Richard Ellis was still a student in 1968 when he first glimpsed the distant universe through a telescope—back when astronomers were squinting at photographic plates and calling anything luminous a quasar. Now, nearly six decades later, the professor of astrophysics at University College London has witnessed something once unimaginable: a peek at cosmic dawn itself, that vanished moment when the universe's very first galaxies ignited from darkness.
It took NASA's James Webb Space Telescope, a 6.5-meter infrared eye that Ellis helped make the scientific case for back in 1995, to push humanity's gaze back far enough. A recent survey using 150 separate narrow sightlines over just 0.6 square degrees of sky—an area only about three times the size of a full moon—has revealed galaxies forming when the universe was only 150 to 200 million years old. For perspective, Ellis notes, a redshift of 3, which once seemed impossibly distant, corresponds to a time when the universe was already a third of its present age. JWST has now shattered that boundary.
What Ellis and his colleagues are finding defies simple expectation. These first galaxies are strikingly tiny—only 60 to 70 light-years across, more like stellar globular clusters than what we think of as galaxies. Yet they punch above their weight: they're producing stars 20 times faster than our own Milky Way. We're seeing them at a remarkably youthful and energetic period in their activity, Ellis explains. They're being caught in the act of creation, burning through their gas with the frenetic intensity of youth.
Understanding how these cosmic infants evolved into the majestic spirals we know today—like the Andromeda Galaxy and the Milky Way itself—is one frontier of galaxy science. But there's a deeper prize: finding the so-called Population III stars, the very first stars ever born, which would contain only hydrogen and helium, no heavy elements at all. The massive ones would have lived for perhaps just 5 million years before exploding, seeding the cosmos with heavier elements. Once they exploded, Ellis notes, they polluted the gas with heavy elements, so they're no longer chemically pristine.
Pinpointing cosmic dawn precisely remains a scientific challenge. Ellis outlines three current methods: discovering a population of galaxies chemically unpolluted by supernova explosions, a notoriously difficult task requiring unequivocal proof of absent oxygen emissions; tracing the sharp decline in star-forming galaxies at increasingly distant reaches of space; and measuring declining chemical abundances with redshift—a path Ellis considers most promising, though it demands far more spectroscopic data than currently available.
A fourth route may soon open. The forthcoming Square Kilometer Array in Western Australia will hunt for the Lyman alpha signature of hydrogen gas at cosmological distances, potentially detecting the radio fingerprint left when galaxies first lit up the universe. We're beginning to see a glimpse of what we call cosmic dawn, Ellis says, the moment when the very first galaxies emerge from darkness. It's a moment that seemed abstract when he was an undergraduate; now it's within view.