Prof Sheds New Light on Stars

Harvard astronomers have developed a new technique to map the structure of nebulae, the cosmic clouds of gas and dust from which stars are born.

By combining near-infrared wavelengths with unusually deep exposures, Professor of Astronomy Alyssa A. Goodman and graduate student Jonathan B. Foster produced scientifically valuable images of cosmic clouds in far higher detail than ever before.

Their “cloudshine” technique has yielded images of nebulae with resolutions that are 50 times higher than previous photographs, according to Goodman.

Fellow astronomers hailed the “cloudshine” finding.

“I agree with Professor Goodman that cloudshine will prove to be very revealing,” the director of the Harvard-Smithsonian Center of Astrophysics, Charles R. Alcock, wrote in an e-mail.

Goodman is also a member of the Harvard-Smithsonian Center.

Foster and Goodman summarized their findings in a paper submitted for publication to the Astrophysical Journal Letters.

Traditional images of nebulae, taken by the Hubble Space Telescope, employ only the visible light spectrum. While these images can be impressive, they reveal only the surface of the cosmic clouds—not the deeper and denser regions in which stars are formed.

Foster and Goodman were taking images of a nebula using near-infrared bands—which are far outside the visible light range—when they found something new. They discovered that ambient light from the surrounding stars was illuminating their cloud.

Astronomers previously had observed “reflection nebulae,” which are illuminated by stars within the cloud. The phenomenon observed by Foster and Goodman, which they termed “cloudshine,” is unique because the light source emanates from outside the cloud.

“While reflected starlight at optical wavelengths has been used to study dust in the galaxy, it’s impossible to use optical light to disentangle regions of intense star formation where there is so much bloody absorption that optical light can’t get out,” wrote Doyle Professor of Cosmology John P. Huchra. “‘Cloudshine’ is really a neat way of beating that absorption.”

Additional research led by an assistant professor at the University of California-San Diego, Paolo Padoan, revealed that the color of a nebula’s cloudshine is correlated to its density. Less dense areas appear relatively blue, and denser areas appear relatively red. Foster and Goodman’s images can thus be used to map a cloud’s interior structure.

“By using the reflective light, we’ll be able to see the exact shape and density structure of the cloud,” explained Foster. “That shape is determined by the different physical processes that go on.”

“The role of these different forces determines not only the shape of the cloud, but also how stars form out of the cloud,” Foster said. “We’ll see...what the regions that are about to form stars really look like.”