Structure of the Universe

Galaxies

A galaxy is the basic structural unit of matter

in the universe.

A galaxy is a collection of stars (usually 100 billion or more), gases and dust held together by gravity. It is believed that

the universe is made up up of more than 100 billion galaxies.

Galaxies are classified by their shape: elliptical, irregular or spiral.The Milky Way Galaxy

is spiral-shaped.

Stars and their Energy Production

A star is the most visible piece of matter in a galaxy; it is a large ball of gas that produces a

large amount of energy. This ball of gas is held together by gravity.

Most of the energy produced by a star is a result of nuclear fusion. Nuclear

fusion is the combining of smaller elements to make larger one. In this

process, some of the mass is converted into energy.

In our sun, hydrogen nuclei is converted into helium. Less than 1% of

this mass is converted to energy.

Nuclear fusion requires a tremendous amount of heat and pressure.

The energy from the sun (through nuclear fusion) is radiated into space in the form of electromagnetic radiation.

In our sun, hydrogen is combined to make

helium.

Characteristics of Stars

RT = Pg. 15

The chart shown is a tool used by scientists to make comparisons between stars

based on their surface temperature and luminosity.

Luminosity is the rate at which a star emits energy

with relation to our sun if all stars were the same distance

from an observer.

The chart shows a pattern between the surface

temperature of a star and its luminosity.

As a star “cools”, the color of the star will change.

Star TypesRT = Pg. 15

Main Sequence1. Most of a star’s life span is

in main sequence.2. Average size

Giants1. 10X larger or more than the

sun2. Red, orange, yellow in color

Super Giants1. Very Bright!2. 100-1000x larger than the

sun.3. End stage of star

development; usually followed by a supernova.

White Dwarfs1. Very small (Earth-sized)2. Very hot; not so bright!3. End stage of star

development; usually followed by a black dwarf

Star Origin and EvolutionGas and dust Matter originates from “Big Bang”.

Matter collects, gravity forms and nuclear fusion begins

Main Sequence Star

Red Giant forms

White dwarf forms as fuel is used up.“Death” of a

star; Black dwarf

Super Giant forms

Neutron star forms; very dense

Black hole forms; extreme gravity field created

Supernova!

Star Evolution for

stars of similar mass

to that of the Sun.

Star Evolution for stars more massive than the Sun.