The most massive black hole has been discovered in the "Cosmic Horseshoe."

In 2007, during the Sloan Digital Sky Survey, astronomers discovered the gravitationally lensed system known as the "Cosmic Horseshoe" (SDSS J1148+1930), which was later studied using the Hubble Space Telescope.

The images obtained confirmed its structure, allowing for a view of both the horseshoe-shaped "ring" and the lensing galaxy as they appeared approximately four to five billion years ago and ten billion years ago, respectively. This means that the nearest massive galaxy acts as the "lens," while the "ring" is formed by the bent light from a more distant object.

Now, a team of astrophysicists led by Carlos R. Melo-Carneiro from the Federal University of Rio Grande do Sul in Brazil has presented a new analysis of the "Cosmic Horseshoe." The results of their study, published on the Cornell University preprint server, indicate that at the center of the lensing galaxy, there likely resides a record-setting black hole with a mass of about 36 billion solar masses.

The astrophysicists reached this conclusion upon discovering what is known as a "radial arc" in the system. If arcs are oriented along the radial direction from the center of the lensing object (such as a cluster of galaxies), they are sometimes referred to as "radial arcs," in contrast to "tangential arcs," which are elongated along a circle around the center. It is through the study of radial arcs that scientists learn about the presence of supermassive black holes and other characteristics.

Thus, by re-examining the images obtained from Hubble, the authors of the scientific paper analyzed the shape and position of the radial arc and the "ring" (the outer arc), and then, using the MUSE spectrograph mounted on the VLT telescope, measured the velocities of stars at different points in the galaxy.

By combining both data sets into a unified model, the astrophysicists concluded that at the center of the lens lies a component similar to a black hole with a mass of approximately 36 billion solar masses. For comparison, the mass of the supermassive black hole Sagittarius A*, located at the center of the Milky Way, is about four million solar masses.

Since the host galaxy itself is extremely massive and the obtained mass of the central object is quite large, the researchers suggested that this object may reflect another "branch" in the evolution of giant galaxies and could have formed either through a series of mergers of large galaxies and black holes or through rapid mass accumulation.

As the discovery was made using an indirect method, a broader sample of gravitational lenses similar to the "Cosmic Horseshoe" will be needed to confirm the results. This will allow scientists to "weigh" supermassive black holes at different stages of evolution and explain why some of them become so massive.