1. The Big Bang, Galaxies, & Stars

2. Big Bang theory – Origin of the Universe
Big Bang marks the inception of the universe
Occurred about 13.7 billion years ago
All matter and space was created
Not a huge explosion that hurled matter in all directions. Technically, there was no “bang”
Technically, matter is not moving outward in all directions. Reality: space expands

3. Big Bang Evidence
Distant galaxies are moving away from each other – Doppler Red Shift. Hubble (1929) – the farther away the galaxy is the faster it is moving away.
Cosmic Microwave Background Radiation – Penzias & Wilson (1965). Left over radiation from the “explosion”

4. Raisin bread analogy of an expanding universe

5. Expansion Evidence for Big Bang
Electromagnetic Energy - Type of energy given off in the form of transverse waves
Different types of electromagnetic energy are distinguished by their different wavelengths

6. Page 14 of the ESRT

7. Electromagnetic Spectrum – humans can only see one part of spectrum – visible light

8. Expansion Evidence Most stars are made of Hydrogen & Helium gas.
Elements that emit specific wavelengths within the electromagnetic spectrum.
The spectral line pattern can be used to identify the star rather like a fingerprint or bar code.

9. Red Shift – Blue Shift
In 1929, Edwin Hubble observed that spectral lines emitted by stars in distant galaxies were considerably Red shifted.
If a galaxy or star were moving toward the earth, the spectral lines would show a blue shift.
When scientists look at the spectrum of radiation emitted by stars in far away galaxies they noticed the positions of the characteristic wavelengths are shifted to the shorter (blue light end of spectrum) or longer (red light end of spectrum) wavelengths depending on whether the star is coming towards you or moving away.
In 1929, Edwin Hubble observed that spectral lines emitted by stars in distant galaxies were considerably Red shifted.

11. Shifting of Wavelengths is called the Doppler Effect
Change in the wavelength of light emitted by an object due to its motion
Movement toward “squeezes” the wavelength
Shorter wavelength
Light shifted toward the blue end of the spectrum
Movement away stretches the wavelength
Longer wavelength
Light shifted toward the red end of spectrum

13. RED SHIFT – BLUE SHIFT
The greater the degree of shift of the spectral lines, the faster the object is moving away
The star light DOES NOT appear red or blue (it still appears as white light from the star)
The “bar code” for each element either shifts to the shorter wavelength blue end of the spectrum or to the longer wavelength red end of the spectrum

15. What is the best inference that can be made concerning the movements of Galaxies A, B, and C?

16. Structure of the Universe
Hubble Telescope allowed scientists to infer the structure of the universe
A GALAXY is a collection of billions of stars held together by gravity
Over l00 billion galaxies
spiral – elliptical - irregular

18. Our solar system is part of the spiral Milky Way Galaxy

19. Edge-on view of the Milk Way Galaxy

21. Elliptical Galaxy

22. Spiral galaxy in the constellation Andromeda

23. Barred Spiral

24. Understanding Stars Grouping of stars and the classification system has changed over time with more advanced tools

25. STELLAR SPECTRAL CLASS
Grouping the stars based on their temperatures

26. Each class of star has a unique pattern of lines (“bar code”) to identify it.
Hydrogen
Hydrogen
Hydrogen
Sodium
“Hottest”
“Coldest”

27. Hertzsprung-Russell Diagram
Comparing temperature and brightness for various stars

28. Hertzsprung-Russell Diagram aka Luminosity and Temperature of Stars Diagram – NOT A MAP
DIAGRAM IS A USEFUL WAY TO FOLLOW CHANGES THAT TAKE PLACE AS THE STARS LIVE OUT THEIR LIVES
Diagram is made by plotting (graphing) each star's LUMINOSITY (brightness) and TEMPERATURE (as reflected by color) COMPARED TO THE SUN
It is readily apparent that the H-R Diagram is not uniformly populated, but that stars preferentially fall into certain regions of the diagram. The majority of stars fall along a curving diagonal line called the main sequence but there are other regions where many stars also fall.

29. Which groups of stars are the BRIGHTEST?

30. Which group of stars is the HOTTEST?

31. Which groups of stars are the SMALLEST and DIMMEST?

32. Schematically, stars fall into regions shown below with respect to the sun.

33. Most stars are on the Main Sequence because that is where they spend most of their lives
Our sun is an average main sequence star
Luminosity of 1
Temperature 5500°C – yellow in color
Consider stars cooler than, but brighter than the sun. These must be very large stars (Red Giants), whereas stars bluer than the sun but less luminous must be quite small ( White Dwarfs).
We will see that the H-R Diagram is an extremely useful way to follow the changes that take place as a star evolves. Most stars are on the Main Sequence because that is where stars spend most of their lives, burning hydrogen to helium through nuclear reactions. As stars live out their lives, changes in the structure of the star are reflected in changes in stars temperatures, sizes and luminosities, which cause them to move in tracks on the H-R Diagram.

34. What color stars are hottest? Coldest? Red Super Giants
Red Giants
MAIN SEQUENCE
COLOR AND TEMPERATURE ARE RELATED!
White Dwarfs

35. Star Formation A star is born when nuclear fusion starts.
Gravity pulls hydrogen atoms together. As trillions of hydrogen atoms are compressed the temperature increases.
Once the temperature reaches ~15 million ºC, nuclear fusion begins and a star is born.

36. Space is filled with the stuff to make stars – mostly hydrogen gas.
Image of the pillars of creation inside the crab nebula
Columns of hydrogen gas and dust that is the beginnings of stars

37. At 15 million degrees Celsius in the center of the star - nuclear fusion begins

39. As long as the forces of gravity and thermal pressure are balanced, the star exists on the main sequence.

40. Life Cycle of Stars – Depends upon their original mass
After they spend their life as main sequence star ….
Sun size > expand to red giant in about 5 billion years > white dwarf > black dwarf
Super giant > supernova >
very high mass – black hole
high mass – neutron star

43. Star Life Cycle: Stars are like humans
Star Life Cycle: Stars are like humans. They are born, live and then die.
Takes about 1-3 years
Protostar takes 10 million years
Nebula – cloud Protostar – new, just
of gas and dust forming star

44. Main Sequence (like the sun)
Red Giant (Betleguise) – once the star runs out of hydrogen and the balance of forces is upset.
Main Sequence (like the sun)
From start to finish in main sequence takes about 11 billion years
From the finish of the main sequence – red giant takes about 100 million years

45. DEPENDING ON THE ORIGINAL MASS
White Dwarf: Smaller stars Supernova: Star that
shrink and cool and has died an explosive
eventually become cold death.
black dwarves.
This takes about 10,000 years from the end of red giant stage

46. Star Dies – Star casts off shell
Star Dies – Star casts off shell . It creates nebula that can take a variety of shapes – Ant Nebula

49. JUST FOR FUN Validity of the following slides is unknown?
But it is still cool to imagine the sizes of things in space …

50. Terrestrial Planets – Earth largest solid, smaller, denser

51. Earth compared to Jovian Planets gaseous, large, low density

52. All planets compared to Our Sun
No longer considered a planet