What you actually saw is the new 16 Man raid World Boss. Two bosses actually spawned. The one you mentioned and the "Nightmare Pilgrim". The Nightmare Pilgrim is a lot smaller than The Thing from the Stars (Very Lovecraftian name) but if you click that object again and look around you'll notice him spawn too. This boss cannot be killed without a special item that costs 30 daily comms which you can find on Belsavis. The fact that no one on your server knows about this is actually quite troubling.... that or you don't have a hardcore raiding guild on that server. He drops Blackhole (ilvl 146) gear which is better than Rakata (ilvl 140) but not as good as Campaign (ilvl 146). Once you defeat it, it'll give you a 5 hour buff that increases all main stats by 50 and a debuff that prevents you from killing him again for another 5 days.