Recall what you know about the Big Bang.

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1 What is this?

2 Recall what you know about the Big Bang.

3 Most of the normal matter in the universe is made of what elements? Where do we find most of this normal matter?

4 Interstellar medium (ISM) The universe is obviously not empty. Even the SPACE between the stars and galaxies is not empty The interstellar medium (ISM) consists of gas and dust. Gas is mainly hydrogen, a little bit of helium, but also contains small amounts of other elements and molecules. Average density is typically around 1 atom per cubic centimeter.

5 The interstellar medium is not uniform, but varies in density and temperature. It tends to form clumps The clumps in the interstellar medium are clouds or nebulae (one nebula, two nebulae) composed of the previously mentioned elements.

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13 Imagine.. You are observing one of these regions of space. A cloud of gas and dust is beginning to collapse inward.

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15 Why is it collapsing? What causes the collapse?

16 Team up. With a group, (no more than four people), predict what will happen (or what could happen) during the next several billion years in regards to this collapsing cloud. (write this out as a chronology, a timeline, or a concept map.)

17 What is happening to the atoms and molecules as this cloud condenses?

18 What physical interactions or forces cause the behaviors described in the previous question?

19 What do you expect will happen to the temperature? As a result, what happens to the interactions between atoms and molecules?

20 What is happening? What does it look like now?

21 Do you think there is a limit to the temperature and pressure in this ball of gas and dust? What are the atoms and molecules doing when they reach this limit?

22 Now, what does it look like?

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24 Stars form Conclude.

25 TYPES OF NEBULAE Emission nebulae Absorption Nebulae Planetary Nebulae Reflection nebulae Supernova Remnant Dark nebulae Molecular Clouds

26 Emission nebulae Emission nebulae emit their own light because luminous ultraviolet stars (spectral type O,B) ionize gas in the nebula. The gas then emits light as the electrons return to lower energy levels. In this image Red = Hydrogen, Green = Oxygen, Blue = Sulfur.

27 Reflection nebulae do not emit their own light. Dust scatters and reflects light from nearby stars. Reflection nebulae The Pleiades

28 Dark nebula Dark nebula are so opaque that the dust grains block any starlight from the far side from getting through. Horsehead Nebula

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31 Molecular clouds Dark nebulae are usually molecular clouds Molecular clouds are relatively dense and are very cold, often only 10 K ( C). Giant molecular clouds can contain as much as 10 4 solar masses (10,000 times more massive than our sun) of gas and be 10 light years across. Molecular clouds are the primary sites for star formation.

32 Eagle Nebula a.k.a. The Pillars of Creation Why?

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35 Eagle nebula in infrared

36 Star birth can begin in giant molecular clouds

37 Protostars form in cold, dark nebulae Visible (left) and infrared (right) views of the Orion nebula show new stars. These new stars can only been seen in infrared because the protostar s cocoon nebula absorbs most of the visible light.

38 Zoomed in on the protostars of the Orion Nebula, and their cocoon

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41 Summarize the steps that lead up to the formation of a star.

42 So HOW do Protostars form by the collapse of molecular clouds? Clouds must form dense and cold clumps or cores to collapse What triggers their collapse is somewhat a mystery. Shockwaves from a nearby supernova? Compression waves in a spiral galaxy? Once it is triggered, gravity of the core causes it to continue to collapse and also pull in more gas

43 As the gas/dust falls in, it picks up speed and energy. It is slowed by friction and the energy is converted to heat. As long as the protostar is transparent, the heat can be radiated away. When the protostar becomes so dense it is opaque, then the heat stars to build up, the pressure increases, and the rapid collapse slows. Cold and dark Why is being opaque important?

44 Gas in the cloud keeps falling onto the protostar. The collapsing gas tends to start rotating around the protostar as it falls in forming a disk and a jet. Eventually, the protostar develops a wind, like the solar wind but much stronger. This outflowing wind stops the infalling matter. The protostar keeps contracting under it own gravity. The protostar is powered by gravity via contraction - not by fusion,yet. The protostar becomes a star when it has contracted so much that it is dense and hot enough to begin nuclear fusion.

45 If there is not enough mass/material Nuclear Fusion will not occur A Brown Dwarf Star will form Technically not a star because no nuclear fusion Kind of like a large Jupiter-type planet

46 Brown Dwarfs

47 When nuclear fusion takes place in the protostar, the star enters the Main Sequence. It is now considered a real star.

48 Describe the hydrogen fusion process (also known as the proton-proton chain)

49 Beryllium-6 forms here, but quickly annihilates

50 In the main sequence, fusion takes place at a steady rate. The outward force of fusion is balanced by the inward force of gravity. HYDROSTATIC EQUILIBRIUM Therefore, a star maintains a specific size as a direct result of the rate of fusion and the mass (which causes the gravity).

51 Star (like our sun) Structure Core Where nuclear fusion occurs Envelope Supplies gravitational pressure to keep core contained

52 Main Sequence Evolution The star begins with a finite amount of hydrogen Fusion changes H to He Core gradually shrinks and Star gets hotter and more luminous. Why does the core shrink?

