Stars

1
Stars Temperature

• Hotter objects emit shorter wavelengths
• Cooler objects emit longer wavelengths
• Ex. Sun is a medium hot (5800 K or about 5500
  C) star and emits X-rays
• Cooler stars emit infrared
• Determining surface temperature by maximum
  emitted wavelength (Wiens Law)
• NOTE 0 degrees Celsius 273 Kelvin
• -273 degrees Celsius 0 Kelvin

2
Stars Color

• 25,000 K star looks blue
• 6,000 K star looks yellow (like our sun)
• 3,000 K star looks red
• Chemical composition of burning gas
• Determined by passing light through a prism to
  generate a spectrum
• Light passed through nebula may have absorption
  lines
• Ex. Sun is 74 Hydrogen, 25 Helium, 1 Other
• Spectral Class combination of temperature and
  chemical composition
• Signified by a letter O, B, A, F, G, K, M
  (hottest to coolest)
• Our sun is G2

3
Stars Finding Distance by Brightness

• Why do you think stars would be different
  brightness levels?
• Apparent Brightness combination of energy
  emitted and distance from Earth, brightness
  decreased by square of distance.
• Intrinsic Brightness known as LUMINOSITY,
  measured in watts.
• If you know the apparent and intrinsic
  brightness, you can figure distance.

4
Star Evolution

• Group 1 Star Formation Birth (11-1)
• Group 2 Star Energy Helium Fusion
• Group 3 Stellar Structure and Energy Transport
  (11-3)
• Group 4 Why is there a Main Sequence?
  (p.262-267)
• Group 5 Post-Main-Sequence Evolution (12-2)
• Group 6 Evidence of Evolution Star Clusters
  (12-3)

5
Stars Motion Determined by Light

• Doppler Effect Motion of a lights source
  affects its observed wavelength of light
• Approaching observer, waves compressed, shortened
  wavelengths (BLUESHIFT)
• Moving away from observer, waves spread out,
  lengthened wavelengths (REDSHIFT)
• Perpendicular motion to observer does not shift
  the wavelength

6
Remember that old commercial?

• Draw a person or an ear to represent the
  observer.
• Animations of Doppler Effect

7
EW We are going to be reviewing today for the
final next Monday. Write down what the big
bang theory and evidence for it are.
8
Tuesday, June 3rd, 2014

• LT I will be able to discuss the big bang
  theory, evidence for it and star life cycles.

• Agenda
• -Review for final next week
• -can use note card on final
• Tomorrow
• -Climate Change

9

• Origins
• began with a large explosion called the big bang
  theory
• only energy before this, no matter
• first hydrogen and helium were formed
• larger elements were formed later by stars

10
The Big Bang Theory
11
(No Transcript)
12
Big Bang Theory

• Expansion indicates a denser, hotter past
  uniform, hot gas that cools as it expands
• NOT an explosion from a point, but a simultaneous
  expansion from all places
• 13.7 billion years ago

13
Big Bang

• EVIDENCE
• 1. Cosmic microwave background radiation
  noise, same in all directions
• 1965 Arno Penzias and Robert Wilson
• 2. Expansion measured by Hubble constant
• Distant galaxies are redshifted (based on
  electromagnetic spectrum)
• This is the doppler effect being applied to light
  
• 1929 Edwin Hubble
• 3. most elements in universe are H and He (light
  elements)
• Created during first moments of Big Bang
• when stars reach the end of their life cycle,
  they distribute C, O, and Fe into the universe
• if the universe was older, there would be more C,
  O, and Fe

14
Expanding Universe

• All distant galaxies are redshifted. What does
  this mean about their distance from us?
• Hubble Law further away a galaxy is, the faster
  it is speeding away
• If we can determine how fast the universe is
  expanding (aka Hubble constant), we can determine
  the AGE OF THE UNIVERSE!

15
(No Transcript)
16

• Continuation of Expanding Universe
• is expanding, therefore must have been smaller
  at one point
• evident by galaxies red shift
• most look red because they are moving away from
  us
• if they were moving towards us, they would look
  bluer (blue shift)

17
Observers looking at an object that is moving
away from them see light that has a longer
wavelength than it had when it was emitted (a
redshift), while observers looking at an
approaching source see light that is shifted to
shorter wavelength (a blueshift).
18
(No Transcript)
19
Cosmic background radiation

• scientists found noise in our galaxy that was
  the cosmic microwave background radiation
  predicted by the Big Bang theory
• The radiation can only be detected with a radio
  telescope which makes it show as a faint glow.
• Thermal radiation thought to be left over by Big
  Bang
• Happened 300,000 years after The Big Bang (so
  still about 13.7 billion years ago!)

20
What is a radio telescope?

• Radio waves are a form of electromagnetic
  radiation, just like visible light!
• How they work?
• -waves bounce off a radio telescope, with this
  information computers can make images of the sky!

21
Can make images like this of our Universe!
22
New Evidence!

• Theory of inflation
• -first proposed in 1980s but recently found
  evidence for it!
• -Found evidence that the universe was expanding
  exponentially seconds after the Big Bang

23
Life Cycle of Stars

• Our sun is an average star in our solar system!
• life cycle varies depending on the size
• For most stars, 90 of life cycle is spent fusing
  hydrogen that turns into helium
• all begin life inside a huge cloud of gas (mostly
  hydrogen) and dust called a nebula

24
When an average star ends its life cycle!

• hydrogen fusion stops
• Fusing of helium begins to create heavier
  elements (like oxygen, iron)
• no more energy exploding outward
• gravity pulls matter inwards
• First makes a large red giant
• outer layers often expand and drift away creating
  a planetary nebula
• VERY high density, bright, and is called a white
  dwarf

25
Life cycle of Larger Stars

• for larger stars
• elements up to iron are fused together
• eventually may turn into a supernova
• quickly collapses because run out of energy and
  gravity is now the strongest force
• core collapses and then rebounds outward with a
  shock wave that makes a bright explosion
  (supernova)
• at this point, the heavier elements are finally
  created
• if the leftover core is very, very dense, it may
  form a very small neutron star or a black hole
  with VERY powerful gravity

26
(No Transcript)
27
Cosmology

• How did the cosmos begin, and what will happen to
  it?
• Study of the history and future of the universe
• Universe everything that exists in space and
  time