Hold your breath: oxygen found in the very early Universe Read time: 3 minutes Every breath you take contains a lot of oxygen. Oxygen gas is an important ingredient of our atmosphere. Without it, there would be no human life on Earth. Astronomers know that all oxygen atoms in the Universe were produced in stars. When the Universe was born in the Big Bang, some 13.8 billion years ago, there was no oxygen at all. Oxygen atoms only formed later, in the interiors of stars, by a process known as nuclear fusion. When a star explodes as a supernova, the oxygen atoms are blown into space. Eventually, some of them found their way into the cloud that spawned our Solar System. Using ALMA, astronomers have now detected the very earliest oxygen atoms in the Universe. They observed a galaxy that is so far away that its light took 13.28 billion light-years to reach us. In other words: we see the galaxy as it was 13.28 billion years ago – just some 500 million years after the Big Bang. In the galaxy’s light, the astronomers detected radiation that is emitted by glowing oxygen atoms. Apparently, there was already oxygen around when the Universe was just 500 million years old. Never before has oxygen been detected at such an early stage in cosmic history. So, what exactly happened in those first 500 million years? The astronomers think they know. Just 250 million years after the Big Bang, the galaxy was already forming, and the first massive stars started to shine. They produced a lot of oxygen in their cores (as well as other elements), and when they exploded, the oxygen was blown into space. However, the supernova explosions also blew most of the star-forming gas out of the galaxy. As a result, the formation of new stars stalled. But a few hundred million years later, the gas started to fall back, and there was a new burst of star formation. The energy of these later generation of stars caused the oxygen atoms to glow. Something similar may have happened in our own Milky Way galaxy, when it was just a few hundred million years old. Over time, as more and more stars ended their lives in supernova explosions, the amount of oxygen atoms increased. Eventually, some of them became incorporated in the cloud of gas and dust from which our Solar System formed. Next time when you take a deep breath, take a moment to realize that you’re breathing star stuff! What? The glowing oxygen atoms were detected in a faint, remote galaxy known as MACS 1149-JD1. Oxygen atoms normally have six electrons orbiting the nucleus. But because of the energy of neighboring stars, most oxygen atoms had lost two of their electrons. As a result, they started to glow at infrared wavelengths. When this infrared light travels toward Earth on its 13.28 billion-year-journey, the light waves are stretched by the expansion of the Universe, all the way into millimeter waves that can be observed by ALMA. Who? In 2016, Japanese astronomer Akio Inoue of Osaka Sangyo University already studied oxygen in the distant Universe, together with his colleagues. Another group, led by Nicolas Laporte of the University of Toulouse in France, carried out similar observations. In 2017, the two competing groups decided to work together. The new, larger team is led by Akio’s colleague Takuya Hashimoto. The new ALMA results on the detection of oxygen in the galaxy MACS 1149-JD1 have been published in the scientific weekly magazine Nature. ALMA URL