If you look up into the sky on a clear night, you would see thousands of stars. There are surely many more that you would need a telescope to see. But there are not stars everywhere. You can zoom in further and further with bigger and bigger telescopes, until eventually you find gaps where you simply don’t see stars. For a long time it was thought that the gaps were empty, until the Hubble telescope peered through the darkness by taking a 200 hour exposure of a supposedly empty patch of sky. What it revealed was a universe full of galaxies of all shapes and sizes, some relatively nearby, some as far as the beginning of the universe. And every single space in the sky that looks empty is instead filled with thousands of galaxies, showing the immensity of the structure of our universe.
By looking as closely as we can at these incredible images of the far reaches of our universe, we can see as far back as we ever will, all the way to the first stars and galaxies that formed in our universe. By looking at more distant objects, we are looking into the past, seeing back in time. In the above image, the most distant faint galaxy ever has been discovered, named Tayna.
The Tayna galaxy is thought to have formed when the universe was only 400 Million years old, shortly after the decoupling of light and matter, when the universe cooled and became large enough for a beam of light to travel without smashing into a particle.
Studying these earliest structures helps us understand how the universe evolved and grew from a soup of elementary particles to the vast galaxy superclusters we see at present. When we identify the first galaxies we can constrain the timeline for their formation and make predictions about what we should see today.