This is so cool! A group of astronomers, have identified one of the longest known structures in the Milky Way. It stretches some 3900 light-years and consists almost entirely of atomic hydrogen gas. This filament, called “Maggie”, could represent a link in the matter cycle of the stars. Analysing the measurements suggests that the atomic gas in this lane converges locally to form molecular hydrogen. When compressed in large clouds, this is the material from which stars eventually form.
Source: J. Syed, J. D. Soler, H. Beuther, et al. The “Maggie” filament: Physical properties of a giant atomic cloud Astronomy & Astrophysics (2021) https://www.mpia.de/news/science/2021-16-maggie