Let Us Ponder Stars

Few of us have the time or inclination to ponder the nature of stars, where they form and how they come to be, which if nothing else reflects an impoverished curiosity about our own atomic genealogy. Every atom in our bodies, every atom shaping an unforgettable face or reddening an infected hangnail, every atom of every thread of DNA in each of the 100 trillion cells we trundle about each day—every one of those atoms save hydrogen was exhaled at some earlier point in the history of the universe by an exploding star. And if that ancestry fails to move us, we might at least remember that our fragile and privileged ecological niche in an extremely vast and inhospitably frigid cosmos depends on the proximity of one particular star, the sun, which is gentle enough to warm an orchid yet variable enough to touch off ice ages, distant enough to spare us the roar and force of its inferno, dependable enough that we can set our circadian clocks against it and get up each day to ponder such mysteries as the origin of stars. Stars do not just happen. They result from complex astrophysical processes; they are milky accretions of dust and gas that ignite into luminous beacons of light, light conceived in a manner as mysterious and miraculous as the birth of a pearl, and the evolution of these cosmological jewels occurs only in special birthing places, and only under the right conditions. Any effort to identify those birthing grounds, often referred to as “stellar nurseries,” sends astronomers down a path of celestial cartography, and it is a path that has been traveled with singular success by radio astronomy in the post-World War II era.

   [Stephen S. Hall, Mapping the Next Millennium, Vintage, 1993, p. 308]

This paragraph is part of an introduction to a chapter in Hall’s book on mapping stellar nebulae—rather than on the subject of how elements came into existence. Hence it does not get into the greater mysteries of that subject, among them that, in order even to have genealogies ourselves, three different stars had to come into being. Of those the first two had to have lived out their lives and sent their products into space—there to form stars or planets. And the third sun gives us life. An earlier post on that subject, “Bodies Made of Diamonds” (link) provides a summary.

Bodies Made of Diamonds

I was reading an essay in an old book of mine. It dates to 1956 and was published by Scientific American. The paper, by William A. Fowler, then working at the W.K. Kellogg Radiation Laboratory at Cal Tech, is titled “The Origin of the Elements.” Attempts to understand how the elements originated, Fowler tells us, began by measuring their abundance in the cosmos. Now people know this, in a sense, but in another they do not: hydrogen is the most abundant element. If you weighed the cosmos, 76 percent of its weight would be the weight of hydrogen. If you counted all of the atoms, 93 percent of all atoms are hydrogen. Helium, in turn, accounts for 23 percent of the weight and 7 percent of the atoms. What is left? Almost nothing. Of the most abundant elements in our body only hydrogen in water is abundant. Others, like oxygen, carbon, nitrogen, calcium, potassium, etc., are in the 1 percent of weight and the less than 1 percent of atoms in the universe. Our bodies belong to the rarest of rare objects in the cosmos. We have bodies made of diamonds. And that view is not commonly held.

Here’s another wonder to ponder. Fowler traces how elements formed from protons and neutrons after the Big Bang. He mentions George Gamow and Fred Hoyle. Gamow offered the broad hypothesis: everything is made of protons and neutrons—but don’t ask how those two got made. Hoyle produced a plausible theory of the process—actually many interlocking processes—by means of which heavier elements like carbon, nitrogen, and oxygen were formed—also how the really heavy characters like radium could have come into being. Hoyle proposed that elements formed, and still form, inside of stars. But the interesting wrinkle is that the first red giant processing “virgin” hydrogen could only make the basic starting blocks: helium, carbon, oxygen, neon, and a little iron. All of the other, heavier elements—and the lighter nitrogen—required the following sequence: this first sun dies; it spews all of its mass into the cosmos; the handful of newly minted elements, not least a lot of helium, mix with great clouds of virgin hydrogen; that cloud in turn collapses by gravitational forces into a second generation star. Finally, that star, now containing some already heavier elements, will manage to create the whole periodic table. But that sun, too, must die and spew out its product into the void. The products must form planets. A third generation star must then appear and shed its light onto this “diamond” of a world in order to produce from its substance the vehicles that carry us.

Science is a process of looking, seeing, measuring, hypothesizing, and then, later, revising. It amused me to read the following sentence in Fowler’s paper: “Gamow starts from the postulate … that the cosmos started from a core which exploded in a primordial ‘big bang’ some five billion years ago.” I found one of my penciled annotations in the margin, a circle around the word “five” and then a comment. The comment says: “13.5 billion in 2004, 48 years later.”

Yes—look, see, think, and revise. Five hundred years from now the theory might be that a great fiery dragon spat out the elements in anger when challenged by an upstart humanity riding the Starship Enterprise.
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The book is The Universe, a Scientific American Book, 1956, New York.