HNRS 227 Lecture 18 October 2007 Chapter 12. Stars, Galaxies and the Universe presented by Dr. Geller

Transcription

1 HNRS 227 Lecture 18 October 2007 Chapter 12 Stars, Galaxies and the Universe presented by Dr. Geller

2 Recall from Chapters 1-11 Units of length, mass, density, time, and metric system The Scientific Method Speed, velocity, acceleration, forces, work and energy Newton s Laws of Motion and Gravitational Attraction Conservation of energy, sources of energy Temperature and heat Phases of matter and thermodynamics Wave motion, reflection, and refraction Properties of light, electricity and magnetism The Periodic Table and Bohr Model of the Atom Chemical reactions, water and solutions Nuclear reactions and nuclear energy

3 Chapter 12 Highlights (there are differences from the textbook) The Night Sky Birth and Structure of Stars The Measure of Stars Brightness, temperature, spectral class, H-R Diagram Life and Death of Stars Galaxies The Big Bang

4 Astronomical Measurements Understand these terms Angular measure Astronomical Unit Light Year kly, Mly Parsec kpc, Mpc

5 Recall 1st Law of Thermodynamics In an isolated system, the total amount of energy, including heat energy, is conserved. ENERGY IS CONSERVED

6 Recall 2nd Law of Thermodynamics Two key components heat flows from a warmer body to a cooler body entropy increases remains constant or increases in time

7 Phases and Phase Diagram

8 Maxwell s Equations Maxwell E&M unifies electricity and magnetism into electromagnetism

9 Recall Light Basics Planck Curves Wien s Law Stefan-Boltzmann s Law

10 Recall Planck s Radiation Curves A way to depict frequency (inverse of wavelength) versus intensity Intensity Frequency

11 Recall Wien s Law Peak wavelength is inversely proportional to the temperature of the blackbody Cooler Body Intensity Hotter Body Peak Wavelength Frequency

12 Recall Stefan-Boltzmann Law Energy radiated by blackbody is proportional to the temperature to the 4th power Energyvs. Temperature E = σ T 4 Energy Temperature

13 Recall Doppler Shift A change in measured frequency caused by the motion of the observer or the source classical example of pitch of train coming towards you and moving away wrt light it is either red-shifted (away) or blue-shifted (towards)

14 Question for Thought Why are astronomical distances not measured with standard reference units of distance such as kilometers or miles? A Because astronomical distances are so small. B Because astronomical distances are so large. C Because astronomical distances are not precise. D Because astronomical distances cannot be measured. E All of the above.

15 Question for Thought What is a light year? A B Unit of distance Distance traveled by light in a year C Approximately 6 trillion miles or 10 trillion kilometers D E All of the above None of the above

16 The Night Sky Not in textbook, but understand these terms: Right Ascension; Declination; Altitude; Azimuth

17 The Birth of Stars Like Our Sun Gas cloud Fragmentation Protostar Kelvin-Helmholz Contraction Hayashi Track Ignition Adjustment to Main Sequence

18 The Structure of Stars Like Our Sun Core Radiative Zone Convective Zone Photosphere Chromosphere Corona

19 Question for Thought Describe the forces that keep a star in a state of hydrostatic equilibrium. A B C D E Fusion Gas pressure Gravity All of the above None of the above

20 How Bright is It? More Terms Apparent Magnitude (from Earth) Brightness from Earth Absolute Magnitude Luminosity Apparent magnitude if all stars at same distance (10 pc)

21 How Hot Is It? Remember Wien s Law

22 Classes for Spectra O,B,A,F,G,K,M There are also subclasses 0 9 A9 hotter than F0 B0 cooler than O8 A0 hotter than A9

23 H-R Diagram Plots temperature vs. true brightness

24 Question for Thought Which best explains that a red giant is very bright, but with a low surface temperature? A B C D E Wien s Law and the surface area of a giant star. Kirchoff s Law and the continuous spectrum. Stefan Boltzmann s Law and the surface area of a giant star. All of the above. None of the above.

25 Death of Stars like Sun Hydrogen Core Depletion Hydrogen Shell Burning ("Red Giant Branch") Helium Flash Helium Core Burning/Hydrogen Shell Burning ("Helium MS" "Horizontal Branch") Helium Core Depletion Helium Shell Burning Asymptotic Giant Branch Planetary Nebula White Dwarf

26 Lives of Stars of all Masses

27 The Milky Way Our Galaxy has a disk about 50 kpc (160,000 ly) in diameter and about 600 pc (2000 ly) thick, with a high concentration of interstellar dust and gas in the disk The Sun orbits around the center of the Galaxy at a speed of about 790,000 km/h It takes about 220 million years to complete one orbit About 300 billion total stars

28 Question for Thought What is the Hertzsprung-Russell A B C D E diagram? What is its significance and how can it be used? A plot of density versus temperature. A plot of temperature versus radius of stars. A plot of luminosity versus velocity of stars. A plot of temperature versus velocity of stars. A plot of temperature versus luminosity of stars.

