© 2012 Pearson Education, Inc.

The Universe

But first, let’s talk

about light!

© 2012 Pearson Education, Inc.

The study of light • Light is fast!

• All forms of radiation travel at 300,000,000

meters (186,000 miles) per second

• Since objects in space are so far away, it

takes a while for light to get to Earth.

• Studying light from stars and galaxies is like

looking into the past!

• Examples:

• It takes 8 minutes for sunlight to reach earth

• Light we get from Andromeda, the closest galaxy

to us, left there 2.5 million years ago!

© 2012 Pearson Education, Inc.

The study of light

• Electromagnetic radiation

• Visible light (a.k.a. “white light”) is only

one small part of an array of energy

© 2012 Pearson Education, Inc.

The study of light

• Most waves are either too short or too long

for our eyes to detect.

• Our eyes can only see visible light, “white

light”

• White light consists of an array of various

visible wavelengths.

• As white light passes through a prism, the

color with the shortest wavelength is bent

the most, etc., dispersing its component

colors.

© 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc.

The electromagnetic spectrum is

an array of energy

Hig

her

en

erg

y; “h

otte

r sid

e”

Lo

wer

en

erg

y; “c

old

er

sid

e”

© 2012 Pearson Education, Inc.

The Universe is HUGE!

Bigger than we can imagine…

• Hundreds of billions of galaxies (each with

hundreds of billions if stars)

• Ex: there are about a million galaxies in the

cup of the Big Dipper

• More stars than grains of sand in all the

beaches on Earth

© 2012 Pearson Education, Inc.

Distances in Space

Units of measurement

• Kilometers and miles too cumbersome to use

• Astronomical Unit: the distance from the Earth

to the Sun

• Light-year: the distance light travels in a year

• One light-year is 9.5 trillion kilometers

(5.8 trillion miles)

© 2012 Pearson Education, Inc.

Astronomical Unit (A.U.)

Q: What did the Earth say to the Sun to

get it’s attention?

A: A.U., over there!

© 2012 Pearson Education, Inc.

Light-year: the DISTANCE light

travels in a year

© 2012 Pearson Education, Inc.

Universe

• The universe is everything that exists in

space and time.

• Are there other universes?

• Consists of all matter and energy that

exists now, in the past, and in the future.

© 2012 Pearson Education, Inc.

Which of these is part of the

Universe?

© 2012 Pearson Education, Inc.

Galaxies

• Galaxies are collections interstellar

matter, stars, and stellar remnants

bound together by gravity.

• Galaxies are classified by their shape.

© 2012 Pearson Education, Inc.

Three Types of Galaxies:

1. 1. Spiral

2. 2. Elliptical

3. 3. Irregular

4. Within these categories there are many

variations.

© 2012 Pearson Education, Inc.

Spiral Galaxy Messier 83

© 2012 Pearson Education, Inc.

Spiral Galaxies

• Flat, disk-shaped objects with a central bulge

• Have arms (usually two) extending from the

center

• Central bulge contains older stars, often

giving it a yellowing color, while younger,

hotter stars make up the arms.

• Often appear bluish due to an abundance of

young stars

• Contain a lot of interstellar matter (gas and

dust) that provides material for new stars to

form.

© 2012 Pearson Education, Inc.

Spiral Galaxies

© 2012 Pearson Education, Inc.

Elliptical Galaxy

© 2012 Pearson Education, Inc.

Elliptical Galaxies

• Ellipsoidal shape (spherical shape)

• Don’t have spiral arms

• Have only a little interstellar matter

• Low rates of star formation

• Often appear yellow to red in color due to

an abundance of older stars

© 2012 Pearson Education, Inc.

Elliptical Galaxy

© 2012 Pearson Education, Inc.

Irregular Galaxies

• No symmetry; do not have a well

developed shape or structure.

• Stars are spread unevenly

• Many were once spiral or elliptical galaxies

that were distorted by the gravity of a

larger neighbor.

© 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc.

The Milky Way Galaxy

http://www.dvidshub.net/image/699908/milky-way-bar

© 2012 Pearson Education, Inc.

The Milky Way Galaxy

http://www.dvidshub.net/image/699908/milky-way-bar

Artist’s picture…

100,000 LY in diameter

© 2012 Pearson Education, Inc.

The Milky Way Galaxy

http://www.windows2universe.org/the_universe/Milkyway.html

© 2012 Pearson Education, Inc.

The Milky Way Galaxy

http://spaceuniversez.blogspot.com/2012/12/galaxy-milky-way-pictures.html

© 2012 Pearson Education, Inc.

Which galaxy is our solar system

inside?

• Called: The Milky Way

• Spiral galaxy

-Thin disk with a central bulge

• Diameter of Milky Way is 100,000 light

years.

