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Download Main-sequence stars - Stellar Populations
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Stellar Populations Synthesis Most of this information you already figured out yourself during the inquiry A little extra information is included to connect some of those ideas together By Marc Rafelski Parts of this are © 2006 Pearson Education Inc, publishing as Addison-Wesley Where do stars come from? Gravity: Gas contracts to form clumps Gas: Enough gas that is hot enough - starts nuclear fusion Nuclear fusion: halts the gravitational collapse like a continuous nuclear explosion This is what our sun is doing now, and will do for next 5 billion years From CLS Inquiry: Thermal Radiation 1. Hotter objects emit more light per unit area at all wavelengths. 2. Hotter objects’ peak intensity is at shorter wavelengths. Hottest stars: 50,000 K Coolest stars: 3,000 K Sun’s surface: 5,800 K Most massive stars: 100 MSun Least massive stars: 0.08 MSun (MSun is the mass of the Sun) Organization via graphs can depict different properties of stars: Temperature Luminosity Color Radius Lifetime Mass Most stars fall somewhere on the main sequence of the graph Main-sequence stars are fusing hydrogen into helium in their cores like the Sun Luminous mainsequence stars are hot (blue) Less luminous ones are cooler (yellow or red) High-mass stars Low-mass stars Mass measurements of main-sequence stars show that the hot, blue stars are much more massive than the cool, red ones The mass of a normal, hydrogenburning star determines its properties such as luminosity and color. Mass and Lifetime Sun’s life expectancy: 10 billion years Until core hydrogen (10% of total) is used up Life expectancy of 10 MSun star: 10 times as much fuel, uses it 10,000 times as fast 10 million years ~ 10 billion years x 10 / 10,000 Life expectancy of 0.1 MSun star: 0.1 times as much fuel, uses it 0.01 times as fast 100 billion years ~ 10 billion years x 0.1 / 0.01 Examples of stars on main sequence High Mass: High Luminosity Short-Lived Large Radius Blue Low Mass: Low Luminosity Long-Lived Small Radius Red Off the Main Sequence • Stellar properties depend on both mass and age: those that have finished fusing H to He in their cores are no longer on the main sequence • All stars become larger and redder after exhausting their core hydrogen: giants and supergiants • Most stars end up small and white after fusion has ceased: white dwarfs Large radius Stars with lower T and higher L than main-sequence stars must have larger radii: giants and supergiants Stars with higher T and lower L than main-sequence stars must have smaller radii: white dwarfs Small radius Luminosity So really the graph would look something like this Temperature Massive blue stars die first, followed by white, yellow, orange, and red stars