1. 
   Gravitational forces cause nebula to shrink

The interstellar medium (Nebula) is the gas and dust that is found between many stars. It is mostly hydrogen and some other trace elements. Some areas have heavier gases than other regions. Within the mixture there are large clouds of denser gases than other areas of the mixture.

2. Spheres of matter build with in the clouds

• The clouds center collapses further and concentrates into a gas/solid mass (ball)
• the temperatures really increases to form a PROTOSTAR
  • Temperature increase due to:
    • Collision between atoms creating friction
    • Increased pressure due to increased density

3rd Stage of
Stars Evolution:

Giants
and Supergiants

1. Happens when almost all of the hydrogen atoms inside of the core have fused into Helium atoms.
   
2. Without H as a source of fuel the core contracts under the force of the stars gravity.
   
   1. Stars core temperature increases as the core contracts
      
   2. The stars shell of gas expands and cools
      
3. The increased core temperature causes the mainly He left to change into carbon atoms.

Size:

Giants:
10X bigger than our sun

Supergiants:
100 X bigger than our sun

This Hubble Space Telescope image shows Sirius A, the brightest star in our nighttime sky, along with its faint, tiny stellar companion, Sirius B.

Astronomers overexposed the image of Sirius A [at center] so that the dim Sirius B [tiny dot at lower left] could be seen.

A white dwarf star begins its life by casting off a cocoon that enclosed its former self.  In this analogy, however, the Sun would be a caterpillar and the ejected shell of gas would become the prettiest of all! The above cocoon, the planetary nebula designated NGC 2440, contains one of the hottest white dwarf stars known. The white dwarf can be seen as the bright dot near the  photo's center.

Credit: H. Bond (STScI), R. Ciardullo (PSU), WFPC2, HST, NASA 

Credit - www.fcaglp.unlp.edu.ar/evolgroup/

White dwarf either dies out into a dead star
Black Dwarf
which would be the end of stars life:

Or

during the cooling process it might explode
which is called a NOVA.

This telling March 29 burst in the constellation Leo, one of the brightest and closest on record, reveals for the first time that a gamma-ray burst and a supernova -- the two most energetic explosions known in the Universe -- occur essentially simultaneously, a quick and powerful one-two punch.

Image / Movie Credit:
National Aeronautics and Space Administration
http://www.nasa.gov/centers/goddard/news/topstory/2003/0618rosettaburst.html

Pulsars are rapidly-spinning neutron stars. These stars have very strong magnetic fields. Jets of charged particles are ejected from the magnetic poles of the star. This material is accelerated, producing beams of radiation (light) of all wavelengths from the magnetic poles.

The "north" and "south" poles of the magnetic field may not coincide with the star's rotational poles, as shown in the image below. This means that the beams of light sweep around as the star rotates.

We see a pulsar when one of its beams of radiation crosses our line-of-sight. A pulsar is like a lighthouse. The light from a lighthouse appears to be "pulsing" because it only crosses our line-of-sight once each time it spins. Similarly, a pulsar "pulses" because we see bright flashes every time the star spins. This is illustrated below. Credit Information / Photos - www.airynothing.com/.../sources/pulsars.html

Scientists at the Canadian Institute for Theoretical Astrophysics (CITA) and NASA have captured unprecedented details of the swirling flow of gas hovering just a few miles from the surface of a neutron star, itself a sphere only about ten miles (16 km) across.

Image / Movie Credit:
National Aeronautics and Space Administration
http://www.nasa.gov/centers/goddard/news/topstory/2003/0618rosettaburst.html

Astronomers have finally confirmed something they had long suspected: there is a super-massive black hole in the center of our Milky Way galaxy. The evidence? A star near the galactic center orbits something unseen at a top speed of 5000 kilometers per second. Only a black hole 3 million times more massive than our Sun could cause the star to move so fast.

Still, a key mystery remains. Where did the black hole come from? For that matter, where do any super-massive black holes come from? There is mounting evidence that such "monsters" lurk in the middles of most galaxies, yet their origin is unknown. Do they start out as tiny black holes that grow slowly, attracting material piecemeal from passing stars and clouds? Or are they born big, their mass increasing in large gulps when their host galaxy collides with another galaxy?