1. Stars
Chapter 30
Pages 775-

2. Star
A ball of gases that gives off a tremendous amount of electromagnetic energy
Notice that I did not say light
Stars emit all wavelengths of the electromagnetic spectrum

3. Analyzing Starlight
Astronomers analyze stars by looking at the light they emit
They use a spectrograph
A spectrograph separates light into different colors or wavelengths
Stars produce a display of colors and lines called a spectrum

4. Three types of spectra Emission or bright line
Absorption or dark line—dark line shows composition and temperature
Continuous

5. Sources of Spectra

6. Star classification
If we look at a star with a spectroscope we see dark lines called absorption spectra
These lines indicate the star’s chemical composition

7. The most common element in stars is hydrogen

8. Each chemical element has a characteristic spectra in a given range of temperatures

9. The colors and lines indicate the elements that make up a star

10. Chemical Composition Lab
Use the transparency and the paper copy to identify the elements found in the “Spectra of Unknown Composition”
Slide the transparency up and line the unknown spectra just above the Calcium lines
Are all lines present?
Then calcium is in the star
List results in two columns on your 3x5 card
Elements Present and Elements Not Present

11. Color and Stars Think of a candle Hottest part is blue
Red is the cool part at the top

12. Examples
Temperature?
Composition?

13. Apparent Motion of Stars
Time lapse photography show a circular pattern revolving around the star Polaris
We know Polaris as the North Star
It is located directly above the North Pole so as the Earth spins the stars appear to move

14. Doppler Effect
The apparent shift in the wavelength of light emitted by a light source moving toward or away from a viewer

15. Which is closest?
See how the lines shift farther to the red end of the spectrum as a star is farther away
The lines are from Ca, H, Na, and Mg

16. parallax
The apparent shift in a stars location when viewed from different locations in orbit
The closer the star is, the more it appears to move

17. Another view of parallax

18. Absolute vs. Apparent Magnitude
Absolute—how bright a star actually is
Apparent—how bright it appears from Earth

19. Stellar Evolution Section 2
Page 781

20. The Hertzsprung Russell diagram –HR Diagram
90% of stars are found on a diagonal line called the main sequence
Hotter on the left cooler on the right
Brighter at top dimmer at bottom

21. Another View of the HR Diagram

23. Birth of Stars Nebula—interstellar clouds of gas and dust
Drawn together by gravitational attraction called accretion
Begins to spin as it condenses
This huge ball of gas is called a protostar

24. Birth of a Star Part 1

25. Birth of a star
This ball continues to be drawn together by gravitational attraction
When temperatures inside reach about 10million Kelvins nuclear fusion begins
This produces a huge amount of radiant and thermal energy
Ignition of nuclear fuel marks the change from protostar to star

27. A Red Giant you know--Betelgeuse
Orion

28. Main sequence star
Most of a star’s life is spent as a main sequence star
Its size, temperature, and color are relatively stable
During this time it burns up its supply of hydrogen
What happens next depends on the star’s size

29. Red Giant
When the sun has burned all its hydrogen, the helium core will contract because of gravity
The rise in temperature will ignite the helium in the core and the core expands to become a red giant
Our sun will reach this stage in about 5 billion years

30. Famous Red Giants
Antares

31. The fate of stars differs according to their size

32. (Low mass stars)
Small stars will shrink and throw off the outer layers in rings becoming a planetary nebula
The shrunken core that remains is a white dwarf
There is no nuclear fusion, it is only glowing hot
If it is a binary star it may form a nova,
or,
When the core cools it becomes a black dwarf

33. Medium Mass stars—like the sun
Become RED GIANTS
Starts to burn helium-contracts because of gravity
This raises the temperature and the star expands
Our sun will reach this stage about Billion years from now

34. White Dwarf
What remains after the star swells and ejects the outer layers
What remains no longer burns fuel
It slowly cools
It is now a stellar remnant
It can change color as it cools

36. Black Dwarf
A cold, dark lump of matter that remains when a star has burned out and cooled off

37. Life cycle of a low mass star
Nebula
Protostar
Main sequence
Red Giant
Planetary nebula
White Dwarf
Black Dwarf

38. Binary star interaction

39. High Mass Stars have a different fate
They burn faster
And
Die differently

40. High mass stars
After the main sequence, stars with a mass much greater than the sun can burn and create larger and larger elements
When it gets to iron, it takes too much energy to create other elements so it collapses
This causes a supernova, this is when heavier elements are made

41. After a supernova a high mass star may become a
neutron star or a
black hole if it is VERY massive

42. Life Cycle of a High Mass Star
Protostar
Main sequence
Red giant or red supergiant
Supernova
Neutron star or black hole

43. Black Holes
Singularity—density is infinite
Event Horizon

44. So how does the life cycle of a high mass star differ from a small mass star?
High mass burn quicker and brighter and burn out faster
They also have a different fate

45. Groups of Stars Main sequence—diagonal line
Red Giants– bright and cool
Supergiants—brighter and cooler
White Dwarfs—dim and hot
Spectral Class
OBAFGKM
Oh Be A Fine Girl Kiss Me

46. Revisit the HR diagram Where are stars most of their lives?
Where are they when they begin to die?
What are they after they use up their fuel?

47. H-R diagram

48. How is the Life cycle of a high mass different????
Starts the same but burns faster and ends differently
Either
Supernova then
Neutron star
Black hole

49. Large Mass Stars have a different fate
They end in a supernova
Generate the elements of life
The inner part implodes to form a super dense neutron star

50. The Hertzsprung Russell diagram –HR Diagram
90% of stars are found on a diagonal line called the main sequence
Hotter on the left cooler on the right
Brighter at top dimmer at bottom

51. Lab—HR diagram Study lists and answer 21.1 &21.2 Temp on horizontal
Absolute magnitude on vertical
Note graph lines are not equal
Chart nearest stars with a (+) sign
Chart brightest stars with a
Show stars on both as circled +
Use an * to show the sun on the diagram

52. Word bank for paragraph
Black holes
Nebula
1 million
1 thousand
Light years
Parsec
White dwarf
Magnitude
Red giant
Black dwarf
Fusion
Fission
Temperature
Massive
Neutron star
Condense
Closer
Super nova

54. Pulsars emit low frequency radio transmissions
A few emit X-rays or visible light
The picture to the left is a gamma ray burst animation

55. Extremely Massive stars
Extremely massive stars that undergo gravitational collapse may become a
Black Hole

56. Event horizon—point of no return

58. Gravity Lensing— or how we know where they are
Image copyright © 1998 by John Chang.

59. NASA Life Cycle of Stars Review

60. Lab—HR diagram Study lists and answer 21.1 &21.2 Temp on horizontal
Absolute magnitude on vertical
Note graph lines are not equal
Chart nearest stars with a (+) sign
Chart brightest stars with a
Show stars on both as circled +
Use an * to show the sun on the diagram