It’s wonderful to watch the fascination on people’s faces when you explain to them that studying distant objects in the Universe means looking back in time! Reach out to the furthest corners of the Cosmos and you can see objects so far away that the light left them long before our Solar System even existed. With the commissioning of the JWST the race was on to push the boundaries even further and hunt down the most distant galaxy in the Universe and maybe even the first galaxies to ever have formed.
JWST was launched back in December 2021 on board an Ariane 5 rocket. It arrived at its final destination 1.5 million kilometres from Earth and from there, began operations. Among many other things it has focussed its attention on Pandora’s Cluster in Sculptor, using its Near Infrared Camera. Individual exposures of 4-6 hours were captured totalling 30 hours of data to build a ‘deep-field’ image of the area.
The particularly portion of the sky was chosen because of the presence of several galaxy clusters that would act as gravitational lenses, providing a natural magnification of more distant objects. The final image revealed 60,000 objects which were narrowed down to 700 and final 8 that were thought to be among the first galaxies in the Universe.
Alas not quite, but second most distant galaxy (named Uncover Z-13) had been discovered, at a staggering distance of 33 billion light years. That last statement may jar with some of you because we know the Universe is 13.77 billion years old so how can we have a galaxy at a distance of 33 billion light years? It’s not an error, the light from Z-13 left when the Universe was only 330 million years old. It has then travelled for 13.4 billion years to reach us but in that time the Universe has expanded, dragging the galaxy along with it so it is now at an estimated distance of 33 billion light years.
The team revealed another galaxy which ranked fourth in the distance table but what surprised the researchers from the multi-national team was that they large compared to other galaxies at this distance. I should note not large by galaxies that we see in today’s Universe, Z-13 (and Uncover Z-12) are around 2,000 light years across in comparison to the Milky Way which is about 100,000 light years across. The early Universe was much smaller and galaxies were smaller and compressed by comparison. At these distance, galaxies usually appear as a red spot in images but, due to their larger size, these two appear more like a fluffy balls as described by the researchers who published their paper in the journal Astrophysical Journal Letters.
Studying galaxies at these distances allows us to explore the early Universe and learn more about its evolution. Decoding their light (using spectroscopic instruments) which has travelled through the rarefied hydrogen gas that permeated the early Universe is just one way that we can use distance galaxies to try to understand the particles that existed and physics that governed the Universe shortly after the Big Bang.