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Starry Monday at Otterbein

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Winter constellations are up: Orion, Taurus, Gemini, Auriga, ... Mars in Aries. Due North. Big Dipper points to the north pole. West the Autumn Constellations ... – PowerPoint PPT presentation

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Title: Starry Monday at Otterbein


1
Starry Monday at Otterbein
Welcome to
  • Astronomy Lecture Series
  • -every first Monday of the month-
  • January 9, 2006
  • Dr. Uwe Trittmann

2
Todays Topics
  • Lifecycle of Stars
  • The Night Sky in January

3
Feedback!
  • Please write down suggestions/your interests on
    the note pads provided
  • If you would like to hear from us, please leave
    your email / address
  • To learn more about astronomy and physics at
    Otterbein, please visit
  • http//www.otterbein.edu/dept/PHYS/weitkamp.asp
    (Obs.)
  • http//www.otterbein.edu/dept/PHYS/ (Physics
    Dept.)

4
The Lifecycle of the Stars
5
Reminder Hertzsprung-Russell-Diagrams
  • Hertzsprung-Russell diagram is luminosity vs.
    spectral type (or temperature)
  • To obtain a HR diagram
  • get the luminosity. This is your y-coordinate.
  • Then take the spectral type as your x-coordinate.
    This may look strange, e.g. K5III for Aldebaran.
    Ignore the roman numbers ( III means a giant
    star, V means dwarf star, etc). First letter is
    the spectral type K (one of OBAFGKM), the arab
    number (5) is like a second digit to the spectral
    type, so K0 is very close to G, K9 is very close
    to M.

6
Reminder Spectral Classification of the Stars
  • Class Temperature Color Examples
  • O 30,000 K blue
  • B 20,000 K bluish Rigel
  • A 10,000 K white Vega, Sirius
  • F 8,000 K white Canopus
  • G 6,000 K yellow Sun, ? Centauri
  • K 4,000 K orange Arcturus
  • M 3,000 K red Betelgeuse

Mnemotechnique Oh, Be A Fine Girl/Guy, Kiss Me
7
Constructing a HR-Diagram
  • Example Aldebaran, spectral type K5III,
    luminosity 160 times that of the Sun

L
1000
Aldebaran
160
100
10
1
Sun (G2V)
O B A F G K M
Type
0123456789 0123456789 012345
8
The Hertzprung-Russell Diagram
  • A plot of absolute luminosity (vertical scale)
    against spectral type or temperature (horizontal
    scale)
  • Most stars (90) lie in a band known as the Main
    Sequence

9
Mass and the Main Sequence
  • The position of a star in the main sequence is
    determined by its mass
  • ?All we need to know to predict luminosity and
    temperature!
  • Both radius and luminosity increase with mass

10
The Fundamental Problem in studying the stellar
lifecycle
  • We study the subjects of our research for a tiny
    fraction of its lifetime
  • Suns life expectancy 10 billion (1010) years
  • Careful study of the Sun 370 years
  • We have studied the Sun for only 1/27 millionth
    of its lifetime!

11
Suppose we study human beings
  • Human life expectancy 75 years
  • 1/27 millionth of this is about 74 seconds
  • What can we learn about people when allowed to
    observe them for no more than 74 seconds?

12
Theory and Experiment
  • Theory
  • Need a theory for star formation
  • Need a theory to understand the energy production
    in stars ? make prediction how bight stars are
    when and for how long in their lifetimes
  • Experiment observe how many stars are where when
    and for how long in the Hertzsprung-Russell
    diagram
  • ? Compare prediction and observation

13
Nuclear Fusion is the energy source of the Stars
  • Atoms electrons orbiting nuclei
  • Chemistry deals only with electron orbits
    (electron exchange glues atoms together to from
    molecules)
  • Nuclear power comes from the nucleus
  • Nuclei are very small
  • If electrons would orbit the statehouse on I-270,
    the nucleus would be a soccer ball in Gov. Bob
    Tafts office
  • Nuclei made out of protons (el. positive) and
    neutrons (neutral)

14
Nuclear fusion reaction
  • 4 hydrogen nuclei combine (fuse) to form a helium
    nucleus, plus some byproducts
  • Mass of products is less than the original mass
  • The missing mass is emitted in the form of
    energy, according to Einsteins famous formulas
  • E mc2
  • (the speed of light is very large, so there is a
    lot of energy in even a tiny mass)

15
Further Reactions Heavier Elements
  • Start 4 2 protons ? End Helium nucleus
    neutrinos
  • Hydrogen fuses to
    Helium

