Sigma Centari was a space platform occupied by the Terran Dominion during the Second Great War and was in constant combat with the zerg. It was heavily fortified and had numerous missile turrets for defense against attacks by zerg mutalisks. This resulted in a stalemate between the two sides.
Abathur chose this platform to test the re-assimilated brood lords, after recovering their essence from some local feral brood lords and incorporating it into the existing mutalisk strain. On Kerrigan's orders, the brood lords attacked the platform and destroyed the base's planetary fortress, ending the stalemate.