By Kim Howey
Astronomy professor J. Ward Moody has gone from plowing his family farm to plowing the Milky Way and, in his efforts, has uncovered a significant and unusual carbon star lurking in a corner of the galaxy.
The star, known as CV5, provides a link between existing theories of star formation and galaxy formation. Astronomers believe the galaxy formed from a collapsing gas cloud. In the process, stars remain where they were formed, so the stars on the outer edges of the galaxy were present when the galaxy first began collapsing. CV5 sits on this outer edge where few stars exist and is possibly the oldest documented carbon star.
“Its dynamics, how it moves, its chemical composition tell us about what the galaxy was like at that very, very early age,” Moody says. “Just as we study dinosaur bones to better understand life on earth, we study this kind of dinosaur star to better understand the population of stars in the galaxy.”
CV5, like most stars, began as 98 percent hydrogen and helium. As it has aged and cooled, it has transformed these two elements into carbon. When looking at CV5 through a prism, Moody saw an unusual arrangement of its light colors, called a signature. “This had a signature like nothing I’ve ever seen before,” Moody says. Instead of a balanced arrangement of all the rainbow’s colors, large patches across the spectrum were missing. These patches, termed “valleys,” were where the carbon had absorbed the star’s light. The deeper the valley, the more carbon exists in a star.
“CV5 has some of the deepest valleys ever measured,” Moody says. “This makes it the most carbon-rich star ever discovered. Nobody knew that carbon stars could have features as deep as what we discovered. It’s another notch in our understanding of stars.”
This discovery process began in 1986 when Moody was searching for quasars and galaxies. Using a survey telescope at the National Optical Astronomy Observatory in Arizona, he created 20 Schmidt telescope survey plates–eight-square-inch negatives that measure an area of the Milky Way spanning 10 full moons in diameter. Using a microscope, Moody painstakingly examined each object on the negative, looking for objects with unusual spectra.
“I grew up on a farm, and the only thing I can compare this kind of work to is plowing, which I hated with a passion, because you go back and forth all day long making slow progress because the tractor has such a tiny blade compared to the field size,” Moody recalls. “That’s what we do with these plates, except we get the microscope out and stare at a field about the width of your little finger. We simply go back and forth across each plate, gazing at each star.”
After two years of identifying images, a small trace of light, labeled number 5 on his plate, still baffled him. With a large telescope, he obtained a higher resolution spectrum of the star, which broke down the colors in the spectrum. Red, indicative of a low temperature, was the dominating color. The deep valleys in the spectrum indicated CV5 was possibly an extreme example of a carbon star. Moody spent three months researching carbon stars–a field of study outside his expertise in galaxy formation–and finally concluded that the object is an unusually carbon-rich star.
“CV5 is an intriguing anomaly for further carbon star study and a significant indicator of the elements, dynamics, and time involved in the formation of the Milky Way,” Moody says. Several experts in the field of carbon stars are planning to continue studies on CV5, and Moody plans to return to galaxy formation research.
Moody estimates that only .001 percent of the stars in the galaxy have been studied, so more discoveries are imminent as Moody and his colleagues work together on projects such as this. “There’s a tremendous thrill of discovery,” Moody says. “When you see something there and you know it’s something strange and real, it’s very exciting.”