ASTR 1040 – October 10 Exams Graded and to be returned in recitation Average: 76 (B+ center to curve) Next Exam October 26 or November 2 Problem Set 3 to be posted soon Next Observatory Opportunities: October 12 and 17 at 8pm

Red Giants

Nucleus Earth Orbit

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.

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

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

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

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

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

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

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

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

Earth vs White Dwarf

Earth vs. Sun

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

WD Density 1 cubic centimeter masses one ton! 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!

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?

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

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

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!

Chandrasekhar Limit The Chandrasekhar Limit for a White Dwarf is 1.4M 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.

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.

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.