Joy of Science Experience the evolution of the Universe, Earth and Life

•  Review of last class •  Introduction to Astronomy

•  Contents of today’s lecture •  Quiz time

Review 1 Review

n  The Sun is currently classified as

A. a main-sequence star B. a white giant C. a red giant D. a white dwarf E. neutron star

Review 1 Review

n  The Sun is currently classified as

A. a main-sequence star B. a white giant C. a red giant D. a white dwarf E. neutron star

Review 2 Review

n  The most abundant element in the universe is

A. neutrinos B. hydrogen C. carbon D. helium E. iron

Review 2 Review

n  The most abundant element in the universe is

A. neutrinos B. hydrogen C. carbon D. helium E. iron

Review 3 Review

n  The net effect of the three-step process that produces energy in the Sun is called

A. proton burning B. deuterium burning C. hydrogen burning D. helium burning E. carbon burning F. iron burning

Review 3 Review

n  The net effect of the three-step process that produces energy in the Sun is called

A. proton burning B. deuterium burning C. hydrogen burning D. helium burning E. carbon burning F. iron burning

Review 4 Review

n  During the first step of energy production in the Sun

A. three helium-3 nuclei fuse to form a carbon-12 nucleus B. two protons fuse to form deuterium, a positron and a neutrino C. deuterium and a proton fuse to form hydrogen atoms D. two helium-3 nuclei fuse to form deuterium and a neutrino

Review 4 Review

n  During the first step of energy production in the Sun

A. three helium-3 nuclei fuse to form a carbon-12 nucleus B. two protons fuse to form deuterium, a positron and a neutrino C. deuterium and a proton fuse to form hydrogen atoms D. two helium-3 nuclei fuse to form deuterium and a neutrino

Edward Hubble and the expanding universe - Experience the evolution of the Universe

Today’s Keywords cosmology, Edward Hubble, galaxy,

cosmic microwave background (CMB), big bang, dark matter, dark energy

May 6, 2011

Outline of today’s lecture

0. Introduction 1. Edwin Hubble’s discoveries 2. Big Bang theory 3. Dark side of universe – dark matter, dark energy

Cosmology n  Cosmology: Study of structure and history of entire universe

n  Edward Hubble’s discoveries: - Galaxies (before 1920’s, the Milky Way galaxy was thought as the only group of stars in the cosmos, i.e. Our galaxy = the entire universe ) - Redshift of galaxies n  From Hubble’s discoveries and other astronomical evidences, a theory

of the beginning of universe has been established è Big Bang!

n  The fate of universe is ???

Introduction

Galaxies n  Galaxies: collections of stars n  Before Hubble, telescopes could see nearby stars to Earth (the

solar system) in the Milky Way n  Hubble measured the distance of extremely faint stars and

found the distance is far outside the bunds of the Milky Way è the nebula containing the measured stars is Andromeda nebula, and now called Andromeda Galaxy n  Our galaxy (Milky Way) - Spiral galaxy: 75% of brighter galaxies in sky - Flattened disk of 100,000 light-year across - Central bulge has most of our galaxy’s stars - Sun is located in the halfway out from the center

Hubble’s discovery 1

Spiral galaxy

Our galaxy

Milky Way

Galaxies (cont’d) n  Other kinds of galaxies - Elliptical galaxies : 20% of brighter galaxies - Irregular and Dwarf galaxies: faint but probably most common in universe n  Earth (a planet) à Solar system (Sun: a star) à Our galaxy à

Local cluster à Supercluster à Observable universe n  Number of galaxies in universe: hundreds billions, each with hundreds billions of stars n  Optical point-like stars in sky may be a star in the Milky Way

galaxy, may be a light-reflected planet in our solar system, e.g. Venus, or a cluster of galaxies!

Hubble’s discovery 1

Redshift of galaxies

n  Redshift: lights from stars (or galaxies) have red-shifted spectrum an example of Doppler effect à going away object has shorter wavelength coming close object has longer wavelength

Hubble’s discovery 2

Doppler effect in sound

Doppler effect in light

Red-shift Blue-shift

Redshift of galaxies n  Redshift: lights from stars (or galaxies) have red-shifted spectrum an example of Doppler effect à going away object has shorter wavelength coming close object has longer wavelength è Distant galaxies are moving away from Earth è The universe is expanding! n  Hubble’s law: ‘ The farther away a galaxy is, the faster it recedes.’ à Imagine a raisin-bread dough è We can determine the distance to galaxies by measuring the redshift of the light we receive è Hubble constant from Hubble’s law provide the expansion rate of universe, hence, the age of universe of about 14 billion years

Hubble’s discovery 2

Analogy of expanding universe : raisin-bread dough

AB

CAB

C

Big Bang n  Big Bang theory: idea that universe began at a specific moment in

time and has been expanding ever since n  Universe began as an infinitely hot, dense concentration of energy n  Evidences for big bang - Universal expansion - Cosmic microwave background (CMB) radiation: microwave radiations fall on Earth from all directions in a form of background signals (continuous noise) à hot universe at early time still give off electronic radiation and it would be characteristic of an object at a few degrees above absolute zero à confirmed by satellite telescope data - Abundance of Light elements: abundance of hydrogen, helium-3,4 and lithium are already predicted in Big Bang theory

Expanding universe

History of universe n  All matter heats up when it is compressed n  Universe began from a hot, dense state and has been

expanding and cooling ever since n  Time of changes of state in universe according to changes of

temperature è ‘freezing’ (imagine the freezing of water)

Expanding universe

Dark matter n  Visible world in Universe is only 4 % of entire universe! n  Dark matter: interact only with gravitationally n  First evidence for dark matter: galactic rotational curve

Dark universe

observed

expected

Galactic rotational curve

Dark energy - future of universe

Fates of universe n  Open universe: gravity (mass of universe) < Hubble expansion n  Closed universe: gravity > Hubble expansion à ‘Big Crunch’ n  Flat universe: gravity = Hubble expansion

Dark energy: a source of force acting to push galaxies apart à a sort of antigravity n  Fates of universe depend on amount (or density) dark energy

Dark universe

Quiz 1

n  The presence of CMB radiation is good evidence for

A. the internal makeup of the Sun B. the account of creation in Genesis C. the steady-state universe D. the big bang theory

Quiz 1

n  The presence of CMB radiation is a good evidence for

A. the internal makeup of the Sun B. the account of creation in Genesis C. the steady-state universe D. the big bang theory

Quiz 2

n  The Milky Way, the galaxy within which we live, is A. an irregular dwarf galaxy B. a quasar galaxy C. an elliptical galaxy D. a spiral galaxy

Quiz 2

n  The Milky Way, the galaxy within which we live, is A. an irregular dwarf galaxy B. a quasar galaxy C. an elliptical galaxy D. a spiral galaxy

Quiz 3 n  A large assembly of stars together with gas, dust, and other materials

that is held together by the forces of mutual gravitational attraction is called

A. a solar system B. a planetary system C. a galaxy D. the cosmos

Quiz 3 n  A large assembly of stars together with gas, dust, and other materials

that is held together by the forces of mutual gravitational attraction is called

A. a solar system B. a planetary system C. a galaxy D. the cosmos