The core finally cools into a white dwarf, then a black dwarf. This is what happens when a normal-sized star dies. If a really huge star dies, it has so much mass that after the helium is used up, it still has enough carbon to fuse it into heavy elements like iron. When the core turns to iron, it no longer burns.
Just so, how does a star die out?
Most stars take millions of years to die. When a star like the Sun has burned all of its hydrogen fuel, it expands to become a red giant. This may be millions of kilometres across - big enough to swallow the planets Mercury and Venus.
How long does it take for a star to collapse?
So, how long does a supernova take to explode? A few million years for the star to die, less than a quarter of a second for its core to collapse, a few hours for the shockwave to reach the surface of the star, a few months to brighten, and then just few years to fade away.
How long is the life of a star?
Stars live different lengths of time, depending on how big they are. A star like our sun lives for about 10 billion years, while a star which weighs 20 times as much lives only 10 million years, about a thousandth as long. Stars begin their lives as dense clouds of gas and dust.