ALMA finds most-distant oxygen in the Universe
ALMA OBSERVATORY/DICYT Astronomers detected a faint but definite signal of oxygen in a galaxy located 13.28 billion light-years away from us, through observations using the Atacama Large Millimeter/submillimeter Array (ALMA). Breaking their records, this marks the most distant oxygen ever detected in the Universe. Referencing infrared observations, the team determined that star formation in the galaxy started at an unexpectedly early stage: 250 million years after the Big Bang.
“I was thrilled to see the signal of the most distant oxygen,” explains Takuya Hashimoto, the lead author of the research paper published in the journal Nature and a researcher at Osaka Sangyo University and the National Astronomical Observatory of Japan.“This detection pushes back the frontiers of the observable Universe.”
An international team of astronomers led by Hashimoto used ALMA to observe a distant galaxy called MACS1149-JD1. They detected a signal from ionized oxygen in the galaxy. The infrared light emitted from oxygen was stretched to microwave wavelengths by the expansion of the Universe before it reached Earth and was observed by ALMA. The team measured the change in the wavelength of the light and found that the signal had traveled 13.28 billion light-years to reach us, making it the most distant, or oldest, oxygen ever detected by any telescope. Besides, a weaker signal of neutral hydrogen emissions was independently found with the European Southern Observatory’s Very Large Telescope; the distance determined from this observation is consistent with the range based on the oxygen observation. MACS1149-JD1 is the most distant galaxy with a precise distance measurement.
For a period after the Big Bang, there was no oxygen in the Universe. Oxygen was created in stars and then released when the stars died. The detection of oxygen in MACS1149-JD1 indicates that an earlier generation of stars had been already formed and expelled processed oxygen by the epoch of observation, which is only about 500 million years after the beginning of the Universe.
The team then reconstructed the star formation history in the galaxy using infrared data taken with the NASA/ESA Hubble Space Telescope and NASA Spitzer Space Telescope. The observed brightness of the galaxy is well explained by a model where the onset of star formation was another 250 million years ago.
The model indicates that the star formation became inactive once after the first ignition, and then revived at the epoch of the ALMA observations; 500 million years after the Big Bang. The astronomers suppose that the first star-formation burst blew the gas away from the galaxy, which would suppress the star formation. Then, the gas returned to the galaxy leading to the second burst of star formation. The massive newborn stars in the second burst ionize oxygen, and it’s those emissions that have been detected with ALMA.
“The mature stellar population in MACS1149-JD1 implies that stars were forming back to even earlier times, beyond what we can currently see with our telescopes. This has fascinating implications for finding `cosmic dawn’ when the first galaxies emerged” adds Nicolas Laporte, a researcher at University College London / Université de Toulouse and a member of the research team.
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. Several months later, Nicolas Laporte and his team used ALMA to detect oxygen at 13.2 billion light-years away. Now, the two teams merged into one and achieved this new record. “This reflects both; the competitive and the collaborative nature of the forefront of scientific research,” said Inoue.
Richard Ellis, a senior astronomer at University College London (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! Since we are all made of processed stellar material, this is really finding our own origins.”