A fragment of a recent deep field image from the Webb Image: SCIENCE: NASA, ESA, CSA, Tommaso Treu (UCLA) IMAGE PROCESSING: Zolt G. Levay (STScI)
A deeper look through a massive cluster has revealed two galaxies formed shortly after the Big Bang.
In late June, the Webb Space Telescope set its eye on two of the most distant galaxies we’ve seen to date. These galaxies existed several hundred million years after the Big Bang, making them some of the first light sources to emerge in the universe.
The galaxies are in the vicinity of Abell 2744, a giant galaxy cluster (actually a mixture of four smaller clusters) in the constellation Sculptor. One of these galaxies arose just 450 million years after the Big Bang, and the other about 350 million years later. These galaxies have a redshift of 10.5 and 12.5. Because the universe is expanding, light is stretched to longer, redder wavelengths as it travels through space. So an object with a higher redshift is farther away and older than one with a lower redshift. These two galaxies are similar in age to the Maisie Galaxy, a distant object discovered in a Webb deep field image that had a redshift of 11.8.
The universe is about 13.8 billion years old, and the first stars did not appear until several hundred million years later. That makes these galaxies some of the oldest known light sources in the universe (excluding cosmic microwave radiation, the glow from the Big Bang, which emerged about 380,000 years after the event).
The Abell 2744 cluster is about 3.5 billion light-years away, but these recently discovered galaxies are older. In fact, from our perspective they are billions of light-years further away than Abell 2744 and so their light is very dim. But the primordial light sources are gravitationally lensing the galaxy cluster, meaning their light is bent and magnified by an object in the way. Gravitational lenses focus distant light, making it easier to see objects far away. Astronomers take advantage of this cosmic quirk to find the oldest known stars and even to repeatedly observe one-off events like supernovae, as photons of light from those events follow multiple paths around massive objects.
This is not the first time we have photographed Abell 2744. In 2014, the Hubble Space Telescope had already taken an image of this gigantic cluster of galaxies. At the time, Hubble’s deep field images were the deepest observations ever made of such an object. However, Webb’s keen vision has allowed older light sources beyond the cluster to be focused.
According to a statement from the Space Telescope Science Institute, these two ancient galaxies are tiny compared to our own (the Milky Way is about 100,000 light-years across). Abell 2744 is also known as the Pandora Cluster because of all the objects it contains. But unlike the mythological box, the Pandora Cluster only brings us good things.