The Universal Context of Life (Chap 3 – Bennett & Shostak)

1 February 2007 - Lecture 46 February 2007 – Lecture 5HNRS 228 - AstrobiologyProf. Geller

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, UniverseBig 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)

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

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

The Following Slides are from HONORS 227

1st Law of Thermodynamics

In an isolated system, the total amount of energy, including heat energy, is conserved.ENERGY IS CONSERVED

2nd Law of Thermodynamics

Two key componentsheat flows from a warmer

body to a cooler bodyentropy increases remains

constant or increases in time

Phases and Phase Diagram

Planck’s Radiation Curves

A way to depict frequency (inverse of wavelength) versus intensity

Frequency

Intensity

Wien’s Law

Peak wavelength is inversely proportional to the temperature of the blackbody

Intensity

Frequency

Cooler Body

Hotter Body

Peak Wavelength

Stefan-Boltzmann Law

Energy radiated by blackbody is proportional to the temperature to the 4th power

•E = σ T4

Energy vs. Temperature

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10000

20000

30000

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60000

0 2 4 6 8 10 12 14 16

Temperature

Ener

gy

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 awaywrt light it is either red-shifted (away) or blue-shifted (towards)

The Birth of Stars Like Our Sun

Gas cloud Fragmentation ProtostarKelvin-HelmholzContraction Hayashi Track Ignition Adjustment to Main Sequence

The Structure of Stars Like Our Sun

CoreRadiative ZoneConvective ZonePhotosphereChromosphereCorona

How Bright is It?

Apparent Magnitude (from Earth)Absolute Magnitude

How Hot Is It?

Remember Wien’s Law

Classes for Spectra

O,B,A,F,G,K,MThere are also subclasses 0…9

H-R Diagram

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

Galaxies

Elliptical GalaxiesS0 (lenticular) GalaxiesSpiral GalaxiesBarred-Spiral GalaxiesIrregular Galaxies

The Big Bang

The Big BangSummary Timescale

Era Epochs Main Event Time after bang

The Vacuum Era Planck EpochInflationary Epoch

QuantumfluctuationInflation

<10-43 sec.<10-10 sec.

The Radiation Era Electroweak EpochStrong EpochDecoupling

Formation ofleptons, bosons,hydrogen, heliumand deuterium

10-10 sec.10-4 sec.1 sec. - 1 month

The Matter Era Galaxy EpochStellar Epoch

Galaxy formationStellar birth

1-2 billion years2-15 billion years

The DegenerateDark Era

Dead Star EpochBlack Hole Epoch

Death of starsBlack holesengulf?

20-100 billion yrs.100 billion - ????

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

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

What CMB means?

Remember Wien’s LawRemember DopplerCOBE results

Putting it into context

Taking the perspective of the universe with you at the center

The CMB remainder...

Using COBE DIRBE data for examining the fine differences

fine structure of the universe⌧led to the galaxies and their location

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.

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 1012 km).

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.

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.

Question for ThoughtDescribe, in general, the life cycle of a star with a mass similar to our Sun.

Gas cloud , Fragmentation, Protostar, Kelvin-HelmholzContraction, 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

Question for Thought

What is the Hubble classification scheme of galaxies?

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 acarbon 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.

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.

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.

Question for Thought

What is the source of the chemical elements of the universe?

Hydrogen, helium and little lithium and beryliumwere 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.

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.

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.

The Following should help

with the story of the formation of

the Solar System

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)

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 oldRadioactive dating of solar system rocks

Earth ~ 4 billion yearsMoon ~4.5 billion years

Observations to be Explained

Most orbital and rotation planes confined to ecliptic plane with counterclockwise motionExtensive satellite and rings around JoviansPlanets have more of the heavier elements than the sun

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

Log Plot of AbundanceLogarithmic Plot of Chemical Abundance of Elements

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H He C N O Ne Mg Si Si Fe

Chemical Species

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bund

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Another Log ViewChemical Abundance vs. Atomic Number (Logarithmic Plot)

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A Linear View of AbundanceLinear Plot of Chemical Abundance

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H He C N O Ne Mg Si Si Fe

Chemical Species

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Another Linear ViewChemical Abundance vs. Atomic Number (Linear Plot)

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Atomic Number

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Planetary Summary

PlanetMass

(Earth=1)Density(g/cm3)

MajorConstituents

MercuryVenusEarthMars

0.060.821.000.11

5.45.25.53.9

Rock, IronRock, IronRock, IronRock, Iron

JupiterSaturn

31895

1.30.7

H, HeH, He

UranusNeptune

1417

1.31.7

Ices, H, HeIces, H, He

Other Planet Observations

Terrestrial planets are closer to sunMercuryVenusEarthMars

Jovian planets furthest from sunJupiterSaturnUranusNeptune

Some Conclusions

Planets formed at same time as sunPlanetary 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

Nebular Condensation Physics

Energy absorbed per unit area from sun = energy emitted as thermal radiatorSolar Flux = Lum (Sun) / 4 x distance2

Flux emitted = constant x T4 [Stefan-Boltzmann]

Concluding from above yields

T = constant / distance0.5

Nebular Condensation Chemistry

Molecule Freezing Point Distance fromCenter

H2 10 K >100 AUH2O 273 K >10 AUCH4 35 K >35 AUNH3 190 K >8 AU

FeSO4 700 K >1 AUSiO4 1000 K >0.5 AU

Nebular Condensation (protoplanet) Model

Most remnant heat from collapse retained near centerAfter sun ignites, remaining dust reaches an equilibrium temperatureDifferent densities of the planets are explained by condensation temperaturesNebular dust temperature increases to center of nebula

A Pictorial View

Pictorial View Continued

HST Pictorial Evidence?

HST Pictorial Evidence?

More Pictorial Evidence

Nebular Condensation Summary

Solid Particles collide, stick together, sink toward center

Terrestrials -> rockyJovians -> rocky core + ices + light gases

Coolest, most massive collect H and HeMore collisions -> heating and differentiating of interiorRemnants flushed by solar windEvolution of atmospheres