16
Fusion is NOT fission!
  • In nuclear fission one splits a large nucleus
    into pieces to gain energy
  • large nuclei ?Fission
  • small nuclei ?Fusion

17
Check Solar Neutrinos
  • We can detect the neutrinos coming from the
    fusion reaction at the core of the Sun
  • The results are 1/3 to 1/2 the predicted value!
  • Possible explanations
  • Models of the solar interior are incorrect
  • Our understanding of the physics of neutrinos is
    incorrect
  • Something is horribly, horribly wrong with the
    Sun
  • 2 is the answer neutrinos oscillate

18
Theory of Star Formation
  • A stars existence is based on a competition
    between gravity (inward) and pressure due to
    energy production (outward)

Heat
Gravity
Gravity
19
Star Formation Lifecycle
  • Stage 1 Contraction of a cold interstellar cloud
  • Stage 2 Cloud contracts/warms, begins radiating
    almost all radiated energy escapes
  • Stage 3 Cloud becomes dense ? opaque to
    radiation ? radiated energy trapped ? core heats
    up

20
Example Orion Nebula
  • Orion Nebula is a place where stars are being born

21
Orion Nebula (M42)
22
Protostellar Evolution
  • Stage 4 increasing temperature at core slows
    contraction
  • Luminosity about 1000 times that of the sun
  • Duration 1 million years
  • Temperature 1 million K at core, 3,000 K at
    surface
  • Still too cool for nuclear fusion!
  • Size orbit of Mercury

23
The T Tauri Stage
  • Stage 5 (T Tauri)
  • Violent surface activity
  • high solar wind blows out the remaining stellar
    nebula
  • Duration 10 million years
  • Temperature 5?106 K at core, 4000 K at surface
  • Still too low for nuclear fusion
  • Luminosity drops to about 10 ? the Sun
  • Size 10 ? the Sun

24
Path in the Hertzsprung-Russell Diagram
  • Stages 1-5

25
Observational Confirmation
  • Preceding the result of theory and computer
    modeling
  • Can observe objects in various stages of
    development, but not the development itself

26
A Newborn Star
  • Stage 6 Temperature and density at core high
    enough to sustain nuclear fusion
  • Stage 7 Main-sequence star pressure from
    nuclear fusion and gravity are in balance
  • Duration 10 billion years (much longer than all
    other stages combined)
  • Temperature 15 million K at core, 6000 K at
    surface
  • Size Sun

27
Mass Matters
  • Larger masses
  • higher surface temperatures
  • higher luminosities
  • take less time to form
  • have shorter main sequence lifetimes
  • Smaller masses
  • lower surface temperatures
  • lower luminosities
  • take longer to form
  • have longer main sequence lifetimes

28
Failed Stars Brown Dwarfs
  • Too small for nuclear fusion to ever begin
  • Less than about 0.08 solar masses
  • Give off heat from gravitational collapse
  • Luminosity a few millionths that of the Sun

29
Main Sequence Lifetimes
  • Mass (in solar masses) Luminosity
    Lifetime
  • 10 Suns 10,000
    Suns 10 Million yrs
  • 4 Suns
    100 Suns 2 Billion
    yrs
  • 1 Sun
    1 Sun 10 Billion yrs
  • ½ Sun
    0.01 Sun 500 Billion yrs

30
Why Do Stars Leave the Main Sequence?
  • Running out of fuel

31
Stage 8 Hydrogen Shell Burning
  • Cooler core ? imbalance between pressure and
    gravity ? core shrinks
  • hydrogen shell generates energy too fast ? outer
    layers heat up ? star expands
  • Luminosity increases
  • Duration 100 million years
  • Size several Suns

32
Stage 9 The Red Giant Stage
  • Luminosity huge ( 100 Suns)
  • Surface Temperature lower
  • Core Temperature higher
  • Size 70 Suns (orbit of Mercury)

33
Lifecycle
  • Lifecycle of a main sequence G star
  • Most time is spent on the main-sequence (normal
    star)

34
The Helium Flash and Stage 10
  • The core becomes hot and dense enough to overcome
    the barrier to fusing helium into carbon
  • Initial explosion followed by steady (but rapid)
    fusion of helium into carbon
  • Lasts 50 million years
  • Temperature 200 million K (core) to 5000 K
    (surface)
  • Size 10 ? the Sun

35
Stage 11
  • Helium burning continues
  • Carbon ash at the core forms, and the star
    becomes a Red Supergiant
  • Duration 10 thousand years
  • Central Temperature 250 million K
  • Size gt orbit of Mars

