What is the largest black hole in the known universe?

Black holes are the most massive objects in the universe. Some weigh only a few solar masses, while others are much larger and more powerful, orchestrating the very dynamics of their galaxy. Among these cosmic ogres, one of them seems to defy all competition. Here’s what we know about this colossal black hole.

What is a black hole?

Black holes form during the gravitational collapse of very massive stars at the end of their life. When a star’s matter burns up and its internal energy source is depleted, gravity takes over and the star collapses in on itself. With the amount of matter available packed into a very small space, gravity then becomes so strong that it digs a hole in the very fabric of space-time. Subsequently, the surrounding material is caught inside and disappears without leaving a visible trace.

There are three types of black holes: stellar which have a mass between about three and a hundred times that of the Sun, those of intermediate sizewhose mass is between one hundred and one million solar masses and the supermassifs which have a mass greater than one million solar masses. Scientists believe that these were formed by the merger of smaller stellar black holes and by the accumulation of massive gas at the center of galaxies.

What is the largest known black hole?

To the present state of our knowledge, the largest black hole known to date is TON 618. You will find it in the center of a galaxy located in the constellation of the Dragon, about 10.4 billion light years of the earth. The mass of this object is estimated to be approximately 66 billion times that of the Sun. For comparison, the supermassive black hole at the center of the Milky Way called Sagittarius A* has an estimated mass of around four million times that of the Sun.

TON 618 has been studied in detail by astronomers using several telescopes, including the Hubble, Chandra, Spitzer and Keck observatories. These studies found that TON 618 emits considerable amounts of energy, which also makes it one of the brightest quasars ever observed. Its illuminating power is estimated at approximately 140 trillion suns.

As a reminder, quasars are extremely luminous astronomical objects due to the enormous amount of matter being absorbed by the central black hole. Because of TON 618’s distance, these observations provided scientists with a unique window into conditions in the early universe, when the first major galaxies formed.

black hole
Artist’s illustration of a black hole. Credits: AlexAntropov86

How was the mass of TON 618 estimated?

The mass of TON 618 has been estimated from several observation methods. The most common is the analysis of the kinematics of stars and gas in the region surrounding the black hole. Scientists can measure the speed of stars and gas orbiting the central black hole by observing the gravitational effects it has on them. The greater the mass of the black hole, the higher the orbital velocities.

Another method is to measure the brightness of the light-emitting source orbiting the black hole. By observing the light emitted by the free-falling gas in these objects, scientists can then estimate the amount of matter being absorbed, and therefore the mass of the black hole.

Although estimates may vary depending on the methods used and the uncertainties associated with each of them, the estimate of 66 billion solar masses for the supermassive black hole TON 618 is considered one of the most reliable to date.

What is the diameter of TON 618?

Note that the diameter of a black hole is not a well-defined physical quantity, as there is no solid surface or visible boundary. A black hole is defined by its event horizon, which is the region of space from which gravity is strong enough to prevent any form of matter or radiation from escaping. The size of the event horizon depends only on the mass of the black hole and not on its density or shape.

Assuming that the mass of TON 618 is about 66 billion solar masses, the event horizon would have a radius of about 2000 AU (Astronomical units where 1 AU equals the average distance between the Earth and the Sun).

To better appreciate this, note that the Kuiper belt, a region of the solar system located beyond the orbit of Neptune composed of thousands of small icy bodies, is at a distance of about 30 and 50 astronomical units (AU) of the Sun. In other words, if the solar system were suddenly placed inside the event horizon of TON 618, it would be inexorably drawn towards the black hole and eventually be absorbed.

However, it is important to remember that this estimate is based on theoretical models. The exact size of the event horizon of this colossal object therefore depends on the accuracy of the latter.