Characteristics of Stars
Elements in Stars
99% Hydrogen (H) and Helium (He)
1-2% Oxygen, Carbon, Nitrogen, Calcium
Sun is 70% Hydrogen and 28% Helium
Produce energy (heat and light) by fusing hydrogen
atoms to make helium
Physical Properties of Stars
Star Color is dependant on surface temperature.
Hot stars = Blue or White, ~30,000 K
Cool stars = Red or Orange, ~3,000 K
The Sun = Orange or Yellow, ~5,500 K
Absolute Magnitude
Stars actual brightness distance of 32.6 light
years from the sun
Depends on size and temperature of the star.
What would the brightest star look like?
At this size, a
dwarf star is too
small to see
1. Each letter represents a star, what type is each and what
color is each?
2. What 2 things does this diagram tell you about stars?
D
C
E
B
A
High Temp Low Temp
Answers…
A – White Dwarf, White
B – Main Sequence, Yellow
C – Main Sequence, Blue
D – Super Giant, Red
E – Giant, Red
Surface Temperature & Absolute
Magnitude (Brightness)
Origin of Stars
Nebulae (huge clouds of hydrogen gas and dust)
1. Diffuse Nebula: visible due to the light provided
by close stars
2. Dark Nebula: blocking other stars
Formation of Protostars
Something outside the nebula triggers the
gravity between gasses and dust
A supernova shockwave
Nebula contract
As the nebula contracts, spots in it start to glow
with heat protostar
Formation of Main Sequence
Stars
Protostar continues to contract Fusion begins
IMPORTANT: STARS ARE ALWAYS TRYING TO
COLLAPSE DUE TO THEIR OWN GRAVITY
It keeps collapsing until the star’s released energy
equals the force of gravity
It is now a Main Sequence Star
Formation of Giants/Supergiants
Hydrogen decreases energy of fusion no longer
balances the force of gravity
Core of the star contracts and get hotter
Increases the rate of fusion for the remaining
Hydrogen
The increased energy causes the outer layers to
expand Giant/Supergiant
Formation of Dwarfs
No fuel Star collapses due to gravity
Squeezes the nuclei together very tightly dwarf
The can glow for billions of years as they cool
Non Massive Star Life Cycle
Nebula
Massive Star Life Cycle:
Supernova
Fusion stops in massive stars forms super
dense core with extremely strong gravity
The gravity causes the star to collapse past the
dwarf stage
Collapse puts intense pressure on the core
Star explodes violently and half its mass is
blown away supernova
Supernova Before and After
Neutron stars
Leftover half of supernova that doesn’t blow up
Its gravity is so strong that all of the atoms
particles (p+, n, e-) are crushed together,
leaving only neutrons
Neutron stars may be 10km wide, are a trillion
times as dense as the sun.
Black Holes
If the star is massive enough, its gravity causes
it to collapse past the neutron phase into a tiny
volume, but humongous density/gravity
Black Hole
The gravity is so great that not even light can
escape
How do we know they exist?
Strong X-Ray emissions from the Cygnus
constellation
When something gets sucked into a black hole,
its atoms get ripped apart and it emits x-rays
Galaxies and Universe
Solar system - the sun, orbiting planets,
asteroids, meteors, and comets
The sun is 1 star in a galaxy, which is a group of
millions or billions of stars held together by
gravity
Our galaxy is in the universe, which contains all
the planets, stars, solar systems, and galaxies
The Milky Way
100 billion stars
Every visible star
It is 1 of 17 nearby
galaxies that make up
the Local Group
Milky Way Facts
Diameter: 140,000 light
years
Width: 20,000 light That’s Us!
years
Sun 23,000 light years
from the center
Sprial Galaxies
Spiral Galaxies central nucleus, arms coming
off the nucleus.
Barred Spiral Galaxies
Elliptical Galaxies
Range from spherical to lens shaped most
common
Irregular Galaxies
Smaller, fainter, and less common, no pattern
Big Bang Theory
Universe began as a dense sphere of
hydrogen.
13.7 billion years ago it exploded, forming a
gigantic, expanding cloud of gas and dust
Evidence
1. Red Shift
2. Microwave Radiation