A new study has revealed that the disk of stars belonging to the Milky Way galaxy is anything but flat and stable. According to astronomers from National Astronomical Observatories of Chinese Academy of Sciences (NAOC), the disk becomes increasingly “warped” and twisted as it extends out from the Milky Way’s center.
The researchers found that the pull of gravity becomes weaker far away from the Milky Way’s interior. The hydrogen atoms making up the far outer disk are no longer confined to a thin plane, but instead give the disk an S-shaped warped appearance.
“It is notoriously difficult to determine distances from the Sun to parts of the Milky Way’s outer gas disk without having a clear idea of what that disk actually looks like,” said study lead author Dr. CHEN Xiaodian.
“However, we recently published a new catalogue of well-behaved variable stars known as classical Cepheids, for which distances as accurate as 3 to 5% can be determined.”
This database is what enabled the team to develop the first accurate three-dimensional picture of our Milky Way, including its far outer regions.
Classical Cepheids are young stars that are up to 20 times as big as the Sun and up to 100,000 times as bright. This composition would imply that they burn through their nuclear fuel very quickly, sometimes in only a few million years, and die young. They show pulsations that can be observed as changes in their brightness, and the extent of the pulsation period can be used to obtain a highly reliable distance.
“Somewhat to our surprise, we found that in 3D our collection of 1339 Cepheid stars and the Milky Way’s gas disk follow each other closely. This offers new insights into the formation of our home galaxy,” said study senior author Professor Richard de Grijs. “Perhaps more importantly, in the Milky Way’s outer regions, we found that the S-like stellar disk is warped in a progressively twisted spiral pattern.”
The team pointed to earlier observations of a dozen other galaxies which also showed such progressively twisted spiral patterns.
“Combining our results with those other observations, we concluded that the Milky Way’s warped spiral pattern is most likely caused by ‘torques’ – or rotational forcing – by the massive inner disk,” said study co-author Dr. LIU Chao.
Dr. DENG Licai concluded, “This new morphology provides a crucial updated map for studies of our galaxy’s stellar motions and the origins of the Milky Way’s disk.”
The study is published in the journal Nature Astronomy.
Image Credit: CHEN Xiaodian