Tokyo: In a first, an international team of astronomers have found firm evidence of the presence of oxygen in the early universe -- only 700 million years after the Big Bang. Using the Atacama Large Millimetre/submillimetre Array (ALMA) telescope in Chile, the team including scientists from Japan, Sweden, Britain and European Southern Observatory found light from ionised oxygen in the SXDF-NB1006-2 galaxy -- making it the most distant unambiguous detection of oxygen ever obtained. SXDF-NB1006-2 lies at a redshift of 7.2, meaning that we see it only 700 million years after the Big Bang. Oxygen in SXDF-NB1006-2 was found to be 10 times less abundant than it is in the Sun, according to the study published recently in the journal Science. "The small abundance is expected because the universe was still young and had a short history of star formation at that time," said study co-author Naoki Yoshida from the University of Tokyo. "Our simulation actually predicted an abundance 10 times smaller than the Sun. But we have another, unexpected, result: a very small amount of dust," he added. The detection of ionised oxygen indicates that many very brilliant stars, several dozen times more massive than the Sun, have formed in the galaxy and are emitting the intense ultraviolet light needed to ionise the oxygen atoms. In the time before objects formed in the universe, it was filled with electrically neutral gas. But when the first objects began to shine, a few hundred million years after the Big Bang, they emitted powerful radiation that started to break up those neutral atoms -- to ionise the gas. During this phase -- known as cosmic reionization -- the whole universe changed dramatically. But there is much debate about exactly what kind of objects caused the reionization. Studying the conditions in very distant galaxies can help to answer this question. "SXDF-NB1006-2 would be a prototype of the light sources responsible for the cosmic reionization," said lead author Akio Inoue from Osaka Sangyo University in Japan.