Free Astronomy Magazine July-August 2019

47 JULY-AUGUST 2019 SPACE CHRONICLES and his team observed the distant galaxy MACS0416_Y1. Because of the finite speed of light, the radio waves we observe from this galaxy today had to travel for 13.2 billion years to reach us. In other words, they provide an image of what the galaxy looked like 13.2 billion years ago, which is only 600 million years after the Big Bang. The astronomers detected a weak but telltale signal of radio emissions from dust particles in MACS0416_Y1. The Hubble Space Telescope, the Spitzer Space Telescope, and the Eu- ropean Southern Observatory’s Very Large Telescope have observed the light from stars in the galaxy; and ! A LMA and Hubble Space Telescope (HST) image of the distant galaxy MACS0416_Y1. Distribution of dust and oxygen gas traced by ALMA are shown in red and green, respectively, while the distribution of stars captured by HST is shown in blue. [ALMA (ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope, Tamura, et al.] from its color they estimate the stel- lar age to be 4 million years. “It ain’t easy,” said Tamura half-lost in a moonage daydream. “The dust is too abundant to have been formed in 4 million years. It is surprising, but we need to hang onto ourselves. Older stars might be hiding in the galaxy, or they may have died out and disappeared already.” “There have been several ideas pro- posed to overcome this dust budget crisis,” said Ken Mawatari, a re- searcher at the University of Tokyo. “However, no one is conclusive. We made a new model which doesn’t need any extreme assumptions di- verging far from our knowledge of the life of stars in today’s Universe. The model well explains both the color of the galaxy and the amount of dust.” In this model, the first burst of star formation started at 300 million years and lasted 100 mil- lion years. After that, the star forma- tion activity went quiet for a while and then restarted at 600 million years. The researchers think ALMA observed this galaxy at the begin- ning of its second generation of star formation. “Dust is a crucial material for planets like Earth,” explains Tamura. “Our result is an important step forward for understanding the early history of the Universe and the origin of dust.”