Objectives: Star Birth and the Main Sequence
Chapter Objectives:
In this chapter we will apply the basic physical principles of gravitational
collapse to the nebulae where star birth occurs. The criteria necessary to
begin the star formation process will be discussed, and stages in the life of
a protostar will be illustrated. The most recent infrared images revealing
these previously hidden star birth milestones will be presented. The
evolutionary tracks calculated for forming stars will be traced out on the
H-R diagram. The limiting masses for stars will be discussed and the brown
dwarfs ("stars that missed") will be described.
Chapter Skills:
After studying this chapter you should be able to
- Identify the most likely locations in our galaxy for star birth to occur.
- Understand the essential principles involved in the interplay of gravity,
pressure, and temperature in star formation.
- Describe the role of the calculation of the Jeans mass (or density) in
predicting cloud collapse.
- Identify the most probable sources of the instabilities leading to star
formation.
- Explain why newly forming protostars would be hidden inside a "cocoon".
- Use the H-R diagram to trace out the stages a protostar evolves through
to become a main sequence star.
- Discuss why the range of possible masses for stars is between 0.08 and
100 solar masses.