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TAMU ASTR 101 - end of HR-diagram and beginning of Chapter 13
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ASTR 101 1st Edition Lecture 24Outline of Last Lecture I. HR diagram, II. stars outside of main sequence, III. star clustersOutline of Current Lecture I. Clicker questions,II. Star birth,Current LectureI. Clicker questions:a. What is the first step in the formation of a protostar? --gravity causes a cloud of cold gas anddust to begin to contract. It will be difficult for the gas to contract if the gas is warm, needs to be cold.b. Why do we think that clouds of gas and dust form stars? --we see young star clusters with gas and dust around them, we can see it through telescopesc. What would happen to a contracting cloud fragment if it were not able to radiate away its thermal energy? --its internal pressure would increase (slowing down the collapsing process). Radiating away its thermal energy would accelerate the collapsing process. II. 13.1 Star birtha. How do stars form? In dark clouds of dusty gas in interstellar space, this diffused gas between the stars in interstellar medium. i. To form a star, we need to balance gravity with pressure. Gravity has to overcome the force of pressure in the cloud. When a gas cloud starts to contract, it becomes denser, heats up, and gravity becomes stronger (conservation of energy). Contraction can continue only if thermal energy is radiated away. Collapse and collapse until it triggers nuclear fusion. ii. As stars begin to form, dust grains that absorb visible light heat up and emit infrared light. Infrared appear as emissions and appear brighter. The longer the infrared, the colder the cloud and the more efficient it is to form stars. Infrared is also brightest where the most stars are forming (ex- the Orion nebula/constellation is very easy to see in our night sky because this region is producing lots of stars. Orion is a dense cloud producing many new stars)iii. Conservation of angular momentum causes the cloud to spin faster and faster as gravity forces the cloud to become smaller. iv. Collision between particles is a reason the gas flattens out into a disc as it rotatesb. How massive are new stars? i. A star forming molecular cloud is typically about a few hundred particles per cubic centimeterThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.ii. It needs at least a few hundred solar masses of material of this cold gas for gravity to overcome pressure. In the end, we want a configuration that is hot and dense enough to form a star. This pull between the force of gravity and the star's pressure works until that is reached. iii. It’s actually quite unnatural to form a single star without any companions (each lump of the cloud in which gravity can overcome pressure can go on to become a star). As a cloud fragments, it generally makes many stars, or a cluster of


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TAMU ASTR 101 - end of HR-diagram and beginning of Chapter 13

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