The Science Of Black Holes
April 2026
Author: Erin - Astrophysicist - Little Star Shop
Imagine an object with so much gravity that nothing, not even light can escape it. This object is real, and is amongst the most bizarre of objects found within the known universe, where time stops and reality as we know it is stretched to its absolute limits - welcome to the black hole. In this extreme environment, an astronaut caught in a Black Hole would undergo a process called spaghettification, where gravity stretches them into a thin strand of atoms, that is infinitely long.
Black holes represent the ultimate cosmic mystery, signifying the end of the stellar phase of a massive star (one which is at least a minimum of 10 times as massive as our sun) which underwent a violent supernova explosion.
The remnant of the star then undergoes complete gravitational collapse inwards, where immense amounts of matter are squeezed into the space about the size of a small city, producing a gravitational field so strong that the known laws of physics break down, the space-time continuum changes, time slows down and nothing, not even light can escape (hence the term 'black hole').
M87 supermassive black hole, and its 4,400 light year long relativistic jet of sub-atomic particles, imaged by the Hubble Space Telescope By NASA
How Are Black Holes Formed?
Creating a black hole requires a massive star- one at least five to ten times larger than our Sun. Throughout its life, a star stays stable by burning fuel, but once it starts producing iron in its core, it hits a dead end. Since fusing iron consumes more energy than it releases, the star can no longer support its own weight. In an instant, gravity wins. The star collapses violently inward, crushing all of its matter into a single point of infinite density known as a singularity. This collapse creates a gravitational pull so powerful that it forms an event horizon, a point of no return.
What Are The Different Types Of Black Holes?
Black holes are observed in a range of sizes, but are classified into four main types, determined mainly by the mass and size of the black hole. These include Primordial, Stellar, Intermediate and Supermassive black holes, all ranging in different sizes and masses.
Primordial Black Holes
Primordial black holes are the universe's oldest relics, theorised to have formed from the high-density fluctuations of the Big Bang rather than the collapse of a star. They are theoretical and believed to have formed seconds after the Big Bang.
Stellar Black Holes
The most common type of Black holes are Stellar black holes, which are found scattered throughout the Milky Way Galaxy, just as massive stars are also scattered throughout. With masses between 4-15 times that of our sun, a stellar mass black hole is considered to be the logical end point of stellar and galactic evolution.
The proof for the existence of stellar-black holes has been a highly studied area for the past four decades, since the discovery and mass estimation of one of the best candidates in the Milky Way, called Cygnus X-1, which was also the first black hole ever discovered.
Cygnus X-1 is a highly irregular and variable source, with flickering X-ray emissions as its companion star, HDE 226868 orbits it. Cygnus X-1 was calculated to have a mass about 7 times that of our sun, due to the gravitational pull noticed in the spectral lines of its companion.
By ESA, Hubble - https://apod.nasa.gov/apod/ap080811
Today, by understanding the evolution of stars and estimating how many stars have masses high enough to form into black holes, astrophysicists can estimate that The Milky Way Galaxy alone has 100 million stellar-mass black holes. To put that number in perspective: our galaxy contains roughly 100 billion to 400 billion stars, meaning that for every stellar black hole, there are roughly 1,000 to 4,000 stars.
In 2019, a team of astrophysicists produced an estimate for the total number of stellar black holes in the entire Universe. The number is staggering- 40,000,000,000,000,000,000, or 40 quintillion stellar black holes, which are believed to make up approximately 1% of the normal matter in the Universe.
Intermediate Black Holes
On the other hand, intermediate black holes act as the "missing link" of the Universe, bridging the gap between stellar-mass and supermassive types with masses ranging from hundreds to hundreds of thousands of times that of our sun.
What Is The Largest Type Of Black Hole?
Supermassive Black holes are the largest type of Black Hole known, with masses greater than one million times that of our sun. Scientific evidence suggests that nearly every large galaxy contains a supermassive black hole at its centre- the origins of which are still unknown. In the centre of our own Milky Way Galaxy lies a supermassive black hole called Sagittarius A*, with a mass equivalent to 4 million suns, found in the direction of the constellation of Sagittarius. The orbits of approximately 90 stars have been studied around the black hole, within an area of 0.002 light years, and it has been determined that the black hole has a spherical mass of 4.3 million solar masses.
Sagittarius A* imaged by the Event Horizon Telescope
How Are Black Holes Studied?
In order for an astrophysicist to study black holes, they need to rely on indirect observations such as the gravitational interactions of the black hole with its surroundings. This is because radiation and light cannot escape the extreme gravitational pull of a black hole, it is essentially invisible to see directly. Because of this, the most effective way to detect a black hole is by observing the gases from nearby stars in orbit. There are three main parameters used to describe black holes, including angular momentum, total energy and mass.
What Are Accretion Disks?
Due to conservation of angular momentum, gas falling into the gravitational field of a black hole will form an accretion disk around the body.
Scientists identify black holes primarily by observing their effects on nearby objects, particularly in X-ray binary systems. In these systems, a visible "ordinary" star orbits an invisible, compact companion.
As matter in the accretion disk continues to be pulled in toward the black hole, friction causes angular momentum to be transported outward, in doing so releasing potential energy and gaining kinetic energy. This causes the gas at the innermost part of the disk to ionize, producing high energy light particles which as a result will heat up, emitting black body radiation. Once the atoms reach temperatures of a few million Kelvin, vast amounts of radiation is emitted into space in the forms of infrared, visible light, ultraviolet light and powerful X-rays that we can detect from the Earth.
It is ironic- powered by bodies that are themselves invisible, black holes easily outshine anything else in the universe.
This visualisation of a black hole with gravitational lensing, warping its surroundings
Telescopes such as the Spitzer Space telescope, XMM-NEWTON, Galex Satellite, Suzuku Telescope, and the Chandra Space telescope are instrumental in observing this area of radiation. The frequencies of the emissions can be used to determine the mass of the Black Hole. Often, accretion disks are accompanied by spectacular jets of sub atomic particles also shooting away from the accretion disk.
Relativistic jets of sub-atomic particles ejecting from the supermassive black hole in Centaurus A
These X-rays provide a map of the environment around the black hole. Because gravity is so intense, it warps spacetime, causing time to slow down and shifting light toward the lower-energy "red" end of the spectrum. As matter in the disk spins toward us, its light is Doppler-shifted to higher energies. By identifying these atomic transmissions, researchers can pinpoint exactly where the energy is being emitted and how the black hole is twisting the space around it.
How Are Black Holes Officially Confirmed In Binary Systems?
The final confirmation of a black hole comes down to a "weighing" process of three factors.
1. Mass Measurement- By tracking the orbit of the visible star, astrophysicists can calculate the mass of the invisible companion
2. The Threshold- A neutron star, which is the other densest object in the universe to a black hole, can only reach about 2 solar masses. If the calculated mass is higher, generally between 3 and 20 solar masses, the object will be officially classified as a black hole candidate, as no other known force could prevent it from collapsing into a singularity.
What Is The Closest Black Hole To Earth?
As of 2026, the closest known black hole to Earth is Gaia BH1. It is located approximately 1,560 light-years away in the constellation Ophiuchus, far enough that it poses absolutely no threat to the Earth.
As our telescopes get stronger and we detect more gravitational waves, we are slowly learning more about these invisible giants. We may not be able to see directly into a black hole, but by watching the light move around them, we are learning more about the origin of our universe than ever before.