It is a well-known fact that the Milky Way consists of a number of spiral arms, however Chinese astronomers have recently discovered that it also has one arm that could extend and completely encircle the galaxy, the International Business Times reports.
The arm has been called the Scutum-Centaurus arm and begins in the centre of the Milky Way, before extending outwards in a counter-clockwise direction. The arm passes between our solar system and the galactic centre, and then stretches to the other side of the Milky Way. The arm last stretched in 2011 when astronomers discovered new molecular clouds past what was believed to be where the arm finished.
According to the latest news article, Chinese scientists from the Purple Mountain Observatory in Nanjing, China, have found more gas clouds even further out. The discovery was made with the use of a large radio telescope with a 13.7 meter dish that searched for radio waves from carbon monoxide—the second most abundant interstellar molecule after hydrogen.
A total of 48 new molecular clouds were discovered, alongside the 24 other clouds that had been found previously. In Letters—an astrophysical journal—the scientists said that the 72 clouds line up along a spiral arm segment that was previously unknown and around 30,000 light-years long.
If this is correct, then it means that the arm makes an almost full rotation of the galaxy, according to the Scientific American. However, there is currently an empty branch of the arm around 40,000 light years from the last reported end of the Scutum-Centaurus and the current end. Looking for clouds within this gap will confirm if they are part of Scutum-Centaurus or a different spiral.