Washington:  After detecting a whiff of oxygen, astronomers have determined that stars in a faraway galaxy formed 250 million years after the Big Bang – a rather short time in cosmic terms – in a finding that sheds light on conditions in the early universe.

Their research, published on Wednesday, provides insight into star formation in perhaps the most distant galaxy ever observed. The scientists viewed the galaxy, called MACS1149-JD1, as it existed roughly 550 million years after the Big Bang, which gave rise to the universe about 13.8 billion years ago.

Light emitted by MACS1149-JD1 traveled 13.28 billon light years before reaching Earth. Looking across such distances lets scientists peer back in time. A light year is the distance light travels in a year, 9.5 trillion kilometres.

The detection of oxygen in MACS1149-JD1 was particularly instructive. The universe initially was devoid of elements such as oxygen, carbon and nitrogen, which were first created in the fusion furnaces of the earliest stars and then spewed into interstellar space when these stars reached their explosive deaths.

The presence of oxygen showed that an even earlier generation of stars had formed and died in MACS1149-JD1 and that star formation in that galaxy began about 250 million years after the Big Bang when the universe was only about 2 per cent of its current age, the researchers said.