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The Rigakubu News
The Rigakubu News, May. 2026
Research Student Communicates to Faculty >
Supermassive Black Holes Driving the Evolution of Massive Galaxies in the Distant Universe
Nobunari Kashikawa (Professor, Department of Astronomy)
Observations by the James Webb Space Telescope (JWST) have revealed that
a galaxy harboring an active supermassive black hole in the universe 12.9 billion years ago
rapidly ceased star formation several hundred million years ago
and is now in the process of evolving into a mature galaxy.
This suggests that the intense radiation emitted by the central black hole as it grew may have
halted star formation in the host galaxy.
Among the stars shining in the night sky, there are likely some that have just been born. Galaxies are constantly giving birth to stars somewhere, thereby maintaining their brightness.Meanwhile, at the center of nearly every galaxy lies a supermassive black hole—weighing between 100,000 and several tens of billions of times the mass of the Sun, yet 10 orders of magnitude smaller than the galaxy itself. Black holes that shine brightly due to the energy emitted as matter falls into them are called “quasars” and are important observational targets in the distant universe.It is known that, despite their vastly different sizes, there is a strong correlation between the masses of a host galaxy and its central black hole. This suggests that the two have grown while influencing each other over the long history of the universe; however, it remains unclear when this relationship began or why such a correlation exists.
Our research group, which had previously succeeded in detecting the host galaxies of quasars in the distant universe for the first time, observed two quasars located 12.9 billion light-years away using the JWST, which currently boasts the highest sensitivity. As a result, we detected absorption lines of neutral hydrogen in the spectra of their host galaxies—a feature not typically observed.This is evidence that there are few young stars within the host galaxies and that their growth has stopped or slowed down following a period of explosive star formation that occurred hundreds of millions of years prior to the observation. Furthermore, we found that one of these quasars exhibits a feature known as a “Balmer break,” indicating that the galaxy is composed of relatively old stars.
It is surprising that a galaxy in the process of ceasing star formation has been discovered in the distant universe 12.9 billion years ago. This is because galaxies with these characteristics had previously only been discovered up to about 8 billion years ago.Analysis of JWST’s multi-wavelength data also revealed that both galaxies are massive galaxies with stellar masses of 60 billion and 40 billion times that of the Sun, respectively.A black hole continues to be active at the center of a massive galaxy that is entering a mature phase and ceasing star formation. It is possible that this black hole, through its intense radiation, heated the gas within its host galaxy, thereby halting star formation. These observations have revealed a new aspect of the co-evolution of these two objects in the early universe.
The results of this study were published in M. Onoue et al., *Nature Astronomy*, 9, 1541 (2025).
The JWST spectrum (light blue) of the host galaxy of one of the observed quasars, J2236+0032, and the galactic model spectrum (dark blue) that best fits it. The inset on the left shows a magnified view of the spectrum near 3 µm. Balmer absorption lines from neutral hydrogen are clearly detected. The inset on the right shows an image of the host galaxy of the detected quasar.