A mass shadow was the hyperspace signature of a large celestial body. Mass shadows could prevent hyperspace jumps, and could pull a ship out of hyperspace, should it venture too close. Because of their nature, mass shadows could threaten a ship with collision. Therefore, mass shadows were feared by travelers. Navigation computers and astromech droids were programmed to calculate routes in hyperspace that deliberately avoid such phenomena. They would also automatically pull a ship out of hyperspace in the event that the ship did indeed come close enough to potentially damage it. Mass shadows occurred naturally, caused by the gravity wells of large celestial bodies such as planets, stars or gas giants. They could also be caused by smaller bodies such as comets.
An artificial mass shadow was created by Galactic Republic Lieutenant Bao-Dur on the planet Malachor V during the Mandalorian Wars under the Jedi General Meetra Surik. Bao-Dur's Mass Shadow Generator was so powerful it trapped and crushed any ships that ventured too close to the planet's surface, killing millions of Mandalorians and Republic soldiers alike. Only an extremely powerful Force user such as Darth Nihilus would be able to pull a ship from the gravity well and escape the planet. The Mass Shadow Generator was used by the Jedi Exile a second time to destroy Malachor V after defeating Darth Traya.
Temporary gravity wells could be created by such ships as the Interdictor-class Cruiser of the Galactic Republic and the Immobilizer 418 cruiser of the Galactic Empire, as well as weapons such as gravity mines and pulsemass generators. Gravity well generators were also installed on the Eclipse and Eclipse II. However, it is unknown if such occurrences can be considered a true mass shadow.
- Star Wars: Knights of the Old Republic II: The Sith Lords (Mentioned only)
- Star Wars: The Old Republic (Mentioned only)
- The Force Unleashed II novel
- Luke Skywalker and the Shadows of Mindor (Mentioned only)
- Dark Force Rising (First mentioned)
- Dark Force Rising audiobook (Mentioned only)
- Specter of the Past
- Specter of the Past unabridged audiobook
- The New Jedi Order: Edge of Victory II: Rebirth
- The New Jedi Order: Enemy Lines I: Rebel Dream
- The New Jedi Order: Ylesia (Mentioned only)
- The New Jedi Order: The Unifying Force