The Life cycle of stars

Stellar Birth

All stars are born in a nebula.

A NEBULA IS A CLOUD OF GAS AND DUST THAT IS LIGHTYEARS THICK. 

Inside this cloud single atoms of gas are pulled together by gravity.  They grow through the process of accretion, from tiny clumps of gas into massive stars.  Within a single nebula hundreds of stars are being born and growing.  They often glow fluorescent colors from the light of young stars.

Fusion:  Powering a star

Stars grow inside the nebula getting bigger and bigger and bigger, accumulating more and more Hydrogen gas until they reach a point called critical mass.  At this point the inward pull of gravity on the star causes individual Hydrogen atoms to fuse together producing the element Helium and HUGE AMOUNTS OF ENERGY.

THIS REACTION IS CALLED FUSION:

H + H ---> HE + ENERGY

THE ENERGY RELEASED BY THE FUSION REACTION IS GIVEN OFF BY STARS AS ELECTROMAGNETIC RADIATION. 

There are many types of electromagnetic radiation that are produced by stars all at the same time.  Each type of electromagnetic radiation is different because they all have different wavelengths. 

When we look at all of the forms electromagnetic radiation together we call it the ELECTROMAGNETIC SPECTRUM.

The Electromagnetic spectrum is shown for you on page 14 of the ESRT.

Each block represents a different type of electromagnetic radiation.  As you move to the left side of the image, the WAVELENGTH DECREASES MAKING THE RADIATION MORE DANGEROUS.  As you move to the right side of the image, the WAVELENGTH INCREASES MAKING THE RADIATION LESS DANGEROUS.

 

STELLAR DEATH

The whole time a star is alive, it is fusing Hydrogens together to make Helium and other elements.  As it uses more and more of its Hydrogen fuel the star begins to age and, when it begins to run out of hydrogen fuel the star begins to die. 

THE EXACT WAY THAT A STAR DIES DEPENDS ON ITS ORIGINAL MASS.

SUN SIZED AND SMALLER STARS

  1. THE FIRST STAGE OF STELLAR DEATH OCCURS AS THE STAR SWELLS UP AND BECOMES A RED GIANT.
  2. EVENTUALLY IT CANNOT SUPPORT ITS OWN MASS AND THE RED GIANT EXPLODES IN A NOVA.
  3. AFTER THE NOVA, THE REMAINING STAR COLLAPSES AND SHRINKS DOWN INTO A TINY WHITE DWARF

SLIGHTLY LARGER THAN THE SUN

  1. THE FIRST STAGE OF STELLAR DEATH OCCURS AS THE STAR SWELLS UP AND BECOMES A RED SUPERGIANT.
  2. EVENTUALLY THE SUPERGIANT EXPLODES IN A SUPERNOVA.
  3. AFTER THE SUPERNOVA, THE REMAINING STAR COLLAPSES AND SHRINKS DOWN INTO A NEUTRON STAR.

VERY LARGE STARS

  1. THE FIRST STAGE OF STELLAR DEATH OCCURS AS THE STAR SWELLS UP AND BECOMES A RED SUPERGIANT.
  2. EVENTUALLY THE SUPERGIANT EXPLODES IN A SUPERNOVA.
  3. AFTER THE SUPERNOVA, THE REMAINING MATERIAL COLLAPSES TO A SINGLE POINT OF INFINITE DENSITY CALLED A BLACK HOLE