The "most distant explosion ever" turned out to be rocket debris

"At the greatest distances of all, gamma-ray bursts mark the universe's most energetic events. Ranging from milliseconds to hours, they're associated with black hole formation. In 2020, a team of astronomers observing GN-z11 reported a transient but brilliant flash of ultraviolet light. Transient candidates included Population III supernovae and the ultraviolet counterpart of a gamma-ray burst. If so, it's a lottery-winning serendipitous coincidence."

"However, many authors warn of satellite foregrounds as confounding factors for extragalactic astronomy. Most space debris pollutes low-Earth orbit. But some possess highly elliptical orbits, like Breeze-M stages of Russia's Proton rockets. One such rocket stage, launched in 2015, was likely the culprit here. In direct sunlight, 13,758 km from Earth, this object crossed Keck's field-of-view at the pivotal moment. A transiting satellite, not a distant cataclysm, caused this flare."

GN-z11's light reaches Earth after 13.4 billion years, so only aggregate starlight, not individual stars, is visible at that distance. Transient brightening events such as supernovae, kilonovae from colliding neutron stars, and gamma-ray bursts can briefly rival an entire galaxy's brightness. In 2020 observers recorded a transient ultraviolet flash from GN-z11, with candidates including Population III supernovae or an ultraviolet gamma-ray burst counterpart. Satellite foregrounds can mimic extragalactic transients; a Breeze-M rocket stage launched in 2015 likely crossed Keck's field-of-view in sunlight at 13,758 km, producing the observed flare. A comprehensive Earth-orbiting satellite database is necessary to prevent such confusion.

Read at Big Think