That thing would be called a Novalith and they've been around since '08 in vanilla. The TEC build them. The Loyalists get them at T6 and the Rebels at T8. Each race has it's own superweapon. The TEC have the nova, the Advent have the Deliverance Engine, and the Vasari have the Kostura.
They do 3500 damage and halve the income of the planet for half an hour. You can't counter them directly, but starbases have upgrades that prevent the loss of a planet through orbital bombardment.
And actually they're far from cheap. They cost 8000 credits plus metal and crystal to build and as of Rebellion, each faction can only construct four whereas in previous installments, you could put one on every planet you had the tactical slots for.
They actually are quite easy to deal with once you learn how to.
EDIT: Mecha, don't troll the noobs. That's just mean. Go back to your troll thread.