The maturity of the stars seen in MACS1149-JD1 raises the question of when the very first galaxies emerged from total darkness, an epoch astronomers call 'cosmic dawn'.
The team determined that, if the oxygen signature was from 500 million years after the Big Bang, then the first stars in that galaxy would have been born about 250 million years post-Big Bang.
The detection of oxygen at MACS1149-JD1 meant that these earlier generations of stars had been already formed and were expelling oxygen just 500m years after the beginning of the universe. As this light travelled the vast cosmic distances to Earth, it became stretched by the expansion of the universe, eventually changing into the distinct millimeter-wavelength light that ALMA is specifically created to detect and study.
To determine when these earlier stars were formed, the team used infrared data taken with the Hubble Space Telescope and the Spitzer Space Telescope and discovered that the observed brightness of the galaxy is well-explained by a model where the onset of star formation corresponds to only 250m years after the universe began.
"The mature stellar population in MACS1149-JD1 implies that stars were forming back to even earlier times, beyond what we can now see with our telescopes", says Nicolas Laporte, an astronomer on the research team. According to Takuya Hashimoto, representing the Japanese University of Osaka, this invention allows to significantly extend the boundary of the Universe studied by scientists.
"With MACS1149-JD1, we have managed to probe history beyond the limits of when we can actually detect galaxies with current facilities".
MACS1149-JD1 is the most distant known galaxy with a precise distance measurement, said the researchers. This period, commonly referred to as "cosmic dawn, ' is of particular interest because it marked the transition from a hot, dense, and almost homogeneous universe to the universe we are more familiar with today - one filled with stars, planets, nebulae, and people".
Researchers think that the earliest stars in the Universe were built in areas with a very high density of matter, even though comprehension of this phenomenon is not yet well-defined.
Richard Ellis, senior astronomer at UCL and co-author of the paper, 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!"
The earliest stars may have been forged just 250 million years after the Big Bang, say scientists who observed a galaxy at a record-setting distance of 13.28 billion light-years from Earth. "Since we are all made of a processed stellar material, this is really finding our own origins".