Enlarge / Some of the galaxies in the JADES images. (credit: NASA, ESA, CSA, M. Zamani)

One of the things that the James Webb Space Telescope was designed to do was look at some of the earliest objects in the Universe. And it has already succeeded spectacularly, imaging galaxies as they existed just 250 million years after the Big Bang. But these galaxies were small, compact, and similar in scope to what we'd consider a dwarf galaxy today, which made it difficult to determine what was producing their light: stars or an actively feeding supermassive black hole at their core.

This week, Nature is publishing confirmation that some additional galaxies we've imaged also date back to just 300 million years after the Big Bang. Critically, one of them is bright and relatively large, allowing us to infer that most of its light was coming from a halo of stars surrounding its core, rather than originating in the same area as the central black hole. The finding implies that it formed through a continuing burst of star formation that started just 200 million years after the Big Bang.

Age checks

The galaxies at issue here were first imaged during the JADES (JWST Advanced Deep Extragalactic Survey) imaging program, which includes part of the area imaged for the Hubble Ultra Deep Field. Initially, old galaxies were identified by using a combination of filters on one of Webb's infrared imaging cameras.

Enlarge / NASA's James Webb Space Telescope reveals the Rho Ophiuchi cloud complex, the closest star-forming region to Earth.

In a feat of galactic archeology, astronomers are using ever more detailed information to trace the origin of our galaxy—and to learn about how other galaxies formed in the early stages of the Universe. Using powerful space telescopes like Gaia and James Webb, astronomers are able to peer back in time and look at some of the oldest stars and galaxies. Between Gaia’s data on the position and movements of stars within our Milky Way and Webb’s observations of early galaxies that formed when the Universe was still young, astronomers are learning how galaxies come together and have made surprising discoveries that suggest the early Universe was busier and brighter than anyone previously imagined.

The Milky Way’s earliest pieces

In a recent paper, researchers using the Gaia space telescope identified two streams of stars, named Shakti and Shiva, each of which contains a total mass of around 10 million Suns and which are thought to have merged into the Milky Way around 12 billion years ago.

These streams were present even before the Milky Way had features like a disk or its spiral arms, and researchers think they could be some of the earliest building blocks of the galaxy as it developed.