Black Holes
A black hole is a region of spacetime where gravity is so strong that nothing, not even light, can escape its pull. Black holes come about after the collapse of massive stars, which become objects so dense that they can distort spacetime to such a great extent. The elusive nature of black holes, with their ability to push physical quantities to extremes, has made them a fascinating subject for both scientists and science fiction filmmakers. As our classical way of understanding physics breaks down at these extremes, the theory of relativity takes centre stage, creating a sense of mystery and intrigue.
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Just as space travel in film has evolved, so too has the depiction of black holes, with notable shifts between the movies : The Black Hole (1979), and Interstellar (2014). Over the years, these cinematic portrayals have reflected growing scientific understanding, particularly in the visual imaging of black holes, however, the mysteries surrounding what happens when entering one remain more speculative. In this section, we will explore the fundamental principles behind black holes, examining how our growing scientific knowledge has led to more accurate representations of these cosmic phenomena on the big screen.
Key Sections
Background
In this section, we provide the necessary background information to understand black holes in our analysis.
In this section, we analyse Interstellar and The Black Hole's depiction of black holes.
In this section, we critically compare the portrayals of the two movies and provide our own accuracy rating.
Background
Theory
Black holes are regions of space where gravity is so strong that not even light can escape. There are two main types: stellar black holes and supermassive black holes. Stellar black holes form when massive stars undergo supernova explosions, and these are the type of black holes that we most commonly observe. Supermassive black holes do not form from the collapse of stars and are found at the centre of nearly all galaxies, including our Milky Way. They can have a mass that is millions, or even billions, times that of the Sun. Scary.
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Stellar black holes form when massive stars exhaust their own nuclear fuel store and can no longer support themselves under the force of their own gravity pulling inwards; the result is a supernova explosion (see gif to the right). A dense core can remain after this supernova, and if its mass is large enough – more than about 3 times the mass of the Sun – the gravitational pull becomes so strong that it, again, cannot withstand the gravitational force acting inwards. So, the dense core collapses, leaving behind a “singularity”, which is surrounded by a boundary called an “event horizon".
Features of Black Holes
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A singularity is a point at the centre of a black hole, at which spacetime curvature becomes infinite, and physical quantities, such as density and temperature, reach extreme, undefined values. At this point, all physics breaks down and no current scientific theories can explain the behaviour which occurs at this point.
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The event horizon is the boundary around a black hole where the escape velocity (the speed an object requires to escape the gravitational pull of an object) becomes equal to the speed of light – a speed unattainable for any object with mass. Anything crossing this boundary – including light itself – can never escape. For a non-rotating black hole, the radius of the event horizon is given by a quantity called the Schwarzschild radius. A larger mass corresponds to a larger event horizon; this means supermassive black holes can be millions of kilometres in diameter! Rotating black holes have a much more complicated structure.
A labelled diagram of a black hole's features, indicating singularity, accretion disk etc.
Diagram adapted from source.
Black holes themselves do not emit light, so why do all the images we see of black holes look like they do? Why are they not truly black as the name suggests? Black holes are often surrounded by a superheated (very high temperature) “accretion disk” - a structure surrounding the black hole, which is comprised of gas and dust. Often, these are formed from debris from nearby stars or gas clouds falling into the black hole. So, while the black hole itself does not produce any visible light (nor could it escape from its gravity even if it did), as the material in these accretion disks spirals inwards and heats up, electromagnetic radiation is emitted (often X-rays). Typically, when we see images of black holes, these have been created using X-rays which originate from the black hole and are later colourized to allow us to visualise them.
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Gravitational lensing is perhaps one of the most fascinating properties of black holes, and it is exactly as it sounds. Because black holes have such large masses and therefore have very strong gravitational fields, they distort spacetime; in doing so, the black hole acts sort of like a giant cosmic lens. Subsequently, light follows a bent path around the black hole, instead of travelling in a straight line. This is what is responsible for the “halo” like object we see on images of black holes – it can actually be light from behind the black hole that curves around it for us to see!
What happens near a black hole?
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Due to the black holes’ immense mass and gravitational field strength, the behaviour surrounding them can be rather unconventional. So, how does this translate to the experience of a crew of astronauts, should they be unfortunate enough to venture near one? Firstly, according to general relativity, time slows down in strong gravitational fields and so, from the perspective of an outside observer, an astronaut falling into a black hole would be seen to slow down on approach to the black hole and never quite reach the event horizon. Meanwhile, from the falling astronaut's perspective, they would fall in normally, as expected, with no change in the passage of time.
