immortality

[burrahobbit]

I thought it said orcs were captured and tortured elves cruelly formed into these horrible creatures.

It does, but it's wrong. Tolkien changed his mind about the origin of Orcs later in his life. Pretty much everything doesn't reflect that, though, as pretty much everything was written before he changed his mind. Orcs aren't Elves, so orcs aren't immortal. I can think of some other interesting questions that follow from this, though, and some even more interesting answers.