Stars 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 produce. 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 colors

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? Mass Temperature 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

Temperature –O - 33,000K+-bluest –B - 10, ,000K-bluish –A - 7, ,000K-blue-white –F - 6, ,200K-white –G - 5, ,000K-yellow white –K - 4, ,250-orange –M - 2, ,850K-red

HR Diagram Four major groups –Super Giants –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.

Giants 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 Dwarf

Big Stars Stars 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 km –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. –Core –Radiation Zone –Convection Zone –Photosphere –Chromosphere –Corona

Core 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 surface. In giant stars it is right next to the core. ~1,000,000 K

Photosphere 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.

Chromosphere Atmosphere of sun Hotter than photosphere due to magnetic activity. –6-20,000 K

Corona 1,000,000 K Extends out several million km. Visible during solar eclipse