Exercises: Life Cycle of Stars and the Hertzsprung-Russell Diagram

A star begins its life inside a huge cloud of gas and dust called a nebula. Gravity pulls the material together until a protostar forms. Name the process that finally makes a star "turn on" and begin to shine, and name the element that is mainly fused in a main-sequence star like the Sun.

The Hertzsprung-Russell (H-R) diagram plots stars using two properties. Name the two properties usually shown on its axes, and state which region of the diagram contains most stars, including our Sun.

Put these stages of a low-mass star like the Sun in the correct order from earliest to latest: white dwarf, main-sequence star, nebula, red giant, planetary nebula, protostar.

Emma studies two main-sequence stars. Star A has a mass about 20 times the mass of the Sun. Star B has a mass about half the mass of the Sun. Compare the two stars' surface temperatures, brightness, and expected lifetimes on the main sequence. Then explain why the more massive star has the shorter lifetime even though it has more fuel.

The table gives data for four stars.

Using what you know about the H-R diagram, classify each star as main sequence, giant or supergiant, or white dwarf. Explain your reasoning for Y and Z.

Mateo says, "When the Sun runs out of hydrogen in its core, it will explode as a supernova." Evaluate his claim. State what will really happen to the Sun, and name the mass condition a star must meet to end its life as a supernova.

Two stars formed at the same time in the same nebula. Star P has a mass about 15 times the mass of the Sun. Star Q has the same mass as the Sun. Describe the complete life cycle of each star, from nebula to final stage. Compare their paths on an H-R diagram, and explain why the Sun's final product is very different from the final product of Star P. Use the terms gravity, fusion, and core in your answer.

A student sees two stars in the night sky. Star R has a luminosity of about 100,000 times the Sun's and a surface temperature of about 3,500 K. Star S has a luminosity of about 0.0001 times the Sun's and a surface temperature of about 12,000 K.

1. a) Place each star in a region of the H-R diagram and name its type.
2. b) Explain how Star R can be so much brighter than Star S even though it is cooler.
3. c) Describe what each star is likely to become, or has already become, in its life cycle.