ASTR 1020 - Exam Results, Problem Sets, and Observatory Opportunities

1. ASTR 1020 – February 28 Exams Graded and to be returned inrecitation Average: 69.0 (B- center to curve) Next Exam March 14 . Problem Set 3 Posted Due 3/2 Problem Set 4 Posted Due 3/7 Problem Set 5 Posted Due 3/9 Next Observatory Opportunities:March 2 and 7 at 7:30pm

2. Red Giants

3. Nucleus Earth Orbit

4. Fate of The Earth We will be swallowed by the Sun In 5 billion years it will start to swell. T will rise on Earth Oceans will boil and then evaporate into space Sun will cover the sky. Giant ruddy ball. Then it will engulf us. Mountains will melt. Planet should survive. Will look like a polished bowling ball.

5. Red Supergiant Meanwhile, down in the core, the C is becoming degenerate. Luminosity is becoming so great it blows the H envelope into space. H H->He He->C C

6. Planetary Nebulae Gas blown out into space and illuminated by central star. The star is the degenerate C core. The Ring Nebula

7. Gorgeous Planetary Nebulae from Hubble Space Telescope Notice Rings. Star has “episodes”

8. Hourglass Shape Star throws material out in its ecliptic plane. That’s the equatorial plane of the star. Creates a dense disk around star.

9. Hourglass 2 Next Explosion is Constrained and Expands as Hour-Glass

10. Globular Clusters Very Old. G stars becoming giants. All the same age and composition Can actually see evolution off the MS

11. White Dwarfs • Held up by electron degeneracy • About the size of the Earth R~5000km • Mass Typically 0.8M • Luminosity ~ .001 L Thin layer of “normal” H Degenerate Carbon

12. Some Famous White Dwarfs • Sirius B • 40 Eridani B • Procyon B All in binaries around nearby stars. Establishes the WD is close and small.

13. Earth vs White Dwarf

14. Earth vs. Sun

15. Mass Radius Relation As mass increases star gets smaller. Like ball of foam.

16. WD Density Water has a density of 1 g/cc Lead 11 g/cc Gold 19 g/cc 100,000 times density of gold! NOT NORMAL MATTER!! 1 cubic centimeter masses one ton!

17. Surface Gravity This is 300,000 gees If you weigh 150lbs on Earth, you would weigh 45 million pounds on a White Dwarf! What would happen to you and your spaceship?

18. Escape Velocity Speed of light is 3x108 m/s, so escape velocity is .02c.

19. Gravitational Redshift Even light loses energy climbing out of this hole. a = 2x10-4 At 5000Å have 1Å shift to red Looks like a 60km/s Doppler Shift

20. Magnetic Field When a star shrinks from 109m to 107m So B increases from 1Gauss to a Million Gauss A million Gauss can rip normal matter apart!

21. Chandrasekhar Limit A peculiarity of Degeneracy Pressure is that it has a maximum mass. Each electron added must find its own quantum state by having its own velocity. But what happens when the next electron has to go faster than light? The Chandrasekhar Limit for a White Dwarf is 1.4M No White Dwarf Can have more than 1.4M Otherwise it will groan and collapse under its own weight. We’ll come back to this later.

22. WDs are Common Every star with less than 5M will end up as a White Dwarf Most stars with mass above 1.3M have reached end of MS life. White Dwarfs are VERY common ~ 10% of all stars Closest is only 2.7pc away. (Sirius B) Will become increasing common as universe ages.

23. Immortal Stars Regular stars need thermal pressure to balance gravity, and they need nuclear reactions to maintain the pressure, so the die when they run out of fuel. Not so White Dwarfs. They are as stable as a rock. Literally. A quadrillion years in the future all the stars will be gone, but the White Dwarfs will still be here. Their glow is fossil energy left from their youth as a regular star. Might die in 1031 years if protons prove to be unstable themselves. That’s 10,000,000,000,000,000,000,000,000,000,000 years! Really don’t know if universe will still be here.

24. Binary Stars • Optical Double appear close together but aren’t really binary • Visual Binary orbiting, but we can see them both • Astrometric Binary proper motion wiggles to show orbit • Spectrum Binary spectra of two stars of different type • Spectroscopic Binary Doppler shift shows orbital motion • Eclipsing Binary light varies Half of all stars are in binaries…. Binary stars are formed at birth. Both components will have same age and composition. Can vary in mass Can be very distant (0.1pc) or touching

25. Spectroscopic Binary

26. Variable Stars Some stars just expand and contract. Eclipsing Binary Algol – “The Devil Star”

27. Russian Variable Star Catalogue Compilation of all the stars that vary. Letter starting with R, followed by Constellation Name After Z starts RR through ZZ, then AA SS Cygni VY Hydrae W Ursa Majoris Gets funny on occasion RU Lupi EZ Sextans

28. Close Binaries Gravity Mid-Point Equal Energy Curves

29. Contact Binaries Very Close Touching Common Envelope Two Nuclear Cores “W Ursa Majoris” star

30. Periods of Contact Binaries By Kepler’s Law: P ~ R(3/2) R = (1/200) AU So P = (1/200)(3/2) years = 3.5x10-4 years = 104 s = 3 hours These contact binaries swing around each other every few hours!

31. Huge Flow of Material from One to Other Mass Transfer Can stop evolution of one and speed up other Gets complicated “Dog Eat Dog” Scenario

32. The Roche Lobe Mass Transfer Binary White Dwarf & Star

33. Mass Transfer Binary Accretion Disk Material Swirls In Friction allows the material to fall and heats while it falls. All the way to the surface

34. Energy Released Huge amounts of energy are released as the material swirls in. Material get hot. Really hot. Like a million degrees Kelvin. Emits ultraviolet and x-rays. We can see these accretion disks with x-ray telescopes!

35. Material Reaches Surface Carbon White Dwarf Layer of H build up on surface Pressure builds on the hydrogen. Material pouring in heats it.

36. Nova One day the hydrogen ignites in huge nuclear rush. Burns like a brush fire from one end of the star to the other. This is called a “Nova”. A new star appears in the sky. Often visible to the unaided eye. Lasts a few weeks to months.

37. Novae Hydrogen explodes into space to create a shell of expanding gas. Gas expands outward at 500km/s The Sun can never go nova! It’s not a white dwarf in a close binary.

38. 3 Kinds of Novae Classical Novae Only seen once Recurrent Novae Seen several times over last few hundred years Dwarf Novae Pop off every few weeks to months It’s just a matter of how fast material is transferring and how much needs to accumulate before the spark.