Introduction: The Scale of Cosmic Monsters

When we talk about the "largest" black hole, we are stepping into a realm of scale that defies human comprehension. These are not the stellar-mass black holes born from collapsed stars, a few times heavier than our Sun. These are the ultramassive black holes, cosmic leviathans that lurk at the centers of galaxies, with masses so great they warp the fabric of space for millions of light-years around them. Identifying the single largest black hole is a surprisingly difficult task. It is a title that changes hands as new discoveries are made, and its measurement is fraught with uncertainty, dependent on distance, technique, and the dynamic environment of the black hole itself [citation:7]. The contest is not just about mass, but about the very limits of how big these objects can theoretically grow before they disrupt the galaxies that host them.

Currently, the crown for the most massive black hole ever discovered is a tight race between two titans: the recently measured behemoth in the galaxy cluster Abell 1201, and the long-reigning champion, Phoenix A*. However, for decades, the name TON 618 stood synonymous with "biggest black hole," and it remains a yardstick against which all others are measured. This article cuts through the uncertainty to present the current record-holders, based on the latest research and observations.

The New Contender: Abell 1201's Hidden Giant

In a groundbreaking study published in February 2026, astronomers announced the discovery of an ultramassive black hole that could be the largest ever recorded [citation:1]. Located roughly 2 billion light-years from Earth at the center of the galaxy Abell 1201, this object is estimated to be more than 30 billion times the mass of our Sun [citation:1].

What makes this discovery truly unique is how it was found. It is the first black hole ever observed using gravitational lensing [citation:1]. This phenomenon, predicted by Einstein, occurs when a massive object (like the galaxy Abell 1201) bends and magnifies the light from an even more distant galaxy behind it. The light acts like a probe, and by carefully analyzing how it was distorted, astronomers could infer the presence and mass of the invisible black hole at the lensing galaxy's center. Lead author James Nightingale of Durham University described it as "similar to shining light through the base of a wine glass" [citation:1]. This technique is revolutionary because it allows us to find black holes in the 99% of galaxies that are too distant or faint for traditional methods [citation:1].

The Reigning Champion: Phoenix A*

Despite the excitement surrounding Abell 1201, the current titleholder for the most massive black hole is widely considered to be Phoenix A*, located at the heart of the Phoenix Cluster, about 8.5 billion light-years away [citation:3]. Its estimated mass is a staggering 100 billion solar masses [citation:3][citation:6][citation:10]. To put that in perspective, this single object makes up about 10% of the total mass of our entire Milky Way galaxy [citation:3]. Its event horizon has a diameter of roughly 590 billion kilometers, which is about 100 times the distance from the Sun to Pluto [citation:3][citation:10].

Phoenix A* is not just massive; it is also incredibly active. It is growing at a phenomenal rate, consuming the equivalent of 60 Suns worth of material every single year [citation:3]. This frenzied feeding likely contributes to the Phoenix Cluster's extreme nature, which hosts one of the highest rates of star formation ever observed, with over 700 new stars born annually [citation:3].

The Legendary Giant: TON 618

For years, the name TON 618 was synonymous with the largest black hole. It was first cataloged in 1957 as a faint "blue star," but astronomers later realized it was actually an incredibly luminous quasar over 10 billion light-years away [citation:2][citation:9]. A quasar is the brilliant, energetic core of a distant galaxy, powered by a supermassive black hole greedily consuming matter. The sheer brightness of TON 618 revealed the presence of a truly colossal engine at its center.

The black hole powering TON 618 is estimated to have a mass of approximately 66 billion Suns [citation:2][citation:6][citation:9]. Its event horizon would be enormous, with a radius of about 1,300 astronomical units (AU)—that's 40 times the orbital distance of Neptune. While it has been surpassed by Phoenix A* and potentially Abell 1201, TON 618 remains a benchmark in astronomy and one of the most massive objects ever discovered. Its luminosity is equivalent to 140 trillion Suns, making it one of the brightest objects in the observable universe [citation:2].

How Do We Weigh a Black Hole?

The uncertainty in the title of "largest" comes down to the difficulty of measuring something you can't see. Different methods are used for different black holes, and each has its own margin of error [citation:7].

- Dynamics: For relatively nearby black holes, like the one in our galaxy, astronomers can measure the speed of stars orbiting the invisible object. The faster they orbit, the more massive the central black hole must be.

- Accretion Disk Physics: For active black holes like TON 618, scientists study the light emitted from the superheated gas swirling around them. By measuring the velocity and temperature of this gas, they can calculate the gravitational force needed to confine it, and thus the black hole's mass [citation:2].

- Gravitational Lensing: This new method, used for Abell 1201, analyzes how light from a background object is bent by the gravity of the black hole and its host galaxy. It's a powerful tool for finding dormant or distant black holes that aren't actively feeding [citation:1].

Conclusion: The Search Continues

So, what is the largest black hole discovered? According to current estimates, the title belongs to Phoenix A*, with a mass of 100 billion Suns [citation:3][citation:6][citation:7]. The newly discovered black hole in Abell 1201 is a strong contender, but its mass of 30 billion solar masses, while enormous, still places it below Phoenix A* [citation:1]. TON 618, at 66 billion solar masses, remains a defining giant in our cosmic catalog [citation:2].

These "stupendously large black holes," or SLABs, push the limits of our theories [citation:7]. How do they grow so big? Was Phoenix A* formed from the collision of multiple supermassive black holes in the early universe [citation:3]? With new missions like the Euclid space telescope expected to find hundreds of thousands of gravitational lenses, the "landscape is about to dramatically change," and the title of the largest black hole may soon be contested once again [citation:1]. The quest to find the universe's ultimate monster is far from over.