The L-Cluster is a system of stars that can only be accessed via special L-Gates. It is the headline feature of the Distant Stars expansion.
The L-Cluster is only accessible through special L-Gates. These appear around black hole systems. When a player enters a system with an L-Gate for the first time, a new event is registered on the situation log. Once you have discovered it, you will need 7 L-gate insight to make it operative. L-gate insight can be purchased from curator enclaves, researched as a repeatable engineering technology, obtained from investigating anomalies, or generated by country events.
The L-Cluster was originally home to the unnamed civilization responsible for constructing the galactic gateway network. Once the network was complete, the nanites used to construct it, known as the Naar-Di-Shav or the Gray Tempest, went rogue and began processing the L-Cluster Civilization for resources. The L-Cluster Civilization sealed the sole L-Gate in their cluster to prevent the Gray Tempest from escaping and consuming the galaxy. When the L-Gates are finally reactivated, the L-Cluster Civilization is completely destroyed, and the entire cluster is infested with the Gray Tempest.
Most planets in the L-Cluster are either Nanite Worlds, completely infested with the nanites, or Shattered Worlds, presumably destroyed by the L-Cluster Civilization in a desperate attempt to destroy the Gray Tempest. Despite the destruction, the L-Cluster is still home to a wide array of valuable, unique strategic resources that cannot be found elsewhere.
Most systems in the L-Cluster will contain 1-3 Tempest Shoals, space fleets controlled by the Gray Tempest with a fleet strength of approximately 50K. When the L-Gates are initially activated, one Tempest Shoal will spawn at each L-Gate in the galaxy except for the L-Gate which was initially activated. Tempest Shoals will continue to spawn from these L-Gates periodically unless a non-Tempest fleet is present in the L-Cluster system containing the L-Gate. The ships do not need to be military ships to prevent Tempest Shoals from spawning.
Every Tempest Shoal is led by a Mothership armed with a titan-class weapon that deals 1-9999 energy damage and which penetrates armor and shields completely. As such, it can destroy any ship with a single shot. The only effective defense against this weapon is evasion. Most Tempest Shoals in the L-Cluster will sit in orbit in aggressive stance, and will occasionally relocate to a different system within the L-Cluster. Outside of the L-Cluster, Tempest Shoals will wander about the galaxy, traveling to and from a set of predetermined systems spread throughout the galaxy. They will pass through activated gateways, but not L-Gates, which instead act as spawn points. They will attack any ship or station they come into contact with, but not planets. Due to their immense damage output, most stationary objects a Tempest Shoal comes into contact with will be destroyed.
Deeper into the L-Cluster is the Nanite Factory, the de facto head quarters of the Gray Tempest. The Nanite Factory is guarded by multiple Tempest Shoals and has about 90K fleet strength itself. Once the Nanite Factory is destroyed, all the nanites will deactivate and the L-Cluster, along with its unique resources, can be safely claimed.