Outline 24:

History of the Universe

and Solar System

The Andromeda Galaxy

A warped spiral galaxy, 150 MLY away and

100,000 LY across.

Galaxies in deep space viewed by the

Hubble space telescope: Looking

back in time

Galaxy clusters viewed from Hubble

space telescope

Colliding Galaxies

Our home galaxy - the Milky Way

The Age of the Universe

• Many published estimates give an age

of 14-18 BY old.

• How are these ages determined?

The Age of the Universe

• The study of light from galaxies indicates

that the universe is expanding. This is

the basis of the Big Bang Theory.

• The velocity of expansion is measured by

the amount of Red Shift in the light from

other galaxies.

Analogy for an expanding universe

where each galaxy moves away from

every other galaxy. No matter where the

observer sits, the universe is expanding.

Map of temperature variation in the Cosmic

Background Radiation (microwaves). The

average temperature is 3 degrees Kelvin. This is

the radiation left over from shortly after the Big

Bang. The lumpiness produced galaxies.

Red Shift of Light Waves

• Light waves are stretched as the galaxies

race away from the earth.

• The spectral lines of the visible spectrum

are shifted towards the red, or longer,

light waves.

• This is an example of the Doppler Effect.

The electromagnetic

spectrum

Low energyHigh energy

Examples of spectral lines produced by absorption

of light by gases in a star’s atmosphere. Each line

represents a chemical element.

Red-shift of light indicates that all galaxies are

moving away from us, indicating that the

universe is expanding.

near

far

Calculating Expansion Velocity

• A spectral line for hydrogen from the sun

has a wavelength of = 6562.85A.

• Light from a nearby star in our galaxy

shows the same spectral line at

1 = 6563.15A.

• Wavelength shift = 0.30A

Calculating Expansion Velocity

• Velocity = (x C

• Velocity = (0.30/6562.85) x C

C = speed of light: 300,000 km/sec

• Velocity = 13.7 km/sec

• So this nearby star is receding from us

at 13.7 km/sec.

Calculating Age

• Time = distance/velocity

• e.g., car trip:

5hrs = 300miles/60 miles/hr.

• The Hydra Galaxy is receding from the

earth at 61 x 103 km/sec.

• Its distance is 3.96 x1022 km

(4 billion light years, based on luminosity

of stars; farther stars are dimmer)

Calculating Age

• Amount of time the Hydra Galaxy has

been traveling?

• Time = distance/velocity

• T = 3.96 x 1022 km/61 x 103 km/sec

• T = 6.5 x 1017 sec (1 year=3.15 x 107 sec)

• T = 2.06 x 1010 years = 20 BY

20 BY??

• Is the Universe 20 BY old?

• No, gravitational forces have slowed

down the galaxies since the Big Bang.• (Note: Recent observations suggest this was the case for the

first 2/3 of the Universe’s history. The expansion rate now

seems to have increased for the last 1/3 of the Universe’s

history. This is explained by “dark phantom energy”, which

is hypothesized to be forming between galaxies and pushing

them apart by repulsive gravitational force. Dark energy is

calculated to be ¾ of the mass-energy of the universe!)

20 BY??

• The present velocities give the

appearance that the galaxies have been

traveling longer than they actually have.

• Thus the estimates of 14-18 BY.

Why the apparent older age?

Consider the following example:

Travel at 100 mph for 2 hours = 200 miles

Travel at 60 mph for 3 hours = 180 miles

Total time is 5 hours. Total distance is 380 miles.

If you were observed traveling at 60 mph and had

covered 380 miles, the assumption would be made

that you had traveled for 6 hours and 20 minutes

(380miles/60mph) rather than 5 hours.

Origin of our Solar System

• The matter in our solar system is

recycled from older stars that exploded

as supernovas.

• Early in the history of our galaxy there

were large stars that ignited, burned

their fuel, and then exploded sending

new elements into space.

Life Cycle of a Star

• Small stars (e.g, the Sun): main sequence,

red giant, white dwarf. (10 BY years)

• Big stars: main sequence, red giant,

supernova. (1 BY years)

• Massive stars: main sequence, red giant,

supernova, black hole. (100 MY

years)

Red Giants

Sun

White Dwarfs (circled)

in our galaxy

Life Cycle of a Star

• Main sequence: hydrogen burns

(nuclear fusion) to form helium

• Red Giant: helium burns (nuclear

fusion) to form carbon, carbon burns to

form oxygen, oxygen burns to form

iron. All elements lighter than and

including iron (56) formed this way.

Life Cycle of a Star

• When a red giant has exhausted its fuel, it

collapses inward by gravity.

• This collapse releases so much energy

through fusion that the star explodes as a

supernova.

• Explosive nucleosynthesis produces all the

elements heavier than iron (57-262) plus all

radioactive elements (except C14).

The Crab Nebula, remnant of a

supernova explosion

2009

Ring nebula formed as a Red Giant

became a White Dwarf

Supernova Explosion, 1987: note

the rings of debris

Supernovas and the Origin of

our Solar System

Was the collapse of the nebular dust

cloud that formed our solar system

triggered by the shock wave from a

nearby supernova explosion? The

answer seems to be yes.

Supernovas and the Origin of

our Solar System

Evidence: Aluminum rich inclusions in

meteorites contain the rare isotope Mg26,

which forms by radioactive decay of

Al26. The 1 MY half life of Al26

indicates it became part of the meteorite

within a few million years (or less) of a

supernova explosion.

Origin of the Solar System

• Stage 1 – slowly rotating nebula

• Stage 2 – contraction to disc as rotation increases

• Stage 3 – material separated into discrete rings distinct from proto-sun

• Stage 4 - Planets form by accretion of material from the discs

A nebular dust cloud similar to the cloud

our solar system formed from.

The birth of

new stars

from giant

gas pillars

The Horsehead Nebula in the

Andromeda Galaxy

The Witch Head

Nebula, about

1000 light years

away in the

constellation

Orion.