Star formation underway 250 million years after Big Bang

In this composite image, a galaxy cluster observed by the Hubble Space Telescope is shown along with a faint member (inset) known as MACS1149-JD1 that was observed by the ALMA instrument. Oxygen distribution is shown in red. The galaxy is believed to contain stars that were shining just 250 million years after the Big Bang. Image: ALMA (ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope, W. Zheng (JHU), M. Postman (STScI), the CLASH Team, Hashimoto et al

Astronomers have observed a galaxy 13.3 billion light years away that includes stars that must have been shining just 250 million years after the Big Bang.

“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,” said Nicolas Laporte, a researcher at University College London and co-author of a paper describing the observations. “We are therefore able to use this galaxy to probe into an earlier, completely uncharted period of cosmic history.”

Using the Atacama Large Millimetre/submillimetre Array (ALMA) and the European Southern Observatory’s Very Large Telescope, the team found extremely red shifted traces of ionised oxygen emitted from a remote galaxy known as MACS1149-JD1 some 13.3 billion years ago. The most likely explanation for the presence of oxygen is that it was cooked up in earlier generations of suns.

A weaker hydrogen emission also was observed by the VLT, indicating a distance consistent with the oxygen observation. MACS1149-JD1 is thus the most distant galaxy ever observed by ALMA of the VLT and the origin of the most distant oxygen ever observed by any instrument.

“I was thrilled to see the signal … in the ALMA data,” said Takuya Hashimoto, a researcher at both Osaka Sangyo University and the National Astronomical Observatory of Japan, lead author of a paper in the journal Nature. “This detection pushes back the frontiers of the observable Universe.”

Oxygen was not created in the Big Bang explosion that gave birth to the universe. Oxygen and other heavier elements were created in the cores of massive stars and then released into the surrounding space when those stars exploded or blew off their outer atmospheres. Those elements, along with hydrogen and helium and other trace elements generated at the birth of the cosmos, then served as the raw materials for subsequent generations.

To find out when the stars in MACS1149-JD1 started shining, Hashimoto’s team used infrared data from the Hubble Space Telescope and NASA’s Spitzer Space Telescope to determine the observed brightness of the galaxy was well explained by a model in which the onset of star formation was well underway just 250 million years after the Big Bang.

But when did the first galaxies form in the early epoch known as “cosmic dawn?” The MACS1149-JD1 observation shows galaxies must have existed before any that are currently detectable.

“Determining when cosmic dawn occurred is akin to the Holy Grail of cosmology and galaxy formation,” said Richard Ellis, senior astronomer at UCL and co-author of the Nature paper. “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.”