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