James Webb discovers the first pair of merging galaxies, a phenomenon that should not have happened at the time

An international group of 27 scientists published a paper in the journal Nature Astronomy announcing the discovery of the earliest pair of merging galaxies. The event was detected at a redshift of Z=9.3127, or about 510 million years after the Big Bang. During that time, finding a galaxy itself was a rare stroke of luck, let alone witnessing a pair of merging galaxies, which was beyond comprehension, Interestingengineering.com reports.

Scientists from Australia, Thailand, Italy, the United States, Japan, Denmark, and China conducted meticulous work, deciphering what they observed in the early universe. The discovery immediately posed a puzzle. Based on the image, these were expected to be young stars around 20 million years old. Spectral analysis using the Webb NIRSpec instrument revealed the age of the stars to be 120 million years, plus or minus 20 million. Further examination of the object led to the conclusion that there was nothing surprising about such a combination. The image revealed two merging galaxies: one young and one massive and old.

The evidence of the merging event is also supported by the presence of a tidal tail in the image. During galaxy mergers, the ejection of matter and even individual stars in the form of a tail or trail is a common occurrence. What makes this event unusual is that at least one of the galaxies did not have enough time to develop, as we imagined before the advent of Webb. James Webb once again presented a surprise by uncovering something that, according to our theories, should not have happened.

The new observations indicate rapid and efficient accumulation of mass and metals immediately after the Big Bang as a result of mergers, vividly demonstrating that massive galaxies with billions of stars existed in the early universe. Hubble did not allow us to see this, and theorists were firm in their convictions. Webb is challenging the understanding of star and galaxy evolution in the early universe. Data for revising basic theories is still scarce, but the foundation is growing, and by the end of the decade, we will likely have a significantly augmented and even altered theory of cosmic evolution.