So to summarize up to this point 1 the hydrogen in a

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So to summarize up to this point: 1> the hydrogen in a molecule cloud collapses to form a weakly glowing protostar. 2> A protostar collapses until it gets hot and dense enough to start nuclear fusion to begin turning its hydrogen into helium. 3> As soon as this nuclear fusion begins, the core stops collapsing and stabilizes--it is now a ______ ____________ star. Explanation: Main sequence. Some protostars don't have enough mass to ever reach the 10 million Celsius required for nuclear fusion to start. These little protostars end up becoming brown dwarfs instead--too big to be a planet and too small to be a star. To continue with the summary: 4> the main sequence star burns until it's used up all of the hydrogen in its core. 5> Once the hydrogen in the core has all been converted into a core of helium, the ___________ ____________ stops. As a result, the core destabilizes and resumes its collapse. : Nuclear fusion. The core of a star maintains its stability only while nuclear fusion is going on to counter the pressure of gravity. If there's no nuclear fusion, then the core is going to keep compressing until it gets hot and dense enough for nuclear fusion to occur.
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Now that the star is no longer burning hydrogen, its time as a main sequence star is done. Continuing with the sequence: 6> While the core is collapsing, the outer envelope is expanding rapidly. 7> Once the core collapses enough, the pressure is great enough to start up nuclear fusion to change the helium into carbon. Once this nuclear fusion starts, the core is stable again and now you have a red giant. 8> Of course, eventually, the red giant will burn through all of its helium, and what happens at that point is going to depend on the _______ of the star. Explanation: Mass. Generally, at this stage, stars are split into low-mass stars and high-mass stars. Low mass stars and high- mass stars are born the same way and go through the same steps up to the red giant stage (high-mass stars just go through the steps much quicker), but after the red giant stage, their paths diverge. If it's a low-mass star, the red giant's core will collapse into a tiny, hot and superdense core while it sheds the outer layers into a beautiful planetary nebula. At this point, the red giant has become a ________ _________. Explanation: White dwarf. A white dwarf is so dense that it's considered to be one of the densest forms of matter in the universe, surpassed only by neutron stars. Although it's hot and superdense, it's not very luminous because it's so small. The white dwarf is a dying star in its final stages--it has no source of energy so it may start out very hot when it's initially formed, but it will gradually radiate away all of its heat and cool down. Below is a pic of a white dwarf; most of what you see is the colorful nebula formed by what used to be the outer layers of the red giant:
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A white dwarf will eventually cool to a point where it's just a dead lump of carbon in space--a ________ __________.
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