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Another, more terrifying, result of a black hole’s properties is the concept of “spaghettification” (yes, this is a real scientific term). Close to a black hole, there is an intense “gravitational gradient”; this means that over short distances, the gravitational effects felt by something vary significantly between parts of the object (such as a person’s head and feet). This means, for our unfortunate astronaut plummeting towards the black hole, they would experience a largely varying gravitational pull acting on their feet and head. Due to this, the astronaut would experience extreme vertical stretching and horizontal compression; the result is spaghettification. The astronaut has now become a very long, and thin, strand of his former self – not so good for the astronaut, as you can imagine.
History
The idea of an object so big that not even light could escape its gravitational pull was first theorised by John Michell in the 18th century. His initial concepts, rather than being based on density, were of incredibly large stars (500 times the radius of the sun) but of a similar density to the sun. Laplace also speculated that if a star were big enough, it would become invisible since any light emitted would be pulled back by its own gravity. These ideas caused some to suggest there may exist some huge but invisible “dark stars” hiding in plain view.
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It wasn't until the 1960s that research into compact objects, including black holes, started to become mainstream, with scientists like Roger Penrose and Stephen Hawking developing the theoretical foundations of black holes, based on Einstein’s theory of general relativity. Find out more about Einstein’s theories in our Special Relativity section. Core elements of this research were about the nature of the event horizon at the Schwarzchild radius, and about the “generic” appearance of singularities, meaning that the formation of singularities under most conditions seems to be an unavoidable outcome. ​
The first strong physical evidence for a black hole came in 1971 with the discovery of Cygnus X-1, an X-ray binary system. The system consists of a massive star and a compact
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object emitting X-rays, which was later confirmed to be a black hole, marking the first direct observational evidence of their existence.
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​The launch of space telescopes like Chandra X-ray Observatory (1999) allowed astronomers to study the behaviour of matter near black holes, particularly the accretion disks around them. These observations confirmed that black holes were real objects, and even though they are invisible, their presence could be inferred by how they affected nearby matter and emitted X-rays.
Chandra X-ray image of Cygnus X-1. ​​
Image sourced from Harvard.
In the early 2000s, astronomers In the early 2000s, astronomers used very long baseline interferometry (VLBI) to image the centres of galaxies, where supermassive black holes are often located. These observations provided indirect evidence for the existence of supermassive black holes, although an actual image remained elusive.
A GIF showing a LIGO simulation of a binary black hole merger creating gravitational waves.​
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Sourced from NPR.
​In a groundbreaking achievement, the LIGO (Laser Interferometer Gravitational-Wave Observatory) collaboration detected gravitational waves from the collision of two black holes in 2016. This confirmed the existence of binary black hole mergers and provided new insights into the nature of black holes through a different form of observation.
First-ever image of a black hole, located at the centre of the galaxy, M87. Obtained, using the Event Horizon Telescope (EHT), April 2019.
​Image sourced from NASA.
The EHT (Event Horizon Telescope) collaboration made history in 2019 by capturing the first-ever image of a black hole, located in the centre of the galaxy M87. This image showed a bright ring (the glowing accretion disk) surrounding a dark centre (the event horizon). This imaging involves highly advanced techniques, like interferometry, where the data from several telescopes are synchronised to simulate a telescope the size of Earth. This achievement confirmed predictions of general relativity and provided an unprecedented look at the behaviour of black holes.
One of the 6m antennas in the submillimeter array at the summit of Maunakea in Hawaii. This array along with other sites around the globe come together to form a single virtual observatory the size of Earth. This is necessary to gain enough resolution to image the supermassive black hole​
Image sourced from Harvard centre for Astrophysics.
A simulation of the plunge into a black hole, aside an explanation.
Visualised by NASA.
Mathematical Appendix
2. Schwarzschild Radius (Event Horizon of a Non-Rotating Black Hole):
1. Escape Velocity:
where:
Escape velocity , , is the speed an object requires to break free and escape a gravitational field.
The Schwarzschild radius defines the boundary (event horizon), beyond which nothing can escape from a black hole.
