Lecture 21 Flashcards
How do we find the mass of a star?
We can use Newton’s Version of Kepler’s Law (p^2=a^34pi^2/GM) on binary stars
What is the maximum mass a star can be?
120 MSun. Stars bigger than this will blow apart as the amount of radiation is too high and cannot be bound together by gravity
What is the minimum mass a star can be?
0.08 MSun
What are main sequence stars fusing in their cores?
Hydrogen into helium
How does the mass of a star relate to its lifetime?
Stars with greater masses have shorter lifetimes
Why do more massive stars die faster even though they have more hydrogen fuel?
They are more luminous so run out of fuel sooner
Roughly what percentage of time do stars spend in the main sequence?
90%
Why are some stars not on the main sequence?
- not fusing hydrogen into helium any more
- near the end of their lives
What do all stellar properties depend on?
Mass
How can we study stars of different masses at various points in their lives?
By looking at star clusters
What are 3 key features of star clusters?
- all the same distance
- all about the same age
- range of different masses
What is an open star cluster?
- 100s to 1000s of stars
- loosely bound by gravity
- young (since older clusters are pulled apart by galactic tides)
What is a globular cluster?
- 100,000 to million stars
- tightly bound- stars are very dense in the core
- usually old
What stars turn off the main sequence first?
High mass stars
Why do stars move off the main sequence and what direction do they turn off?
They run out of hydrogen fuel and cool down slightly, moving to the right
