Title: Starry Monday at Otterbein
1Starry Monday at Otterbein
Welcome to
- Astronomy Lecture Series
- -every first Monday of the month-
- January 9, 2006
- Dr. Uwe Trittmann
2Todays Topics
- Lifecycle of Stars
- The Night Sky in January
3Feedback!
- 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.)
4The Lifecycle of the Stars
5Reminder 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.
6Reminder 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
7Constructing 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
8The 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
9Mass 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
10The 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!
11Suppose 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?
12Theory 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
13Nuclear 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)
14Nuclear 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)
15Further Reactions Heavier Elements
- Start 4 2 protons ? End Helium nucleus
neutrinos - Hydrogen fuses to
Helium
16Fusion is NOT fission!
- In nuclear fission one splits a large nucleus
into pieces to gain energy - large nuclei ?Fission
- small nuclei ?Fusion
17Check 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
18Theory of Star Formation
- A stars existence is based on a competition
between gravity (inward) and pressure due to
energy production (outward)
Heat
Gravity
Gravity
19Star 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
20Example Orion Nebula
- Orion Nebula is a place where stars are being born
21Orion Nebula (M42)
22Protostellar 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
23The 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
24Path in the Hertzsprung-Russell Diagram
25Observational Confirmation
- Preceding the result of theory and computer
modeling - Can observe objects in various stages of
development, but not the development itself
26A 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
27Mass 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
28Failed 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
29Main 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
30Why Do Stars Leave the Main Sequence?
31Stage 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
32Stage 9 The Red Giant Stage
- Luminosity huge ( 100 Suns)
- Surface Temperature lower
- Core Temperature higher
- Size 70 Suns (orbit of Mercury)
33Lifecycle
- Lifecycle of a main sequence G star
- Most time is spent on the main-sequence (normal
star)
34The 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
35Stage 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
36Stage 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
37Planetary Nebulae
38Cats Eye Nebula
39Wings of the Butterfly Nebula
40 41 42 43 44Stage 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!
45Stage 14 Black Dwarf
- Impossible to see in a telescope
- About the size of Earth
- Temperature very low
- ? almost no radiation
- ? black!
46Evolution 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
47Evolution 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
48Neutron 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
49Formation 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
50Review The life of Stars
51The 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
52Moon Phases
- Today (Waxing Gibbous, 80)
- 1/ 14 (Full Moon)
- 1 / 22 (Last Quarter Moon)
- 1 / 29 (New Moon)
- 2/ 5 (First Quarter Moon)
53Today at Noon
- Sun at meridian, i.e. exactly south
5410 PM
- Typical observing hour, early January
-
- Saturn
Mars Moon
55South-West
56Due North
- Big Dipper points to the north pole
57West the Autumn Constellations
- W of Cassiopeia
- Big Square of Pegasus
- Andromeda Galaxy
58Andromeda Galaxy
59Zenith
- 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
61South
- The Winter Constellations
- Orion
- Taurus
- Canis Major
- Gemini
- Canis Minor
62Mark 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.) -
63Mark 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.
-