Where do these clouds of gas come from?
- They could be made of material from the Magellanic Clouds, which are small satellite galaxies associated with the Milky Way.
- They could be from other galaxies in our Local Group, possibly other satellite galaxies.
- Did you know that we have a bunch of satellite galaxies that are all closer than what we call the "nearest galaxy," Andromeda?
- They could be leftovers from its formation.
- They could be due to a "galactic fountain" gushing gas. In regions with a lot of massive stars, supernovae often go off. Supernovae are hot. Supernovae heat the gas around the stars, which causes the gas to rise and form "superbubbles," which leave the Galaxy's disk and go into the halo. As the gas rises, it cools, condenses, and eventually returns back toward the disk.
What's up with the Smith Cloud?
What will happen when the Smith Cloud smashes into us?
Why is the Smith Cloud, and why are high-velocity clouds in general, important to us?
Lockman, F., Benjamin, R., Heroux, A., & Langston, G. (2008). The Smith Cloud: A High-Velocity Cloud Colliding with the Milky Way The Astrophysical Journal, 679 (1) DOI: 10.1086/588838
Lockman, F. (2012). The Milky Way and its gas: Cold fountains and accretion EPJ Web of Conferences, 19 DOI: 10.1051/epjconf/20121908003