An international team of astronomers, while studying the enormous elliptical galaxy Abell 402-BCG, located inside the Abell 402 cluster about 4.4 billion light-years from Earth, has confirmed the existence of a remarkable anomaly. At the very center of this stellar system, a colossal cavity 3,200 light-years across has been found, almost completely devoid of stars.
Further analysis showed that this phenomenon is caused by a pair of supermassive black holes with a record combined mass of about 60 billion solar masses. This system is at least twice as massive as any other known pair of black holes in the Universe.
JWST Destroys the Dust Hypothesis
The mysterious dark spot in the galaxy’s core was first noticed in 2018. At the time, the most likely explanation was thought to be a dense cloud of cosmic dust simply blocking the light of the stars behind it. For years, this anomaly remained an unexplored quiet mystery because of the lack of sufficiently sensitive instruments.
The situation changed when a team led by astronomer Michael McDonald of the Massachusetts Institute of Technology used the James Webb Space Telescope and the ground-based Very Large Telescope. The results of their work, published in The Astrophysical Journal Letters, were intended to finally test the old theory.
The scientists relied on the physical properties of dust: it is more transparent to infrared radiation than to the optical light previously recorded by the Hubble telescope. If a dust veil had been present there, the galaxy’s core would have appeared much brighter in the infrared spectrum. However, the cavity turned out to be equally dark in both wavelength ranges.
This made it possible to completely rule out the dust explanation and prove that the region is truly devoid of stars. According to the researchers’ estimates, the area is missing stars with a combined mass of about 2 billion solar masses, equal to roughly 1% of the galaxy’s total stellar mass.
A Gravitational Sieve for Stars
After ruling out the dust hypothesis, the researchers began looking for a force capable of physically ejecting such a huge amount of matter. At one edge of the cavity, James Webb detected a bright infrared point source with the spectral signature of an active black hole consuming gas and dust.
Further observations using the MUSE spectrograph on the VLT revealed a second source of ionized gas on the opposite side of the void. This confirmed the presence of a second active black hole. These two giants are moving relative to each other at about 370 kilometers per second, orbiting a common center of gravity.
Such a process begins during a galaxy collision. When two systems merge, their central black holes draw closer under the influence of gravity. As they spiral inward, their powerful gravitational pull literally scatters nearby stars outward, creating a starless gap.
McDonald’s team concluded that Abell 402-BCG recently underwent a cosmic collision, and that the detected pair of black holes has been orbiting together for only a few tens of millions of years — a tiny interval on cosmic timescales. Moreover, the broader core structure, 6,500 light-years across, indicates that this region had previously been affected by another ancient merger caused by a black hole with a mass of 50 billion solar masses.
A Unique Snapshot of Cosmic Evolution
Today, these two monsters are steadily moving toward an inevitable merger into a single massive object of enormous size. Individual black holes with masses greater than 60 billion solar masses have been recorded in the Universe only a handful of times, which makes the future product of this merger a unique phenomenon.
The main value of the discovery is that astronomers very rarely manage to observe black holes at such a late stage of convergence in a tight orbit. Computer simulations show that only about 0.5% of massive galaxies at any given moment are in this brief phase of their evolution. Catching the galaxy Abell 402-BCG within such a narrow time window is a remarkable achievement.
Scientists plan to use the collected data to calculate more precisely how often such large-scale intergalactic collisions occur, as well as to improve models of how galactic cores transform under the influence of gravitational titans.
Earlier, we reported on how, in the voids of the Universe, space “whispers” with the echoes of catastrophes.
According to Daily Galaxy
