I checked with admins; they're aware and are investigating the cause and working to resolve it ASAP. Unfortunately as this wasn't something we planned on (not a maintenance outage) we don't have an ETA for the fix yet, but they are looking into it and will get it back up and running as quickly as possible.
Edit: Looks like it should be back up actually; we'll be keeping an eye on it though to try and ensure it doesn't become unstable and go down again.