1. Stars 1.Measuring/Distances to stars 2.Stars aren’t always “there”. They live, they die, we will learn that cycle. 3.Properties of stars: color, brightness, temperatures, fuels, formations... 4.Hertzsprung-Russell Diagram

2. Measuring and Distances Primary distance = light year –9.5 X 10 12 km (9.5 trillion km) –A.k.a. the distance light travels in one year. Fun fact: Position of close stars is determined by parallax –Geometry! Want to be an astronomer? Study MATH! Fun fact: Mass determined by using binary stars.

3. Properties of Stars Temperature and Color are related –Not all stars are created equal! –Very hot stars appear blue (30,000K +). –Cool stars appear red (3,000 K  ). –(This is backwards from the bathroom!) –Medium stars (like the sun) appear yellow (5,000-6,000K).

4. Brightness or Apparent Magnitude How bright a star appears to us is dependant upon three factors: 1.Size of the star 2.Temperature of the star 3.Distance from Earth

5. Absolute Magnitude Absolute magnitude is how bright a star REALLY IS –A star may appear much dimmer than another simply because of its distance. –Scientists “standardize” the stars to figure out the absolute magnitude –(More “negative” # = brighter) –(More “positive” # = dimmer)

6. Hertzsprung-Russell Diagram Diagram that shows the relationship between temperature of stars (x-axis) and the absolute magnitude (y-axis) Hotter (blue) and brighter are upper left. Colder (red) and dimmer are lower right. 90% of stars are main sequence stars. –Prime of their life, livin’ the dream! Nuclear fusion makes them “shine” –Not on main sequence means it is dying! Ex. Red giants/supergiants, white dwarfs

7. H-R Diagram

8. Star life cycle First comes love... Nebula-clouds of dust and gases Very spread out, may contain lots of matter/mass! Remember, Mass = Gravity If there is enough gravity, then matter will contract and the star story begins.

9. Nebula

10. Then comes marriage... As the nebula contracts, gravitational energy is converted into heat energy. After enough contraction and heat (million years), a Protostar is made. –Protostar is not a true star, YET... –Can’t be a star, because the only energy it is giving off is heat due to gravity. (Not making its own energy.) YIPEE!

11. Then comes the baby in the baby carriage! When there is enough heat generated (10 million K) the real star is “born”. Pressure (gravity) within this environment causes nuclear fusion to take place. –Simplified: Hydrogen atoms (1 proton each) crash together to make Helium (2 protons each) and releasing enormous amounts of energy.

12. Main sequence Majority of the star’s “life” is here. Balance between gravity pulling inward and outward pressure from heat/gas of nuclear reaction. Hotter/brighter the star = shorter life Smaller/cooler stars = longer life Yellow stars = average size, temp, and length of life If our sun was a storybook character, we got Goldilocks! Everything is “just right”.

13. Star “death” A.K.A. Falling off the main sequence. When the balance between gravity and outward pressure cannot be maintained. Easy fuel is gone! Star has run out of Hydrogen, going through its Helium (He + He +He = C), making heavier/more massive elements C + C +...= Fe, etc. Gravity has the upper hand. The core of the star is contracting, outer layer is expanding.

14. Burnout path(a.k.a. choose your own adventure!) Path the star takes is determined by mass –Low mass stars (less than 1/2 mass of sun) go from Main Sequence directly to White dwarf. –Medium mass stars (sun sized) become Red Giants. –Massive stars (3X mass of sun) become Red Supergiants.

15. Red Giants/Supergiants Fusion in the core is Helium to Carbon. Core is contracting (due to mass & gravity). Outer layers expanding and cooling. –Explains the red color! Still a fight between gravity inward and pressure outward. Red giants = give off outer layer “gently” to form a planetary nebula. Red supergiants = “give” off outer layer in an implosion called a supernova.

16. Red Giants/Super Giants

17. Supernova

18. The end! Medium mass main sequence  Red Giant  White Dwarf  Black Dwarf White Dwarf- Red giant core has collapsed to about the size(volume) of Earth! –Frame of reference: Started with a star that 1 million Earth’s could fit into! –Giving off leftover heat, and heat from molecular particles –Q: How does the sun compare to a white dwarf star? Black Dwarf-what’s left after all of the heat is gone. Lots of pressure, lots of Carbon, infer diamonds?

19. The end! (again) Massive stars  Red supergiant  supernova  Neutron star or  Black hole Neutron Star- smaller & more massive than White dwarves, so much gravity that electrons combine with protons to make neutrons. (Size of a pea = 100 million tons), –strong magnetic fields + rapid rotation = Pulsars

20. Neutron Star

21. Black Holes Massive stars  Red supergiant  supernova  Neutron star or  Black hole Black holes-smaller and more massive than Neutron Stars –Therefore, have much more GRAVITY –Centered on a point, so much that nothing can escape. –Thought to give off energy (X-rays) as matter is “eaten”.

22. Black Holes Above: Hubble image of dust cloud around a black hole. Right: artist renditions.

23. Life cycle summary