25 October 2017

1. Lifecycles of stars
1. The life of any star is a constant battle against the force of gravity, which tries to pull the star in on itself. Against this unremitting force, stars deploy a variety of countervailing strategies. Some of these strategies allow stars to stave off collapse temporarily and some strategies allow them to stave it off forever. But nothing can protect the largest stars from eventual collapse into a black hole, the ultimate victory of gravity over matter.
2. The birth of stars - All stars begin as diffuse clouds of dust in deep space. Matter is gathered by more thickly somewhere in the cloud and the force of gravity exerted by the clump pulls in neighboring materials. The clump increases in mass and gravitational attraction and more material is pulled in. The cloud starts to collapse around the original concentration of matter.
3. How long will a star live? - This depends on how much hydrogen it has and how fast it is consumed. The larger the star, the shorter its lifetime. The reason for this is because the bigger the star, the greater is the gravitational force trying to make it collapse and the more hydrogen has to be burned to keep the star stable.
4. How does a star die? - Every star must eventually burn up all of its hydrogen, filling the core with helium ash. When the hydrogen is gone, the outward force generated by the nuclear reactions disappears and gravity resumes its inevitable inward march. The inner parts contract and warm up, which produces more energy and the outer regions of the star are pushed farther outward; this creates a red giant. The core continues to contract and soon it is so hot that the helium (ash of hydrogen) starts to fuse. Three nuclei come together to form nuclei carbon and once the helium is consumed the collapse starts again in earnest. The bloated layers are blown off, while the inner region continues to contract. There is no more fuel to burn, so something else has to stop the collapse; that is the electrons. Though, electrons cannot overlap, so when the core has reached the point where they cannot be further collapsed down, the electrons will be stabilized forever with gravity pushing in and the electrons pushing out. A star help up by pressure from electrons is called a white dwarf. It generates no internal energy, has used up all of it’s fuel, and continues to glow for a long time as it cools off. For massive stars, the hydrogen burns quickly, so after a short collapse, it burns the helium into carbon, when the helium exhausts the collapse starts again, the center temperature gets so high even the carbon begins to fuse. This pattern continues, the ashes of each fire serving as fuel for the next. Finally, iron is produced, which is the ultimate nuclear ash. It is impossible to get energy from the iron so the core clogs up. During this collapse the force exerted by the electrons is not enough to overcome gravity. Electrons are forced inside the protons in the core, neutrons are produced, the core shrinks quickly to a sphere of neutrons (a neutron star - about ten miles across).
5. The force of gravity and the pressure of neutrons against each other balance, and providing the force of gravity is not too strong, the core stabilizes.
2. Origin of the Universe (p. 185-193)
1. Over 13 billion years ago was the Big Bang (below). With this at first the universe was too hot for anything to evolve, but over time it cooled and the the sun formed. The spinning from this sent dust, debris, rocky particles, and gases out with joined together and hardened resulting in the planets.
3. Big Bang (p. 185)
1. All of the matter in the universe was concentrated into a tiny mass that exploded to form the universe. We can see, hear, and map the evidence of the Big Bang and through light/sound we can see that our universe is outward expanding.
4. Galaxies (p. 176-181)
1. These are huge collections of gas, dust, and billions of stars and their solar systems of a variety of shapes and sizes, which are held together by gravity.
5. Asteroid Belt
1. This is the region between the inner and outer planets where thousands of asteroids are orbiting the sun (an asteroid is a class of small solar system bodies)
6. Black Holes (p.212, 213)
1. When a large enough mass is concentrated is a small enough volume, it distorts the space around it so severely that a part of space wraps itself up and leaves the rest of normal space behind. It is an object that is so massive and so dense that nothing, not even light, can muster enough energy to escape from its surface.