Star's Life Cycle (Sidebar 3)

Composition and properties of stars
Most stars are hydrogen and helium gas clouds. Stars vary in their temperature and size. The color of a star reveals its temperature. The coolest stars are yellow and red, while the hottest are blue and white.

Origin of stars
Evolutionists do not have a satisfactory theory for the evolution of the first stars. There are some theories for how stars could form, but they require the previous existence of stars. The "birth" of a new star has never been observed. The possibility of such an event is purely speculative, as is the mechanism of such an event.

H-R Diagram Schematic

Life-cycle of a star
H-R diagrams are the standard tools used to study stars' structures and life cycles. H-R diagrams consist of a plot of the stars' temperature (or color) related to its luminosity (or size). Luminosity increases upward, but temperature increases to the left. The usual relationship between a star's size and temperature is direct—the larger the star, the hotter the star. Stars that have this correlation are stable and are said to be main sequence stars (MS). There are two types of exceptions, though. As you can see on the diagram, red giants are very large stars but they are relatively cool. White dwarfs, on the other hand, are very small, but they are very hot.

Astrophysicists have demonstrated quite persuasively that the structure of a star is determined by its mass and composition. MS stars derive their energy from the conversion of hydrogen to helium in their cores. Most astronomers, including some young Earth creationists, believe that "stellar evolution" or life cycle, is a direct result of the composition of the star. As an MS star converts hydrogen to helium, its composition will gradually change with time. It seems that, as a star uses up the hydrogen in its core, conversion to helium begins in a shell outside the core. At this point, the composition of the star has changed from primarily hydrogen to predominately helium. The core will become smaller and hotter, causing the outer layers to expand and cool. The star moves up and to the right on the H-R diagram and becomes a red giant. If the star is large enough, the core will become hotter and denser. At this point helium nuclei can fuse together to form carbon nuclei. The carbon nuclei serve as an energy source, and the core expands and the outer layers are restructured so that the star can become a main sequence star again. Eventually, the energy is used up and the star becomes a red giant again. These processes have not been observed, but are based on sound physics.

The cores of red giants are very dense, and, in fact are very similar to white dwarfs. Through a process that is not completely understood, the outer shells of a red giant blow away, and the star turns to a white dwarf with a gaseous cloud around it. Other red giants are less stable, and explode in a supernova leaving behind a gas nebula and sometimes a pulsar (the core of the star that spins very rapidly). Or a red giant may collapse into a black hole or into a neutron star (an extremely dense structure that gives off light).

New Stars, New Planets?

References
Faulkner and DeYoung. 1991. "Toward a Creationist Astronomy." Creation Research Society Quarterly 28:87-92.