Source: Starfinder Core Rulebook p.107
When you're fully photon-attuned, you can create a simulacrum of a star as a standard action. The star is a 10-foot-radius sphere that fills your square (or one square of your space, if you're larger than Medium) and all squares within 5 feet of that space. Any creature that starts its turn in the same space as the star takes 1d6 fire damage for every 2 solarian levels you have, and any creature that starts its turn outside the star but within 5 feet of it takes half that damage. At 17th level, you can create your star simulacrum as a 15-foot-radius sphere that affects your square and all squares within 10 feet of that space (a total of 21 squares).
Creatures can move through the star, but it exerts a gravitational pull, and any creature inside it or within 5 feet of it must spend twice as much movement for each square of movement that takes it away from the center of the star. The star remains for 1d4+1 rounds, and stays in place even if you later move. You are immune to all effects of your own miniature star.