New measurements indicate that the Milky Way may have a different shape than we thought.
Over the past few years, astronomers have increasingly discovered that galaxies come in three main shapes: elliptical, irregular, and spiral. The majority of known galaxies that fall into this latter category appear to have two distinct “arms” that branch off and split into smaller arms.
But the traditional depiction of the Milky Way is that of a galaxy with one four The main spiral arms extend from a thick central star bulge. This makes our spiral galaxy stand out as an extremely rare, oddly shaped galaxy that must have some very unique properties to give it four main arms.
However, this depiction may be wrong. A team of astronomers has published new research that suggests we’ve been wrong about the shape of the Milky Way for decades, with our galaxy instead having two main arms just like its contemporary spiral galaxies.
Related: Milky Way Galaxy: Everything you need to know about our cosmic neighborhood
The revelation that could reshape our understanding of the Milky Way came when astronomers from the Purple Mountain-based Chinese Academy of Sciences and the National Astronomical Observatories analyzed multiple sources of astronomical data to get a better understanding of the true shape of our galaxy.
Astronomers wrote in paper (Opens in a new tab) Describing their research and conclusions. “In the past two decades, accurate measurements of distances have given us an opportunity to solve this problem.”
The team evaluated data from a new generation of space instruments that can better measure the distance to individual stars, allowing them to measure distances to about 200 stars and begin to piece together a map of the Milky Way. Then they added data from the European Space Agency’s (ESA) Gaia space telescope, which carefully monitors the motion of stars and their position in relation to Earth.
In particular, astronomers have honed in on the hot, massive stars called OB stars in the Gaia data. Because these stars are short-lived, they move very little during the lifetime of burning hydrogen in the main sequence which makes them useful for mapping purposes. Data collected from 24,000 OB stars has been added to the map as well as Gaia observations of more than 1,000 open galaxy clusters.
This led astronomers to suggest that the Milky Way is a narrow spiral galaxy with only two main arms extending from this dense central bar.
“Using the precise locations of very small objects, for the first time, we propose that our galaxy has a multi-arm shape consisting of two-arm symmetry,” they wrote. “It is likely that the arms of Norma and Perseus are the two symmetrical arms in the inner Milky Way. As they extend from the inner galaxy to the outer parts, they branch off, and connect with the arms of Centaur and Sagittarius, respectively.”
In the outskirts of the Milky Way, the astronomers wrote, are distant, fragmented, irregular arms not connected to the central bulge of the galaxy where the majority of its stars reside. The fragmentation of the spiral arms may be caused by the collision of our galaxy with other galaxies or even galaxy clusters in its ancient history.
The team of astronomers concluded that this new model of the Milky Way’s shape could provide an alternative basis for future studies of the galaxy’s structure. They add that more details should be revealed through more observations of nearby radio sources taken by multiple telescopes that would allow their distances to be calculated from Earth, and through improved data from the Gaia spacecraft. Gaia was launched in 2013 and is expected to monitor the universe for at least two more years, until 2025.
Team search is published (Opens in a new tab) In The Astrophysical Journal.
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