Astronomers Find Evidence for Stars Forming Only 250 Million Years after Big Bang
An international team of astronomers has used observations from ESO’s Very Large Telescope (VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA) to determine that star formation in the gravitationally lensed galaxy MACS1149-JD1 started only 250 million years after the Big Bang. This discovery, reported in the journal Nature, also represents the most distant oxygen ever detected in the Universe.
This image shows the galaxy cluster MACS J1149.5+2223 taken with the NASA/ESA Hubble Space Telescope; the inset image is the gravitationally lensed galaxy MACS1149-JD1, seen as it was 13.28 billion years ago and observed with ALMA. Here, the oxygen distribution detected with ALMA is depicted in green. Image credit: ALMA / ESO / NAOJ / NRAO / NASA / ESA / Hubble Team / W. Zheng, JHU / M. Postman, STScI / CLASH Team / Hashimoto et al.
The team, led by astronomers at University College London in the UK and Osaka Sangyo University in Japan, detected a very faint glow emitted by ionized oxygen in MACS1149-JD1.
As this infrared light traveled across space, the expansion of the Universe stretched it to wavelengths more than 10 times longer by the time it reached Earth and was detected by ALMA.
The researchers inferred that the signal was emitted 13.3 billion years ago (or 500 million years after the Big Bang), making it the most distant oxygen ever detected by any telescope.
Oxygen is only created in stars and then released into the gas clouds in galaxies when those stars die. The presence of oxygen in MACS1149-JD1 therefore indicates that a previous generation of stars had already formed and died at an even earlier time.
“I was thrilled to see the signal of the distant oxygen in the ALMA data. This detection pushes back the frontiers of the observable Universe,” said Dr. Takuya Hashimoto, an astronomer at both Osaka Sangyo University and the National Astronomical Observatory of Japan.
“This is an exciting discovery as 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,” added Dr. Nicolas Laporte, a postdoctoral researcher at University College London.
“We are therefore able to use this galaxy to probe into an earlier, completely uncharted, period of cosmic history!”
In addition to the glow from oxygen picked up by ALMA, a weaker signal of hydrogen emission was also detected by VLT.
The distance to the galaxy determined from this observation is consistent with the distance from the oxygen observation. This makes MACS1149-JD1 the most distant galaxy with a precise distance measurement.
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The scientists also reconstructed the earlier history of MACS1149-JD1 using infrared data taken with the NASA/ESA Hubble Space Telescope and NASA’s Spitzer Space Telescope.
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.
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.’
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 currently directly detect them.
“Determining when cosmic dawn occurred is akin to the ‘Holy Grail’ of cosmology and galaxy formation,” said Professor Richard Ellis, senior astronomer at University College London.
“With MACS1149-JD1, we have managed to probe history beyond the limits of when we can actually detect galaxies with current facilities. 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.”
“With this discovery we managed to reach the earliest phase of cosmic star formation history,” Dr. Hashimoto said.
“We are eager to find oxygen in even farther parts of the Universe and expand the horizon of human knowledge.”
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Takuya Hashimoto et al. 2018. The onset of star formation 250 million years after the Big Bang. Nature 557: 392-395; doi: 10.1038/s41586-018-0117-z