Anna's Refried Beans
When you look at the stars in the night sky do you ever wonder what they are made of? Are stars the stuff of fate, celebrity, and love, or worked-over matter like refried beans?
I’ve never managed to catch a falling star, but according to the textbooks, I can not only touch what the stars are made of, I am myself made of the same things. And so are you. About 98% of the molecules in our bodies are the combination of hydrogen and oxygen elements that we call water. Those, plus carbon and nitrogen, make up the bulk of the many elements we’re made of, and that the stars are, too.
I asked my 10-year-old granddaughter, Sydney, what she’d say stars were made of, and she surprised me: “Helium,” she said, and looked at me quizzically. A budding astrophysicist? Astrophysicists think that all the elements we know started with hydrogen just after the Big Bang. In the subsequent explosions hydrogen fused into helium, and then helium fused into carbon, and then into oxygen, nitrogen, iron, and so on down the line. The heavier elements, such as sulfur, calcium, and iron, are fused in explosive supernovae.
When astronomers look through prisms at the light from the stars and the supernovae and compare it with the prismatic light they can make in a laboratory here, they can see the unique signatures of each one of these elements in both places. They think that the kinds and the amounts of the elements that they see in the light of a given star tells them how hot it is and how old it is. That is, a blue-white star like Spica probably has a surface temperature of between 11,000 and 25,000 K (water boils at 373 K, iron at 1808 K) and is younger than reddish Antares which has a surface temperature of less than 3,500 K. Our yellowish Sun at a surface temperature of 5,500 K is some place in between these; it’s a typical middle-aged star, formed about 9 ½ billion years after that Big Bang, and after a succession of other explosions.
G292.0+1.8 Supernova remnant. Scattered through the image are bluish knots of emissions containing material that is highly enriched in newly created oxygen, neon, and magnesium produced deep within the original star and ejected by the supernova explosion. Image credit: NASA-MSFC
Astronomers look at supernovae and at nebulae, postulating that in them they are seeing not only the end of a star but the possible beginning of the next one. The vast quantity of stuff—gas and dust—that is thrown off in a supernova explosion will become the matter that condenses in a million years or so into a new star. The result of the explosion is what we see in the spectacular displays that the Hubble Space Telescope has photographed. This condensation, they say, is how our Sun, its planets, and the rest of the matter in our Solar System may have originated. Therefore, it appears that, long before you or I were born, the elements we are made of were being fused in space. Didn’t you always suspect that some of us at least were from outer space? And that parts of you are 14 billion years old? Give or take a year or so.
Granted that the text books can give us a lot of proof about the chemical composition of a star, about its temperature and its age using physics and mathematics and geology, can there be other, just as useful, ways of knowing what a star is?
Recently I asked a professor of astronomy what he’d say a star is made of. His answer came at once: “Pixie dust.” Several points in that answer continue to intrigue me. “Dust” fits in with what astrophysicists say about the origins of stars. But however complicated and precise their mathematics is, it doesn’t answer the question of what triggers the action of gravity to reverse the violent outburst of a supernova and start the condensation of dust into granules into pebbles into bigger and bigger balls. Or the question of why some balls end up too small to become stars (Jupiter) and some become huge (the diameter of Rigel is 100 times that of the Sun). Or simpler questions like why the Sun rises in the west on Venus instead of in the east as it does in the rest of the solar system.
Could it be that this pixie quality keeps leading us on to try to reach the stars? Is that why the stars are winking at us? Or do they just want refried beans for supper?