It is derived in setting in Equation [1] and solving for r . It is the boundary at which an object would require in order to escape once passed - impossible, as the speed of light, c, is the fastest allowed speed by the laws of physics. So, inside the Schwarzschild radius, an object can never escape.
where:
Interstellar
The Black Hole
Interstellar, as one of the most scientifically ambitious science fiction films of its time, goes to great lengths to accurately depict the concept of black holes, particularly through the portrayal of Gargantua, the supermassive black hole that serves as the central focal point of the film’s narrative. The film’s portrayal benefits from the consultation of theoretical physicist and writer Kip Thorne, who helped ensure the depiction of black holes in the film was accurately based on a modern understanding of theoretical physics related to black holes and general relativity. In fact, the visuals were so advanced that Kip later published 2 scientific papers based on the gravitational lensing effects that were generated for the movie.
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Black Hole Features
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In Interstellar, Gargantua is depicted with a detailed accretion disk, rotating at high velocity, and surrounded by a luminous ring of hot gas and dust. This is scientifically accurate. The film also presents the event horizon, the boundary beyond which nothing can escape, including light. The event horizon’s depiction is particularly notable as it adheres to the predictions of general relativity. The filmmakers took special care to ensure that the way light behaves near the black hole – including gravitational lensing – is realistic. This is especially true for the iconic image of Gargantua, where the black hole appears distorted and surrounded by a glowing, circular ring of hot gas. The singularity itself, however, is not explicitly shown, though it is implied by the narrative.
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Despite the overall accuracy, the film does take some creative liberties in terms of the mechanics of how objects interact with the black hole. The idea of surviving close proximity to Gargantua and the possibility of using it as a slingshot manoeuvre stretches scientific realism. As previously mentioned, this would likely result in extreme tidal forces and spaghettification, a process where an object would be stretched into long strands due to gravitational gradients. Interstellar does not realistically explore these consequences, instead choosing to focus on the dramatic effect of entering the black hole.
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Visual Imaging​
An image of Gargantua, the supermassive black hole featuring in Interstellar.
Image sourced from wikipedia.
The visual depiction of Gargantua, and the way light bends around the black hole due to its immense gravitational pull, is one of the standout aspects of Interstellar. The filmmakers worked closely with physicists to ensure that the black hole’s appearance was accurate to the most current theories in astrophysics, even going as far as to generate complex visual simulations. The result is a highly realistic portrayal that mirrors the observations made by the EHT team in 2019 when they captured the first-ever image of a black hole (M87*). The EHT image showed a bright, circular ring of light surrounding a dark centre, which aligns closely with the depiction of Gargantua in the film.
While Interstellar’s black hole, visually speaking, is very striking, it's important to note that the actual process of capturing an image of a black hole, such as the one accomplished by the EHT, involves capturing electromagnetic radiation emitted by the gas around the event horizon, rather than from the black hole itself. This concept was well-represented in the film, showing how the black hole is surrounded by the glowing accretion disk, but it takes creative liberties when portraying how the light behaves near the singularity.
Journey Into The Black Hole
As the Endurance spacecraft approaches Gargantua, the film takes dramatic license in its depiction of the journey into the black hole. Although the approach is depicted with significant accuracy in terms of the relativistic effects and the warping of space-time near the black hole, the actual process of entering a black hole is a topic that is far from fully understood. In reality, any object that crosses the event horizon would be subjected to immense tidal forces, resulting in spaghettification – a stretching effect due to the difference in gravitational pull from the black hole’s centre to its edge.
In Interstellar, the Endurance is able to survive this, which is a significant deviation from current understanding. The astronaut inside, rather than being torn apart, undergoes a surreal and somewhat mystical experience when he passes through the event horizon, entering a tesseract-like space where time becomes a physical dimension. While it is stunning to watch, and a powerful conclusion to the narrative of the film, this scene stretches scientific plausibility, as no one knows what would happen in this scenario – the true effects of crossing the event horizon remain a mystery.
The Black Hole, released in 1979, is another classic science fiction film that attempts to explore the concept of black holes, but with a very different approach to scientific accuracy. The film was created during a time when our understanding of black holes was still developing, and many of the ideas that we take for granted today were not yet fully understood. Despite this, The Black Hole does make some noteworthy attempts to depict a black hole and its features, though it suffers from some significant inaccuracies.
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Black Hole Features
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The black hole in The Black Hole is portrayed as a dark, ominous sphere surrounded by a glowing accretion disk, similar to the depiction in Interstellar. However, the film does not go into the same level of detail regarding the mechanics of the black hole. The accretion disk is shown glowing with intense light, though the scientific accuracy of how this light is emitted is not fully explored. The event horizon, which marks the boundary where nothing can escape, is mentioned but not depicted in any great detail. In fact, much of the film glosses over the scientific principles behind the black hole, focusing instead on the dramatic and mysterious aspects of the object. The singularity itself is not clearly defined, and much of the action revolves around the events taking place near the black hole, rather than exploring its fundamental characteristics.
