Astronomers have made several spectacular new discoveries through observations made by the Atacama Large Millimeter / Submillimeter Array (ALMA) and the Very Large Telescope (VLT) of the European Southern Observatory (ESO) in Chile. First, they discovered the farthest galaxy ever discovered, the galaxy MACS1149-JD1, whose signal was emitted 13.3 billion years ago (or 500 million years after the Big Bang).
But that’s not all: The astronomers, led by Takuya Hashimoto of the Osaka Sangyo University and National Astronomical Observatory of Japan, also found oxygen in the distant galaxy — clearly also the most distant tracesof oxygen ever discovered in the universe. Third, this observation also implies that star formation in the far-distant galaxy MACS1149-JD1 began at an unexpectedly early stage, just 250 million years after the Big Bang.
The presence of oxygen is a clear sign that there must have been previous generations of stars in this galaxy. Soon after the Big Bang, there was no oxygen in the universe; the element was first produced by the fusion processes of the first stars and then released when these stars died. The detection of oxygen in MACS1149-JD1 shows that these earlier star generations must have already formed 500 million years after the beginning of the universe and had emitted the oxygen.
But when did this first star formation phase come about? To answer this question, the team reconstructed the earlier history of MACS1149-JD1 using infrared data taken with the NASA/ESA Hubble Space Telescope and the NASA Spitzer Space Telescope. They found that the observed brightness of the galaxy is well explained by a model in which the onset of star formation took place only 250 million years after the creation of the universe.
The state of the stars in MACS1149-JD1 raises the question of when the very first galaxies emerged from total darkness, an time which astronomers romantically refer to as the “cosmic twilight”. By determining the age of MACS1149-JD1, the team has effectively demonstrated that galaxies existed earlier than the ones we can currently see directly.
“Today, we see this galaxy as it was at the time when the universe was only 500 million years old – in which it already contains a population of developed stars,” explains Nicolas Laporte, a researcher at University College London (UCL) in the UK and second author of the article. “So we are in a position to dive through this galaxy into an even earlier, completely unknown period of cosmic history.”
Richard Ellis, senior astronomer at UCL and co-author of the work, summarizes the significance of the discovery even more dramatically: “There is renewed optimism we are getting closer and closer to witnessing directly the birth of starlight. Since we are all made of processed stellar material, this is really finding our own origins.”