Milky Way has long spiral arm that 'encircles the whole galaxy'

Among the many spiral arms it has, the Milky Way galaxy has one that could extend all the way around to almost wrap the galaxy, according to a study by Chinese astronomers.

The spiral arm called Scutum–Centaurus starts in the centre and winds outward in a counter-clockwise direction, passing between our solar system and the galactic centre to stretch all the way to the other side of the Milky Way.

In 2011, the arm was last given a stretch after scientists noticed new molecular clouds beyond what was believed to be its end.

Now Chinese scientists from Purple Mountain Observatory in Nanjing, China, have spotted gas clouds even further.

They used a large radio telescope with a 13.7-metre dish to search for radio waves from the next most abundant interstellar molecule after hydrogen which is carbon monoxide.

In the process, they detected 48 new molecular clouds as well as the 24 others that earlier observers had seen.

Writing in The Astrophysical Journal Letters, they say that 72 clouds line up along a previously unknown spiral-arm segment that is around 30,000 light-years long.

This would mean that the Scutum-Centaurus almost makes a full 360-degree turn around the galaxy, writes the Scientific American.

The only missing data is a 40,000 light year long gap from the end of the arm last reported and the present one.

This suggests the new clouds could also be part of another spiral. Looking for clouds in the gap could further confirm if they belong to the Scutum-centaurus or are part of another spiral.