Stellar Evolution

1
Stellar Evolution

• The life-cycle of stars

2
What is a star?

• LARGE GLOWING BALL OF GAS
• Composed of H and He
• Fixed points of light in space
• Undergo fusion in their cores
• Generate heat and light
• Give off tremendous radiation

3
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.

4
Star Energy (cont)

• Hydrogen fusion
• H H ? He
• Helium fusion
• He He ? Be
• As the mass of elements increases, energy
  production increases

Energy
More Energy
5
Properties of Stars

• Color Temperature
• Brightness
• Apparent vs. Absolute
• Size Mass
• Composition

6
Hertzsprung-Russel Diagram

• A graph showing the surface temperature and
  absolute brightness of a group of stars
• Used to compare several properties of stars and
  estimate their sizes and distances
• Shows star color, size, temperature and
  brightness

7
H-R Diagram
8
Low mass
Protostar
High mass
9
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)
10
Protostar

• Gravity pulls a nebulas dust and gas into a
  denser cloud
• As a nebula heats up, it contracts
• A contracting cloud of dust with enough mass to
  form a star

11
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

12
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

13
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

14
Planetary Nebula

• Energy from star becomes to decrease no more
  elements to fuse
• Star begins to collapse
• Dying star surrounded by gases

15
Nova/Super Nova

• The core of a giant star produces too much energy
  in its 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

16
(No Transcript)
17
(No Transcript)
18
White Dwarf

• Stars decrease in size same diameter as earth,
  mass stays the same
• Mass of sun, size of Earth
• DENSITY INCREASES TREMENDOUSLY
• Solid, but still hot, so it is glowing
• Luminosity decreases

19
Neutron stars

• Form from the remains of extremely massive stars
  after a supernova.
• Very small 30 km across
• Density of 2 x 1014
• Would be comparative to 1 sugar cube mass of
  humanity

20
Black hole

• If the cores mass is even greater/denser than a
  neutron star, it collapses.
• Surface gravity is so great that no matter can
  escape itnot even electromagnetic waves!

21
The fate of our Sun