Purity of Essence: The Oldest Objects in the Universe
The Big Bang—that elemental explosion that kicked everything off 13.7 billion years ago—created a universe that was much simpler than our universe today. It contained only two primary elements, hydrogen and helium, along with two trace elements: deuterium and lithium. The stars in the early universe were composed of only those elements. They shone brightly and clearly, driven by nuclear fusion as the hydrogen at their cores burned into helium. But the nuclear fusion in those early stars was not simply reactive, it was creative. It cooked up new, heavier elements, too, things like iron and nitrogen and oxygen. When those early stars burned out, when their nuclear fusion stopped and they exploded into supernovae, they thrust those new elements into space to become the building blocks of the next generation of stars. Those stars, in turn, cooked up their own elements and catapulted them into the mix. Over billions of years, the universe became heavier, more metallic, more diverse. The idea that we are star dust isn’t metaphorical: The elements that comprise our bodies—carbon, calcium, phosphorous and the like—were literally concocted in stars.
But what of those initial stars, the purest ones? Astronomers seek them to learn what the elders can teach us about the origins of the universe. “The holy grail,” says Kudritzki, “is to find them.” To do that, astronomers are looking in two places. The first is as far out in space as possible—for, as you might remember from physics class, to look into space is also to look back in time. Find an object that’s thirteen billion light years away and you’ve found an object that’s thirteen billion years old. At such huge distances, though, astronomers can’t make out individual stars, so they detect what they can—galaxies or supernovae or gamma ray bursts—and then take spectra readings, which detail the chemical compositions of their findings.
The second place astronomers are looking is right on Earth’s doorstep, in the galactic halo of the Milky Way, a vast nimbus that is home to the primordial stars of our own galaxy. The proximity provides far greater precision; Keck and Subaru are able to use high-resolution spectrographs to analyze individual stars in the galactic halo and find the most metal-poor, or meta-pure, among them. The work to find that holy grail—a pure hydrogen-and-helium star—continues, but the astronomers are closer all the time. “We’ve now found stars with a hundred thousand times less metal than our sun,” says Kudritzki, “and we are almost there, at the beginning.”
As far as who’s actually recorded an image of the most distant thing, that prize is traded off as various telescopes make their detections. At the time of this writing, the record rests with Mauna Kea’s Gemini Northern Telescope, which two years ago captured an image of a gamma ray burst that occurred just over thirteen billion years ago, a mere 630 million years after the Big Bang. The picture shows just a tiny, fuzzy blip of light, and as with HR 8799, you’ve got to know what it is before you marvel: What you’re looking at is the light of a vehement explosion that has traveled over thirteen billion light years across the universe and only just arrived to Earth. It’s the oldest thing we’ve ever seen.