Only a few varieties of stars end their lives this way and astronomers sort the explosions into two basic categories: type Ia supernovae and type II supernovae. While the exact self-destruction process varies with each type, all stellar explosions ultimately depend on the star's enormous mass.
When a Star Collapses
Type II supernovae are also known as core-collapse supernovae. These explosions only occur with stars at least eight times the size of our own (eight solar masses).
To understand exactly what takes place, you have to see a thriving star as a balance of inward and outward forces. The star's own mass exerts an inward pull of gravity, while the nuclear fusion reactions in its core apply an outward push of pressure. One force tries to expand the star; the other tries to crush it.
"Stars spend their life fusing various elements by nuclear reactions into heavier elements," says author and astrophysicist Mario Livio of the Space Telescope Science Institute. "For example, our own sun fuses hydrogen atoms into helium atoms, and that's the source of its energy."
Yet a star can only carry on this balancing act to a point. Eventually, the star's core turns to iron and without the outward push of fusion, the star collapses in on itself. Core temperature skyrockets under this intense pressure, breaking down the iron nuclei and causing the core itself to break down.
"The core collapses down to stupendous density," says Livio, "at which point there is something that is called a bounce. It's like when something hits a brick wall. The core collapses up to a point where it becomes extraordinarily hard to squeeze it anymore."
The bounce takes the form of a powerful shock wave, which blasts the entire steller envelope (several solar masses worth of material surrounding the core) away at a speed of 10,000 miles (16,093 kilometers) per second.
Read more at Discovery News
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