The universe hides a monster: a record black hole that fascinates researchers, “probably the most massive”
Image of “cosmic horseshoe” captured by the Hubble space telescope. The orange central galaxy, located about 5 billion light years away, deforms the light of a background galaxy (blue arc) by gravitational lens effect. The enlargement shows a very low image formed near the ultramassive black hole – a key index which made it possible to estimate its mass at 36 billion suns. © NASA/ESA/TIAN LI (University of Portsmouth) – License: CC by 4.0
At 5 billion light years of the earth, in one of the most massive galactic systems ever identified-the Cosmic Horseshoe-rests a sleeping black hole whose dimensions defy the imagination. Its mass is equivalent to that of 36 billion suns, which makes it one of the ten largest known black holes, and perhaps even number 1 in the classification.
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The most gigantic black hole never observed?
It is one of the ten most massive black holes ever discovered, and probably the most massive.
To give an idea of the gap: Sagittarius has*, the black hole in the center of our Milky Wayweighs “only” 4.15 million solar masses. This is not the first time that this cosmic monster has attracted attention. In February 2025, astronomers had already identified it, evaluating its mass at around 35 billion suns. The new measures, published this summer, refine this estimate at 36 billion and confirm its rank in the Top 10 (or even at the top) of the most massive known black holes.
This discovery is all the more remarkable since the object is no longer actively nourished by matter. Without luminous accretion disc, it blends into cosmic darkness. The researchers therefore had to resort to another clue: its extreme severity. By distorting space-time, this colossus acts like a giant magnifying glass on the light of galaxies located in the background. It is the phenomenon of gravitational lens, described by Einstein, which revealed its presence.
We have detected the effect of the black hole in two ways: by altering the path of light which passes nearby, and by moving the stars of the internal regions of its galaxy at vertiginous speeds.
In the case of Cosmic Horseshoe, the almost perfect alignment of the galaxies creates a spectacular light arch, close to a “Einstein ring”. By combining the analysis of this deformed light and the vertiginous speed of stars close to the galactic center (almost 400 km/s), scientists were able to precisely measure the mass of this monster.
What is particularly exciting is that this method makes it possible to detect and measure the mass of ultramassive black holes hidden throughout the universe, even when they are completely silent.
This observation confirms a strong link between the size of a galaxy and that of its central black hole: by growing, the galaxies channered from matter to their nucleus, nourishing and growing their black hole.
We believe that the size of the galaxies and that of their central black hole are intimately linked.
The Cosmic Horshoe, classified as “Fossil group”, could be the last step in this evolution. An overview of what awaits, in billions of years, the future merger between the Milky Way and Andromeda.
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