Type II Supernova

As massive red supergiants age, they produce "onion layers" of heavier and heavier elements in their interiors. However, stars will not fuse elements heavier than iron. Fusing iron doesn't release energy. It uses up energy. Thus a core of iron builds up in the centers of massive supergiants.

Eventually, the iron core reaches something called the Chandrasekhar Mass , which is about 1.4 times the mass of the Sun. When something is this massive, not even electron degeneracy pressure can hold it up.

The core collapses. Two important things happen:

• Protons and electrons are pushed together to form neutrons and neutrinos.

  Even though neutrinos don't interact easily with matter, at densities as high as they are here, they exert a tremendous outward pressure.

• The outer layers fall inward when the iron core collapses. When the core stops collapsing (this happens when the neutrons start getting packed too tightly -- neutron degeracy), the outer layers crash into the core and rebound, sending shock waves outward.

These two effects -- neutrino outburst and rebound shock wave -- cause the entire star outside the core to be blow apart in a huge explosion: a type II supernova!

Supernovae are really bright -- about 10 billion times as luminous as the Sun. Supernovae rival entire galaxies in brightness for weeks. They tend to fade over months or years.

During the supernova, a tremendous amount of energy is released. Some of that energy is used to fuse elements even heavier than iron! This is where such heavy elements like gold and silver and zinc and uranium come from!

The material that gets ejected into space as a result of the supernova becomes part of the interstellar medium. New stars and planets form from this interstellar medium. Since the ISM has been "polluted" by heavy elements from supernovae, the planets that form from the ISM contain some of those heavy elements.

The collapsed core is also left behind by a type II supernova explosion. If the mass of the core is less than 2 or 3 solar masses, it becomes a neutron star. If more than 2 or 3 solar masses remains, not even neutron degeneracy pressure can hold the object up, and it collapses into a black hole.

---

The upper figure above depicts photographs taken both before and after the explosion of Supernova 1987A. These photographs were obtained from the Universe:Origins and Evolution Homepage.

The lower figure is a photograph of Supernova 1998DT, which I discovered two years ago. The photo was taken by the Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory.


Back to the Stellar Life Cycle Flow Chart