Stars evolved and are still evolving, just like the universe. This evolution takes millions of years.
The Facts Are .....
The theory that the sun and the stars produce their radiation from gravitational collapse was replaced by the nuclear-fusion theory in 1930. This change was to account for the billions of years that evolution demands for the age of the universe, but which the old theory could not accommodate. The failure of the neutrino catching experiment to verify the nuclear-fusion theory means that it must now be concluded that stars radiate due to gravitational collapse. As a logical consequence of this, stars must be nowhere near as old as evolution demands. 
The chemical composition of stars should change if they go through an evolutionary thermonuclear life cycle. The observations are, that stars of supposedly vastly different ages, have roughly the same chemical composition. This indicates that the evolutionary theory is in error, and places in doubt the vast ages of the universe. 
Stars are said to 'evolve' over millions of years, 'proof' of the evolution of the universe without observation. Star FG Sagittae, however, has been observed to change from a blue star to a yellow star in only 36 years. 
In 2000 B.C. the star Sirius was described by the Egyptians as being red in colour. Cicero in 50
B.C. described it as red, as did Ptolemy in 150 A.D. Sirius today is described as a 'white dwarf' - not a
'red giant'. According to evolutionary theory on the life cycle of stars, it should have taken at least 100,000 years for Sirius to collapse into a white dwarf. There is obviously error in the evolutionary theory of the ages of the stars. 
If the thermonuclear evolutionary life cycle of the sun was factual, it would have been fainter and cooler in the distant past. The estimated energy output at that time would have only been 5% less than today, however, it would have caused the earth to be solidly frozen in a crust of ice. These would be conditions unsuitable for life to evolve. 
"For the past 15 years we have tried, in collaboration with many colleagues in astronomy, chemistry, and physics, to understand and test the theory of how the sun produces its radiant energy (observed on the earth as sunlight). All of us have been surprised by the results: there is a large, unexplained disagreement between observation and the supposedly well established theory. This discrepancy has led to a crisis in the theory of stellar evolution; many authors are openly questioning some of the basic principles and approximations in this supposedly dry (and solved) subject." 
- Science, Vol. 191, 1976 p:264
- Paul D. Ackerman "It's a Young World After All", Baker Book House: Grand Rapids (Michigan), 1993 p:59-60
- New Scientist, September 14, 1991 p:28-41
- Paul D. Ackerman "It's a Young World After All", Baker Book House: Grand Rapids (Michigan), 1993 p:67
- Science News, Vol. 111, 1977 p:154
- Written by John N. Bahcall and Raymond Davis, Jr. in their article "Solar Neutrinos: A Scientific Puzzle", in Science Vol. 191, 1976 p:264