The Milky Way with the Earth’s solar system indicated by the dot within the circle.

A Wartburg College professor has contributed to a new study that hopes to resolve the debate over the shape of the Milky Way.

Dr. Charles Figura, professor of physics and director of the college’s Platte Observatory, was part of the team that reaffirmed that the galaxy, which includes Earth, has four spiral arms, not just two as observed by NASA’s Spitzer Space Telescope in 2008. 

The findings of the 12-year study led by astronomers at the University of Leeds in Britain were reported Tuesday in the Monthly Notices of the Royal Astronomical Society. The researchers relied on radio telescopes in West Virginia, Hawaii, Australia, Chile and China as well as data from space telescopes.

Figura worked with the paper’s lead author, James Urquhart of the Max Planck Institute for Radio Astronomy in Bonn, Germany, for more than five years doing data analysis and some of the writing.

The project had an inherent degree of difficulty. Astronomers have a difficult time observing the structure of the Milky Way just as a person can’t see the shape of a forest when they’re in it. Research in the 1950s, though, suggested four arms.

“Radio astronomy observations of cold neutral hydrogen gas indicated specific details of the spiral-arm structure of the Milky Way and laid the groundwork for the idea of a roughly four-armed galaxy,” Figura said. 

But a 2008 study using observations by the Spitzer Space Telescope concluded two of the Milky Way’s arms were major with significantly more nebular gas and star formation, while the other two arms were minor.

For the new survey, researchers studied 1,650 “massive” stars — at least eight times larger than the sun — and plotted the distances between them and Earth. The massive stars live for a relatively short time — “only” about 10 million years — and tend to be found in the arms where they were formed.

“These stars cannot migrate nearly so far as smaller, longer-lived stars can,” Figura said.

“A galaxy’s spiral arms are not permanent structures with resident nebulae and stars,” he added, “but are much more like traffic jams. Just as cars enter the traffic jam from behind and creep out the front, material — gas and stars — enters from behind and creeps out the front. 

“Our analysis of massive stars shows a distribution of these stars among the four arms that indicates that all four have similar massive star ‘birthrates,’ which contradicts the 2008 view of major and minor arms.”  

The researchers stressed the Spitzer findings were “incomplete,” but “not incorrect.”

“Spitzer is looking at a broader range of stars, including lower-mass stars that live much longer and can migrate further from the spiral arms,” Figura said. “This can make the arms appear to host fewer stars than they actually do. It’s also possible that star formation in the arms is episodic, and waxes and wanes over time.”