The Universal Context of Life

Transcription

1 The Universal Context of Life (Chap 3 Bennett & Shostak) 1 February Lecture 4 6 February 2007 Lecture 5 HNRS Astrobiology Prof. Geller

2 Overview of Chapter 3 The Universe and Life (3.1) Age, Size, Elements, Laws The Structure, Scale, and History of the Universe (3.2) Planets, Solar System, Galaxy, Local Group, Supercluster, Universe Big Bang Theory of creation of universe Evidence for expansion, age and composition The Nature of the Worlds (3.3) The solar system and its formation (remember 227)

3 Overview of Chapter 3 A Universe of Matter and Energy (3.4) Atoms, Energy, Electromagnetic Radiation, Spectroscopy Changing Ideas about the Formation of the Solar System (3.5) Nebular Condensation Model

4 Food for thought... The grand aim of all science is to cover the greatest number of empirical facts by logical deduction from the smallest number of hypotheses or axioms. Albert Einstein, 1950

5 The Following Slides are from HONORS 227

6 1st Law of Thermodynamics In an isolated system, the total amount of energy, including heat energy, is conserved. ENERGY IS CONSERVED

7 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

8 Phases and Phase Diagram

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

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

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

12 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)

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

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

15 How Bright is It? Apparent Magnitude (from Earth) Absolute Magnitude

16 How Hot Is It? Remember Wien s Law

17 Classes for Spectra O,B,A,F,G,K,M There are also subclasses 0 9

18 H-R Diagram

19 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

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

21 The Big Bang

22 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 -????

23 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

24 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

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

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

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

28 Question for Thought What is a light year and how is it defined? The light year is a unit of distance. It is defined as the distance traveled by light in a year, about 6 trillion miles or 10 trillion kilometers.

29 Question for Thought Why are astronomical distances not measured with standard reference units of distance such as kilometers or miles? Because astronomical distances are so large (1 ly = 9.5 x km).

30 Question for Thought Which stars have the longest life span? The lowest mass stars have the longest life span. Red dwarfs can live 100 billion years. Stars like our Sun live about 10 billion years.

31 Question for Thought What is the Hertzsprung-Russell diagram? What is its significance and how can it be used? Basically a plot of temperature vs. luminosity. You can determine the approximate age of a star cluster with an H-R Diagram. You can follow the life cycle of a star with an H-R Diagram.

32 Question for Thought Describe, in general, the life cycle of a star with a mass similar to our Sun. Gas cloud, Fragmentation, Protostar, Kelvin-Helmholz Contraction, Hayashi Track, Ignition, Adjustment to Main Sequence, 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

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

34 Question for Thought What is a nova? The explosive outburst of a star that is part of a binary star system. A white dwarf can accumulate hydrogen on its surface until it builds up so much hydrogen around the carbon core, that it gets hot enough to cause fusion. This fusion explosion of the shell of a carbon white dwarf blows as a nova, a very high increase in the luminosity of the star. The star can undergo a nova explosion many times, as it is not destroyed in the process.

35 Question for Thought What is a supernova? The catastrophic explosion of a star. It can be a star that is part of a binary star system or a standalone star. In the case of a standalone star, it is a star that is so massive that it goes through all of the fusion steps possible up to iron. Supernovae explosions result in the formation of either a neutron star or black hole.

36 Question for Thought Describe the forces that keep a star in a state of hydrostatic equilibrium. Fusion generates energy that pushes out from the center of a star. Also gas pressure maintains a push out from the center. The weight of the star (gravity) keeps pulling the stellar material to the center of its mass.

37 Question for Thought What is the source of the chemical elements of the universe? Hydrogen, helium and little lithium and berylium were made in the big bang formation of the universe. All other chemical elements up to Uranium (#92) were formed in stars. Elements up to iron are formed in stars during their life cycle. Elements beyond iron are born in supernovae explosions.

38 Question for Thought How do you explain that a red giant is very bright, with a low surface temperature? While the surface temperature of a red giant is relatively low (~3000 K) the star is so large that it is emitting a lot of light in accordance with Stefan-Boltzmann s Law and the surface area of a star.

