Observations of the extremely distant galaxy MACS1149-JD1 made by the Atacama Large Millimetre/submillimetre Array (ALMA) and European Southern Observatory’s Very Large Telescope (VLT) revealed evidence for star formation just 250 million years after the Big Bang. This discovery also marks the most distant oxygen ever detected in the universe as well as the most distant galaxy ever observed by either ALMA or the VLT.
ALMA and an international team of astronomers detected a very faint glow in MACS1149-JD1 that exposed the presence of ionised oxygen. The infrared light detected came from a source on the other side of the universe, and this is a universe that continues to expand. The cosmic expansion stretched the wavelength of the light by more than ten times by the time it reached Earth and found its way to ALMA. Analysis of the signal revealed that the light was emitted 13.3 billion years ago, which is just 500 million years after the Big Bang. This is the most distant oxygen emission ever detected by any telescope and also suggests that there must have been earlier generations of stars in the galaxy.
“I was thrilled to see the signal of the distant oxygen in the ALMA data,” says Takuya Hashimoto, a researcher at both Osaka Sangyo University and the National Astronomical Observatory of Japan. “This detection pushes back the frontiers of the observable universe.”
In addition to this oxygen detection, a weaker hydrogen signal from the same galaxy was detected by the VLT. Similar distance measurements were made on the hydrogen signal, and the results were consistent with the oxygen observations. By having two consistent distance measurements, astronomers can safely say that this is the most distant galaxy observed by both ALMA and the VLT.
“This galaxy is seen at a time when the universe was only 500 million years old, and yet it already has a population of mature stars,” explains Nicolas Laporte, a researcher at University College London (UCL) in the United Kingdom. “We are therefore able to use this galaxy to probe into an earlier, completely uncharted period of cosmic history.”
After the Big Bang, the universe was just made up of hydrogen and helium, with no oxygen at all. Oxygen was only created after the first stars synthesised it via nuclear fusion and then expelled it into the cosmos after the star’s death. So for oxygen to be detected in a galaxy just 500 million years after the Big Bang, this implies that earlier generations of stars must of synthesised it.
In an attempt to find out when these stars could have existed, astronomers used infrared data collected by NASA/ESA’s Hubble Space Telescope and NASA’s Spitzer Space Telescope to model the evolution of MACS1149-JD1. The model that best explains the current observations is where an onset of star formation occurred only 250 million years after the birth of the universe.
The fact that stars in MACS1149-JD1 have aged relatively rapidly in young galaxies makes astronomers question the emergence of the first galaxies formed out of total darkness, a period after the Big Bang called ‘cosmic dawn’. Determining the age of MACS1149-JD1 has allowed this team of astronomers to make the strong case that galaxies existed sooner than those that have been directly detected.
Richard Ellis, senior astronomer at UCL, concludes: “Determining when cosmic dawn occurred is akin to the holy grail of cosmology and galaxy formation. With these new observations of MACS1149-JD1 we are getting closer to directly witnessing the birth of starlight! Since we are all made of processed stellar material, this is really finding our own origins.”
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