Let others pursue the fattest grouse or the most massive buck. A new breed of 21st-century hunters is on the chase, their weapon the most advanced telescopes, their prey bigger than the solar system.
For the past few years, scientists have been engaged in a fierce competition to bag the most distant galaxies in the cosmos, galaxies that existed less than a billion years after the Big Bang, the colossal explosion that founded the universe. Records have been set, broken and broken again, while astrophysicists joust over which early galaxies are real and which are embarrassing errors.
The contest is more than a "fast and furious race," as one scientific paper called it. The quest for the farthest galaxies has shed light on the evolution of the young universe but now researchers hope to pinpoint the onset of "cosmic dawn," when starlight from newborn galaxies first bathed the universe.
"The Holy Grail right now is to find that moment and to find the very earliest galaxies," says astrophysicist Richard Ellis of Caltech. "We've been pushing the frontiers further and further back."
Snaring a distant galaxy is a lot harder than netting the most elusive fish. The farthest galaxies are, to human eyes, "literally invisible," says the University of Texas-Austin astrophysicist Steven Finkelstein, whose team holds one distance record. He explains that when light from far-off galaxies travels to telescopes in our neck of the cosmic woods, any visible light is transformed along the way into a light "redder than our eyes can see," though it's visible to the right kind of cameras and telescopes.
Such "redshifted" light spends billions of years journeying to the vicinity of Earth. The information encoded in the light gives scientists a picture of galaxies as they were billions of years ago - essentially the baby pictures of the universe. The farther away the galaxy, the further back in time we see.
"Telescopes are time machines (that) let us peer back into the past," says astrophysicist Garth Illingworth of the University of California-Santa Cruz, via e-mail. "The light from distant objects takes so long to reach us that we see them when they were much younger."
For years, scientists could peer back no further than roughly 12 billion years ago, when the universe was about 780 million years old. Finally, in 2009, astronauts fitted the Hubble Space Telescope with a new camera, called Wide Field Camera 3, that revolutionized the galaxy-hunting business. Wide Field 3 is far more efficient than its predecessor on the Hubble, and it can see very red light, just the right color for detecting the most distant galaxies.
When Wide Field 3 produced its first batch of data in 2009, competing groups of scientists pounced on it and quickly found dozens of galaxies much deeper in time than seen before.
Researchers have serious scientific objectives in seeking out distant objects, but there's also "the thrill of the chase," agrees Illingworth in an interview. "We do love getting the highest redshift one" - meaning the farthest galaxy - but "you're lucky if the record lasts for six months. Then you've got to go back and do it again."
"There has to be a scientific reason for doing it. Otherwise it's just a stunt," astronomer Mark Dickinson of the Tucson-based National Optical Astronomy Observatory says of hunting distant galaxies. But "there's the horse-race aspect of it, and that's good fun."
Researchers have discovered roughly 200 galaxies that were in existence less than 780 million years after the Big Bang, according to research by Illingworth and his colleagues. Along the way, researchers have relentlessly pushed back toward the beginning of it all. At first, the farthest galaxies detected were at 650 million years since the Big Bang, then only 500 million years, and now even 450 million years or less, though those figures are the subject of debate.
The problem is that the competition, and the difficulty of trying to identify star clusters billions of miles away, can lead to mistakes.
"There are plenty of cautionary tales out there about distant galaxies that have proven to be wrong," Finkelstein says. There's the galaxy reported, to great fanfare, at roughly 600 million years after the Big Bang, a date since proven wrong. Or the record-holder estimated at a mere 380 million years, which scientists refer to as having a "redshift" of 11 or 12, that new research shows may actually be at just under 3,300 million years after the Big Bang.
"The jury may still be out" on that one, says Arizona State University astrophysicist James Rhoads, "but to be honest, I'm putting a case of beer against redshift 11."
While debate continues on the record-holder, everyone can agree that the distant galaxies amassed so far have helped illuminate the childhood of the universe. For example, scientists now believe that the hydrogen fog that permeated the early universe was cleared by the starlight from "huge numbers of really rather faint, small galaxies," not a few ultra-large galaxies, Illingworth says. "This was somewhat unexpected." He describes the galaxies at that time as close-packed, perhaps colliding with one another to trigger bursts of star formation.
"If one were back there, it would be a very different sight looking out into the night sky," he says. "You'd see small, bright, blue clumps all over the place."
Though there's still much to learn, Hubble can't help much more. It has looked about as far back as it can possibly see, and now researchers are waiting eagerly for the opening of an array of new ground-based telescopes and for the 2018 launch of NASA's James Webb Space Telescope, which should allow researchers to detect galaxies not long after the Big Bang.
"We won't be satisfied until we get there," Ellis says. "We need to go just that little bit further back, and we're very close."
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