TLDR;
This video explores the science behind black holes, inspired by the movie Interstellar. It covers Einstein's theories of relativity, the formation and types of black holes, what one might experience falling into one, and whether they pose a threat to the universe.
- Black holes were discovered thanks to Einstein's Theory of Relativity.
- Black holes are formed from the collapse of massive stars.
- Supermassive black holes exist at the centre of most galaxies.
- The event horizon marks the point of no return.
- Despite their power, black holes aren't as dangerous as commonly believed.
Intro [0:00]
The video opens by referencing the film Interstellar, particularly the scene where Cooper falls into a black hole named Gargantua. The film depicted space-related concepts in a scientifically accurate way. The video aims to explore the accuracy of the film's portrayal of black holes and what might actually happen if one were to fall into one.
Einstein’s Theory of Relativity [1:51]
The history of black holes is relatively recent, with their existence being unknown a century ago. Black holes were discovered thanks to Einstein's Theory of Relativity, which has two parts: the Special Theory of Relativity (1905) and the General Theory of Relativity (1915). The Special Theory explains how speed affects time, leading to kinematic time dilation, where time slows down for someone travelling at high speeds relative to a stationary observer. The General Theory explains gravitational time dilation, where stronger gravitational force slows down time. This was depicted in Interstellar, where one hour on a planet near a black hole equalled seven years on Earth. Einstein visualised space-time as a fabric that bends due to the mass of objects, affecting not only physical objects but also energy forms like light. This bending creates gravity, which can be so strong that it absorbs light, leading to the concept of black holes. While Einstein's theory suggested the possibility of such objects, he was initially skeptical about their real existence. A key point in Einstein's theory is that gravity's influence is limited by the speed of light.
How Black Holes are formed? [6:35]
Despite the sensational name, a black hole isn't an actual hole in space. Black holes are formed by stars. Stars maintain equilibrium through a continuous nuclear fusion reaction that produces heat and light, creating an outward force balanced by the inward force of gravity. When a star's fuel (Hydrogen or Helium) runs out, the outward force diminishes, and gravity causes the star to collapse on itself.
Life Cycle of a Star [7:53]
The fate of a star after it runs out of fuel depends on its mass. Smaller stars become red giants, then planetary nebulas or white dwarfs. Huge stars turn into red super giants, explode as supernovas, and leave behind a core. If the core is small, it becomes a neutron star; if larger, it becomes a black hole. For a star the size of our Sun to become a black hole, it would need to compress to a diameter of only 50 km. However, our Sun will not become a black hole, as proven by Subrahmanyan Chandrasekhar, who established the Chandrasekhar Limit. This limit states that a white dwarf cannot be more than 1.4 times the mass of our Sun; beyond this, it becomes a neutron star or a black hole.
Stellar vs Supermassive Black Holes [10:16]
There are mainly three to four types of black holes. Stellar black holes are the most common, formed from collapsed stars, with an estimated 10 million to 1 billion in the Milky Way. Primordial black holes are theoretical, as small as an atom but with the mass of a mountain. Supermassive black holes are enormous, exceeding the mass of a million Suns and fitting within a space the size of our solar system; they are believed to exist at the centre of every major galaxy, including Sagittarius A at the centre of the Milky Way. A fourth type, intermediate black holes, may exist between the sizes of stellar and supermassive black holes, but no proof has been discovered yet.
The Golden Ring around Black Hole [11:45]
Black holes aren't big black balls that suck everything in; they have distinct features like the accretion disk, a ring of gaseous matter and debris attracted by the black hole's gravity. This material revolves at high speeds, heating up to millions of degrees Celsius and emitting electromagnetic radiation, mainly X-rays. The accretion disk was accurately depicted in Interstellar, though its orange colour is a representation of X-rays, which are invisible to the human eye; the actual colour would be closer to blue. The first photo of a black hole in 2019 used yellowish-orange to represent the accretion disk. The disk's brightness varies due to the Doppler Beaming effect: particles spinning towards us appear brighter, while those spinning away appear dimmer. The accretion disk creates an optical illusion due to gravity, making it seem like it covers the top and bottom of the black hole because gravity bends the light. Additionally, there's the Photonsphere, where light orbits the black hole, theoretically allowing one to see the back of their head. Beyond this is the Event Horizon, the boundary where gravity is so strong that nothing, not even light, can escape.
What if you Fall Inside? [16:07]
Crossing the event horizon means there's theoretically no escape. The depiction in Interstellar of Cooper entering a five-dimensional space after crossing the event horizon is speculative. At the centre of a black hole is the Singularity, a region where the curvature of space-time is infinite. The mesh of space-time is stretched infinitely, and time slows down infinitely. What this means for someone inside a black hole is unknown, leading to various theories. One theory suggests that light reflects off multiple points inside the event horizon before reaching the Singularity, potentially making things visible. The photo taken by the Event Horizon telescope in 2019 practically proved the existence of black holes, about 100 years after they were proven theoretically. If you fall into a black hole, you would likely disintegrate due to the gravitational force and die in milliseconds.
Are Black Holes Dangerous? [18:25]
Despite their fearsome reputation, there's no need to be scared of black holes. The misconception that black holes suck up all matter and will eventually end the universe is incorrect. Supermassive black holes at the centre of galaxies have planetary bodies and stars revolving around them, similar to how planets revolve around the Sun. Maintaining a safe distance from a black hole ensures safety.
