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

D C E B A Low Temp High Temp 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 Low Temp High 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) Diffuse Nebula: visible due to the light provided by close stars 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 Red Shift Microwave Radiation