They are called white dwarfs.
its called a super nova.
Massive Stars.
Massive Stars.
No, but some stars end their life by becoming a black hole.
The massive stars turn into gas
The most massive stars will end up as black holes. Those are the stars that have more than approximately 3 solar masses at the end of their life - i.e., AFTER the supernova explosion.
A small amount might get out with solar (or stellar) wind. But mainly, at the end of the life of larger stars, there is a violent explosion called a supernova, that ejects a large part of the star's material into space.
A Protostar.
A supernova
There are all types of stars in the Milky Way.See related question
I am not aware of any specific element "signaling" this. Towards the end of a stars life, however, relatively large amounts of heavier elements are produced.
They are not. A supernova is an explosion of a star. Blue stars usually end their lives in such explosions.