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The Black Hole does not accurately depict the extreme tidal forces or the concept of spaghettification. Instead, it takes more creative liberties, suggesting that the crew could survive a journey into the black hole without experiencing the violent consequences predicted by physics. This is a clear departure from reality, as any object approaching a black hole would be torn apart by the extreme gravitational gradients before reaching the event horizon.
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Visual Imaging​​
The visual effects of The Black Hole, especially for its time, were impressive. However, the depiction of the black hole itself is far less scientifically accurate compared to Interstellar. The filmmakers used traditional film techniques to represent the black hole, creating a swirling mass of light and darkness that surrounds the centre of the object. While visually engaging, this representation does not capture the complexity of how light behaves near a black hole, and the glowing accretion disk is exaggerated for dramatic effect. Unlike Interstellar, there was no consultation with astrophysicists to ensure the accuracy of the black hole’s appearance. As a result, the depiction of the black hole feels more like a traditional science fiction trope than a grounded representation of modern astrophysics theories.
An image from The Black Hole (1979) showing the robot Maximilian atop some kind of mountain ‘inside’ the black hole
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Image sourced from Dust on the VCR
Journey Into The Black Hole
In The Black Hole, the crew of the spaceship Palomino is sucked into the black hole in the film’s climax. The journey into the black hole is portrayed as a surreal, dreamlike experience, with the characters passing on a journey through a series of strange and colourful visual phenomena evoking heaven and hell. The crew then mysteriously reappear in a totally different part of the universe – seemingly arriving back at Earth. However, this depiction clearly diverges significantly from our understanding of what would actually happen. Instead of experiencing spaghettification or being crushed by tidal forces, the crew seems to simply pass through the event horizon without consequence. This portrayal is far more fantastical than scientifically plausible and reflects the film’s broader tendency to prioritise spectacle over accuracy. ​
​In contrast to Interstellar, which presented a realistic yet speculative approach to what might happen inside a black hole, The Black Hole goes for a purely narrative-driven approach, where the rules of physics are purposely bent for dramatic effect. The visual effects are striking but not grounded in any real scientific principles, which detracts from the film’s realism in comparison.
We rate: "Interstellar"
We rate: "The Black Hole"
How do they compare?
When comparing the two films, Interstellar stands out for its commitment to scientific accuracy. In collaboration with Kip Thorne, the visual effects crew of Interstellar managed to produce a visual agreeable with equations of general relativity and black hole physics. In contrast, The Black Hole focuses more on creating a visually engaging experience, rather than striving for utmost scientific accuracy. While both films explore the concept of a black hole, Interstellar provides a more realistic portrayal of the features of a black hole, such as the accretion disk, event horizon, and the potential dangers of spaghettification, albeit with some dramatic liberties. The Black Hole’s depiction is definitely a more artistic and narrative-oriented one, however, there are some scientific successes of the movie. Despite very limited literature on the topic being available at the time, The Black Hole does successfully represent the black centre of the black hole and also appears to illustrate a form of accretion disk circling the black hole. Whether this was simply an addition meant to enhance the mystique surrounding the black hole, or they were truly intending to depict an accretion disk, we are uncertain. However, it is undeniable that The Black Hole certainly depicts something that shares some resemblance to that which we have come to understand in science today. 
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When it comes to what is to be found beyond the event horizon, both films take a similarly fictitious approach. Interstellar, in a unique blend of abstract scientific ideas and make-believe, the main character, ‘Cooper’, is captured by higher-dimensional beings from the future inside a tesseract where he can interact with memories of his past in order to send a signal that can save the human race in the present. On the other hand, The Black Hole takes a more fantastical approach, depicting the singularity as a sort of gateway to another world, and even introducing somewhat religious themes.
In conclusion, both films provide considerably good depictions of black holes, which are reflective of the eras in which they were produced. The Black Hole, despite being produced in an era with significantly less scientific understanding, manages to depict something which has, at least, some resemblance to an actual black hole. representing the state of knowledge in the late 1970s and Interstellar. However, Interstellar, benefiting from decades of scientific advancements, as well as significant improvements in CGI and visual effects, undoubtedly portrays the more scientifically accurate depiction of black holes – and it is one to remember.