Four 'Little Red Dot' pairs hint at black hole mergers in early universe

Utilizing infrared images from the James Webb Space Telescope (JWST), an international group of researchers has identified multiple massive black holes, which were actively growing and potentially merging, existing 12.5–12.8 billion years ago. These findings, published on August 31st in the Publications of the Astronomical Society of Japan, could provide insights into the role that black hole mergers played during the early stages of black hole evolution.

The study demonstrates the potential for these mergers to transport substantial amounts of gas toward the centers of galaxies, thereby driving matter towards the central black hole. The researchers employed a new, more refined method for identifying these black hole pairs, as conventional techniques could have mistakenly treated two closely situated black holes as a single, complex object.

This novel pixel-by-pixel color selection method pinpointed four pairs of Little Red Dots (LRDs) positioned extremely close to each other, with distances ranging from a few thousand to a few tens of thousands of light-years—significantly smaller than our Milky Way galaxy's span of 100,000 light-years. To confirm the proximity of these LRDs, the researchers calculated the likelihood of such close pairings occurring by chance based on the number and distribution of LRDs in the region, discovering it to be improbable that all four pairs appeared merely by chance, suggesting a strong clustering of LRDs on a kilo-parsec scale.

Merger events are believed to be instrumental in transporting vast quantities of gas toward the cores of galaxies, facilitating the growth of central black holes. The results of this research imply that black hole mergers in the early universe might also play a significant role in the growth of black holes. In the event that each LRD harbors a growing black hole, these black holes could eventually merge themselves.

Should these mergers transpire, they could potentially be detected by forthcoming gravitational-wave observatories. The forthcoming task for the researchers will involve a more comprehensive examination of the identified dual LRDs and the enhancement of their innovative method through its application to a broader dataset.