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Located in the Phoenix cluster, 5.7 billion light-years from our galaxy, Phoenix A* would have a mass equivalent to 100 billion suns and surpass TON 618, estimated at 40.7 billion solar masses, reigniting the debate about how large supermassive black holes can grow
The black hole Phoenix A* has drawn attention for challenging an old notion about the maximum size of these objects in the universe. Located in the Phoenix cluster, 5.7 billion light-years from our galaxy, it would have a mass equivalent to 100 billion suns.
This number places Phoenix A* above TON 618, a hyperluminous quasar that, until two years ago, was considered the largest known black hole. TON 618 has an estimated mass of 40.7 billion times the mass of the Sun and is 10.4 billion light-years from Earth.
What makes a black hole so difficult to observe
Black holes are among the most extreme objects ever identified in the universe. Their gravity is so intense that not even light can escape after crossing the event horizon, the boundary where space-time begins to behave extremely.
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For this reason, photographing a black hole is a complex task. The first direct image of a supermassive black hole was obtained in 2019 by the Event Horizon Telescope, showing the object M87*, at the center of the elliptical galaxy Messier 87.
M87* has a mass billions of times greater than that of the Sun. Even so, estimates based on the size of their galaxies indicate that there are 38 known black holes larger than it.
Phoenix A* surpasses the old estimated limit
Before Phoenix A* entered this discussion, there was the idea that black holes would not exceed 50 billion solar masses. The estimate attributed to the object in the core of the Phoenix A galaxy broke this threshold significantly.
The Phoenix A galaxy is at the center of the Phoenix cluster, discovered in 2010 by the South Pole Telescope. This cluster is among the largest ever known and is also notable for being the one that emits the most X-rays.
Size helps explain the impact of the discovery
The visual comparison between Phoenix A*, TON 618, and Neptune’s orbit shows the unusual scale of this object. The estimated size is so large that it could swallow the entire Solar System, at least in size comparison.
Even with impressive numbers, the mystery remains. The interior of a black hole remains inaccessible, and it may never be possible to know what exists beyond the event horizon. This combination of scale, distance, and uncertainty keeps these objects among the fascinating topics of modern astronomy today.
The study of black holes
Black holes help scientists study some of the most extreme limits of physics. As they concentrate a lot of mass in compact regions, they allow for the investigation of intense gravity, the behavior of light, and effects on space-time.
In the case of supermassive black holes, the interest also lies in the relationship with the galaxies where they are found. Even when they cannot be seen directly, their presence can be estimated by surrounding effects, associated emissions, and calculations related to the size of the galaxies. Therefore, objects like Phoenix A* expand the discussion on how far these systems can grow.
The estimate of 100 billion solar masses for Phoenix A* appears in a study published in 2016 in the journal Astronomy & Astrophysics, which proposed a search strategy for the most massive central black holes in galaxy clusters. The work indicates that the nuclear black hole of the Phoenix cluster could have a mass on the order of 10¹¹ solar masses, but this value results from modeling and not from a direct measurement by stellar orbits.
