Division of Science, NAOJ

2025.6.3 highlights

Cosmic Himalayas Quasar Cluster Defies Explanation

The densest cluster of supermassive black holes identified in the Universe. The background image was taken by Hyper Suprime-Cam on the Subaru Telescope. The red and blue shadows represent the density of the supermassive black holes (quasars) and the surrounding hundreds of young, star-forming galaxies, respectively. The white squares frame the quasars, and the larger squares show close up images. (Credit: Subaru Telescope / SDSS, Liang et al.)

A newly discovered cluster of eleven quasars has shattered the previous record of five. Rather than being associated with a dense group of galaxies, these quasars sit on the boundary between two groups of galaxies. This structure, dubbed the “Cosmic Himalayas,” cannot be explained by conventional theories, forcing astronomers to rethink the formation scenarios for quasars.

Quasars are some of the brightest objects in the Universe. A quasar is powered by large amounts of matter falling into the supermassive black hole at the center of a galaxy. Collisions and mergers between galaxies can cause quasar activity by feeding addition matter into the center of a galaxy. Quasar activity peaked in the early Universe, but even then they were relatively rare. So an international research team led by Yongming Liang at the National Astronomical Observatory of Japan was surprised when they found a group of elven quasars in an area of space where you would normally expect to see maybe one, while analyzing data from the Sloan Digital Sky Survey. The previous record holder for quasar over-density had been five.

Follow-up observations with the Subaru Telescope revealed another mystery. The quasars do not coincide with a dense group of galaxies. Instead, they sit on the boundary between two groups. If galaxy collisions and mergers are responsible for quasar activity, then the densest groups of quasars should be found in the densest group of galaxies. A new formation scenario is needed to explain this group of quasars, which could change the way we think about the evolution of other structures in the Universe. The team hopes that new data from next-generation instruments like the Prime Focus Spectrograph on the Subaru Telescope will help to solve the mysteries of the Cosmic Himalayas.

The research team named this formation the Cosmic Himalayas in reference to how the towering Himalayas on Earth form a boundary between plains and plateaus. The Cosmic Himalayas date back 10.8 billion years. As seen from Earth, this cluster lies in the direction of the constellation Cetus.

Figure 1. Cosmic Himalayas Quasar Cluster. The background image is from Hyper Suprime-Cam on the Subaru Telescope. The yellow and blue shadows represent the density of the quasars and the surrounding hundreds of young, star-forming galaxies, respectively. The small white squares frame the quasars, and the larger squares show close-up images. (Credit: Subaru Telescope / SDSS, Liang et al.)

Detailed Article
The Giant Supermassive Black Hole Cluster Discovered in the Distant Universe: New Puzzles in the Cosmic Matter Distribution (Subaru Telescope)
https://subarutelescope.org/en/results/2025/06/02/3559.html

Researchers Involved in this Release
Liang, Yongming (National Astronomical Observatory of Japan)
Masami Ouchi (The University of Tokyo)

Coordinated Release Organization(s)
National Astronomical Observatory of Japan
The University of Tokyo
University of California, Santa Cruz

Paper
Liang et al. “Cosmic Himalayas: The Highest Quasar Density Peak Identified in a 10,000 deg 2 Sky with Spatial Discrepancies between Galaxies, Quasars, and IGM HI” in Astrophysical Journal
https://iopscience.iop.org/article/10.3847/1538-4357/adc1bb