39 Question for Thought Describe the structure of the Milky Way Galaxy. The Milky Way galaxy consists of a core, or central bulge region, and spiral arms. The spiral arms are engulfed in gas and dust of what is referred to as the disk of the galaxy. The Milky Way Galaxy also has a bar. It is a barred spiral galaxy.

40 The Following should help with the story of the formation of the Solar System

41 Questions to Consider How did the solar system evolve? What are the observational underpinnings? Why are some elements (like gold) quite rare, while others (like carbon) are more common? Are there other solar systems? What evidence is there for other solar systems? (to be discussed later in semester)

42 Observations to be Explained Each radioactive nucleus decays at its own characteristic rate, known as its half-life, which can be measured in the laboratory. This is key to radioactive age dating, which is used to determine the ages of rocks. The oldest rocks found anywhere in the solar system are meteorites, the bits of meteoroids that survive passing through the Earth s atmosphere and land on our planet s surface. Radioactive age-dating of meteorites, reveals that they are all nearly the same age, about 4.56 billion years old Radioactive dating of solar system rocks Earth ~ 4 billion years Moon ~4.5 billion years

43 Observations to be Explained Most orbital and rotation planes confined to ecliptic plane with counterclockwise motion Extensive satellite and rings around Jovians Planets have more of the heavier elements than the sun

44 Abundance of the Chemical Elements At the start of the Stellar Era there was about 75-90% hydrogen, 10-25% helium and 1-2% deuterium NOTE WELL: Abundance of the elements is often plotted on a logarithmic scale this allows for the different elements to actually appear on the same scale as hydrogen and helium it does show relative differences among higher atomic weight elements better than linear scale Abundance of elements on a linear scale is very different

45 Log Plot of Abundance Logarithmic Plot of Chemical Abundance of Elements Relative Abundance H He C N O Ne Mg Si Si Fe Chemical Species

46 Another Log View Chemical Abundance vs. Atomic Number (Logarithmic Plot) Relative Abundance Atomic Number

47 A Linear View of Abundance Linear Plot of Chemical Abundance Relative abundance H He C N O Ne Mg Si Si Fe Chemical Species

48 Another Linear View Chemical Abundance vs. Atomic Number (Linear Plot) Relative Abundance Atomic Number

49 Planetary Summary Planet Mass (Earth=1) Density (g/cm 3 ) Major Constituents Mercury Venus Earth Mars Rock, Iron Rock, Iron Rock, Iron Rock, Iron Jupiter Saturn H, He H, He Uranus Neptune Ices, H, He Ices, H, He

50 Other Planet Observations Terrestrial planets are closer to sun Mercury Venus Earth Mars Jovian planets furthest from sun Jupiter Saturn Uranus Neptune

51 Some Conclusions Planets formed at same time as sun Planetary and satellite/ring systems are similar to remnants of dusty disks such as that seen about stars being born (e.g. T Tauri stars) Planet composition dependent upon where it formed in solar system

52 Nebular Condensation Physics Energy absorbed per unit area from sun = energy emitted as thermal radiator Solar Flux = Lum (Sun) / 4 x distance 2 Flux emitted = constant x T 4 [Stefan-Boltzmann] Concluding from above yields T = constant / distance 0.5

53 Nebular Condensation Chemistry Molecule Freezing Point Distance from Center H 2 10 K >100 AU H 2 O 273 K >10 AU CH 4 35 K >35 AU NH K >8 AU FeSO K >1 AU SiO K >0.5 AU

54 Nebular Condensation (protoplanet) Model Most remnant heat from collapse retained near center After sun ignites, remaining dust reaches an equilibrium temperature Different densities of the planets are explained by condensation temperatures Nebular dust temperature increases to center of nebula

55 A Pictorial View

56 Pictorial View Continued

57 HST Pictorial Evidence?

58 HST Pictorial Evidence?

59 More Pictorial Evidence

60 Nebular Condensation Summary Solid Particles collide, stick together, sink toward center Terrestrials -> rocky Jovians -> rocky core + ices + light gases Coolest, most massive collect H and He More collisions -> heating and differentiating of interior Remnants flushed by solar wind Evolution of atmospheres