Free Astronomy Magazine July-August 2018

32 JULY-AUGUST 2018 SPACE CHRONICLES Evidence for stars forming just 250 million years after Big Bang by ESO A n international team of astronomers used ALMA to observe a distant galaxy called MACS1149-JD1. They detected a very faint glow emitted by ionised oxygen in the galaxy. 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. The team 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 de- tected by any telescope. The presence of oxy- gen is a clear sign that there must have been even earlier generations of stars in this galaxy. “I was thrilled to see the signal of the distant oxygen in the ALMA data,” says Takuya Hashimoto, the lead author of the new paper and a researcher at both Osaka Sangyo Uni- versity and the National Astronomical Obser- vatory of Japan. “This detection pushes back the frontiers of the observable Universe.” In addition to the glow from oxygen picked up by ALMA, a weaker signal of hydrogen emis- sion was also detected by ESO’s Very Large Telescope (VLT). The distance to the galaxy de- termined from this observation is consistent with the distance from the oxygen observa- tion. This makes MACS1149-JD1 the most dis- T his image shows the galaxy cluster MACS J1149.5+2223 taken with the NASA/ESA Hubble Space Telescope; the inset image is the very distant galaxy MACS1149-JD1, seen as it was 13.3 billion years ago and observed with ALMA. Here, the oxygen distribution detected with ALMA is depicted in red. [ALMA (ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope, W. Zheng (JHU), M. Postman (STScI), the CLASH Team, Hashimoto et al.] tant galaxy with a precise distance measure- ment and the most distant galaxy ever ob- served with ALMA or the VLT. “This galaxy is seen at a time when the Uni- verse was only 500 million years old and yet it already has a population of mature stars,” ex- plains Nicolas Laporte, a researcher at Univer- sity College London (UCL) in the UK and second author of the new paper. “We are therefore able to use this galaxy to probe into an earlier, completely uncharted period of cosmic history.” For a period after the Big Bang there was no oxygen in the Universe; it was created by the fusion processes of the first stars and then re- leased when these stars died. The detection of oxygen in MACS1149-JD1 indicates that these earlier generations of stars had been already