Variable Stars: What Causes Their Brightness to Vary?

[varsha]

i don't get it. really large stars are unstable and there are frequent outbursts. so they are called variable stars. but when they burst they create a nebula and remain as a star right? how is that? shouldn't they turn into a black hole or a nutron star or just a nebula?

or do they just vary in brightness?

 

[Labguy]

i don't get it. really large stars are unstable and there are frequent outbursts. so they are called variable stars. but when they burst they create a nebula and remain as a star right? how is that? shouldn't they turn into a black hole or a nutron star or just a nebula?

or do they just vary in brightness?

The trouble with an answer is that there are very many different types of variavle stars, and each usually has a different mechanism going on which causes the variability. One type is Cepheids, which you can read about in the thread below.

Otherwise, search on:
(1) Variable Stars
(2) Planetary Nebula
(3) Supernova
- Type II
- Type I
(4) Supernova Remnant(s)
(5) Neutron Stars
(6) Black holes
(7) T-Tauri Stars
etc., etc.

There are probably others, but these subjects would find you plenty to read. Also, and probably most essential, is to Read about the Main Sequence where you'll find that almost all stars are variable at some point in their lives. Usually (huge caveat) it is when they leave the main sequence and enter the giant stage(s) and pulsate on a regular basis for many years. The time period for each star depends (mainly) on original mass and chemical composition.