Metals’ ‘fingerprints’ lead us to first stars
Without stars, life wouldn’t exist. The sun, of course, provides energy, but billions of other stars actually created the atoms of which we’re made.
Any specialty – medicine, physics, auto racing – has its own jargon, its own “insider’s” vocabulary. Specialists use jargon for one of two reasons: It keeps the outsiders out, and it provides a shortcut, an ability to say in one word what would otherwise take many. (Imagine having to say “telephone with a built-in radio transmitter/receiver that allows you to make calls from just about anywhere” rather than “cell phone.”)
As practitioners of one of the oldest sciences, astronomers have had thousands of years to create a rich jargon. Within this specialized vocabulary is a word that astronomers use differently from virtually everyone else in the world.
A “metal,” every non-astronomer knows, is a shiny substance, usually hard, usually heavy, a good conductor of heat and electricity.
To an astronomer, however, a charcoal briquette is made of metal; the air we breathe is made of metals; every element in the universe is a metal, save two.
For some time after the creation, some 13 or so billion years ago, the universe consisted of only the two lightest elements: hydrogen and helium.
Stars are nuclear fusion reactors, and both hydrogen and helium are star fuel. Smashed together, hydrogen and helium nuclei stick – they “fuse” – releasing energy and creating new, heavier atoms in the process. Except for hydrogen, all of the atoms in our bodies – nitrogen in our muscles, iron in our blood, carbon in everything – were created from lighter atoms, billions of years ago, inside stars.
To an astronomer, any element that was not created in the Big Bang, but was instead made inside a star, is a “metal.”
When vaporized and heated, every element glows in a unique combination of colors, a spectral “fingerprint” that allows astronomers to figure out what the stars are made of. Analyzing the light from our sun, we find “metals.” Since any “metals” our sun produces remain trapped within its core, the “metals” we detect must have been present when the sun first formed.
They came from myriads of older stars that, billions of years ago, exploded and contributed their matter to the interstellar medium. Our sun is thus a “second-generation” star, formed from the recycled remains of older stars. It is not a star of the “first generation,” formed solely from the hydrogen and helium of the early universe.
Now that the universe has been “polluted” with metals, first-generation stars can no longer be made. Looking out across space, using their telescopes as time machines, astronomers have searched for first-generation stars – stars made of only hydrogen and helium. The search has been fruitless … until now.
Using an image made by the Hubble Space Telescope as a sort of prospector’s guide, and then using the much larger mirror area (larger light-gathering surface) of the Keck I telescope in Hawaii, astronomers peering close to the edge of the observable universe have found a clump of stars that are so far, and so dim, they’ve stretched our telescopic abilities to the limit. The spectra of these stars reveal no metals. They are stars of the first generation, the first generation of stars to form.
Sometime in the future, astronauts will be working on the Hubble Space Telescope, replacing older instruments with new, more sensitive ones – instruments sensitive enough to study the first stars to have formed in our universe.
Trained as a biologist, Alan Stahler is also an amateur astronomer. He teaches biology and geology at Bitney Springs Charter High School. His science programs can be heard at noon on alternate Tuesdays on KVMR-FM (89.5).
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