1. Stars *Life Cycle of a Star *HR Diagrams

2. Basic Star Info. Vocab Words for “Basic Star Info”… Star
Spectral Class
Luminosity
Absolute Magnitude
Apparent Magnitude
Parallax
Binary Star

3. Basic Star Info.
A Star is a burning ball of gas and dust, producing its own energy.
Each star has different and unique characteristics
Different luminosities, sizes, colors, temperatures, brightness, etc.

4. Basic Star Info. Most stars behave as binary stars.
Binary Stars are two stars that orbit a center of mass and behave as one star.
Sirius A and Sirius B are the most common example of a binary star.

5. Binary Stars

6. Basic Star Info.
A star’s spectral class, temperature and color are directly related to each other.
Spectral Class is a one letter description that scientists use to tell us the color and temperature of a star.
Each star is either an “O” type, “B” type, “A” type, “F” type, “G” type, “K” type or “M” type star.
This is the order of spectral classes from hottest stars to coldest stars!
O type stars are blue
B type stars are blueish-white
A type stars are white
F type stars are yellowish-white
G type stars are yellow
K type stars are orange
M type stars are red

7. Basic Star Info.
A stars luminosity and absolute magnitude are directly related to each other.
Luminosity is the amount of energy coming out of a star.
Luminosity is measured relative to the sun.
The sun is given a luminosity of 1. Each star with more energy has luminosity greater than 1, while each star with less energy has luminosity less than 1.
Absolute Magnitude is the actual brightness of a star, from a short distance away.
The lower the number is, the brighter the star is!
The sun has absolute magnitude of 4.8, so it is not a very bright star!

8. Basic Star Info.
Absolute Magnitude and Apparent Magnitude are very different!
Absolute Magnitude was the brightness of a star from a close distance.
Apparent Magnitude is how a bright a star appears from earth!
This is dependent upon distance because if a star is close to the earth, it is going to appear brighter, even if that star might not be that bright!
The smaller the number is, the brighter the star!
The sun has an apparent magnitude of

9. Basic Star Info.
Parallax is the apparent shift of an object due to a change in the viewers position.
We have already demonstrated parallax using our fingers and in a lab!
Further stars have a smaller parallax than closer stars.
We can use a stars apparent vs. absolute magnitude to determine whether a star is close or far.
A close star will have an apparent magnitude that is brighter than its absolute magnitude.
A far star will have an apparent magnitude that is dimmer than its absolute magnitude.
REMEMBER…the smaller the number, the brighter it actually is!

10. Energy Production Vocab words for “Energy Production”… Hydrogen Fusion
Photon

11. Energy Production
Energy in a star is produced in the same manner as energy in the sun is produced because the sun is a star.
It is produced by constant Hydrogen Fusion reactions occurring in the core of a star.
This is when two hydrogen atoms bond together under an extreme amount of heat and pressure to produce helium and energy.

12. Energy Production The energy is given off in the form of a Photon.
A Photon is a particle of energy traveling through a star.
Each photon takes a totally random and different path through a star, just like they did through the sun!

13. Life Cycle of a Star Vocab Words for “Life Cycle of a Star”… Nebula
Protostar
Brown Dwarf
Main Sequence
Giant
Planetary Nebula
White Dwarf
Black Dwarf
Supergiant
Supernova
Neutron Star
Black Hole

14. Life Cycle of a Star An average star lives for about 10 billion years.
During this 10 billion years a star goes through distinct phases in its “life”.
A star will spend most of its life in the “Main Sequence” phase because that is where it is most stable.
All stars start off in the same way but how they end depends on it’s mass.

15. Life Cycle of a Star
The final product of star’s life is determined when the star is first formed.
The size or mass of a star determines which path it will take during its life cycle.
Stars are classified as…
Sun-like Stars – up to 1.5 times the mass of the sun
Huge Stars – from 1.5 to 3 times the mass of the sun
Massive Stars – more than 3 times the mass of the sun
A star will end it’s life as either a black dwarf, a neutron star or a black hole. The end of a star is determined by the mass of the star.

16. Life Cycle of a Star

17. Life Cycle of a Star Every star begins its life in the nebula.
A Nebula is a “stellar nursery” or a collapsing cloud of gas, dust, A LOT of hydrogen and a little bit of helium.
The Nebula develops a gravitational center called a protostar.
A protostar is the gravitational center of a nebula, which may form into a star. It is not hot enough and there is not enough pressure to create nuclear fusion at this point.
Some protostars never get hot enough or are not large enough for hydrogen fusion to begin. If this is the case, that protostar never becomes an actual star and instead becomes a brown dwarf.

