【天文学】ビッグバンから2億5000万年後に星形成があった

Stars may have begun to form in a particularly distant galaxy when the Universe was just 250 million years old (2% of its current age), reports a study in this week’s Nature.

One of the biggest questions in modern astronomy is when the first stars formed. However, understanding of how stars and galaxies formed during the first 300 million years of the Universe has remained limited.

Takuya Hashimoto and colleagues present spectroscopic observations made between March 2016 and April 2017 of the distant galaxy MACS1149-JD1. They report a redshift (a parameter used to indicate distance) of 9.1096, which suggests that the observations represent an indication of how the galaxy would have looked when the Universe was about 550 million years old. The authors use this precisely determined redshift to demonstrate that the observed red colours of the galaxy represent stellar components. They find that many stars in MACS1149-JD1 were around 300 million years old at that time, meaning that star formation could have started as early as 250 million years after the Big Bang.

Writing in an accompanying News & Views article, Rychard Bouwens concludes that “their discoveries seem certain to inspire similar studies of other galaxies in the distant Universe and provide fuel for observations using the future James Webb Space Telescope.”