Summary:

- The Hubble Space Telescope has observed a puzzling phenomenon in the Andromeda galaxy, the closest major galaxy to the Milky Way.
- Observations show that the outer regions of Andromeda are rotating much faster than expected, suggesting the presence of a significant amount of unseen "dark matter" in the galaxy.
- This discovery provides insights into the distribution of dark matter in Andromeda and could help scientists better understand the formation and evolution of large galaxies like our own Milky Way.