Stellar Evolution

Our Sun, along with most of the stars in our neighborhood, probably formed …

• … about 10 million years ago.

• … a few million years ago.

• … hundreds of millions of years ago.

• … billions of years ago.

• … at the beginning of the universe.

What is the force that keeps a main sequence star

from blowing apart?

• radiation pressure

• electron degeneration pressure

• the strong force

• magnetism

• gravitation

Which event marks the birth of a star?

• collapse of an interstellar cloud

• formation of the planetary nebula

• fusion of hydrogen atoms into helium atoms

• formation of a photosphere

• instability in an interstellar cloud

What happens when an interstellar cloud fragment shrinks?

• It blocks the passage of light.

• Density rises.

• Temperature rises.

• Pressure rises.

• All of these.

A typical protostar may be several thousand times more luminous than the Sun. What is the source of this energy?

• chemical combustion of hydrocarbons

• nuclear fusion in its core

• from the release of gravitational energy as the protostar continues to shrink

• the ionization of the gas as it heats up

• from nearby hot stars or supernovae that have initiated the star formation process

What is characteristic of a main sequence star?

• It has a mass less than the Sun's.

• It has rapid rotation and a strong stellar wind.

• Nuclear fusion in the core varies due to the amount of gravitational contraction that

  occurs and which heavy elements are produced.

• The star is in a state of equilibrium between gravitational contraction and radiation

  pressure.

• All of these answers are correct.

On an H-R diagram, a protostar would be…

• …above and to the right of the main sequence.

• …below and to the left of the main sequence.

• …below and near the right side of the main sequence.

• …above and near the upper left of the main sequence.

• …on the main sequence at the extreme lower right.

What is the force that keeps a main sequence star from collapsing on itself?

• Magnetism

• Gravitation

• The strong force

• Radiation pressure

• Electron degeneration pressure

The single most important determinant of the temperature, density, radius, luminosity, and pace of evolution of a protostar is its

• chemical composition.

• mass.

• magnetic field.

• molecular composition.

• spin.

Compared to lower mass protostars, higher mass protostars enter the main sequence…

• …faster and at a higher luminosity and temperature.

• …faster and at a lower luminosity and temperature.

• …slower and at a higher luminosity and temperature.

• …slower and at a lower luminosity and temperature.

• …at the same rate, but at a higher luminosity and temperature.