20. Nebula

23. Nebula forming a Protostar
Life Cycle of a Star
The following animation will show you how a protostar forms out of nebula
Nebula forming a Protostar

24. Protostar forming a Brown Dwarf
The following animation will show you how a protostar may not ever reach “star” phase and become a brown dwarf.
Protostar forming a Brown Dwarf

25. Life Cycle of a Star
Relative size of a Brown Dwarf.

26. Life Cycle of a Star
If the protostar is hot enough and large enough for fusion to begin the star goes into the Main Sequence of its life.
At this stage, the star is going to remain here and fuse hydrogen into helium and energy until it begins to run out of hydrogen.
Main Sequence is the group of stars with a direct relationship between their temperature and luminosity.
Stars spend the majority of their lives in the main sequence because they are stable.
Our sun is currently a Main Sequence star!

27. Forming of a Main Sequence Star
Life Cycle of a Star
The following animation will show a star going from a protostar in a nebula into Main Sequence phase. The star will remain in Main sequence phase fusing hydrogen for most of its life.
Forming of a Main Sequence Star

28. Life Cycle of a Star
If there is enough gravity, when stars begin to run out of hydrogen to fuse they begin to fuse Helium into Carbon and other heavier elements (up to #26 on the Periodic Table).
Stars go down one of three paths, each determined by the size or mass of the star.

29. Life Cycle of a Star End of a Sun-Sized Star
(up to 1.5 times the mass of the sun).
As a sun-sized star runs out of hydrogen is left with only helium in its core.
The star will move into Giant phase and begin fusing the left over helium.
Giant is the group of stars that is cool, but bright.
Helium is a heavier element to fuse and in order to compensate for this, the outer layers of the star’s atmosphere begin expanding.
This causes the star to come less and less stable.

30. Life Cycle of a Star End of a Sun-Sized Star
(up to 1.5 times the mass of the sun)
Eventually the star will become so unstable and begin to run out of helium.
This point all of those outer, expanded layers will be shed in a stellar wind burst called a planetary nebula.

31. Life Cycle of a Star Sun-Sized Star
(up to 1.5 times the mass of the sun)
Once the outer layers have been shed, we are left with just the remnants of the core of the star.
This core is composed mainly of carbon at this point because it has run out of helium to fuse.
The star is now in White Dwarf phase. This is the group of stars that is hot, but not very bright.

32. Life Cycle of a Star Sun-Sized Star
(up to 1.5 times the mass of the sun)
The star is not large enough to fuse carbon so it stops producing its own energy and begins to cool down.
It cools down to a Black Dwarf, which is the cooled down remnants of a white dwarf.
This is the final stage of a Sun-Sized star’s life!

33. End of Sun-Sized Star's Life
Life Cycle of a Star
The following animation shows a sun-sized star going from the Main Sequence to the end of its life.
This star would eventually cool down and from white dwarf phase and become a black dwarf.
End of Sun-Sized Star's Life

34. A Red Giant You Know End of H fusion - red giant stage
Betelguese - see

35. Polaris: The North Star

36. Red Giant

37. Giants in Cephied Phase
After Helium exhausted, outer layers of star expelled
Planetary Nebulae
Planetary nebula - after He consumed, core collapses again. Outer atmosphere expelled, and then ionized (I.e. glows) by the hot remaining core
From Left to Right:
Ring Nebula - true colors, representing different elements. helium (blue), oxygen (green), and nitrogen (red).
NGC The central star of NGC 2440 is one of the hottest known, with surface temperature near 200,000 degrees Celsius. The complex structure of the surrounding nebula suggests to some astronomers that there have been periodic oppositely directed outflows from the central star, but in the case of NGC 2440 these outflows have been episodic, and in different directions during each episode. The nebula is also rich in clouds of dust, some of which form long, dark streaks pointing away from the central star. In addition to the bright nebula, which glows because of fluorescence due to ultraviolet radiation from the hot star, NGC 2440 is surrounded by a much larger cloud of cooler gas which is invisible in ordinary light but can be detected with infrared telescopes. NGC 2440 lies about 4,000 light-years from Earth in the direction of the constellation Puppis.
NGC colors represent temperatures. Filaments made of dust condense out from the cooling gas. These filaments are rich in carbon
[Images from Hubble Heritage:

38. White Dwarf Cluster

39. White Dwarfs

40. Life Cycle of a Star End of a Huge Star
(from 1.5 to 3 times the mass of the sun)
As a huge star runs out of hydrogen in its core, it begins to fuse the left over helium.
It now enters the Supergiant phase of its life.
A Supergiant is a star that is cool, but very bright.
Helium is a heavier element to fuse and in order to compensate for this, the outer layers of the star’s atmosphere begin expanding. This star is larger, so it expands more than the sun-sized star.
This causes the star to become less and less stable.

41. Supergiant

43. Life Cycle of a Star End of a Huge Star
(from 1.5 to 3 times the mass of the sun)
Eventually the star will begin to run out of helium and become so unstable it will explode as a Supernova.
A Supernova is a large stellar explosion that causes this area of space to temporarily be brighter than its surroundings.

