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Midterm 3 Notes

Midterm 3 Notes - 19.1 Star-Forming Regions Star formation...

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19.1 Star-Forming Regions Star formation is ongoing, star-forming regions are seen in our galaxy as well as others Space between stars & planets nearly perfect vacuum – but filled with extremely low density matter o As much mass in space as in stars o Where new stars are born o Where old stars have exploded their material o o Certain areas in sky more dense with IM than others Star formation happens when part of a dust cloud begins to contract under its own gravitational force; as it collapses, the center becomes hotter and hotter until nuclear fusion begins in the core When looking at just a few atoms, the gravitational force is nowhere near strong enough to overcome the random thermal motion o If gravity dominates, cloud starts to contrast 19.2 The Formation of Stars like the Sun Stars go through a number of stages in the process of forming from an interstellar cloud Stage 1: (surface [Ts] = center [Tc] = 10K,.~ 2 million years) Interstellar cloud: starts to contract, probably triggered by shock or pressure wave from nearby star. As it contracts, the cloud fragments into smaller pieces Stage 2: (Ts 10 K, Tc 100 K. ~ 30,000 years) Collapsing Cloud Fragment: individual cloud fragments begin to collapse. Once the density is high enough, there is no more fragmentation Stage 3: (Ts 100 K, Tc 10,000 K. ~ 100,000 years)
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Fragmentation Stops: the interior of the fragment has begun heating and is about 10,000 K Stage 4: (Ts 3000 K, Tc 1 million K. ~ 1 million years) Protostar: the core of the cloud is now a protostar and makes its first appearance of the H- R diagram: o Still not hot enough to convert H to He o Luminosity ~ 1000 Lsun Planetary formation has begun, but the protostar is still not in equilibrium – all heating comes from the gravitational collapse The last stages can be followed on the H-R diagram: protostar’s luminosity decreases as its temperature rises because it becomes more compact Stage 5: (Ts 4000 K, Tc 5 million K. ~ 10 million years) Protostellar Evolution: o R ~ 10 Rsun, L ~ 10 Lsun o Still not converting H to He o Exhibits violent surface activity – T Tauri phase Stage 6: (Ts 4500 K, Tc 10 million K. ~ 30 million years) Star: the core reaches 10 million K, and nuclear fusion begins. The protostar has become a star. The star continues to contract and increase in temperature until it is in equilibrium Stage 7: (Ts 6000 K, Tc 15 million K. ~ 10 billion years) Main-sequence star: the star has reached the Main Sequence and will remain there as long as it has hydrogen to fuse 19.3 Stars of Other Masses This H-R diagram shows the evolution of stars somewhat more and somewhat less massive than the Sun. The shape of the paths is similar, but they wind up in different
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Midterm 3 Notes - 19.1 Star-Forming Regions Star formation...

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