再问大全Passage 67的一句翻译

gamxiaoyuan

Eventually the nuclear fuel is exhausted, and the pressure drops in the core. With nothing to hold it up, the matter in the center of the star collapses inward, creating higher and higher densities and temperatures, until the nuclei and electrons are fused into a super-dense lump of matter known as a neutron star.
我想问下，既然最终燃料耗尽了，内部开始瓦解了，为什么还会产生大的密度和高温呢？既然从内部开始瓦解，密度不应该是减少的么？
只有太多物质集中在一个狭小的空间里最终形成爆炸才会在内部形成高温高压呀？