• Thickness of Milky Way is 10,000 light

years.

© 2012 Pearson Education, Inc.

Galactic Clusters

• Galaxies are not spread out evenly

through the universe.

• They are grouped together.

• Gravity holds many galaxies together in

groups called galactic clusters

• The cluster our galaxy is in is called the

local group, made of more than 40

galaxies.

© 2012 Pearson Education, Inc.

The Local Group Andromeda galaxy and Milky Way

galaxy are the largest galaxies in our

cluster of more than 40 galaxies.

© 2012 Pearson Education, Inc.

The Origin of the Universe

• The Universe is expanding!

• How do we know? By studying light!

© 2012 Pearson Education, Inc.

Electromagnetic Spectrum

© 2012 Pearson Education, Inc.

The Doppler effect

© 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc.

• When an object

is moving

towards us,

waves coming

from that object

get compressed.

• When an object

is moving away

from us, waves

coming from that

object get

stretched out.

© 2012 Pearson Education, Inc.

Red shifts

• Doppler effect

• The apparent change in the wavelength of

light emitted by an object due to motion

• Movement away stretches the wavelength

• Longer wavelength

• Light appears redder

• Movement toward “squeezes” the wavelength

• Shorter wavelength

• Light shifted toward the blue

© 2012 Pearson Education, Inc.

Red Shifts

• When a source of light is moving away

from an observer, the spectral lines shift

toward the red end of the spectrum

(longer wavelengths).

• The red shift in light from galaxies

shows that all galaxies (except those in

the Local Group) are moving away from

Earth.

• Therefore, the universe is expanding

© 2012 Pearson Education, Inc.

Red shifts

• Doppler effect

• Amount of the Doppler shift indicates the rate

of movement

• Large Doppler shift indicates a high velocity

• Small Doppler shift indicates a lower velocity

© 2012 Pearson Education, Inc.

• The most distant galaxies are receding

fastest

• Hubble’s Law: galaxies recede at speeds

proportional to their distances from the

observer

• The further away, the faster they are moving

away from you

© 2012 Pearson Education, Inc.

Raisin Bread Analogy of an

Expanding Universe

As the dough rises, raisins originally

farthest apart travel greater distances than

those located closer together.

© 2012 Pearson Education, Inc.

Distant galaxies are more red-shifted

© 2012 Pearson Education, Inc.

Therefore…

1. Galaxies are moving away from each

other.

2. The Universe is expanding.

3. The Universe was once smaller.

So, compared to today, how big was the

universe yesterday?

© 2012 Pearson Education, Inc.

Big Bang Theory

• Most complete and most widely

accepted model.

• The universe began with a gigantic

explosion 13.7 billion years ago.

• The explosion released all of the matter

and energy that still exists in the

universe today.

© 2012 Pearson Education, Inc.

Big Bang Theory

• All energy and matter was compressed

into a hot and dense state.

• About 13.7 billion years ago there was a

huge explosion, which continued to

expand, cool, and evolve to its current

state.

• As it cooled, electrons and protons

combined to form hydrogen and helium

atoms, which collected to form the first

nebulae, stars, and galaxies.

© 2012 Pearson Education, Inc.

Big Bang Theory

• The light from the explosion would have

been extremely high energy and short

wavelengths.

• The explosion would have been very hot!

• We should be able to detect the remnant

of that heat.

• Continued expansion would have

stretched the waves so that by now they

should be long wavelength radio waves

called microwave radiation.

© 2012 Pearson Education, Inc.

Big Bang Theory

• Scientists began searching for this cosmic

microwave background radiation

• Discovered it in 1965

© 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc.

• In 1965, Arno Penzias and Robert

Wilson in N.J. were adjusting a radio

antenna.

• Found a steady, dim signal from the sky

as microwave radiation.

• The universe kept cooling until the

radiation reached very long, invisible

wavelengths such as microwaves.

© 2012 Pearson Education, Inc.

Penzias and Wilson

White Noise

Publish First

© 2012 Pearson Education, Inc.

Stars

© 2012 Pearson Education, Inc.

Properties of stars

Stellar brightness

• Controlled by three factors

• Size

• Temperature

• Distance

• Magnitude

• Measure of a star’s brightness

© 2012 Pearson Education, Inc.

Properties of stars

Stellar brightness

• Magnitude

• Two types of measurement

• Apparent magnitude

• Brightness when a star is viewed from

Earth

• Decreases with distance

© 2012 Pearson Education, Inc.

Properties of stars

Stellar brightness

• Magnitude

• Two types of measurement

• Absolute magnitude

• “True” or intrinsic brightness of a star

• Brightness at a standard distance of 32.6

light-years

• Most stars’ absolute magnitudes are

between –5 and +15

© 2012 Pearson Education, Inc.

