DEVIL PHYSICS THE BADDEST CLASS ON CAMPUS IB PHYSICS

DEVIL PHYSICS THE BADDEST CLASS ON CAMPUS IB PHYSICS

TSOKOS OPTION E-6 GALAXIES

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 10 41 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 10 9 to 10 12 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 10 6 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 z 0 0 Redshifted absorption lines (Doppler effect) Proportional to recession speed Only applies line-of-sight z v c

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 Mpc v Hd

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 v Hd If we assume the expansion to be constant, the inverse of H gives us the age of the universe Hubble time v d H 14 billion years d 1 v H 1 T H

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 hg t 10 43 s p c 5

Evolution of the Universe Temperature estimated to be 10 32 K The kinetic energy of whatever particles that existed would be 3 E kt 10 19 k 2 GeV

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 10 27 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 10 50 Forces separate: time = 10-12 s Temperature is about 10 16 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 10 11 K Quarks bind together to form protons and neutrons and their antiparticles Universe was 10-10 of its present size At t = 1s, T = 10 10 K Protons, neutrons, electrons and their antiparticles in thermal equilibrium

Evolution of the Universe Nuclei form: time = 3 min Temperature fallen to 10 9 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 10 4 years At the end, the temperature was 10 4 K The size of the universe was 10-4 of its present size

Evolution of the Universe Atoms form: time = 3 x 10 5 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 10 6 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 10 9 pairs

Matter and Antimatter Particles collided with antiparticles to create photons Photons turned into particles and antiparticles Below 10 13 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?

Homework #1-19