With the help of the Atacama large Millimeter/submillimeter Array, astronomers have detected the earliest signs of oxygen (red) distributed in the galaxy MACS1149-JD1.
The fact that it was an oxygen line is significant: No oxygen was produced in the big bang; it was formed later when hydrogen gas coalesced into the first generation of stars and fusion reactions in their cores forged hydrogen into oxygen and other elements. The observed brightness of the galaxy is well explained by a model where the onset of star formation corresponds to a time only 250 million years after the Universe began.
In a new study set for publication tomorrow in the journal Nature, an global team of astronomers used this impressive array to observe an extremely distant galaxy called MACS1149-JD1. These hot, ionized atoms then "glowed" brightly in infrared light. As this infrared light travelled across space, the expansion of the Universe stretched it to wavelengths more than ten times longer by the time it reached Earth and was detected by ALMA.
It also breaks the record for the oldest oxygen ever detected, at 13.28 billion light-years away (500 million years after the Big Bang) - the smoking gun for that early star formation. This distance estimate was further confirmed by observations of neutral hydrogen in the galaxy by the European Southern Observatory's Very Large Telescope.
"Determining when cosmic dawn occurred is akin to the Holy Grail of cosmology and galaxy formation", said co-author Richard Ellis, an astronomer at University College London, in a press release. To find out, 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. The model indicates that the star formation became inactive after the first stars ignited. The gas then fell back into the galaxy leading to the second burst of star formation.
By establishing the age of MACS1149-JD1, the team has effectively demonstrated the existence of early galaxies to times earlier than those where we can now directly detect them.
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 romantically term "cosmic dawn".
"I am sure that the future combination of ALMA and the James Webb Space Telescope will play an even greater role in our exploration of the first generation of stars and galaxies", said Zheng.
ALMA has set the record for the most distant oxygen several times. In 2016, Akio Inoue at Osaka Sangyo University and his colleagues found the signal of oxygen at 13.1 billion light-years away with ALMA. Now, the two teams merged into one and achieved this new record. This reflects both the competitive and collaborative nature of forefront of scientific research. "We are therefore able to use this galaxy to probe into an earlier, completely uncharted, period of cosmic history!" explained Dr Nicolas Laporte, second author and a postdoctoral researcher at UCL who led the VLT observing campaign".
The stars pumping out oxygen in MACS1149-JD1 are calculated to be approximately 13.3 billion years old, so around 500 million years after the Big Bang, but naturally to reach a stage of emitting oxygen they must have formed much earlier - about 250 million years earlier, say the worldwide team of astronomers who spotted them.
The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under a cooperative agreement by Associated Universities, Inc.
The Atacama Large Millimeter/submillimeter Array (ALMA), an global astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile.