Undergraduate Researcher Watches Baby Galaxies Grow Up

The Milky Way Galaxy's majestic spiral spans 100,000 light years and holds about 300 billion stars. But it hasn't always looked this way. According to one theory, the galaxy we call home had humble beginnings, forming from the collisions of hundreds of "baby" galaxies, each little more than a lump of gas.

Undergraduate researcher Christopher Wolf set out to test this theory of galaxy formation with his advisors, Robin Ciardullo, a Penn State University professor of astronomy and astrophysics, and Caryl Gronwall, a senior scientist in Penn State's Department of Astronomy and Astrophysics. To test this theory, Wolf and his colleagues started at the beginning, by measuring the evolution of baby galaxies."Since light takes a finite amount of time to travel to an observer on Earth, looking out to the distant universe gives us a glimpse back in time. The more distant the galaxy, the younger," Wolf said. "So by looking at galaxies over a range of distances, we can see if they change in shape or brightness over time."

Baby galaxies are typically small, fewer than 7,000 light years across, and look nothing like the Milky Way's grand spiral. Yet these lumps of gas are still relatively easy to find. Bursting with new-star formation, they produce a signature bright band of ultraviolet light called Lyman alpha, giving them their technical name -- Lyman alpha emitters.

Lyman alpha emitting baby galaxies. Credit: NASA, ESA, Caryl Gronwall/Penn State.

"We selected galaxies by measuring how heavily they emit in Lyman alpha," Wolf said. Taking advantage of Penn State's role in the international collaboration MUSYC -- Multi-Wavelength Survey by Yale and Chile -- Wolf compared MUSYC's images of the night sky with additional images taken at the Cerro Tololo Inter-American Observatory in Chile.

"Working with astronomers in both hemispheres was a great experience," Wolf said. "It was nice to work with people who aren't physically together and still be able to get things done."

Wolf found two groups of baby galaxies lying billions of light years away, back when the universe was only 2 to 3 billion years old, compared to its current age of 13.7 billion years. By measuring how the galaxies' properties changed over time, Wolf and his colleagues showed that the baby-galaxy population was fading away as the universe aged.

An artist’s conception of the Milky Way galaxy. Credit: NASA/JPL-Caltech/R. Hurt

"These galaxies may be fading because they're not forming as many stars," Gronwall said. "The other possibility is that there is more dust at later times, making them appear fainter. So even if there is intrinsically the same number of galaxies, we're not seeing all of them."

"Simulations show that baby galaxies collect together to form spiral galaxies," Wolf said. "In our study, we've found observational evidence to support that."

Wolf presented his results at the January 2010 conference of the American Astronomical Society. His work with Ciardullo and Gronwall helped lead the way to his current position as a research assistant at the Mission Operations Center for the Swift Satellite at Penn State, where he is now investigating Gamma-Ray Bursts, the most powerful explosions in the universe.