It comes to a Point in Red Giant Stars, they collapse and all Mass is concentrated in a relatively small Core around 10 Kilometres but with several Masses of our Sun. The physical Situation in this Core are beyond every Imagination. So even the Nukleus´ of Atoms are molten and enriched with socalled Neutrons till only Iron, Chromium and Manganese remain. The Hull consists of these Elements, the inner Core is a ultrahot Plasma of molten Atoms. They emit Radiation not visible in our Range of Sight, so they can only be seen by special Instruments like X-Ray-Telescopes. Ususally they are depicted as blue Objects as in the Images above . Strange is the Fact that despite the huge Masses they have not event Horizons. Next Stations can be a "White Dwarf" or a Black Hole", depending on several Cicumstances. All things have a Career ... Have a good day and follow Your Career in Life, whatwever it may be destined to be or has been choosen! :)