44. Life Cycle of a Star End of a Huge Star
(from 1.5 to 3 times the mass of the sun)
Once the star explodes, we are left with a whirling ball of neutrons.
A Neutron Star is a whirling ball of neutrons left over from a supernova explosion.
This is the final stage of Huge Star’s life!

45. When a star uses up its last fuel, there is no radiation pressure to push outwards against gravity. The star begins to collapse, becoming a neutron star or a black hole – depending on its mass.

47. Supernova !
SN1987A before and after image from Anglo-Australian Observatory. It’s in the LMC, 160,000 light-years distant.
When fusion process no longer produces energy to support the star, the core of the star collapses. With nothing to stop it, the atoms are crushed together, and the infalling material bounces off the superdense core, causing the explosion.
A supernova produces 1040 erg/s (a million times more than the sun). The supernova disperses the elements it has created. In addition, the energy of the explosion creates elements heavier than iron.

48. Remnants
of a
Supernova

50. Neutron Star (yes, the tiny dot)

51. Neutron Star After Supernova (behind nebula)

52. Thermal Image of Neutron Star

53. Size of Neutron and White Dwarf Stars if placed in Grand Canyon

54. Supernova Remnants Optical X-ray
Cas A is 300 years old. The remnant is about 10 light-years in diameter, and 10,000 light-years away.
X-ray: outer shock wave is from the initial supernova explosion ripping through the interstellar medium at 10 million miles per hour. Temperatures may reach 50 million degrees. The inner shock is the ejecta from the SN heating up the circumstellar shell, heating it to 10 million degrees
The optical image of Cas A shows matter with a temperature of about ten thousand degrees. Some of these wisps contain high concentrations of heavy elements and are thought to be dense clumps of ejected stellar material.
Cas A x-ray and optical images from

55. Pulsar

56. Life Cycle of a Star Massive Star
(more than 3 times the mass of the sun)
As a massive star runs out of hydrogen in its core, it begins to fuse the left over helium.
It now enters the Supergiant phase of its life.
A Supergiant is a star that is cool, but very bright.
Helium is a heavier element to fuse and in order to compensate for this, the outer layers of the star’s atmosphere begin expanding. This star is larger, so it expands more than the sun-sized star.
This causes the star to become less and less stable.

57. Life Cycle of a Star End of a Massive Star
(more than 3 times the mass of the sun)
Eventually the star will begin to run out of helium and become so unstable it will explode as a Supernova.
A Supernova is a large stellar explosion that causes this area of space to temporarily be brighter than its surroundings.

58. Life Cycle of a Star End of a Massive Star
(more than 3 times the mass of the sun)
Once the star explodes, a massive star is large enough that the gravity is so powerful everything is sucked into this area of space.
A Black Hole is an area of space where gravity is so intense, nothing, not even light, can escape.
This is the final stage of a Massive Star’s Life!

59. Black hole
Diagram

61. Q u a s r

62. Quasar: Visible Light

64. End of Massive Star's Life
Life Cycle of a Star
The following animation will show how a massive stars goes from main sequence and ends its life.
This animation should say “Supergiant” in place of “Giant”
End of Massive Star's Life

65. Life Cycle of a Star

66. HR Diagram Vocab Words for “HR Diagram”… HR Diagram Supergiant Giant
Main Sequence
White Dwarf

67. HR Diagram
Ejnar Hertzsprung and Henry Russell developed the Hertzsprung-Russell diagram (HR Diagram)
The HR Diagram is a diagram of the stars charted by their luminosity vs. color.
Hertzsprung and Russell originally did this with the thousands of stars visible to the naked eye.
Since techonology has evolved we have been able to chart more stars and link temperature, spectral class and absolute magnitude to the HR Diagram.

68. HR Diagram
Hertzsprung and Russell grouped stars on the HR Diagram that are similar to each other.
They are grouped in 5 categories
Giants
Supergiants
Main Sequence
White Dwarf
Subgiant
The categories also tell us something about where a star is in its life cycle, or the evolution of the star.

69. HR Diagram

74. H-R diagram

75. HR Diagram
You can clearly see the giants, supergiants, main sequence stars and white dwarfs on the diagram.
We defined those words using the group’s brightness and temperature, and you can see how that correlates to where they are located on the diagram.
Subgiant is also on the diagram.
This group of stars is slightly brighter than Main Sequence stars, but not as bright as Giant stars.

76. HR Diagram
The HR Diagram is sometimes called an evolutionary diagram of the stars because it has the different phases of the star’s lives on it.
It does not contain ALL of the stages of ALL of the different types of star’s lives.

77. HR Diagram
This is the evolution of a sun-sized star shown on the HR Diagram