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Monday, August 12, 2013

Why Laser Quest Employees Should Stop Pretending They Have PhDs in Astrophysics

Today our story starts after sailing camp and lunch.  My friends from Maryland are visiting us, and we went with them and their cousins to Laser Quest, a laser tag place in Danvers.  After we got our scorecards for the first round, the guy who gave us them asked us to quiz him.  He got questions including "What are the names of the Seven Dwarves?" and "Who are the five presidents on Mt. Rushmore?" and "When did John Adams die?"  After more easy presidential nonsense, I decided to take it up a notch.  After giving everybody who questioned him prizes because he DID get them right, he didn't give me a prize when I actually stumped him with a differential calculus question ("What is the limit as x approaches 2 of x - 2/x - 2?").  Who is this guy, giving prizes to people who can't stump him and not to somebody who does?  Next, he said "Now I got a question for you people.  After our sun explodes in a supernova, what happens?"  After being stumped with one of the easiest calculus questions there is, Mr. Laser Quest Employee still thinks he's the next Stephen Hawking.  The first thing that ran through my head was "Supernova... Oh, yeah a white dwarf star."  But then I realized what would actually happen first to our sun.  I raised my hand and said "A nebula."  Then he said "No, Okay, next answer."  Then my friend said "Your question is incorrect becau-" 
"Okay, next answer."  Then some teenager said "White dwarf?"
"Yes! Here's your prize!"  He then handed him some tchotchke rubber ball.  The guy was sort of right, but my friend and I were more right.  

Now I will explain why this guy doesn't have his facts right.  Only supergiant and hypergiant stars the size of our galaxy can burst into supernovae.  Our sun will eventually turn into a white dwarf, but with no supernova and after a planetary nebula is formed, like I said.  Let's get started.  In around 5.4 billion years, the Sun will exit its main sequence, which is basically no more of the Sun we know today, getting brighter and bigger.  The first stage will be when it is a subgiant.  This will happen when it has burned up all of its hydrogen fuel after that 5.4 billion years.  During about a half billion years in this subgiant stage, it slowly expands to two times its current size, engulfing the inner planets, including Earth.  After another half billion years, it expands much more rapidly to two hundred times its current size and a few thousand times its current brightness.  It then starts to become a red giant, entering the red giant branch (RGB).  RGB is pretty boring, where the really fat Sun just sits there for a billion years and loses about a third of its mass.   It now only has 120 million years left.  In a few seconds, something called a helium flash occurs where a lot of helium is burned.  In the helium flash, the star contracts because gravity is pushing it in.  Stars don't collapse once they form because they're vey hot, and heat gives pressure.  Once it exhausts all this thermal energy, the star becomes what's called degenerate matter, or Fermi gas.  The heat stops supporting the star, and that's where quantum mechanics works its magic.  Something called the Pauli exclusion principle says that two fermions (certain particles including electrons) cannot be in the same quantum state, which is the exact energy of it.  The degenerate matter is cold, so the atoms enter all the lowest quantum states.  This degenerate matter is so dense that it is easy to find the position of every atom.  The Heisenberg uncertainty principle then says that since we know an atom's position so well, we must know very little about its speed.  We only know that, on average, the degenerate matter atoms are whizzing around near the speed of light.  If another atom is introduced, it is hard for it to assume a low-energy quantum state since all the other atoms already have "dibs" on these states.  After this quantum mechanical pressure, gravity overcomes it and shrinks the Sun, reverting it to only 10 times its current size and only 50 times as bright.  It then enters the horizontal branch (HB).  It basically expands after losing all its helium fuel like it did before RGB, except this time the Sun is bigger and brighter.  This is now the asymptotic giant branch (AGB).  The sun will become very unstable after 20 million years of AGB.  It will become bigger and brighter each time it expands.  This expanding and contracting, called thermal pulsing, will happen to our sun about four times before it loses all its outer mass, which forms a planetary nebula, a giant gas cloud of hydrogen and helium that can form new stars and planets.  The very hot, naked core will finally cool to form a white dwarf, which is where the teenager kind of got it right.  The nebula will survive for only 10,000 years (very short on the cosmological time scale), whereas the white dwarf will survive for trillions before fading to a black dwarf.  Was I going to explain this to him? Definitely not.  I had some laser tag to play!