Specifically, thermonuclear ignition by inertial confinement in the laboratory – as well as the transition from planets to brown dwarfs and stars in nature – takes place via the HED regime.
[3] The HED domain is often defined by an energy density (units of pressure) above 1 Mbar = 100 GPa ~ 1 Million of Atmosphere.
The dense HED regime includes highly degenerate matter, with interatomic spacing less than the de Broglie wavelength.
[3] HED conditions at higher temperatures are important to the birth and death of stars and controlling thermonuclear fusion in the laboratory.
As the iron core accumulates to ~1.4 solar masses, electron degeneracy pressure gives up against gravity and collapses.