New measurements show that the Milky Way galaxy may have a different shape than we thought. In the last few years, astronomers have discovered more and more that galaxies have three basic shapes: elliptical, irregular, and spiral. Most known galaxies falling into this latter category seem to have two distinct “arms” that branch off and split into smaller arms.

The traditional image of the Milky Way, however, is a galaxy that has. four great spiral arms emerging from the thick central bulge of stars. This highlights our spiral galaxy as an extremely rare outlier with a strange shape that must have some very unique properties to give it four major arms.

However, this image may not be correct. A team of astronomers has published new research that suggests we’ve been wrong about the shape of the Milky Way for decades because our galaxy has two main arms, just like modern spiral galaxies.

A discovery that could change our understanding of the Milky Way has come as astronaut scientists from the Purple Mountain-based Chinese Academy of Sciences and the National Astronomical Observatory analyzed multiple astronomical data sources to better understand the true shape of our galaxy.

“Despite many studies, the overall morphology of the spiral structure of the Milky Way remains somewhat unclear,” the astronomers write in a paper describing their research and findings (opens in a new tab). “Over the past two decades, accurate distance measurements have given us the ability to solve this problem.”

The team evaluated data from next-generation spacecraft that can better measure distances to individual stars, allowing them to measure distances to about 200 stars and begin mapping the Milky Way. Next, they added data from the European Space Agency’s (ESA) Gaia space telescope, which precisely monitors the motions of stars and their position relative to Earth.

In particular, astronomers focused on hot, massive stars called OB stars in the Gaia data. Because these stars are short-lived, they move very little during their hydrogen-burning main sequence lifetimes, making them useful for mapping. Data collected from 24,000 OB stars has been added to the map, along with Gaia observations of more than 1,000 scattered galaxy clusters.

This led astronomers to suggest that the Milky Way is a barred spiral galaxy with only two main arms extending from this dense central band.

“Using precise data on the position of very young objects, we suggest for the first time that our galaxy has a multi-arm morphology consisting of two-armed symmetry,” they wrote. “The arms of Norma and Perseus are probably two symmetrical arms in the inner part of the Milky Way. As they expand from the inner part of the galaxy to the outer parts, they bifurcate and join the Centaurus and Sagittarius arms, respectively.”

At the outskirts of the Milky Way are distant and fragmented irregular arms that are not connected to the central bulge, where most of the galaxy’s stars are located, as astronomers write. The disintegration of the spiral arms may have resulted from collisions with other galaxies and even galactic clusters in our galaxy’s early history.

The team of astronomers concluded that this new model of the Milky Way’s shape could provide an alternative basis for future research into the structure of galaxies. They add that more details should be revealed with further observations of nearby radio sources made by multiple telescopes, which will allow them to calculate their distance from Earth, along with advanced data from the Gaia spacecraft. Gaia was launched in 2013 and is expected to observe the universe for at least two more years by 2025.