Stellar Evolution and the Life Cycle of Stars
Stars form from nebulae of gas and dust, spend most of their lives as main sequence stars, and end their lives in ways that depend on their initial mass.
What You Need to Know
Key Concept Diagram
Stars form when gravity causes a cloud of gas and dust (nebula) to collapse and heat until nuclear fusion begins
Main sequence stars fuse hydrogen to helium; the Sun is a main sequence star expected to live ~10 billion years
Low-mass stars end as red giants then white dwarfs; high-mass stars explode as supernovae and may form neutron stars or black holes
The Hertzsprung-Russell (H-R) diagram plots stars by luminosity vs temperature, grouping them into categories
Key Vocabulary
Nebula
A cloud of gas and dust in space from which stars and planetary systems form
Main sequence
The stage of a star's life where it fuses hydrogen to helium; most stars, including the Sun, spend the majority of their life here
Supernova
A catastrophic explosion that occurs when a massive star exhausts its nuclear fuel and its core collapses
White dwarf
The dense, hot remnant of a low-to-medium mass star's core after it has shed its outer layers
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
What is the primary nuclear reaction occurring in a main sequence star?
Question 2
How does the final stage of a massive star differ from that of a low-mass star like the Sun?
Question 3
What is a nebula?
Key Concepts Summary
- ●Stars form when gravity causes a cloud of gas and dust (nebula) to collapse and heat until nuclear fusion begins
- ●Main sequence stars fuse hydrogen to helium; the Sun is a main sequence star expected to live ~10 billion years
- ●Low-mass stars end as red giants then white dwarfs; high-mass stars explode as supernovae and may form neutron stars or black holes
- ●The Hertzsprung-Russell (H-R) diagram plots stars by luminosity vs temperature, grouping them into categories