How Do Intermediate Black Holes Form?

Intermediate black holes are the rarest and least understood type of black holes, and information about them and their origin remain elusive to this day. They have masses that range somewhere between 100 to a million times that of the sun, making them the “in-betweeners” of stellar and supermassive classes of black holes.

How Do Intermediate-Mass Black Holes Form

Though definitive proof of this kind of black hole remains rare, a number of studies over the past few decades have helped uncover intriguing evidence suggesting the presence of these cosmic middleweights, as well as theories about how they came to be. According to experts, intermediate-mass black holes probably form in one of several ways.

Some believe that they started out as their own entities in the aftermath of the big bang.

However, another possibility the scientists have raised is that they are formed from the merging of multiple stellar-size black holes that often happen in crowded areas of galaxies, but did not have enough mass to collapse into a supermassive black hole.

Others suggest that they may have originated at the core of very low-mass dwarf galaxies that have been swallowed by bigger, more massive galaxies. This was backed by the discovery of the HLX-1 black hole, an intermediate black hole that was believed to be at the center of a dwarf galaxy before it was devoured by the much larger elliptical galaxy ESO 243-49.

Discovery of Intermediate Black Holes

While astronomers already suspected the existence of middleweight black holes, it was only in 2009 that they discovered the HXL-1 which appears to have the characteristics of an intermediate black hole sitting out in its host spiral galaxy. It is about 20,000 times the mass of our Sun and was found spewing a lot of x-ray and radio flares that indicate the presence of a young-massive cluster of blue stars encircling the black hole.

Other Types of Black Holes

Stellar Black Holes

A stellar-mass black hole is the result of an extremely massive star collapsing under its own weight. They are the most common and understood type of black hole, ranging from about 5 to 10 solar masses depending on the initial size of the imploding star, and are believed to be the seeds for the formation of supermassive black holes.

Stellar-mass black holes can be found in binary systems where one star is pulling matter from its companion. They can also form when two stars collide resulting in an extremely powerful explosion.

Gravitational waves are emitted by stellar mass black holes which can be detected by observatories on Earth. These waves provide valuable information about their astrophysical properties, indicating their size and mass with great accuracy.

Supermassive Black Holes

Supermassive black holes, the biggest kind of black hole in the cosmos, have masses that may range from millions to billions of times that of our sun. They’re believed to form at the center of galaxies when a dense cluster of stars collapses in on itself.

Sagittarius A* is a supermassive black hole that is found at the center of our Milky Way galaxy. It is 4 million times more massive than the Sun but is still relatively smaller than supermassive black holes in other galaxies.

To this day, it still remains a mystery to scientists how supermassive black holes came to be. However, studies of distant galaxies suggest that some of these monsters were formed very early after the birth of the universe.


There are several findings and theories about how intermediate black holes are formed, but concrete evidence remains hidden to astronomers. There is still much to learn about black holes of all sizes, but recent discoveries and technology are bringing us closer to understanding these strange and fascinating objects.

Andy Morgan