Star Stuff

Star Stuff January 16, 2018


Starry Night by Van Gogh
Vincent Van Gogh, “The Starry Night” (1853);  Wikimedia Commons


Some material from Chris Impey, University Distinguished Professor and Deputy Head of the Department of Astronomy at the University of Arizona, taken from his book How It Began: A Time-Traveler’s Guide to the Universe (New York and London: W. W. Norton and Company, 2012):


Imagine atoms in the universe scattered like playing cards.  Instead of the normal suits and numbers, these cards are labeled as elements of the periodic table.  The dominant elements are hydrogen and helium; everything else is amazingly rare.  In terms of number of atoms, the universe is made up of 88 percent hydrogen, 12 percent helium, 0.060 percent oxygen, 0.026 percent carbon, 0.025 percent neon, and less than 1 part in 10,000 of all other elements.  In the analogy of playing cards it’s as if we marked all aces and two of the kings as helium atoms and the rest as hydrogen.  We’d have to search through 32 decks of cards to find anything other than those two elements.  If we had the patience to search 240 decks, or 12,500 cards, we’d find one nitrogen card, three neon cards, three carbon cards, and five oxygen cards.  Everything else is hydrogen or helium.  To find a single iron card, you’d need to sift through 190,000 cards or 3600 decks.  Precious metals like gold, silver, and platinum are incredibly rare, cosmically speaking.  Just 1 in 10 billion atoms, so gold at the current price is a steal.  Imagine a huge Walmart store, emptied of goods and filled from floor to ceiling with decks of cards.  You’d have to go through all of them to be sure of finding one gold atom. (88-89)


The Solar System has a large amount of helium relative to hydrogen.  Helium is made in main sequence stars like the Sun, but there’s too much to be explained by stellar fusion . . .  (89)


As biological creatures, we’re partial to carbon.  Some esoteric nuclear physics explains why carbon is as rare as it is, and why it isn’t so rare that life couldn’t exist.  Two helium nuclei can fuse to make a beryllium nucleus, but it’s radioactive with a half-life of a hundred-trillionth of a second.  A star needs a central temperature of 100 million degrees to fuse the two nuclei together faster than they fall apart naturally.  Only stars more massive than the Sun ever reach central temperatures this high.  In the 1950s, astrophysicist Fred Hoyle realized that a special nuclear resonance greatly increased the probability of a third helium nucleus fusing with beryllium, and so forming carbon.  The fact that carbon exists at all is essentially a coincidence of nuclear physics!  (89-91)


All the heavy elements beyond iron in the periodic table are created by massive stars.  About half of those atoms are made in the atmospheres of those stars by stealth as neutrons are captured by the heavy nuclei.  This process only goes up to bismuth, the heaviest stable element.  The other half are created in the paroxysm of the star’s death.  Collapse is followed by an explosion called a supernova, and elements as massive as radioactive uranium and plutonium can be created in seconds in the billion-degree blast wave.  Those heavy elements include gold.  (92)



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