The Pistol Star: luminous, not hottest

The Pistol Star is an exceptionally luminous and massive blue variable star, but it is not the hottest known: its effective temperature is estimated at about twelve thousand kelvins. By comparison, NASA gives at least two hundred thousand kelvins for the central star of nebula NGC 2440. A star is not kept from “breaking apart” by gravity alone: in hydrostatic equilibrium, gravity is balanced by the internal pressure gradient.