天文学：JW宇宙望遠鏡観測結果の早期発表をもとにした非常に遠方の大質量銀河の発見

Observations of a population of candidate massive galaxies that formed around 500–700 million years after the Big Bang are published in Nature today. These galaxies are more massive than has been expected for this early point in time. The observations, part of the first release of data from the James Webb Space Telescope (JWST), offer insights into early galaxy formation.

Massive galaxies with stellar masses as high as 100 billion times that of the Sun have been identified at redshifts z ~ 6, approximately one billion years after the Big Bang, but it has been difficult to find massive galaxies at even earlier times. Redshift is a measure of the age of an astronomical object: due to the expansion of the Universe, light from distant objects shifts to wavelengths towards the red end of the spectrum — the redder the image, the more distant the object is.

Ivo Labbé and colleagues searched for massive galaxies in the first 750 million years of cosmic history by selecting candidates at high redshifts (z = 6.5 and z = 9.1), as observed by the JWST. The authors identify six candidate massive galaxies with redshifts between z = 7.5 and z = 9.1 with masses up to ten billion times that of our Sun, including one galaxy with a possible stellar mass 100 billion times that of the Sun.

The mass of the observed galaxies exceeds expected values. If verified with spectroscopy, these findings provide evidence to suggest that galaxies grew massive quicker than expected early in the history of the Universe.