Astronomers believe they have identified a pair of extremely luminous black holes that are spinning toward each other, and could meet in a titanic collision in less than a century. This merger would be so violent that its effects could be detected from Earth by our measuring instruments, reveals Live Science.
Drawing on several decades of radio observations, researchers have re-examined an ultraluminous object located around 500 million light years from our solar system, previously classified as a blazar, that is to say the very active heart of a galaxy animated by a supermassive black hole. The detailed analysis revealed the presence of a hidden jet of energy, a sign that this object would not be alone but composed of two black holes close to collision, perhaps in less than a hundred years. Dust on a galactic scale.
“We expect only one merged black hole to remain”says Silke Britzen, an astronomer at the Max Planck Institute for Radio Astronomy in Bonn, Germany, who compares the duo’s current movement to a kind of cosmic dance whose next steps intrigue researchers. The study, published March 27 in the journal Monthly Notices of the Royal Astronomical Society, opens a rare window into the final moments before such gravitational monsters merge.
Blazars are among the brightest objects in the Universe: they are active galactic nuclei that swallow enormous quantities of matter and project jets of very high-energy radiation towards Earth. But in the case of the blazar at the center of the Markarian 501 galaxy, something was wrong. The changing orientations of his jet, observed for years, cast doubt on the presence of a mystery guest.
A natural magnifying glass
To solve this puzzle, the team sifted through more than 83 datasets collected by the international Very Long Baseline Array. The results showed that in addition to the large main jet, a second jet described a counterclockwise loop around the center of the object. Scientists estimate that each of these jets is powered by a supermassive black hole, the mass of which is between 100 million and a billion times that of the Sun.
Silke Britzen says she was stunned when she realized that a second jet was hidden in the data, finally seeing there the key to the functioning of this extraordinary system. In June 2022, the two black holes aligned almost perfectly, to the point that the gravity of the main black hole distorted the light from the second jet into an almost complete circle, known as Einstein’s ring.
This phenomenon of gravitational lensing, comparable to a natural magnifying glass produced by an intense gravitational field, reinforces the hypothesis that this blazar is in fact powered by a pair of supermassive black holes. According to calculations, the two stars would describe a common clockwise orbit approximately every 121 days, separated by a distance equivalent to only 250 to 540 times that which separates the Earth from the Sun, a remarkable proximity on a cosmic scale.
Little by little, this distance should decrease, irremediably leading to the merger of the two black holes. Researchers believe this cataclysm will release gravitational waves – ripples in space-time generated by the most violent events in the universe – even more powerful than those detected during previous black hole mergers.
If this scenario is confirmed, gravitational wave detectors on Earth should pick up this exceptional signal. It would then offer new information on the properties of this duo of black holes and, more broadly, on the way in which supermassive black holes grow and transform the galaxies that shelter them.
