A Summer Puzzle

Students aim summer efforts at Professor Julie Dahlstrom's ongoing research into the mystery of diffuse interstellar bands

August 23, 2011

Last fall, Carthage physics professor Julie Dahlstrom and a team of researchers from five other institutions were awarded a $1.15 million grant from the National Science Foundation to study diffuse interstellar bands (DIBs). This summer, Prof. Dahlstrom involved two Carthage sophomores in her research as part of the Summer Undergraduate Research Experience.

For Brianna Faint, '14, of Kenosha, and Zachary Troyer, ’14, of Joliet, Ill., it was a valuable opportunity to closely study one of the great puzzles in observational astrophysics.

"The DIBs mystery has persisted for nearly a century," said Zachary. "It is exciting that a first research project puts me in the line of generations of scientists who came before me."

DIBs: A great unknown

Diffuse interstellar bands are unidentified absorption features seen in the spectra of hot, bright stars. "At present, astronomers have observed approximately 300 DIBs," Prof. Dahlstrom said. They are presumed to be visible evidence of organic substances in clouds of gas and dust that exist between the Sun and other stars. "They suggest the presence of tens, perhaps hundreds of organic molecules as yet unknown in laboratories on Earth," Prof. Dahlstrom said.

For their summer projects, Zachary and Brianna looked at different aspects within the study of these mysterious compounds. Brianna's project involved estimating how sensitively spectograph and telescope can detect and measure very broad features.

Zachary spent the summer studying a specific molecule that has been proposed as one of many carriers for the diffuse interstellar bands. "His task was to examine spectra of interstellar sight lines in regions where characteristic absorption features are predicted from laboratory spectroscopy and test whether the measured features could arise from the same compound in space," Prof. Dahlstrom said.

Said Zachary: "This topic is a big hole in the understanding of the cosmos because we simply have no idea what causes these DIBs. Helium was first discovered in the spectra of the sun, so perhaps we may someday find something life-changing embedded in the patterns the DIBs leave."

Lifelong skills

Both students' projects involved the use of data from high-resolution optical spectroscopy to evaluate the chemical composition and physical conditions in these clouds of gas and dust. "The projects both require learning about spectroscopy and the interpretation of spectra, which is a useful skill that transfers readily to almost all of the sciences," Prof. Dahlstrom said. "Regardless of what their future scientific efforts endeavors may be, Zach and Brianna will benefit from having delved into these methods for assessing physical conditions and chemical composition of materials located in such remote places and under such strange conditions that they cannot be studied in a lab."

Zach was able to determine that the simple organic molecule he was studying, propadienylidene, is not the carrier for two well-known DIBs because its molecular spectra is not present in the source spectrum.

"Brianna's study played an important role in revising the data reduction methods that are in use for this study," Prof. Dalhstrom said. She was able to calibrate the onset breadth at which the spectrograph can no longer reliably detect absorption features.

The students also honed their critical thinking and problem-solving skills, and exercised tenacity and focus, Prof. Dahlstrom said. "My job is to introduce my students to the ambiguities, frustrations and exhilaration of scientific research," she explained. "In a classroom setting, we usually emphasize the problems with straightforward, clear answers whose correctness can be assessed readily. Research is not so clear-cut, and its lack of clarity can be a shock."

"I am proud to be involved in this project, grateful for Carthage, and excited to find something new and wonderful about the cosmos for the first time in my life," Zachary said.

Brianna said she hopes to continue her research "and learn even more about DIBs, so that any future SURE participants who take up this project will have even more to discover."

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