What is an Omega molecule in Star Trek and why is it so dangerous?

The devious space pirate Nus Braka (Paul Giamatti) has been a recurring villain in Starfleet Academy ever since he took over the USS Athena in the series premiere. His grand plan is finally revealed in episode 9, “300th Night,” and it involves using Omega molecules, an extremely dangerous substance first introduced in Star Trek: Voyager. Here’s a lesson on Star Trek history to explain why that’s such a problem for the United Federation of Planets.