29 Question for Thought What is its significance and how can it be used? A B C D E You can determine the number of planets around a star. You can determine the number of stars in our galaxy. You can determine the mass of stars. You can determine the approximate age of a star cluster with an H-R Diagram and follow the life cycle of a star with an H-R Diagram. You can do all of the above.

30 Question for Thought Which is the last stage of the life cycle of a star with a mass similar to our Sun? A Neutron star. B Black hole. C White dwarf. D Red dwarf. E Yellow dwarf.

31 Question for Thought What are the stages of a star, like our Sun, as it gets to be a Main Sequence Star? A Gas cloud, Fragmentation, Protostar, Ignition, Kelvin-Helmholz Contraction, Hayashi Track, Adjustment to Main Sequence B Gas cloud, Ignition, Fragmentation, Protostar, Kelvin-Helmholz Contraction, Hayashi Track, Adjustment to Main Sequence C Gas cloud, Fragmentation, Protostar, Kelvin- Helmholz Contraction, Hayashi Track, Ignition, Adjustment to Main Sequence D Gas cloud, Fragmentation, Kelvin-Helmholz Contraction, Hayashi Track, Ignition, Protostar, Adjustment to Main Sequence

32 Question for Thought Which stars have the longest life span? A The highest mass stars. B The lowest mass stars. C The intermediate mass stars. DThe Red Giants. E The Protostars.

33 Question for Thought What is a supernova? A The explosion of a star like our Sun. B The birth of a star (nova means new star). C The explosive outburst of a star that is part of a binary star system. D The end of the universe. E The catastrophic explosion of a star resulting in the formation of a neutron star or black hole.

34 Question for Thought What is a nova? A The explosion of a star like our Sun. B The birth of a star (nova means new star). C The explosive outburst of a star that is part of a binary star system. D The end of the universe. E The catastrophic explosion of a star resulting in the formation of a neutron star or black hole.

35 Galaxies Elliptical Galaxies S0 (lenticular) Galaxies Spiral Galaxies Barred-Spiral Galaxies Irregular Galaxies

36 Question for Thought Which type galaxy is most like the Milky Way Galaxy? A E3 B Sc C SBb D Sa E SBc

37 The Big Bang

38 Question for Thought What is the source of the heavier chemical elements of the universe beyond atomic mass 3? A The planets. B The stars. C The big bang. D The gas clouds. E The interstellar medium.

39 The Big Bang Summary Timescale Era Epochs Main Event Time after bang The Vacuum Era Planck Epoch Inflationary Epoch Quantum fluctuation Inflation <10-43 sec. <10-10 sec. The Radiation Era The Matter Era Electroweak Epoch Strong Epoch Decoupling Galaxy Epoch Stellar Epoch Formation of leptons, bosons, hydrogen, helium and deuterium Galaxy formation Stellar birth sec sec. 1 sec. - 1 month 1-2 billion years 2-15 billion years The Degenerate Dark Era Dead Star Epoch Black Hole Epoch Death of stars Black holes engulf? billion yrs. 100 billion -????

40 Question for Thought What is the Hubble classification scheme of galaxies?

41 Question Within what era of the Big Bang are we now living? A Electromagnetic Era B Radiation Era C Matter Era DPlanck Era E GUTS Era

42 Question In what era was the universe was dominated by all portions of the electromagnetic spectrum? A Microwave Era B Radiation Era C Matter Era D Invisible Era E Visible Era

43 The Evidence So Far Evidence for a Big Bang expansion of the universe Distant galaxies receding from us everywhere the same remnants of the energy from the Big Bang a very hot body that has cooled 2.7 K cosmic background radiation the primordial abundance of chemical elements

44 Cosmic Background How hot would the cosmic background radiation be close to 3 K first noticed by Penzias and Wilson confirmed by COBE satellite Mather and Smoot won 2006 Nobel Prize for this

45 What CMB means? Remember Wien s Law Remember Doppler COBE results

46 Putting it into context Taking the perspective of the universe with you at the center

47 The CMB remainder... Using COBE DIRBE data for examining the fine differences fine structure of the universe led to the galaxies and their location

48 iclicker Question The cosmic background radiation has a spectrum similar to that of A a blackbody at about 30 K. B a blackbody at 300 K. C a blackbody at about 30 K. D E the Sun points of light.