The authors used a precise position provided first by the Einstein Probe and refined on the ground by the ATLAS optical telescope to pinpoint the Fast X-ray Transient in space via observations with the Very Large Telescope in Chile and the Grantecan Telescope in Spain. "These observations show that this explosion happened when the Universe was less than 10 per cent of its current age -- the light has been travelling to us for 12 billion years. The combination of the distance and the brightness means this explosion gave off more energy in a few seconds than the Sun will over its entire life," noted Andrew Levan of Radboud University, first author of the study. These extreme energies, along with the detection of gamma-rays by the Fermi satellite, suggest that the Fast X-ray Transients are related, at least sometimes, to the extremely powerful gamma-ray bursts that have been studied for half a century. "A real question is if all of the Fast X-ray Transients come from gamma-ray burst-like systems, or if there is much more diversity. Our paper shows that many of them might be gamma-ray bursts, but there are good reasons to think there is much more still to discover", added Jonker.
Surprise
However, this explosion still had one surprise up its sleeve. When examining the observations from the Very Large Telescope, it became apparent that there is very little material, particularly hydrogen, surrounding this burst. Hydrogen acts like a filter for ultraviolet light, blocking it from passing through the Universe. However, in the history of the Universe, around the time of this Fast X-ray Transient, the Universe underwent its last global change in a process called reionisation, where the hydrogen between galaxies was hit with ultraviolet light and "reionised". The challenge is that almost all the ultraviolet light created by stars in the Universe is blocked by hydrogen in the galaxy in which it sits. "Our observations show that perhaps 10% of the ultraviolet light created in the host galaxy of the Fast X-ray Transient is escaping to ionise the Universe. This is the most distant event where we can directly see light escaping from around stars. Galaxies like this are probably really important for reionisation," said Andrea Saccardi, CNES Fellow at CEA Paris-Saclay, and third author of the paper.
These observations are of one of the first events detected by the Einstein Probe. "In the year since this first object we have found and studied another 20 of these outbursts, they are living up to their promise as an exciting new way to explore both how stars end their lives, and also what the Universe was like in the distant past", concluded Levan.