The life cycle of stars, containing many different phases, is one of the most complicated subjects that scientists are learning about and trying to understand.  All stars start their life from a cloud of gas that is made up of mainly hydrogen and helium with a few other elements thrown in there.  From there, the star becomes a protostar, which is basically a prototype of a star.  In this phase, the star begins to fuse hydrogen atoms to make helium atoms.  If the star gets hot enough, it will begin a long middle age phase, which is the star’s main sequence.  Once the star has a high enough helium content in its core, the core contracts and it releases energy in the form of gravity.  The star then expands, becoming a red giant or a supergiant depending on the mass of the star.  The last phase of a star’s life cycle includes, becoming a planetary nebula, if it is a low-mass star, and then it will become a white dwarf.  However, if the star is too massive, it will supernova and collapse into a neutron star, such as a pulsar.  If the core collapses completely, it will disappear and become a black hole.

Recently, scientists suggest that there is yet another phase that a star goes through before death.  This phase is called an electroweak star, which is suggested to occur between the neutron star and black hole stages.  As their source for energy, electroweak stars convert quarks into leptons.  This energy could possibly stop the star from collapsing into a black hole.  This is still only a theory, since it is extremely difficult to differentiate an electroweak star from an ordinary star, if one is ever detected.  To be able to be more accurate on this topic, scientists need to comprehend stars better than they already do.

Article Link: http://www.sciencedaily.com/releases/2009/12/091214131132.htm