The Milky Way arches across the night sky above the Yarlung Zangbo Grand Canyon in the Tibet autonomous region. (PHOTO PROVIDED TO CHINA DAILY)
BEIJING – Chinese astronomers have recently transformed our understanding of the spiral structure of the Milky Way. They determined that it is more like a common multiple-arm galaxy, rather than a special galaxy with four spiral arms extending from its inner parts to its outer parts.
Largely speaking, there are three types of spiral galaxies in the universe. Grand-design spiral galaxies are characterized by clear, long and symmetrical spiral arms. Flocculent galaxies are fragmented, consisting of many short, irregular and patchy segments.
About 83 percent of multiple-arm spiral galaxies have an inner two-arm symmetry and several irregular arms in their outer parts. Only about 2 percent have four spiral arms extending to their outer regions, and astronomers previously believed that the Milky Way was of this special four-arm type
Multiple-arm spiral galaxies are of an intermediate type. About 83 percent of such galaxies have an inner two-arm symmetry and several irregular arms in their outer parts. Only about 2 percent have four spiral arms extending to their outer regions, and astronomers previously believed that the Milky Way was of this special four-arm type.
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Astronomers from the Purple Mountain Observatory and the National Astronomical Observatories, both institutions under the Chinese Academy of Sciences, used all available high-precision astrometric data to trace and identify the spiral arms of the Milky Way.
The study, published in The Astrophysical Journal, shows that the Milky Way is a multiple-arm galaxy that has two-arm symmetry – the Perseus and Norma Arms – in its inner parts, which extend to outer parts and split into several long, irregular arms.
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"The result makes the Milky Way no longer look special. The research team is preparing for higher-precision measurements in the future, with the hope of finally uncovering the spiral structure of the Milky Way," said Xu Ye, a lead researcher at the Purple Mountain Observatory.