STARS

1. STARS Init 2/20/2008 by Daniel R. Barnes Note: As always, this presentation contains images taken without permission from the world wide web. This presentation should not, therefore, be copied or distributed. In fact, its very existence may be illegal.

2. Our Sun Our sun is a typical star and is powered by nuclear reactions, primarily the fusion of hydrogen to form helium.

3. Our Sun The sun is about 109 times the diameter of the earth. The sun has about 300,000 times the mass of the earth. The sun coughs out tongues of plasma that are much larger than the earth itself. Pictured at left is a coronal mass ejection. The picture of the sun is real, but the image of the earth here is superimposed. The earth has never been that close to the sun in real life.

4. Our sun is a typical star and is powered by nuclear reactions, primarily the fusion of hydrogen to form helium. Our Sun

5. Nuclear fusion is also used to boost the power of fission explosions in “hydrogen bombs”. Our Sun

6. Nuclear fusion is also used to boost the power of fission explosions in “hydrogen bombs”. Apparently, there are a lot of misconceptions about the role of hydrogen fusion in “hydrogen” bombs. Apparently, “hydrogen bombs” derive most of their power from uranium fission, not hydrogen fusion. According to Wikipedia, scientists working on “hydrogen” bombs never called them “hydrogen bombs”. Hydrogen fusion’s role in a thermonuclear device is to increase the yield of the fissioning materials (uranium, plutonium). Our Sun

7. Our Sun The sun gives out a continuous “solar wind” made of electrically charged particles that may fly at speeds of millions of miles per hour. The solar wind changes the shape of the earth’s magnetic field lines.

8. Red Giant *As the name implies, red giants are HUGE. They’re not all the same size as each other, but they are all big. *The little white dot is how big our sun is right now, compared to the red giant Antares, the biggest one shown in the picture at left.

9. Red Giant *Our sun, and other stars of of low to medium mass, swell up to become red giants when they run out of hydrogen in their cores. The process is somewhat complicated. Please take a deep breath.

10. Red Giant Helium in the core begins fusing to become carbon and oxygen Hydrogen in the star’s core finishes turning into helium Core heats up Radiated heat expands outer layers of star to giant size Hydrogen fusion in the core stops Core pressure increases Core cools Gravity in the core strengthens Core shrinks

11. Red Giant *A red giant has no hydrogen left in its core, but the helium there fuses to form carbon and oxygen. The hydrogen outside the core fuses to form helium, which then sinks down to join the core and burn with the rest of the helium there.

12. White Dwarf * Is the leftover remains of a red giant that ran out of nuclear fuel * Has a mass comparable to the sun, but a size comparable to the earth, and, therefore . . . * Has a very very high density – Denisties vary, but a grape sized-piece of white dwarf matter might have as much mass as a truck. *No nuclear reactions – Therefore, what heat they have is left over from the days when the star did carry out nuclear reactions *Low luminosity, yet a very high temperature *Small size means not much surface area, resulting in slow cooling and low luminosity despite high temperature *Eventually, they turn into black dwarves, but this process is so slow that maybe the universe is too young for any to have gotten to that stage yet.

13. White Dwarf This graphic shows the relative sizes of IK Pegasi A (left), IK Pegasi B (lower center) and the Sun.

14. White Dwarf * Is the leftover remains of a red giant that ran out of nuclear fuel * Has a mass comparable to the sun, but a size comparable to the earth, and, therefore . . . * Has a very very high density – Denisties vary, but a grape sized-piece of white dwarf matter might have as much mass as a truck. *No nuclear reactions – Therefore, what heat they have is left over from the days when the star did carry out nuclear reactions *Low luminosity, yet a very high temperature *Small size means not much surface area, resulting in slow cooling and low luminosity despite high temperature *Eventually, they turn into black dwarves, but this process is so slow that maybe the universe is too young for any to have gotten to that stage yet.