A team of space scientists from the Purple Mountain Observatory of the Chinese Academy of Sciences and the National Astronomical Observatory has found that the traditional view that the Milky Way galaxy has four arms is wrong. In an article published in the journal Astrophysical Journal The group describes their analysis of multiple data sources in an attempt to get the true shape of the Milky Way.

For years, astronauts have imagined the Milky Way galaxy as a spiral shape with a central bulge and four main spiral arms and several other smaller branches. Telescope technology has improved in the last few years, and it has been noticed that the vast majority of galaxies have only one of three basic shapes: spiral, irregular, and elliptical. In addition, most have two main branches with spirals that split into smaller branches.

This type of split is believed to occur due to collisions with other galaxies or clusters. Such observations suggest that the Milky Way would be extremely rare if it were a four-armed spiral galaxy. And if that was the case, there must have been some unique qualities that would lead to such a unique shape. Researchers in this new effort suggest that we’re more likely to misunderstand the shape from the start. They believe that the Milky Way, like many other galaxies, has only two main arms.

The research team came to this conclusion after analyzing data from next-generation spacecraft, each equipped with technology that allows us to measure the distance of stars from us. The team notes that such an instrument has a long-base interferometer that can very precisely measure distances to microwave-emitting stars. They used it to measure 200 such stars, which they used to map the Milky Way.

The team also used data from the Gaia space observatory, which is used to map the positions of stars relative to Earth and to each other. They focused their attention on OB stars, which is beneficial because they don’t move much after formation. They collected data on 24,000 of them and added it to the map they created. They also added data for nearly a thousand open cluster stars, again courtesy of Gaia.

The team then matched the position of the stars to the spiral, and by doing so, found that the most likely shape of the Milky Way was a bridged spiral with two main arms extending outward from the rod. Other short branches are more distant and irregular and are not connected to the main structure.