Stellar Evolution

‘The life-cycle of stars’

Star Energy

• Nuclear Fusion – a nuclear reaction in which to atoms are fused together…

• New elements are created and energy is released.

• This process is responsible for creating ALL elements found in the universe…

in other words, we are all made from star dust.

Star Energy (con’t)• Hydrogen fusion

H + H He +

• Helium fusionHe + He Be +

• As the mass of elements increases, energy production increases

Energy

More Energy

1. Nebula

• A cloud of gas and dust

• Gravity causes the cloud to collapse and condense

• Temperatures begin to increase = Glows

• Fusion begins at VERY high temps.

(Some of the extra gas and dust may form planets)

Main Sequence Stars

• Core reaches a temp of ~15 million K.

• Hydrogen begins to fuse into Helium in the core.

• ~90% of stars lifetime is spent in the main sequence stage.

•Classified based on temperature and luminosity

Giant Stars

• Core decreases in size as

• All (or most) H is consumed

• He fusion is occurring – producing more energy

• Diameter increases x10• Surface temp decreases

as star expands

Super Giants

• Form from massive stars• A chain of reactions take

place in the core producing He, C, O, Ne, Mg, Si, S, Ar, Ca, Ti, Cr, Fe

• Highest temperature = Blue Super Giants

• Usually explode in a tremendous event called a supernova

Nova/Super Nova• The core of a giant star

produces too much energy in it’s core and causes the outside of the star to expand.

• The outer layer of gasses are blown out to space (nova, or supernova), leaving behind a small, hot core…

White Dwarf

• Stars decrease in size ~ same diameter as earth, mass stays the same

• Mass of sun, size of Earth • DENSITY INCREASES

TREMENDOUSLYD = 1,000,000 g/cm3

1 sugar cube > 1 car• Solid, but still hot, so it is glowing• Luminosity decreases

Neutron stars

• Form from the remains of extremely massive stars after a supernova.

• Very small ~ 30 km across• D = 2 x 1014

• 1 sugar cube = mass of humanity

The fate of our Sun