Milky Way may have four spiral arms

Evidence suggests the Milky Way galaxy has an additional two spiral arms. That makes four.

The exact number of arms in the Milky Way's spiral has long been a point of debate among astronomers. But most previous data suggested the galaxy had just two.

But new research by a team of astronomers from Federal University of Rio Grande do Sul, in Brazil, bolsters the case for a four-armed galaxy. The scientists used NASA's WISE infrared telescope to map the location of the galaxy's most prolific star-forming regions. In a scientific paper, published recently in the Monthly Notices of the Royal Astronomical Society, the scientists argue young embedded star clusters are ideal markers of galactic structure.

"The present results indicate that the galaxy's embedded clusters are predominantly located in the spiral arms," the researchers explained.

Researchers used infrared observations, combined with an advanced algorithm, to both pick up on stellar energy unobscured by dust and ensure their mapping efforts weren't contaminated by stray starlight from background stars on the same sight lines.

"The embedded clusters in the present sample are distributed along the Sagittarius-Carina, Perseus, and outer arms," the team said. "Our results favor a four-armed spiral galaxy, which includes the Sagittarius-Carina, Perseus, and outer arms."

Still, the researchers weren't willing to put it in stone. They tempered their conclusions by pointing to the sun's unavoidable influence -- a hinderance to getting a more accurate picture of the galaxy's shape.

"Despite efforts aimed at improving our understanding of the galaxy's structure, questions remain."