Source: Starfinder Core Rulebook p.104
As a move action, you can draw on the properties of dark matter to increase your density, allowing you to resist physical damage. You gain damage reduction 1/-. This increases to DR 2/- at 6th level and increases by 1 again every 3 solarian levels thereafter. This benefit lasts for 1 round or until you leave graviton mode.
When you are attuned or fully attuned, your DR from dark matter is equal to half your solarian level.