Study: 'Missing' arms of our Milky Way galaxy are actually there

LEEDS, England, Dec. 17 (UPI) -- A study of massive stars confirms our galaxy has four spiral arms, ending debate sparked by telescope images suggesting only two arms, British astronomers say.

The shape of our Milky Way galaxy cannot be observed directly from Earth because we are on the inside looking out, they say, but observation of its stars and their distances from us can help deduce it shape, scientists at the University of Leeds said.

"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," said Melvin Hoare of the university's School of Physics & Astronomy, a co-author of the research paper.

In 2008 images of about 110 million stars captured by NASA's Spitzer Space Telescope only showed evidence of two spiral arms in the Milky Way.

In the new study, radio telescopes in Australia, the United States and China observed about 1,650 massive stars that, when their distances and luminosities were calculated, revealed a distribution across four spiral 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 are much less common than their lower mass counterparts because they only live for a short time, meaning they are only found in the arms in which they formed, astronomers said.

"Star formation researchers, like me, grew up with the idea that our Galaxy has four spiral arms," Hoare said. "It's great that we have been able to reaffirm that picture."