The Graviton Lance is an Exotic Secondary Weapon in Destiny 2.
It’s rewarded automatically for the main mission “Riptide” on Titan moon. After the mission you must speak with Sloane and can pick one of three exotics.
Exotic Name: Graviton Lance
Type: Pulse Rifle (Secondary)
Required Level: 11
Item Description: Think of space-time as a tapestry on a loom. This weapon is the needle.
Special Ability #1: Black Hole — 3rd shot in the burst does high damage.
Special Ability #2: Kills with this weapon cause enemy targets to detonate.
Acquired by: Beat the ‘Sacrilege’ main mission on IO and you can pick it as a quest reward from Fragment Researcher Ashermir.