Interstellar matter

• Between the stars is “the vacuum of

space”

• Nebula

• Cloud of interstellar matter (dust and gases)

• About 90% hydrogen, 9% helium, 1% dust (heavier

elements

• Two major types of nebulae

• Bright nebula

• Glows if it is close to a very hot star

• Two types of bright nebulae

• Emission nebula

• Reflection nebula

© 2012 Pearson Education, Inc.

Bright nebula

• Glows if it is close to a very hot star

• Two types of bright nebulae

• Emission nebula

• Gets its visible light from fluorescence of ultraviolet

light from a star in or near the nebula

• Fluorescence is the conversion of ultraviolet light to

visible light

• Reflection nebula

• Reflect light of nearby stars because they are more

dense

• have more dust (usually carbon compounds)

© 2012 Pearson Education, Inc.

Emission Nebula (LagoonNebulae)

© 2012 Pearson Education, Inc.

A faint blue reflection nebula

in the Pleiades star cluster

© 2012 Pearson Education, Inc.

Dark Nebula

• Dark nebulae

• Too far from any bright stars

• appear dark because not illuminated

• Contain the same material that forms

bright nebulae

© 2012 Pearson Education, Inc.

Dark Nebula (Horsehead Nebula –

in the constellation Orion)

© 2012 Pearson Education, Inc.

Flame and Horsehead Nebulae

© 2012 Pearson Education, Inc.

North American and Pelican Nebulas

© 2012 Pearson Education, Inc.

Idealized Hertzsprung-Russell

diagram

© 2012 Pearson Education, Inc.

Hertzsprung-Russell diagram

Shows the relation between stellar

• Brightness (absolute magnitude/luminosity) and

• Temperature

Diagram is made by plotting (graphing) each

star’s

• Brightness (absolute magnitude/luminosity) and

• Temperature

© 2012 Pearson Education, Inc.

Hertzsprung-Russell diagram

Parts of an H-R diagram

• Main-sequence stars

• 90 percent of all stars

• Form a band through the center of the H-R

diagram

• Stars spend most of their active years as these

• Sun is in the main-sequence

• Giants (or red giants)

• Large

• Very luminous

• Upper-right on the H-R diagram

© 2012 Pearson Education, Inc.

Hertzsprung-Russell diagram

Parts of an H-R diagram

• Giants (or red giants)

• Very large giants are called supergiants

• Only a few percent of all stars

• White dwarfs

• Fainter than most main-sequence stars

• Small (approximate the size of Earth)

• Lower-central area on the H-R diagram

• Perhaps 10 percent of all stars

© 2012 Pearson Education, Inc.

Idealized Hertzsprung-Russell

diagram

© 2012 Pearson Education, Inc.

Stellar Evolution

(Life Cycle of Stars)

© 2012 Pearson Education, Inc.

Stellar evolution

• Stars exist because of gravity

• Two opposing forces in a star are

• Gravity – contracts

• Thermal nuclear energy – expands

• The mass of the star will determine what it

will end up as

© 2012 Pearson Education, Inc.

Protostar

Protostar

Black

Dwarf

Main Sequence Stars

© 2012 Pearson Education, Inc.

Protostar Black

Dwarf

Main Sequence Stars

Main

Sequence

Star

Life Cycle of an Average Star

© 2012 Pearson Education, Inc.

Protostar

Black

Dwarf

Life Cycle of a Massive (BIG) Star

Main Sequence Star

© 2012 Pearson Education, Inc.

Stellar Evolution of an

Average Star

© 2012 Pearson Education, Inc.

Stellar evolution

• Stages

• Nebula

• Gravity contracts cloud

• temperature rises

• Begin to radiate long-wavelength (red) light

• Not a star yet! Instead, a protostar is forming in the

nebula!

© 2012 Pearson Education, Inc.

Stellar evolution Stages

• Protostar

• Gravitational contraction of gas

• cloud continues to heat

• Core reaches 10 million K

• Hydrogen nuclei fuse to make helium nuclei

• Process is called hydrogen fusion (or hydrogen burning)

• Energy is released! Now a star! A main sequence star!

• Outward pressure increases due to heat

• Eventual the outward pressure is balanced by gravity

pulling in

• Star becomes a stable main-sequence star

© 2012 Pearson Education, Inc.

Fusion: combining of lighter nuclei to

form a heavier nucleus, releasing

energy. Only happens in the cores of

stars.

© 2012 Pearson Education, Inc.

Dr. Octopus – Spiderman 2

www.newscientist.com

© 2012 Pearson Education, Inc.

