  This M.Sc. thesis in Engineering Physics is an overview of the present theory
of quark-gluon plasma (QGP) as well as an analysis of the stability criterion
for possible stable cosmic QGP objects left over from the quark-hadron
transition in the early Universe. It covers fundamental ideas of the formation
and decay of the plasma, including the standard model, QCD, and the MIT bag
model. I discuss the equation of state of a QGP and the possible signatures for
a plasma created in heavy-ion collisions. Astrophysical aspects of QGP are put
forward, including compact stars and the quark-hadron transition in the early
Universe. The possible role of QGP objects as cosmic dark matter is mentioned.
The analytic part is an investigation of possible stability among cosmic QGP
objects from the early Universe. A model is suggested where a pressure balance
makes a QGP stable against gravitational contraction and hadronization. The
mass/radius relationship for stability also forbids a direct gravitational
collapse. Finally, the possibility of stable cosmic QGP objects is critically
discussed.
