Free Astronomy Magazine July-August 2018

33 JULY-AUGUST 2018 SPACE CHRONICLES that the observed brightness of the galaxy is well-explained by a model where the onset of star formation corresponds to 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 romantically term “cosmic dawn”. By establishing the age of MACS 1149-JD1, the team has effectively demonstrated that galaxies existed earlier than those we can currently directly detect. Richard Ellis, senior astronomer at UCL and co-author of the paper, concludes: “Determin- ing 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.” T his computer graphics movie shows the probable star for- mation history in the galaxy MACS1149-JD1. The self-grav- ity of matter creates filamentary structures and the density at the intersections of the filaments increases. Around 200 million years after the Big Bang, active star formation ignites in the high density regions, which leads to the formation of galaxies. The gas in the galaxy is blown off by active stellar wind and supernovae, then the gas returns to the galaxy and causes an- other burst of star formation. [ALMA (ESO/NAOJ/NRAO)] formed and expelled oxygen by just 500 million years after the begin- ning of the Universe. But when did this earlier star forma- tion occur? To find out, the team re- constructed the earlier history of MACS1149-JD1 using infrared data taken with the NASA/ESA Hubble Space Telescope and the NASA Spitzer Space Telescope. They found !