36
Stage 12
  • Inner carbon core becomes dead it is out of
    fuel
  • Some helium and carbon burning continues in outer
    shells
  • The outer envelope of the star becomes cool and
    opaque
  • solar radiation pushes it outward from the star
  • A planetary nebula is formed

Duration 100,000 years Central Temperature 300
? 106 K Surface Temperature 100,000 K Size 0.1
? Sun
37
Planetary Nebulae
  • Eye of God Nebula

38
Cats Eye Nebula
39
Wings of the Butterfly Nebula
40
  • The Ring Nebula (M57)

41
  • Eskimo Nebula

42
  • Stingray Nebula

43
  • Ant Nebula

44
Stage 13 White Dwarf
  • Core radiates only by stored heat, not by nuclear
    reactions
  • core continues to cool and contract
  • Size Earth
  • Density a million times that of Earth 1 cubic
    cm has 1000 kg of mass!

45
Stage 14 Black Dwarf
  • Impossible to see in a telescope
  • About the size of Earth
  • Temperature very low
  • ? almost no radiation
  • ? black!

46
Evolution of More Massive Stars
  • Gravity is strong enough to overcome the electron
    pressure (Pauli Exclusion Principle) at the end
    of the helium-burning stage
  • The core contracts until its temperature is high
    enough to fuse carbon into oxygen
  • Elements consumed in core
  • new elements form while previous elements
    continue to burn in outer layers

47
Evolution of More Massive Stars
  • At each stage the temperature increases
  • ? reaction gets faster
  • Last stage fusion of iron does not release
    energy, it absorbs energy
  • ? cools the core
  • ? fire extinguisher

48
Neutron Core
  • The core cools and shrinks
  • nuclei and electrons are crushed together
  • protons combine with electrons to form neutrons
  • Ultimately the collapse is halted by neutron
    pressure
  • Most of the core is composed of neutrons at this
    point
  • Size few km
  • Density 1018 kg/m3 1 cubic cm has a mass of
    100 million kg!

Manhattan
49
Formation of the Elements
  • Light elements (hydrogen, helium) formed in Big
    Bang
  • Heavier elements formed by nuclear fusion in
    stars and thrown into space by supernovae
  • Condense into new stars and planets
  • Elements heavier than iron form during supernovae
    explosions
  • Evidence
  • Theory predicts the observed elemental abundance
    in the universe very well
  • Spectra of supernovae show the presence of
    unstable isotopes like Nickel-56
  • Older globular clusters are deficient in heavy
    elements

50
Review The life of Stars
51
The Night Sky in January
  • Long nights, early observing!
  • Winter constellations are up Orion, Taurus,
    Gemini, Auriga, Canis Major Minor ? lots of
    deep sky objects!
  • Saturn at opposition

52
Moon Phases
  • Today (Waxing Gibbous, 80)
  • 1/ 14 (Full Moon)
  • 1 / 22 (Last Quarter Moon)
  • 1 / 29 (New Moon)
  • 2/ 5 (First Quarter Moon)

53
Today at Noon
  • Sun at meridian, i.e. exactly south

54
10 PM
  • Typical observing hour, early January
  • Saturn

Mars Moon
55
South-West
  • Plejades
  • Mars in Aries

56
Due North
  • Big Dipper points to the north pole

57
West the Autumn Constellations
  • W of Cassiopeia
  • Big Square of Pegasus
  • Andromeda Galaxy

58
Andromeda Galaxy
  • PR Foto
  • Actual look

59
Zenith
  • High in the sky
  • Perseus and
  • Auriga
  • with Plejades and the Double Cluster

60
South-West
  • The Autumn
  • Constellations
  • W of Cassiopeia
  • Big Square of Pegasus
  • Andromeda Galaxy

61
South
  • The Winter Constellations
  • Orion
  • Taurus
  • Canis Major
  • Gemini
  • Canis Minor

62
Mark your Calendars!
  • Next Starry Monday February 6, 2005, 7 pm
  • (this is a Monday
    )
  • Observing at Prairie Oaks Metro Park
  • Friday, January 20, 630 pm
  • Web pages
  • http//www.otterbein.edu/dept/PHYS/weitkamp.asp
    (Obs.)
  • http//www.otterbein.edu/dept/PHYS/ (Physics
    Dept.)

63
Mark your Calendars II
  • Physics Coffee is every Wednesday, 330 pm
  • Open to the public, everyone welcome!
  • Location across the hall, Science 256
  • Free coffee, cookies, etc.
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