Main-sequence turnoff

Definition

The main-sequence turnoff is the point on the Hertzsprung-Russell diagram where a star leaves the main sequence after exhausting its core hydrogen fuel. It provides crucial information about the age and evolution of star clusters.

5 Must Know Facts For Your Next Test

1. The position of the main-sequence turnoff is used to estimate the age of star clusters.
2. Stars at the main-sequence turnoff have completed hydrogen fusion in their cores and begin fusing helium or other elements.
3. The temperature and luminosity of stars at the turnoff point can reveal their initial mass.
4. Main-sequence turnoff occurs earlier for more massive stars because they burn their fuel more quickly.
5. By plotting a cluster's stars on an H-R diagram, astronomers can identify the main-sequence turnoff to understand stellar evolution.

Review Questions

• How does the main-sequence turnoff help astronomers determine the age of a star cluster?
• What changes occur in a star when it reaches the main-sequence turnoff?
• Why do more massive stars reach the main-sequence turnoff sooner than less massive stars?

Related terms

Hertzsprung-Russell Diagram: A graph that plots stars' luminosity against their surface temperature, used to study stellar evolution

Hydrogen Fusion:

The process by which hydrogen nuclei combine to form helium, releasing energy, and powering main-sequence stars

Star Cluster: A group of stars formed from the same molecular cloud and bound together by gravitational forces