14 DAY TRIAL // The conclusions of a new, 12-year study on the structure of our galaxy suggest that the Milky Way has four spiral arms after all, instead of two. Over the past couple of decades, the number of arms our galaxy has has been the subject of many debates within the astronomical community.
The new research may finally bring a conclusion to this long-standing debate, say investigators at the University of Leeds. They conducted the new Red MSX Source (RMS) survey, which took 12 years to complete, and which paints a complex and complete image of the Milky Way in all its glory.
The RMS survey identified around 1,750 embedded, young massive stars throughout the Milky Way, which then enabled them to determine the distribution patterns of recent massive star formation in the galaxy. Astronomers have known for years that the locations of stellar nurseries are spatially-correlated with the spiral arms of any galaxy.
Details of their study were first published online in the November 14 issue of the esteemed journal Monthly Notices of the Royal Astronomical Society, Nature World News reports. The Leeds team says that establishing the exact number of arms our galaxy has is complicated because we will within it.
For other galaxies, figuring out the number of arms they have is simply a matter of pointing our telescopes at the objects. Within our own galaxy, however, the process is infinitely more complex, as scientists have to analyze star motions and formation patterns, and then figure out if the distributions they see are more in tune with a 2- or 4-arm model.
“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,” says University of Leeds professor Melvin Hoare, who co-authored the new paper. He is also an RMS survey team member.
The reason why this study focused on massive stars is two-fold. In addition to being much more luminous than objects the size of the Sun, these stars are also short-lived, as their main sequence lasts for only a few hundred million years (as opposed to the Sun's 10 billion years).
As such, they have no time to migrate from one spiral arm to the other. Therefore, the locations of the stellar nurseries were they have formed can be used to analyze the distribution of hydrogen clouds throughout the Milky Way. This measure can in turn yield more clues about the number of arms the galaxy has.
A recent analysis by Spitzer scanned 110 million stars, but was unable to find evidences of more than 2 spiral arms. This “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 explains.
“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,” he concludes.