How Much Does a Black Hole Weigh Compared to the Sun

The Sun has a mass of 1.989 × 10³⁰ kilograms. That figure is so large that in astrophysics it stopped making sense to use kilograms, so a unit of its own was created: the solar mass (M☉). When we talk about black holes, this unit becomes essential, because their masses range from a few times the Sun’s to billions of times more. Let’s compare real figures, no vague estimates.

What exactly is a solar mass

One solar mass equals 1.989 × 10³⁰ kg, which is almost two thousand trillion trillion kilograms. It’s the standard reference in astrophysics because comparing giant objects in kilograms produces unmanageable numbers. Saying “this black hole has 10 solar masses” is much clearer than writing 1.989 × 10³¹ kg.

The Sun, with all its mass, represents 99.86% of the total mass of the solar system. If you want to see how it compares with the planets orbiting it, check out how much Earth weighs compared to other planets in the solar system, a good reference point before jumping to even bigger scales.

Black hole mass compared to the Sun: the three types

Not all black holes weigh the same. They’re classified into three main categories according to their mass:

• Stellar black holes: between 3 and 100 solar masses, formed by the collapse of massive stars.
• Intermediate-mass black holes: between 100 and 100,000 solar masses, a range that’s poorly studied and hard to detect.
• Supermassive black holes: from 100,000 up to billions of solar masses, hosted at the center of galaxies.

The difference between the lower and upper extremes is a factor of one billion. That gap is bigger than the one between a grain of sand and a mountain.

How much a typical stellar black hole weighs

Cygnus X-1, one of the most studied black holes, has an estimated mass of 21.2 solar masses. That’s equal to 4.22 × 10³¹ kg. To form, the progenitor star originally needed more than 20 solar masses before collapsing, since much of its mass is lost in the earlier supernova explosion.

The theoretical minimum limit for a stellar black hole is 3 solar masses (the Tolman-Oppenheimer-Volkoff limit). Below that value, the collapsed object is a neutron star, not a black hole.

How much a supermassive black hole weighs

Sagittarius A*, the supermassive black hole at the center of the Milky Way, has a mass of 4.3 million solar masses. In kilograms, that’s 8.55 × 10³⁶ kg. Compared to Cygnus X-1, it’s more than 200,000 times more massive.

But Sagittarius A* is modest compared to other documented cases. TON 618 has an estimated mass of 66 billion solar masses, making it one of the heaviest black holes known. Multiplying that figure by the mass of the Sun gives 1.31 × 10⁴¹ kg, an amount that exceeds the combined mass of thousands of entire galaxies if we compared them only by stars.

To get a sense of the scale of the galaxy hosting these giants, it’s worth checking how big the Milky Way is expressed in light-years, because mass and galactic size are closely connected.

Solar mass vs black hole: why the comparison isn’t linear

A common mistake is thinking that a black hole’s physical size grows in step with its mass. That’s not entirely true, but there is a direct relationship between mass and the Schwarzschild radius (the size of the event horizon):

• A black hole with 1 solar mass has a Schwarzschild radius of 2.95 km.
• Sagittarius A*, with 4.3 million solar masses, has a radius of approximately 12.7 million km, about 18 times the Sun’s radius.
• TON 618, with 66 billion solar masses, would have a Schwarzschild radius of about 1,300 astronomical units, larger than the orbit of many objects in the solar system.

This means that, unlike a star, a supermassive black hole can have an average density lower than water, despite concentrating an enormous mass, simply because its volume is also huge.

How the mass of a black hole is calculated

Astrophysicists don’t weigh a black hole directly: they observe its gravitational effect on nearby objects. The main methods are:

• Orbits of nearby stars: the orbital velocity of a star or gas around the black hole is measured and Kepler’s third law is applied.
• Accretion disk: the radiation emitted by material falling toward the black hole is analyzed, revealing its mass and growth rate.
• Gravitational waves: in black hole mergers, the pattern of the signal detected by observatories like LIGO allows the masses of both objects to be calculated with great precision.

The first black hole merger detected via gravitational waves, in 2015, involved objects of 36 and 29 solar masses that merged into one of 62 solar masses, releasing the equivalent of 3 solar masses as pure gravitational energy.

Converting solar masses to kilograms and tons

Working with solar masses is useful in astrophysics, but sometimes you need to express those figures in more manageable units for comparisons or specific calculations. If you want to convert the resulting mass to metric tons to get a more down-to-earth sense of the magnitude, you can use Glosaria’s kilograms to metric tons calculator: enter the result in kilograms from your solar mass calculation and instantly get its equivalent in tons, with no manual conversion errors.

For example, Cygnus X-1’s mass (4.22 × 10³¹ kg) is equal to 4.22 × 10²⁸ tons. These are figures that no standard calculator handles well without scientific notation, so a specialized tool avoids unit conversion errors.

What mass limits exist for black holes

There’s a clear lower limit (3 solar masses), but the upper limit is more debated. Current models suggest that supermassive black holes can’t grow indefinitely because matter accretion is self-limiting: once a certain mass is reached, the radiation emitted by the accretion disk pushes away the surrounding gas and slows growth.

The estimated theoretical upper limit is around 50 billion solar masses, although objects like TON 618 come very close to that ceiling, sparking debate about whether there are still-unexplained growth mechanisms, such as direct mergers between already supermassive black holes.

Frequently asked questions

What’s the heaviest known black hole?

TON 618 is one of the heaviest known candidates, with an estimated mass of 66 billion solar masses, equivalent to 1.31 × 10⁴¹ kilograms. It’s located about 10.4 billion light-years from Earth.

How many solar masses does the Milky Way’s black hole have?

Sagittarius A*, the supermassive black hole at the center of our galaxy, has a mass of approximately 4.3 million solar masses, equivalent to 8.55 × 10³⁶ kilograms.

What’s the minimum mass needed for something to collapse into a black hole?

The theoretical minimum limit is 3 solar masses, known as the Tolman-Oppenheimer-Volkoff limit. Below that value, the resulting collapsed object is a neutron star instead of a black hole.

Why is solar mass used instead of kilograms to measure black holes?

Because figures in kilograms are so large that they become unmanageable and hard to compare mentally. Using solar mass as a reference unit (1.989 × 10³⁰ kg) allows astronomical objects to be compared with much smaller, more understandable numbers, like saying “10 solar masses” instead of “1.989 × 10³¹ kilograms”.

Can a black hole lose mass over time?

Yes, through a process called Hawking radiation, although it’s extremely slow. For a stellar-mass black hole, the time needed to fully evaporate far exceeds the current age of the universe, so in practice its mass only increases by absorbing nearby matter.