Questions: Introduction to Stars and Their Life Cycles

Question 1

What is the source of a star's energy?

• A. Stars burn fuel like a campfire
• B. Stars are heated by friction from spinning
• C. Nuclear fusion — hydrogen atoms are fused into helium in the star's core, releasing enormous energy
• D. Stars reflect light from other, brighter stars

Answer: (C)

Stars produce energy through nuclear fusion. In the core, temperatures and pressures are so extreme that hydrogen nuclei are forced together (fused) to form helium. This process converts a tiny amount of mass into a huge amount of energy (following Einstein's E=mc²). The Sun fuses about 600 million tons of hydrogen every second.

Question 2

Why do more massive stars have shorter lifespans than less massive stars?

Model answer: More massive stars have more fuel (hydrogen) but burn through it much faster because they need much higher core temperatures and fusion rates to support their enormous weight. A star 10 times the Sun's mass might have 10 times the fuel but burns it 10,000 times faster, lasting only millions of years instead of billions.

This is counterintuitive — you would expect more fuel to last longer. But the relationship between mass, luminosity, and lifetime is non-linear. Luminosity increases roughly as mass to the 3.5 power. So a star with 10x the Sun's mass is about 3,000x more luminous and burns through its fuel roughly 300x faster.

Question 3

The Sun will eventually explode as a supernova.

• T. True
• F. False

Answer: False

Only stars significantly more massive than the Sun (roughly 8+ solar masses) end as supernovae. The Sun is a medium-sized star. In about 5 billion years, it will expand into a red giant (engulfing Mercury and Venus), shed its outer layers as a planetary nebula, and its core will collapse into a white dwarf — a small, dense remnant that slowly cools over billions of years. No explosion.