What defines the main-sequence lifetime of a star? a. Thermonuclear fusion of He

Question

What defines the main-sequence lifetime of a star?

a. Thermonuclear fusion of He into C in the core

b. Thermonuclear fusion of H into He in the core

c. An electron degenerate pressure state in the core

d. Thermonuclear fusion of He into C in the shell

e. Thermonuclear fusion of H into He in the shell

What is the first indication that we receive on the Earth that a Supernova explosion has happened somewhere in the sky?

a. A pulsar is detected

b. The Aurora are exceptionally bright

c. A handful of neutrinos are detected

d. Radio signals are interrupted

e. We see the light from the supernova

Explanation / Answer

1] Option b is correct

The overall lifespan of a star is determined by its mass. Since stars spend roughly 90% of their lives burning hydrogen into helium on the main sequence (MS), their ‘main sequence lifetime’ is also determined by their mass.

Massive stars need higher central temperatures and pressures to support themselves against gravitational collapse, and for this reason, fusion reactions in these stars proceed at a faster rate than in lower mass stars. The result is that massive stars use up their core hydrogen fuel rapidly and spend less time on the main sequence before evolving into a red giant star.

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