Week 8

Our galaxy, the Milky Way, has approximately 200,000,000 stars and has a supermassive black hole in the center that has the mass of 4 million Suns. It is the hub around which galaxies form and take shape. 

• Black holes smaller than about 4 solar masses evaporate by emitting Hawking Radiation.

• Nebulas are any large cloud of gas and dust from which stars can be born. Supernova explosions can create remnants called nebulas.

• Stars, planets, and galaxies form much the same way. Gravity pulls in matter. The spiraling is due to every particle having an initial velocity and the totaled average of force and motion (see video)

• A star is formed when Hydrogen fusion begins. The energy of fusion sweeps out lighter particles and gases from the inner solar system (solar wind). This is why the inner planets are rocky and the outer planets are gassy.

Gravity pulls matter towards the core and the energy of fusion creates pressure that pushes against gravity. Gravity and pressure are equal during the main sequence and then fluctuate during the giant phase. 

In the giant phase of a star's life Iron fusion does not produce energy and the star begins to contract. Unburned fuels begin to ignite with increased temperature and pressure. The star expands to many times its original size until it again fuses as much fuel as it can at that temperature. In the final moments of a star it falls quickly toward the core creating temperatures of 1 billion degrees. The falling material simultaneously bounces off of the core and fuses any remaining elements in a violent supernova. 

• Star LIfe Cycles - stars are formed in nebulas which are mostly hydrogen gas (the most abundant element in the Universe). Gravity pulls the gas together. The friction and pressure at the center cause nuclear fusion of Hydrogen. Hydrogen to Helium fusion marks the main sequence of a star's life cycle. The giant phase begins when Helium fusion starts.

Massive stars live short lives and end as a neutron star or black hole. Less massive stars have longer lives and end as a white dwarf. 

Star Life Cycles 

Stars Study Guide

1. Know what elements are being produced in stars and when.

2. What causes stars to go supernova?

3. What did the first stars in the Universe most likely look like?

4. What causes stars to contain layers of elements inside?

5. Know the relationship between molecular motion and temperature.

6. Know the relative temperature of different color stars.

7. Predict what will happen to stars of different masses during their life cycle.

8. Know the structure of, solar systems, galaxies, and stars.

9. Know what stars are made of, where they form, and what they produce when they die.