Hubble Catches Some of the Earliest Stars Ever Formed on Camera

The Hubble Space Telescope has been sending back iconic and stunning photos of space for decades. But it just caught something particularly special on tape: early stars, from the beginning of the universe. And not only are they some of the earliest stars we've ever seen, their very existence confirms some of our theories about early star formation.

Researchers found(Opens in a new window) more than 500 galaxies that existed less than a billion years after the Big Bang. NASA says this discovery sheds tremendous light (pun intended) on our knowledge of the earliest days of the universe -- an era that, until quite recently, we knew little about. Ten years ago, we hadn't found even a single galaxy that existed when the universe was just a billion years old.

The Hubble's survey of this particular area came after the Sloan Giant Arcs Survey. In this case, the Hubble was able to use an effect known as gravitational lensing to see the most distant regions of space at 10x the fidelity it could have managed on its own. Gravitational lensing requires a massive object between ourselves and the object we want to view. As the light from the object we're attempting to view passes very massive things on its way to our eyes, the light from the original object is warped and bent. But when it eventually reaches Earth, we can see further back into the past than we would otherwise.

Lensing can result in a distorted image of space, though: Like a funhouse mirror, strong lensing effects can lead us to see multiples of things, or smear galaxies into almost unrecognizable shapes. It takes a great deal of computational detective work to make sure we're using the right "decoder ring" for the effects that we see, but the rewards are commensurate. These edge-on galaxies would otherwise have been naught but a blurry streak; lensing let Hubble see them in clear resolution.

These galaxies are much smaller than the Milky Way, and naturally extremely blue-ish, which indicates they're busy creating a huge number of stars (or were, 11.7 billion years ago, given how long its taken to get here). But they're also highly redshifted, which tells us that they're traveling away from us at extreme velocities.

"Finding so many of these dwarf galaxies, but so few bright ones, is evidence for galaxies building up from small pieces -- merging together as predicted by the hierarchical theory of galaxy formation," said astronomer Rychard Bouwens of the University of California, Santa Cruz, who led the Hubble study. The resulting several reports are pre-published on arXiv, and due to appear in the next issue of The Astrophysical Journal.

There's been a long-running argument in astronomy over whether these early galaxies and their rate of star production was hot enough to reheat the cold hydrogen gas that existed in the aftermath of the Big Bang. These ancient dwarf galaxies produced stars at roughly 10x the rate that galaxies produce now. While this isn't hard observational evidence of Population III stars, these very ancient and highly redshifted galaxies can still tell us important things about the deep reaches of time: they date from the period known as cosmic dawn, when the bubbles of plasma blown by nascent stars heated and re-ionized their cold, opaque environment until its opacity gave way to the clear vacuum we see today.

Those stars may well be the long-sought Population III. It may have taken more than just stars to re-ionize the whole visible universe; supermassive black holes could have been part of the equation. But Hubble, and the upcoming James Webb Space Telescope, will help us find these answers.

Seeing these starburst galaxies shows there were enough galaxies one billion years after the Big Bang to finish reheating the universe, said team member Garth Illingworth of the University of California, Santa Cruz. "It highlights a period of fundamental change in the universe, and we are seeing the galaxy population that brought about that change," he said.