Editing Stellar classification (section)

==Stellar remnants==
{{Main|Neutron star|Black hole|Exotic star}}
Stellar remnants are objects associated with the death of stars. Included in the category are [[white dwarf]]s, and as can be seen from the radically different classification scheme for class&nbsp;D, stellar remnants are difficult to fit into the MK system.

The Hertzsprung–Russell diagram, which the MK system is based on, is observational in nature so these remnants cannot easily be plotted on the diagram, or cannot be placed at all. Old neutron stars are relatively small and cold, and would fall on the far right side of the diagram. [[Planetary nebula]]e are dynamic and tend to quickly fade in brightness as the progenitor star transitions to the white dwarf branch. If shown, a planetary nebula would be plotted to the right of the diagram's upper right quadrant. A black hole emits no visible light of its own, and therefore would not appear on the diagram.<ref name="chan-var-hr">{{cite web |url=http://chandra.harvard.edu/edu/formal/variable_stars/bg_info.html |title=Pulsating Variable Stars and the Hertzsprung-Russell (H-R) Diagram |publisher=Center for Astrophysics {{!}} Harvard & Smithsonian|date=9 March 2015 |access-date=23 July 2016}}</ref>

A classification system for neutron stars using Roman numerals has been proposed: type I for less massive neutron stars with low cooling rates, type II for more massive neutron stars with higher cooling rates, and a proposed type III for more massive neutron stars (possible exotic star candidates) with higher cooling rates.<ref>{{Cite journal |arxiv = astro-ph/0204233|doi = 10.1051/0004-6361:20020699|bibcode = 2002A&A...389L..24Y|title = The cooling neutron star in 3C 58|journal = Astronomy & Astrophysics|volume = 389|pages = L24–L27|year = 2002|last1 = Yakovlev|first1 = D. G.|last2 = Kaminker|first2 = A. D.|last3 = Haensel|first3 = P.|last4 = Gnedin|first4 = O. Y.|s2cid = 6247160}}</ref> The more massive a neutron star is, the higher [[neutrino]] flux it carries. These neutrinos carry away so much heat energy that after only a few years the temperature of an isolated neutron star falls from the order of billions to only around a million Kelvin. This proposed neutron star classification system is not to be confused with the earlier Secchi spectral classes and the Yerkes luminosity classes.