Outline 8:History of the Universe

and Solar System

The Andromeda Galaxy – One of hundreds of billions of galaxies, each

with hundreds of billions of stars

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

2012: Hubble looks back 13.2 billion years in deepest view yet

http://www.cbsnews.com/8301-205_162-57520513/hubble-looks-back-13.2-billion-years-in-deepest-view-yet/?tag=cbsContent;cbsCarousel

The Hubble eXtreme Deep Field, made up of some 2,000 images taken over a decade, provides a stunning "time tunnel" capturing light from dim proto galaxies within 500 million years of the big bang. (NASA)

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. (1 angstrom = 1 x 10-10m)

• 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.

Hydrogen through Iron form in Red Giants. The rest in Supernovae.

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

Ring nebula formed as a Red Giant became a White Dwarf

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

(most aluminum is Al27). 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.

Supernovas and the Origin of our Solar System

• If the meteorite had formed later than the supernova explosion (>10 MY), then the Mg26 would not be in the aluminum-rich inclusion. Instead, it would be with other atoms of magnesium (Mg24).

Al27 and rare Al26

Al27 and rare Mg26

Half life of 1 M.Y.

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.

Oldest Galaxy, 13.1 BY old