Lesson Four Topics

Lesson Four Overview
Star Formation
Stellar Nurseries
Star Life
Star Death
Supernovae
Supernova Remnants
Pulsars
Black Holes

	Activities and Quizzes

Lesson Four : Star Life

Once a star emerges from its stellar nursery, it lives quietly fusing the hydrogen in its core to produce helium.Low-mass stars like our Sun continue fusing hydrogen for about ten billion years.

As the star fuses more hydrogen into heium, it develops a core of helium with outer layers of hydrogen. Since the star has no immediate source of heat to resist the pull of gravity from the helium core, the core temperature rises, causing it to expand and push away the outer hydrogen shell causing the star to swell. These layers cool, and the star enters its first red giant phase.

For a small star (such as our sun), all of the helium in the core is eventually fused into carbon and all activity in the core ceases.

A larger star, several time the mass of our sun, initially undergoes the same basic process but at a faster pace. When it reaches the stage at which the core has fused into carbon, it continues nuclear fusion to form heavier elements than carbon, like oxygen, neon, silicon, sulfur and so on.

As each new element undergoes nuclear fusion, the star swells to form increasingly larger red giant stars. Eventually, all of the materials avaible to the core are fused into iron and the nuclear processes cease. What happens at this point is determined by the remaining mass of the star following its final red giant stage.