Astronomy 113. Dr. Joseph E. Pesce, Ph.D Joseph E. Pesce, Ph.D.

Transcription

1 Astronomy 113 Dr. Joseph E. Pesce, Ph.D.

2 The Big Bang & Matter

3 17-2 Cosmology ³ The study of the origins, structure, and evolution of the universe ³ Key moments: ² Einstein General Theory of Relativity ² Hubble s observation of expanding universe

4 17-3 Olber s Paradox ³ A simple question: Why is the sky at night dark? You are here ³ Everything is the same for a long way in all directions

5 17-4 Assumptions ³ Assumption: the universe is infinitely big ³ Assumption: the universe is infinitely old ³ Assumption: the universe is uniform

6 17-5 Olber s Paradox ³ If the universe is infinitely large and uniform, why is the night sky not bright? You are here ³ Every sight line will eventually hit a star

7 17-6 The Answer ³ The universe can t be infinitely large and old

8 17-7 Definitions Cosmological Principle: ³ Universe is Isotropic & Homogenous ³ We are not in a special place Isotropic: the universe is the same in all directions ³ There s no preferred direction Homogenous: At the largest scales, the universe is uniform; pretty much the same everywhere; same physical concepts apply

9 17-8 Expansion & Big Bang Hubble s Law: v r = H o * D ³ Universe expanding so must have been smaller, more dense in past ³ George Gamow proposes an initial explosion: The Big Bang ³ 1/H o gives age of universe = Billion years old (confirmed independently) ³ Redshift: space stretches as photon flies through it = stretching redshift

10 17-9 ³ Demonstration Expansion & Big Bang Hubble s Law: v r = H o * D

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12 17-11 Alternate Theories ³ Steady State Model of Fred Hoyle, Herman Bondi, and Tom Gold ³ Universe infinitely big and old, expands forever, matter constantly being created ² Coming from jets in AGN (in some views) ³ Big Bang ironically name by Hoyle

13 17-12 Evidence for Big Bang ³ Roll time back: universe begins as an extremely hot (10 12 K) singularity ³ High-energy radiation field ³ As universe expands, radiation cools ³ Radiation should permeate entire universe, even today ³ Cosmic Microwave Background (CMB) radiation

14 17-13 Detection of CMB ³ Arno Penzias & Robert Wilson, Bell Labs (Nobel Prize) ³ CMB at 2.74K ³ Isotropic and smooth Consistent with Big Bang but NOT Steady State

15 17-14 Detection of CMB

16 17-15 Isotropy Problem ³ To be as smooth as the CMB is, the parts of the universe had to communicate with each other ³ But universe is too big for this to be possible 13 Billion ly 26 Billion ly

17 17-16 Inflation ³ Solution to Isotropy problem is inflation ³ seconds after Big Bang, universe expanded orders of magnitude (atom to grapefruit) ² The inflationary epoch ² Somewhat strange, but related to dark energy

18 17-17 Inflation Evidence

19 17-18 Unification of Forces ³ Four fundamental forces today ² Gravitation (dominant today, but VERY weak. Operates over larger scales than others) ² Electro-magnetic ² Strong nuclear (holds protons & neutrons together) ² Weak nuclear (important in radioactive decay) ³ Were combined into one at beginning ² During Planck time ( seconds after BB)

20 17-19 Post Big Bang Timeline ³ Planck time ( seconds after BB) ³ s (T=10 32 K): Gravity freezes out ³ s (T=10 27 K): Strong force freezes out ³ s: Inflation of universe by ³ s (T=10 15 K): EM/Weak forces separate ³ 10-6 s (T=10 13 K): Protons & neutrons can exist

21 17-20 Matter/Antimatter Pair Production Pair Annihilation ³ For T < 1s: matter/antimatter co-exist ³ There should be equal matter and antimatter, annihilating each other. But not the case ³ 1 EXTRA particle of matter for every billion particles of antimatter ³ Good for us!

22 17-21 Timeline Continues ³ T = 1 3 minutes: nuclei form, destroyed by gamma-rays ³ After T = 3 minutes, Temp too cool for fuse nuclei ² H, He, Li, Be formed ³ T < 300,000 years: atoms ionized by photons; only nuclei survive: RADIATION DOMINATED ³ T > 300,000 years: atoms can form: MATTER DOMINATED UNIVERSE (still more radiation than matter)

23 17-22 Decoupling ³ T=300,000 years Transition called: Decoupling (Temp = 3,000) ³ T < 300,000 yrs: plasma only ³ T > 300,000 yrs: H atoms form, universe becomes transparent ² Era of Recombination ² CMB is Fossil of this period ² We can t see further back in time (prior universe is opaque)

24 17-23 Structures ³ Then what? ² Stars form ² Galaxies form q Where do blackholes come in? ³ All happens very soon after decoupling ³ Galaxies seem to be made up of small pieces

25 17-24 Energy Budget of Universe

26 17-25 Age of the Universe ³ Related to Hubble s Constant (1/H ~ age) ² Must be at least 10,000 yrs old (tree rings) ² Must be at least 200 million yrs old (Cepheid light travel time) ² Must be at least 4.6 billion yrs old (meteor dates) ² Must be at least 10 billion yrs old (redshifts of quasars; globular cluster ages) ³ Measured accurately and with multiple methods as: billion years old

27 Thank You!