53 Gradual change in size of Sun because of shrinking core Now 40% brighter, 6% larger, 5% hotter

54 Main Sequence Evolution (in star size of our sun) Fusion changes H to He Core eventually depletes its supply of H Eventually there is not enough H to maintain energy generation in the core Core starts to collapse

55 Predict what happens next.

56 Red Giant Phase Helium core No nuclear fusion (not yet) Gravitational contraction produces energy Hydrogen layer Nuclear fusion still occurring Envelope Expands because of increased energy production Cools because of increased surface area Density decreases (spread too thin)

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58 Helium Flash Helium core Eventually the core gets hot enough to fuse Helium into Carbon. This causes the temperature to increase rapidly to 100 million K and there s a sudden flash when a large part of the Helium gets burned all at once. H layer Envelope

59 Red Giant after Helium Ignition Helium burning core Fusing Helium into C, O Helium rich core Hydrogen burning shell Fusing H into He Envelope Expands because of increased energy production

60 Two He-4 fuse to form Be-8 (unstable and breaks down quickly). If another He-4 encounters Be-8 before it breaks down, C-12 forms. If there is enough heat in the core of the star, O-16 may eventually form. This process continues (all the way to Iron) to create elements in higher mass (hotter) stars.

61 Sun looses mass via winds Creates a planetary nebula Leaves behind core of carbon and oxygen surrounded by thin shell of hydrogen Hydrogen continues to burn

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63 Planetary nebula

64 Planetary nebula

65 Planetary nebula

66 Hourglass nebula

67 White dwarf in the center Star burns up rest of hydrogen Nothing remains but core of Oxygen and Carbon White dwarf cools but does not contract Electrons balance gravity No energy from fusion, no energy from gravitational contraction The only energy is either residual, from compact electrons, or a little of both. White dwarf slowly fades away If enough time has passed, a dark white dwarf star may be called a black dwarf.

68 If a white dwarf is in a binary star system (two stars), hydrogen from the larger companion star will accumulate on the surface, causing an explosive reaction. A nova is a cataclysmic nuclear explosion caused by the accretion of hydrogen onto the surface of a white dwarf star. It is an event that may happen repeatedly.

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70 NOVA

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72 NOVA

73 Type 1a Supernova

74 Type 1a Supernova Similar situation to a NOVA, but with a very precise and repeatable luminosity. strips away all envelope gasses of the companion star. Occurs when gas buildup reaches 1.4 solar masses. Used as what we call a Standard Candle to calculate distances in space.

75 What about stars larger than the sun? They are considered high-mass stars. Blue Giants White Giants Green Giants Purple giants (ultraviolet) Shorter lifespan the larger they are. When they age, they become supergiants rather than red giants.

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81 oh boy When these stars die

82 b

83 Types 1b and 1c supernovae are categories of stellar explosions that are caused by the core collapse of massive stars.

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87 Types 1b and 1c supernovae The core collapses. Gravitational pressure causes fusion to occur at an extremely rapid pace. Fuel is used up quickly and an explosion occurs.

88 Type 2 supernovae occur when the outward force of fusion no longer balances the inward force of gravity. Solar mass of 9 or greater.

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90 The core collapses at speeds of 100,000+ km/sec

91 Supernova remnant The Crab Nebula

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96 Supernova Remnants can become Molecular clouds These Molecular clouds are going to already contain all of the elements on the Periodic Table, which explains the existence of terrestrial planets like Earth. Our Sun is what we call a second (maybe third) generation star. Molecular clouds are relatively dense and are very cold, often only 10 K ( C). Giant molecular clouds can contain as much as 10 4 solar masses (10,000 times more massive than our sun) of gas and be 10 light years across.

97 In the center of the remnant, the leftover core of the supergiant star may become a neutron star. -A neutron star is a type of remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event -composed almost entirely of neutrons -has a mass between 1.35 and about 3 solar masses (3 times the mass of the sun), with a corresponding radius of about 12 km (about the distance across New York City) -One teaspoon of matter from a neutron star would weigh as much as planet Earth!

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99 First image of a neutron star in visible light

100 Pulsar (a type of neutron star)

101 Pulsars are highly magnetized, rotating neutron stars that emit a beam of electromagnetic radiation. The word pulsar is a contraction of "pulsating star"

102 The first pulsar was observed in July 1967 they dubbed their discovery LGM-1, for "little green men" (a name for intelligent beings of extraterrestrial origin). The hypothesis that pulsars were beacons from extraterrestrial civilizations was never serious but some discussed the far-reaching implications if it turned out to be true.

103 Four distinct classes of pulsars are currently known to astronomers, according to the source of energy that powers the radiation: Rotation-powered pulsars, where the loss of rotational energy of the star powers the radiation Accretion-powered pulsars where the gravitational potential energy of accreted matter is the energy source Magnetars, an extremely strong magnetic field powers the radiation. Gamma Ray Pulsars: A new fourth class of pulsars that emit only gamma rays

104 If the solar mass is high enough (20 or greater), it will collapse further into a black hole.

105 Evidence for existence of black holes Gravitational Lensing (seen left) Predicted by theory of relativity Effects on nearby stars (below)

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107 Your task 1. If you have been given a picture, find the person who has the matching description. If you have a description, find the person who has the matching picture. 2. Once you have them matched, as a class, arrange your pairs (pictures with descriptions) on the chalkboard in chronological order (NOT NUMERICAL ORDER) based on stellar life cycle. 3. Use a piece of chalk to write one thing that is occurring in that star in its respective stage.

108 What if? the protostar doesn t have enough mass? the white dwarf star at the end is too close to it s companion? Then what? Then What? the protostar has a very high mass? Then what? What causes the star to expand to this size? What causes the eventual collapse? Then what happens? the mass of the collapsing star is solar mass 20 or greater?

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