Stellar evolution

Stages

• Main-sequence stage

• Star fusing hydrogen into helium

• In a balanced state where the pull of gravity

inward is balanced with the gas pressure outward

• Stars age at different rates

• Massive stars use fuel faster and exist for only a

few million years

• Small stars use fuel slowly and exist for perhaps

hundreds of billions of years

• 90 percent of a star’s life is in the main sequence

© 2012 Pearson Education, Inc.

Stellar evolution Stages

• Red giant stage

• Hydrogen in the core is consumed, leaving a

helium rich core

• The core contracts due to gravity winning the fight

with gas pressure

• This makes more heat as gravitational energy is

converted to heat energy

• Hydrogen fusion continues in the shell

surrounding the core at a faster rate

• Star’s outer area expands becoming a red giant

• Surface cools

• Surface becomes red

© 2012 Pearson Education, Inc.

Stellar evolution

• Still red giant stage:

• Core is collapsing, becoming hotter

• helium is converted to carbon (and oxygen)

• Eventually all nuclear fuel is used

• The star is not massive enough to continue fusion

of heavier elements

• Gravity squeezes the star, forming a very dense

core

• The outer layers continue to expand and it enters

the planetary nebula stage

© 2012 Pearson Education, Inc.

Red Giants

© 2012 Pearson Education, Inc.

Supergiants

Betelgeuse (in

the

constellation

Orion) is a red

supergiant!

It is HUGE!

© 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc.

Stellar evolution • Planetary nebula stage

• Outer layers continue to expand outward,

forming a cloud of gas

• At the center is the core, or the white dwarf

• White dwarf stage

• Has nearly exhausted its nuclear fuel

• Collapsed to a small size

• Outer gases have expanded away

• Black dwarf stage

• All energy is exhausted

• No longer emits energy

© 2012 Pearson Education, Inc.

Planetary Nebula (Helix Nebula –

closest to our solar system)

© 2012 Pearson Education, Inc.

Planetary Nebulas

© 2012 Pearson Education, Inc.

Protostar Black

Dwarf

Main Sequence Stars

Main

Sequence

Star

Life Cycle of an Average Star

© 2012 Pearson Education, Inc.

Stellar Evolution of a

Massive Star

© 2012 Pearson Education, Inc.

Protostar

Black

Dwarf

Life Cycle of a Massive (BIG) Star

Main Sequence Star

© 2012 Pearson Education, Inc.

• All previous stages and processes are the

same except for when it reaches the red

giant stage.

• Instead, it will become a red supergiant

Stellar evolution – massive star

© 2012 Pearson Education, Inc.

• Red supergiant stage

• Large enough to continue fusion reactions up

to and including iron

• Supernova stage

• Violent burst or explosion of light

• Occurs when all nuclear fuel is gone and the

core implodes due to strong gravitational field

• A shock wave results, blasting the star’s outer

shell into space

• Produce a hot, dense object that is either a

neutron star or a black hole

Stellar evolution – massive star

© 2012 Pearson Education, Inc.

Supernovas • Supernovas are the only event in nature

that is energetic enough to cause fusion of

elements heavier than iron on the periodic

table!

© 2012 Pearson Education, Inc.

• Either neutron star or black hole

• If the remains of the supernova are three

times the mass of the sun or less, there will be

a neutron star.

• Three is the magic number!

• If more massive, gravity wins and collapse

occurs, forming a black hole

• A black hole’s surface gravity is so great that even

light cannot escape

Stellar evolution – massive star

© 2012 Pearson Education, Inc.

• Neutron star

• Remnant of a supernova

• Gravitational force collapses atoms

• Electrons combine with protons to produce

neutrons

• Small size, very dense!

• Strong magnetic field

• First one discovered in early 1970s

• In Crab Nebula (remnant of an A.D. 1054

supernova)

Stellar evolution – massive star

© 2012 Pearson Education, Inc.

Remains of Supernova of A.D. 1054

Crab Nebula in the constellation Taurus

© 2012 Pearson Education, Inc.

Remains of Supernova of A.D.

1054 Crab Pulsar in Crab Nebula

© 2012 Pearson Education, Inc.

• Black hole

• More dense than a neutron star

• Intense surface gravity lets no light escape

• As matter is pulled into it

• Becomes very hot

• Emits X-rays

• First one to be identified was Cygnus X-1, a

strong X-ray source

Stellar evolution – massive star

© 2012 Pearson Education, Inc.

• What about tiny stars (less than 1/2 the mass

of the sun)

• Remember, final stage depends on mass

• Red giant collapses

• No planetary nebula stage

• Becomes a white dwarf

Stellar evolution – low mass stars

© 2012 Pearson Education, Inc.

Evolution of stars with various masses

© 2012 Pearson Education, Inc.