There has been mixed data on whether our Galaxy has two or four "spiral arms"; but recent observations may have cracked the case.
Researchers can't actually see what the Milky Way looks like from an observers standpoint since we are "on the inside looking out." By observing the stars inside the Galaxy scientists can get a better idea of its shape, a Royal Astronomical Society (RAS) news release reported.
"The Milky Way is our galactic home and studying its structure gives us a unique opportunity to understand how a very typical spiral galaxy works in terms of where stars are born and why," Professor Melvin Hoare, a member of the RMS Survey Team in the School of Physics & Astronomy at the University of Leeds and a co-author of the research paper, said in the news release.
Back in the 1950s researchers looked at gas clouds in the Milky Way that act as star "nurseries." Through these observations the researchers determined the Milky Way had four "arms."
Data from NASA's Spitzer Space Telescope looked at light emitted by about 110 million "grown up" stars. The telescope was only to detect two Milky Way arms.
The recent study employed telescopes from Australia, the U.S., and China to look at about 1650 massive stars. By looking at the star's locations the researchers were able distinguish for Galactic arms.
"It isn't a case of our results being right and those from Spitzer's data being wrong -- both surveys were looking for different things," Hoare said. "Spitzer only sees much cooler, lower mass stars -- stars like our Sun -- which are much more numerous than the massive stars that we were targeting."
Massive stars only live for about 10 million years, which is a relatively short lifespan. The stars are also only found in the arms. The recent observations could explain why there have been data discrepancies regarding the arms in the past.
"Lower mass stars live much longer than massive stars and rotate around our Galaxy many times, spreading out in the disc. The gravitational pull in the two stellar arms that Spitzer revealed is enough to pile up the majority of stars in those arms, but not in the other two," Hoare said. "However, the gas is compressed enough in all four arms to lead to massive star formation."
"Star formation researchers, like me, grew up with the idea that our Galaxy has four spiral arms. It's great that we have been able to reaffirm that picture," Hoare said.
