Chapter 13: Stellar Evolution

You should be able to write a three or so paragraph essay giving details of how a star is born, ages, and dies. The essay should include a brief description of the physical processes that make things happen.

Specifics to be learned:

Protostars and their formation

Basic features of stellar structure - Review from Chapter 10 the following

hydrostatic equilibrium

thermal equilibrium

energy generation

opacity

convection

Role of temperature in nuclear burning and synthesis of heavy elements

Life expectancy of stars

Difference in evolution of low- and high-mass star

Be able to sketch changes of star's properties in HR diagram with an evolutionary track.

Causes of a star's death

Cause and features of supernova explosions

Basic message of this chapter is that

Stars form from interstellar gas clouds as gravity compresses and heats the gas.

As the star's hydrogen reaches a temperature of about one million degrees, it begins to fuse into helium.

The released energy raises the star's internal pressure and stops its collapse

The star then is a main sequence star.

Eventually the hydrogen is used up and the core readjusts, shrinking and heating.

The higher temperature increases the rate of fuel burning and the star brightens and swells into a red giant

High- and low-mass stars evolve very differently, with the former ending their life as supernovas and the latter as planetary nebula (although this is an over simplification). The reason for this difference is that high-mass stars can burn heavier elements as they evolve.

The nuclear burning in massive stars is what created the elements of which we and the Earth are composed.

These elements are blown into space where they can eventually be incorporated into planets only when those massive stars reach the end of their life and explode.

Our existence thus depends on the death of massive stars.

Dead and dying stars leave compact remnant "stars" such as white dwarfs, neutron stars, black holes.