CH 20 HW

What is hydrostatic equilibrium in a star?

The balance between the force of gravity directed inward and thermal pressure directed outward.

Why is radiation necessary for a star to maintain hydrostatic equilibrium?

If the energy were not radiated away, the balance would be upset and the star would grow larger or explode.

A star will evolve off the main sequence when it uses up what?

All of its hydrogen.

Why are red-giant stars so named compared to other stars on the H-R diagram?

They are cooler.

When the Sun is on the red-giant branch, where will it be found on the H-R diagram?

Upper right of the H-R diagram.

After the core of a Sun-like star starts to fuse helium on the horizontal branch, what happens to the core?

It becomes hotter with time.

When the Sun leaves the main sequence, what will happen to it?

It will become brighter.

Compared to the Sun, stars plotted near the bottom left of the H-R diagram are what?

More massive.

What supports a white dwarf?

The pressure of tightly packed electrons.

What will a star like the Sun end up as?

A white dwarf.

Do astronomers have more observational evidence for the evolution of Sun-like stars or high-mass stars?

Astronomers have much more observational evidence for the evolution of Sun-like stars than that of high-mass stars.

On the main sequence, how do massive stars burn their hydrogen fuel?

They burn their hydrogen fuel more rapidly than the Sun.

Which method is used observationally to determine the age of a star cluster?

The luminosity of the main sequence turn-off point.

As a 4-10 solar mass star leaves the main sequence on its way to becoming a red supergiant, what happens to its luminosity?

It first increases, then decreases.