The Pirates of Zebulon
The Pirates of Zebulon operated out of several ancient alien temples on the jungle world of Zebulon Prime. They were led by the pirate lord Ral Duris, who had a Sith advisor known as Lady Aldera. The pirates operated a fleet of a least three ships, including the Grey Lurker (the ship the crew just won at auction, and captured in their first fight with the pirates on the Prime) the Death Dream (the ship captured at the Emerald Cliffs) and the Obsidian Phoenix (the flagship, and the one ship never captured). They also had a handful of starfighters that flew in tandem with their larger vessels.
After the pirates' crushing defeat at the Emerald Cliffs, they fled Zebulon. Lady Aldera was believed to have been sealed inside an ancient alien complex next to the Emerald Cliffs as a result of the cataclysmic explosion at the end of tat fight. No one has heard from Ral Duris and the Obsidian Phoenix in weeks, but it is believed that he has left the Vargis Tau system.
Ral Duris and his pirates were known to have connections to Taris, primarily through Zaxor, the hacker they'd hired to compromise Zebulon's planetary network, Although in league with a Sith, they did not use any Sith military hardware; it was all standard (or at least, standard black market) gear.
Meanwhile, the alien temples remain on Zebulon Beta (indeed, the Unified Force Academy was built inside one of the temples) and Zebulon Prime. Some have connections, even strong connections, to the Force, which you assume is what attracted the Sith in the first place.
The DeadStar
Not long after defeating the pirates, the crew of the Aeon Harrier took on a job to recover an old remote droid processor from the wreckage of the Starworm. While there, they ran into the salvage ship DeadStar and a few of her Sith ugly starfighters, which was apparently there for the same reason.
Important note: Sith uglies are starfighters that have been hacked together from the remains of Sith starfighters and some other ships; in this case, the result was a starfighter capable of hyperspace jumps. Even 15 years after the Great Sith War there's still a lot of old Sith and Republic military hardware floating around in space, and it's not uncommon for salvagers, pirates, mercenaries and even honest traders to incorporate tech from both sides into their operations.
Galactic Lore checks at the time revealed that the Starworm is owned by a Rodian named Geelo who operates out of Taris. He operates a starship salvage yard and parts business and has an reputation unsavory and underhanded business dealings. Some have accused him of operating a shipjacking business, but formal charges, even if filed, have never stuck.
After the Aeon Harrier beat out the DeadStar for the remote droid processor and jumped away, Geelo apparently decided to pull some strings, getting the Commerce Court on Taris to place a lien against the crew of the Harrier for $15,000 and getting a government bounty placed on the heads of the crew.
Recently, the DeadStars showed up on Zebulon Beta trying to make good on their lien, and threatening to capture our heroes and bring them back to Taris in an effort to get them to pay.
Who's Who?
To the best of your knowledge, the DeadStar and the Pirates of Zebulon are not related, though both have ties to Taris. It should be noted though, that Taris is effectively the regional capitol of this area of the Outer Rim; almost everyone has some sort of connection that runs back to it. Just like many businesses in NJ or PA have ties to New York City.
You strongly believe that Geelo (the DeadStar's captain) is a criminal mastermind in all but name, but one who's has a knack for operating just within the bounds of the law. He also appears to have powerful political friends on Taris itself.
Meanwhile, the pirates led by Ral Duris are *clearly* outlaws. However, you actually know very little about them -- after defeating the pirates and driving them from the system, the party hasn't done any follow up on exactly who Ral Duris is and how he came to be in the Vargis Tau in the first place. In hindsight, this is probably because half the party thought he was in cahoots with the DeadStar.
Going forward, Ral Duris and his pirates are still out there ... somewhere. Jeelo and the DeadStar are a more immediate threat because of their semi-legitimate standing and their successful manipulation of the Commerce Court on Taris to get the lien and the bounties against the Aeon Harrier crew.
As for the Sith? No one knows. The Dark Lady Aldera has not been seen in weeks, nor have any of her Sith apprentices. It is possible she died in the explosion at the Emerald Cliffs ... but the Jedi are skeptical that a mere cave in could take out a powerful Sith force user. Exactly who she is -- and who she might serve -- remains unknown.