Chapter 16 summary.docx

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Astronomy & Astrophysics
Michael Reid

Chapter 16 summary: 16.1 STELLAR NURSERIES  Where do stars form:  Stars form in cold, relatively dense molecular clouds  Solid grains of interstellar dust prevent visible light from passing through these clouds, but we can use infrared observations to see what’s going on inside them  Why do stars form:  A star can form in molecular cloud only when gravity is strong enough to overpower the outward push of thermal pressure  Stars tend to form in clusters because gravity can more easily overcome pressure in more massive molecular clouds  A large cloud fragments into many smaller clumps of gas as it contracts, because the advantage of gravity over pressure increases as a clump of gas shrinks in size 16.2 STAGES OF STAR BIRTH  What slows the contraction of a star-forming cloud:  A contracting cloud begins its transformation into a star when its core stars trapping the thermal energy released by gravitational contraction  As pressure begins to push back harder, the contraction slows down and the central part of the cloud becomes a protostar  Meanwhile, matter from the surrounding cloud rains down upon the protostar, increasing its mass  What is the role of rotation in star birth:  Conservation of angular momentum ensures that a young protostar spins rapidly, and much of the material falling inward toward a protostar ends up in a spinning protostellar disk  Friction in the disk can transfer angular momentum away from the inner parts of the disk, allowing gas to accrete more easily into the protostar  Some protostars drive powerful jets outward along the disk’s rotation a
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