Understanding how galaxies are created has long been a critical study for scientists. In a study published in this week’s Science, an international team of scientists have discovered the most distant, and therefore oldest, signs of oxygen in the Universe.
The galaxy in question is SXDF-NB1006-2, which was discovered in 2012 and is a 13.1 billion light years from Earth, less than a billion years from the Big Bang. Using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile, the researchers were able to detect radiation emitted from doubly ionised oxygen, or O2+. Concentrated levels of O2+ can be found in nebulae, interstellar clouds of dust, hydrogen, helium and other ionised gases, which provide the building blocks for planets and planetary systems and gives an insight into what the Universe was like in ancient times.
It was calculated that the amount of oxygen detected in SXDF-NB1006-2 equates to an amount much smaller than that of our Sun. “This galaxy contains one tenth of oxygen found in our Sun,” explains co-author Naoki Yoshida. “But the small abundance is expected because the Universe was still young and had a short history of star formation at that time.”
At its inception around 14 billion years ago, the Universe contained only hot ionised gas clouds composed of electrons and ions of hydrogen and helium (the two lightest elements). After 400,000 years it began to cool and electrons and hydrogen ions combined to form neutral hydrogen atoms, and then nothing until the first generation of stars formed several hundreds of millions of years later. The first stars were formed by gravitational forces pulling gas clouds and dust together, generating heat and initiating nuclear reactions, which fuels all stars.
These stars also emitted strong radiation that reionised hydrogen once more, and generated the formation of heavier elements, such as oxygen. Studying heavy elements in distant galaxies can provide clues as to what triggered reionisation events and the composition of the first stars.
“This is the first step to understanding what kind of objects caused cosmic reionisation,” says co-author Youichi Tamura.
Further observations using the ALMA telescope are already underway with the aim of collecting higher resolution images with more details about the amount of ionised oxygen in SXDF-NB1006-2 and its motion.