What does it mean to have two stars with the same spectral type (e. g k3) but different luminosity classes? what physical property distinguishes a k3v star from a k3l star? stellar evolution 9. list the stages that a sun-like star will pass through after it leaves the main sequence. 10. how do protostars generate their luminosity? how do protostars change as they move toward the main 11. what two features are essential for a star to be on the main sequence? 12. describe in broad terms how stars generate their energy after they leave the main sequence. what are the differences that appear in this process between low- and high-mass stars? 13. what kind of stars experiences a helium flash? which types experience a supernova? 14. what happens in the core of a star during a core collapse supernova? i5. what is the evidence for black holes?