The Secret of Very Massive Galaxies Unveiled by the Most Powerful Space Telescope Ever Built

Released: 4th Nov., 2022, Academia Sinica, Institute of Astronomy & Astrophysics (ASIAA), Taiwan

The most massive galaxies in the Universe can be ten times more massive than our Milky Way, and evidence suggest that most of their masses were formed within a very short period in the early Universe. Exactly how they assemble so much mass during their short formation lifetime has kept astrophysicists scratching their heads.

Now a research team led by Chian-Chou Chen at the Academia Sinica Institute of Astronomy and Astrophysics has used the data taken by the newly launched James Webb Space Telescope (JWST) and unveiled in the most exquisite detail ever the structures of these massive galaxies during their formation period. The team has found that these galaxies not only form masses in a speed that is over one hundred times faster than that of the Milky Way, but also form these masses in compact regions that are close to the center of these galaxies. On the other hand, the team has also found that while these central regions are in an active phase of mass assembly, most of the masses in the entire galaxies are found in the outskirts, potentially formed in the previous formation epochs.

These findings are enabled the first time thanks to the high spatial resolution offered by the JWST (Figure 1), as well as its capability of observing in mid-infrared, where the underlying mass structures can be more faithfully unveiled. These findings have helped astrophysicists move a key step forward in understanding the formation mechanisms of these very massive galaxies.

“This work demonstrates the power of the JWST in revolutionizing our understanding about how do galaxies form and evolve. Since JWST has sufficient fuel for at least two decades, scientists expect to make more groundbreaking discoveries with this most powerful space telescope ever built,” said the lead author Chian-Chou Chen.

Figure 1. Sizes in observed wavelengths of our sample galaxies are shown in grey points. The median values of each waveband are shown in larger black points. Empty symbols are previous measurements. On the top we show cutout images with from HST, Spitzer, and JWST of one of our sample galaxy, and these cutouts are aligned vertically roughly to the wavelengths shown in the x-axis below. Our results suggest that in the active formation phase massive galaxies form their masses in the central compact regions, although most of their masses are located in the outskirts, presumably formed in the previous formation episodes. Credit: Chen et al.

More Information:

This research was presented in a paper “JWST Sneaks a Peek at the Stellar Morphology of z ∼ 2 Submillimeter Galaxies: Bulge Formation at Cosmic Noon” by Chen et al. appeared in Astrophysical Journal Letters.

The team is composed of Chian-Chou Chen (ASIAA, Taiwan), Zhen-Kai Gao(ASIAA, Taiwan; NCU, Taiwan), Qi-Ning Hsu (ASIAA, Taiwan; NTU, Taiwan), Cheng-Lin Liao (ASIAA, Taiwan; NTU, Taiwan), Yu-Han Ling (ASIAA, Taiwan), Ching-Min Lo (ASIAA, Taiwan), Ian Smail (Durham University, UK), Wei-Hao Wang (ASIAA, Taiwan), and Yu-Jan Wang (ASIAA, Taiwan)

Media Contact:

Dr. Chian-Chou Chen, Email:, Tel: +886 2 2366 5438