Astronomers have found the Milky Way’s first known ‘feather’. It is the gaseous structure bridges two of the galaxy’s spiral arms.
The structure of our galaxy, the Milky Way, is very hard to determine from the inside. However, telescopes operating at under-explored wavelengths are starting to overcome this. The latest is a wavy filament of cold, dense gas stretching at least 6,000 light-years close to the galactic centre, which may be the galaxy’s first known “feather”, a structure seen in other spiral galaxies. The unusual structure could be a subbranch of the galaxy’s Norma arm, or it could be a “feather” connecting between the Norma arm and the 3 kpc arm, the innermost arm yet discovered.
Rather than being shaped like a bird’s feather, however, the discovery has a pattern like a sinusoidal wave. This inspired the team to name it as the Gangotri wave, after the glacier that is the source of India’s longest river, the Ganges. In Hindi and other Indian languages, the Milky Way is called Akasha Ganga, “the river Ganga in the sky,” says astrophysicist Veena V.S. of the University of Cologne in Germany.
Gangotri is between 6,000 and 13,000 light-years long, and lies within 17,000 light-years of the Galactic Center. Its total mass is thought to be at least 9 million times that of the Sun.
The path of Gangotri is determined by tracing carbon monoxide across the sky as traced by several sky survey projects. Only a tiny proportion of Gangotri’s mass would actually be CO, and even less with the carbon-13 molecule whose velocity is tracked, but the gas acts as a tracer for more abundant, but harder to detect, hydrogen and helium.
Other galaxies have gaseous plumage, but when it comes to the Milky Way, “it’s very, very difficult” to map the galaxy’s structure from the inside out.