ALMA finds oxygen in the early Universe
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Astronomers have detected oxygen in a distant galaxy. The galaxy is so far away that its light has taken 13.1 billion years to reach us. That means that we see the galaxy as it was 13.1 billion years ago, when the Universe was ‘only’ 700 million years old. So it’s also fair to say that astronomers have detected oxygen in the early youth of our Universe. The discovery was made with the ALMA observatory in Chile.
Oxygen is a gas. It’s one of the main constituents of the atmosphere. People and animals need oxygen to breathe. But the discovery of oxygen in the early Universe doesn’t mean there were people or animals around back then: 13.1 billion years ago, there was no life.
Still, the new discovery is very important. When the Universe was born (13.8 billion years ago), it contained only the two very lightest elements in Nature: hydrogen and helium. All other elements, including oxygen, have been produced at a later stage, in the hot interiors of stars. So the discovery of oxygen only 700 million years after the birth of the Universe tells you something about the evolution of the very first stars.
And there’s more. The oxygen in the distant galaxy was ‘doubly ionized’. That means that the oxygen atoms have lost two of their electrons. This can only occur if there’s a lot of high-energy radiation around. That radiation must come from other young giant stars, dozens of times more massive than our own Sun.
The relative amount of oxygen discovered in the distant galaxy is not very large: about ten times smaller than the relative amount in our own Sun. That’s because the Universe was still young – not much oxygen had been produced back then. The amount of carbon gas and dust particles in the distant galaxy is even smaller.
The new discovery reveals that the very first stars produced a lot of energetic radiation. Because there was so little dust around, this radiation could easily escape the galaxy. So probably the first stars were able to clear up the murky fog of cold hydrogen gas that was present in the space between galaxies.
All in all, the oxygen discovery is a good example of the way in which ALMA observations can reveal a lot of information on what was going on in the very early Universe.
The oxygen was discovered in a distant galaxy known as SXDF-NB1006-2. This is a very small and faint galaxy, at a distance of 13.1 billion light-years. During their 13.1-billion-year trip from the galaxy to the Earth, the light waves were stretched by the expansion of the Universe, just like a wiggly line on a piece of rubber is stretched when you pull the rubber. As a result, the waves from doubly ionized oxygen were stretched from 88 micrometers to 725 micrometers, making them observable to ALMA.
The discovery was made by a group of astronomers from Japan, Sweden, the United Kingdom and the European Southern Observatory, led by Akio Inoue of Osaka Sangyo University in Japan. Before they were allowed to use ALMA to search for oxygen in distant galaxies, Akio and his colleagues first carried out computer simulations to show that the signal would indeed be detectable. The discovery was published on 16 June 2016 in the international weekly magazine Science.