The Milky Way isn’t a stable disk of stars, new research has discovered, but in fact is warped and twisted the further away from the centre you look.
Scientists from the Chinese Academy of Sciences’ national astronomical observatories (NAOC) have discovered the unusual shape and published their findings in the journal Nature Astronomy.
From a distance, the Milky Way does indeed look like a thin disk of stars which orbit a mysterious centre every few hundred million years.
At the centre of our galaxy is a supermassive black hole, but also hundreds of billions of stars and a huge mass of dark matter, which hold everything together with gravity.
But farther away from this inner core, the hydrogen atoms which make up most of the gas disk are no longer tightly bound to the thin plane and buckle above and below it.
This S-like warped appearance is revelatory for scientists who are trying to accurately image the Milky Way.
“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 Dr Chen Xiaodian.
Dr Chen, a researcher at NAOC and the lead author of the study, explained that a discovery of new stars helped the astronomers create a more accurate image of the galaxy.
“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,” said Dr Chen.
This new database has allowed the team to create the first accurate three-dimensional picture of the Milky Way all the way out to its most distant regions.
The classical Cepheids Dr Chen described are young stars that can be up to 20 times as massive as the sun, 100,000 times as bright.
These huge stellar masses very literally live fast and die young, burning through their nuclear fuel rapidly – sometimes in just a few million years.
One of the key signals they let off are pulsations of brightness, lasting between a day and a month, and this burst of light can be used to measure their distance.
“Somewhat to our surprise, we found that in 3D our collection of 1,339 Cepheid stars and the Milky Way’s gas disk follow each other closely. This offers new insights into the formation of our home galaxy,” added Professor Richard de Grijs.
Prof de Grijs, of Macquarie University in Sydney, Australia, and senior co-author of the paper, added: “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.”
“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 Dr Liu Chao, senior researcher and another co-author of the paper.
“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,” explained Dr Deng Licai, senior researcher at NAOC and again a co-author of the paper.