Stars - MrCrabtreesScience

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Transcript Stars - MrCrabtreesScience

The Suns of Other Worlds
What are Stars?
• Giant
• Luminous
• Plasma.
– Energized Gas
• Powered by fusion of hydrogen or heavier elements
• Stars are NOT burning
– No oxygen
How do we learn about Stars?
• Studying the electromagnetic spectrum.
• We can only see a tiny bit of the light stars
• Visible light
• Stars emit lots of different kinds of ‘light’
How did we learn about the EMS?
• Sir Isaac Newton
• If you pass sunlight through a prism it
separated out into a spectrum of all the
Infrared Light
• William Herschel discovered IR by accident.
• Do colors have temperatures?
• He found that an area just beyond the red part of
the spectrum was hotter.
• He named that invisible light infra-red meaning
beyond red
Ultraviolet (UV) Light
• Johann Ritter
• Found chemicals that darkened when
exposed to sunlight had a greater reaction
just above the violet end of the spectrum
• Ultra-violet, meaning above violet.
What can we learn about Stars?
Stage of Development
Chemical Composition
Star Light, Star Bright…
• Absolute magnitude
– How much light a star produces
• Apparent magnitude
– How much light actually makes to Earth
• Absolute magnitude requires we know the
distance to the star.
How Far?
• Parallax
– The apparent movement of an object
seen at different viewpoints.
– The more the object moves (the
greater the parallax), the closer it is.
– The Hipparcos satellite
• Color
• Different Temperature
– Mass
– Temperature
• Missing Color
– Shows presence of other chemicals
• Spectra
– A view of the color produced by a star
Hertzsprung-Russell Diagram
• If you make a graph of stars
brightness and color stars fall into
certain areas
• Stars move through these areas as
they age
Types of Stars
• Two different methods
– Temperature
• Color alone
– Age
• Color and brightness
• HR Diagram
O - 33,000K+
B - 10,500 - 30,000K
A - 7,500 - 10,000K
F - 6,000 - 7,200K
G - 5,500 - 6,000K
K - 4,000 - 5,250
M - 2,600 - 3,850K
-yellow white
HR Diagram
• Four major groups
Super Giants
Main Sequence
White Dwarfs
• Some ‘stars’ didn’t get graphed
Neutron Stars
Black Holes
Black Dwarfs
Brown Dwarfs
Main Sequence Stars
Dwarf stars
Beginning of stars life
Bigger, hotter stars spend less time here
Fusing hydrogen as their main fuel.
• Larger(10x) and brighter than main
sequence stars
• Average main sequence stars that have run
out of hydrogen for fusion.
• Helium fusion is more explosive
– outward pressure >inward
Super Giants
• Largest and brightest of all stars
– 10-70 times size of the sun
– 30,000+ times as bright as the sun
• Large MSS that ran out of hydrogen
• Short life spans
White Dwarfs
• The smallest and faintest of all stars
– Stopped fusion process
– Glow only due to stored energy
• Mass of sun, size of earth
• The final stage of most stars lives
• Eventually cool to form Black Dwarfs
Star Life Cycles
• Nebula – birth place of stars
• Protostars – baby stars
– Gravity and fusion pressure not balanced yet
– Brown Dwarf – failed star
• MSS – first stage of a stars life
• What happens next depends on mass of star
Sun-like Stars
Run out of hydrogen
Outer layers expand
Red giant
Outer layers eventually drift off into space
– Planetary nebula
• Hot core remains as a White Dwarf
• Hypothetically if heat is gone becomes a Black
Big Stars
• Stars 1.5-3 times mass of sun
• Become Red Super Giants
• Fuse heavier elements until core is iron
– Collapses, causes explosion
• Super Nova
– Create all other elements
– Planets, people
Neutron Stars
• Neutrons.
• 2x times mass of sun.
• 20-40km
– Extremely dense
– Teaspoon - 5,000,000,000,000kg
• Gravity makes surface perfectly smooth
Giant Stars
Also become red super giants.
Same onion structure
Same Super Nova
If remaining core is >3 times the mass of the sun it
forms a Black Hole
• All the matter is squeezed into a space smaller
than an atom.
• Light can’t escape
Black Hole
• Any matter falling into a black hole produces
deadly gamma rays.
• Event Horizon
– Distance from the center of the black hole beyond
which nothing can escape
• Spaghettification
– Youtube video
Star Structure
• Stars are made of several layers that each
have differing properties.
Radiation Zone
Convection Zone
• Site of Nuclear Fusion
• Extreme amounts of pressure
• 10,000,000 K
Radiation Zone
• Pressure from the core balance pressure
from above layers, particles don’t move.
• Energy bounces around inside this layer for
an average of 170,000 years.
• 7-2,000,000 K
Convection Zone
• Energy moves with motion of plasma.
• In main sequence stars, CZ is near the
• In giant stars it is right next to the core.
• ~1,000,000 K
• Coolest Layer (6,000K)
• Sun spots
– Disruptions in magnetic field
• Solar Flares
– Violent explosions that send sub atomic
particles into space.
– Affect satellites, astronauts, power grids.
• Atmosphere of sun
• Hotter than photosphere due to magnetic
– 6-20,000 K
• 1,000,000 K
• Extends out several million km.
• Visible during solar eclipse