Looking at objects far away in the universe is like looking back in time, a very useful consequence of the finiteness of the speed of light. Very distant objects are therefore very young objects, as they were when the universe was also young. Imagine the surprise, then, of astronomers who found a very distant galaxy that looks extremely old.
This "beyond possible" galaxy is known by the snappy title of ZF-UDS-7329. Observations by the James Webb Space Telescope revealed that the galaxy’s light comes from 11.5 billion years ago and its massive stellar population was already in place 13 billion years ago - close to the 'cosmic dawn'.
The mass of all the stars in ZF-UDS-7329 is at least twice that of the stars in our galaxy, the Milky Way. And our galaxy has taken billions of years to get this big. How a galaxy got so enormous in just several hundred million years from the dawn of the universe is a conundrum.
"This pushes the boundaries of our current understanding of how galaxies form and evolve. The key question now is how they form so fast very early in the universe," says co-author of the study published in Nature, Dr Themiya Nanayakkara.
As JWST continues to probe into the distant past of deep space, it will no doubt continue to discover that the early universe was more complicated than previously thought.
"Galaxy formation is in large part dictated by how dark matter concentrates," Associate Professor Claudia Lagos of the University of Western Australia said. "Having these extremely massive galaxies so early in the universe is posing significant challenges to our standard model of cosmology. This is because we don't think such massive dark matter structures as to host these massive galaxies have had time yet to form."