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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
High Temp Low Temp
A
B
E
DC
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?
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
years Sun 23,000 light years
from the center
That’s Us!
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
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