DEVIL PHYSICSTHE BADDEST CLASS ON

CAMPUSIB PHYSICS

TSOKOS OPTION E-6GALAXIES

Introductory Video:The Big Bang Theory

Objectives

Understand the Hubble classification scheme of galaxies and describe the structure of the Milky Way galaxy

State the Hubble law and solve problems using this law, v = Hd

State the meaning of the Hubble constant

Identify significant epochs in the life of the universe

Understand the term inflationary universe

An Introduction to Our Galaxy

Types of Galaxies Milky Way

Our galaxy About 200 billion stars

Our sun is one of them A spiral galaxy Diameter – 100,000 ly Thickness – 2000 ly Mass – 4 x 1041 kg Our solar system – 30,000 ly from center

Period is 225 million years

Types of Galaxies Milky Way

Types of Galaxies

Spiral Galaxies Milky Way is one Central disc – flattened nucleus, spiral arms,

halo of older faint stars Diameter – 6000 pc to 30,000 pc Mass – 109 to 1012 solar masses New stars formed mainly in the spiral arms Most common type, about 50%

Types of Galaxies

Spiral Galaxies Barred spirals

Bar of stars runs through central bulge and disc

Spirals start from ends of bar instead of disc

Types of Galaxies

Elliptical Spherical or ellipsoidal

shape Almost entirely older stars Almost no interstellar gas

Very little star formation activity

45% of all galaxies

Types of Galaxies

Irregular 5% of all galaxies No regular symmetry,

almost chaotic looking Intense star formation

activity Possibly caused by

collision of two regular galaxies

Star Clusters

Types of Galaxies

Local Group

Milky Way part of this cluster of 20 galaxies

Extends over 10,000,000 ly Collections of clusters are called

superclusters Our supercluster believed to be 15 x

106 pc across

Steady State Theory

Edwin Hubble and the Expanding Universe

Galactic Motion

Observed as early as 1914 All but the closest galaxies

appeared to be moving away at enormous speeds

Redshifted absorption lines (Doppler effect) Proportional to recession

speed Only applies line-of-sight

c

vz

z

0

0

Hubble’s Law Galaxies move away with speeds

proportional to their distance The more distant, the faster it moves

away H is the Hubble constant (slope of

graph) 72 km/s·MpcHdv

Hubble’s Law Implied that in the past, galaxies were

closer together Universe started as a point mass As space expanded, distance between

clumps of mass (galaxies) increased like two points on a balloon as it is inflated

Hubble’s Law Radius of the universe in arbitrary units

as a function of time

Hubble’s Law If we assume the expansion

to be constant, the inverse of H gives us the age of the universe – Hubble time ≈ 14 billion years

HT

Hv

d

Hd

v

Hdv

1

1

The Big Bang

Evolution of the Universe

Planck time – the earliest point we can find in which quantum gravitational effects are not dominant

From the fundamental constants h, G and c

sc

hGt p

435

10

Evolution of the Universe

Temperature estimated to be 1032 K The kinetic energy of whatever

particles that existed would be

GeVkTEk1910

2

3

Evolution of the Universe

Forces are unified: time = 10-43 s Strong nuclear and electroweak forces

unified Leptons indistinguishable from quarks and

turned into each other Strong nuclear force separates: time =

10-35 s Strong nuclear force decoupled from the

electroweak force Temperature falls to 1027 K

Evolution of the Universe

Inflation begins: time = 10-35 s Rapid period of expansion called

inflationary epoch Lasted no more than 10-32 s Size of the universe increased by factor of

1050

Forces separate: time = 10-12 s Temperature is about 1016 K Four fundamental forces (gravity,

electromagnetism, strong nuclear, and weak nuclear) behave as separate forces

Universe was 10-16 of its present size

Evolution of the Universe

Nucleons form: time = 10-2 s Temperature fallen to 1011 K Quarks bind together to form protons and

neutrons and their antiparticles Universe was 10-10 of its present size At t = 1s, T = 1010 K Protons, neutrons, electrons and their

antiparticles in thermal equilibrium

Evolution of the Universe

Nuclei form: time = 3 min Temperature fallen to 109 K Protons and neutrons start to combine to

form nuclei of light atoms – nucleosynthesis

Applying the laws of thermodynamic equilibrium, it can be determined that there were 14 protons for every 2 neutrons

Evolution of the Universe

Nuclei form: time = 3 min Two neutrons combine with two protons to

form a helium nucleus leaving 12 protons to form hydrogen nuclei

The mass of 12 hydrogen atoms is 12u and the mass of one helium atom is 4u

This ratio (75% H – 25% He) still exists today and is one of the strongest pieces of evidence for the Big Bang Theory

Evolution of the Universe

Nuclei form: time = 3 min This epoch lasted from t = 3 min until 104

years At the end, the temperature was 104 K The size of the universe was 10-4 of its

present size

Evolution of the Universe

Atoms form: time = 3 x 105 years Electrons join with protons to form neutral

atoms of hydrogen Called the period of recombination even

though they weren’t combined before Previously, photons bouncing off electrons

kept their energy in thermal equilibrium with radiation (photons)

From this point on, the universe is matter-dominated

Evolution of the Universe

First stars and galaxies form: time = 0.5 x 106 years Half a million years after the Big Bang Universe has cooled sufficiently for fusion

to occur Cold enough for fusion?

Our solar system formed just over a billion years after the Big Bang

Matter and Antimatter

Does it really matter? -- Yes Early universe had nearly equal

amounts of particles and antiparticles

Theory is that there was a very slight asymmetry in particle-antiparticle pairs 1 extra particle for every 109 pairs

Matter and Antimatter

Particles collided with antiparticles to create photons

Photons turned into particles and antiparticles

Below 1013 K, photons no longer reverted

Particle/antiparticle annihilation continued until only the fragment of extra particles remained to form matter

That formed the matter we have today

Summary Review Do you understand the Hubble

classification scheme of galaxies and describe the structure of the Milky Way galaxy?

Can you state the Hubble law and solve problems using this law, v = Hd?

Can you state the meaning of the Hubble constant?

Can you identify significant epochs in the life of the universe?

Do you understand the term inflationary universe?

QUESTIONS?

#1-19

Homework