studying the light emitted by the stars in Flagellan, we have been able to map the changes in its rate of star birth since the collision first began one billion years ago,” says Liu. “It’s a perfect system to study the effects of major collisions on the evolution of galaxies — and it looks really cool, too!”

Indeed, Flagellan was named by a colleague of Liu’s who thought the galaxy resembles a microorganism that moves around using a whip-like tail called a flagellum.

Liu, as astrophysics professor at the College of Staten Island, has been studying the stars as part of NASA’s Cosmos Hubble Space Telescope Program — an ongoing survey of nearly 2 million distant galaxies aimed at mapping the evolution of the universe.

Flagellan’s also captivating because there is strong evidence that a hidden, supermassive black hole is lurking at its center. The strength of radio wave emission from the center has fluctuated dramatically over these past two decades — a telltale sign of a supermassive black hole.
“This is why I keep coming back to Flagellan and making new measurements — there’s a lot going on in this distant, enigmatic object,” says Liu, who is also an associate of the Hayden Planetarium and Department of Astrophysics with the American Museum of Natural History.

Liu and his colleagues have traveled to Arizona, California, New Mexico, Chile and elsewhere around the world to look at Flagellan through ground-based and radio-based telescopes. But when he’s not gazing at faraway galaxies, he teaches at CSI and runs both the Verrazano School honors program and The Macaulay Honors College at CSI.

“I’m enabling students to reach their highest potential, that’s the reward of being an administrator,” says Liu, who earned degrees from Harvard University and the University of Arizona, and held postdoctoral positions at the Kitt Peak National Observatory and at Columbia University. “But I don’t do it alone. I have wonderful staff at both programs who work hard to make sure the students get the best education.”

Liu knew he wanted to be a scientist and professor since his senior year in high school. Even before joining the CUNY faculty, as a full-time scientist at the American Museum of Natural History he helped develop public lecture series, educational exhibits and teacher education programs. At CSI he tries to make astrophysics fun for the students.

“Every once in a while I’ll break out in a song, ‘Black holes don’t suck but if you fall in one, that’s your new home,’ or rap ‘I like Big Bang and I cannot lie, astronomers can’t deny!’ When do you learn best? When you have fun! I feel that teaching is an extension of who I am as scholar and a human being,” says Liu.

“If in real life I love my work and love bringing that knowledge to people, it’s going to come out in a classroom. I’m happy to jump up and down in a classroom. I want students to be engaged.”

When Liu arrived at CSI 10 years ago, he decided to help develop graduate- and doctoral-level courses in astrophysics at CUNY, which had none at the time.
He felt the University wouldn’t be complete without them.

So for the first two years that CUNY offered graduate astrophysics classes through the CUNY Graduate Center, Liu was the only professor teaching them. Now there’s an astrophysics group within the CUNY physics doctoral program with 10 full-time faculty members from various CUNY schools.

And Liu’s graduate student Stephanie Fiorenza, the University’s first doctoral student in astrophysics in decades, is now part of a growing number of like-minded young scientists in the program. “I’m very committed to making the program better for other students,” says Fiorenza, who has made the most of her time as a University doctoral student. Fiorenza has been awarded grants from the National Science Foundation to conduct astrophysics research in India and Japan, and this spring she studied at Kitt Peak National Observatory in Arizona.

“We have developed programs to help CUNY students study astrophysics from undergrad all the way to Ph.D. level,” says Liu. “I wanted CUNY to make that contribution. I didn’t do it alone. We had a lot of people involved. We’re expanding, we’re moving forward.”

Liu does the bulk of his own research on galaxies in the summer, when he runs a joint CUNY-AMNH program through a grant from the National Science
Foundation. Flagellan and other galaxies are out there in the universe, waiting for him to notice any changes that may have occurred when he wasn’t looking — too busy grading papers and helping honors students get research opportunities.

“Galaxies change on timescales of many millions of years,” Liu says. “So our effort to study changes in a galaxy like Flagellan is akin to a mayfly studying the aging process of a tortoise! That said, my colleagues and I have indeed observed changes. It’s tremendously exciting and rewarding to watch the universe evolving right before our eyes.”