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  • Writer's pictureSven Piper

Black Holes

Updated: 7 days ago


Artist's impression of a black hole
Artist's impression of a black hole (Credit: ESO, ESA/Hubble, M. Kornmesser)

Black holes are among the most fascinating and mysterious objects in the universe. Their gravitational forces are so strong that not even light can escape. They challenge our understanding of physics and fascinate scientists and the public alike. They take their name from the American physicist John Archibald Wheeler.


Black holes are primarily formed from the remnants of massive stars, which collapse catastrophically under their own gravity after their nuclear fuel is exhausted. This collapse results in a supernova, an explosive event that can outshine entire galaxies and lead to the formation of a black hole.


Their gravitational forces are so great that not even light can escape them once it has crossed the event horizon, also known as the Schwarzschild radius. The material is attracted in a spiral and collects in the so-called accretion disk before it is swallowed up. As the material heats up very strongly due to frictional forces, high-energy radiation is emitted.


The event horizon is a “boundary” between normal space and the space of the black hole, where we have to apply the theory of quantum mechanics, as we are moving in microscopic space, in contrast to general relativity, which describes macroscopic space. Once something has passed through it, it is sucked inside at the speed of light, so that according to the laws of special relativity, nothing can escape it, as nothing can move faster than light.


First image of a black hole


First image of a black hole
First image of a black hole (Credit: Event Horizon Telescope Collaboration)

The photo shows the silhouette of a supermassive black hole against a background of bright, glowing gas. The black hole is located in the center of the elliptical galaxy Messier 87 (M87), 53 million light years away from Earth. It contains 6.5 billion solar masses.


The Event Horizon Telescope team (or EHT team for short), is a network of radio telescopes that worked together to form a virtual Earth-sized telescope. It observed the black hole for two weeks in April 2017 and another week in 2018. The data collected was so extensive that it had to be physically transported to a central location for processing.


The photo of the black hole confirms Einstein's general theory of relativity, which describes gravity as a deformation of space-time. [1]


Hawking radiation


Although they are called 'black holes', they are not completely black. Stephen Hawking discovered that they emit radiation, known as Hawking radiation. This phenomenon helps to avoid violations of the second law of thermodynamics. It is based on the assumption of a vacuum state in which virtual pairs of particles and antiparticles are constantly created and disappear again in accordance with Heisenberg's uncertainty principle. Due to the strong gravitational forces of the black hole, these pairs can be separated and one particle falls into the black hole while the other escapes into space. This quantum mechanical process could lead to the disintegration of black holes over many billions of years.


Gamma ray bursts


Black holes are also associated with the mysterious gamma ray bursts (GRBs), the most powerful explosions in the universe after the Big Bang. It is assumed that this is the “birth cry” of a black hole.


Artist's impression of how a black hole sucks up material from a stellar companion
Artist's impression of how a black hole sucks up material from a stellar companion (Credit: ESO/L. Calçada/M.Kornmesser)

Spaghettization


It is interesting to note that the tidal forces near the event horizon of larger black holes are weaker, allowing closer approach without being torn apart. These tidal forces are also responsible for the fact that an object would be spaghettized, i.e. drawn out.


Alternatives


Some scientists have questioned the nature of black holes, and alternative theories such as dark energy stars or gravastars have been proposed. However, these ideas are highly speculative and there is currently no conclusive evidence to support them. The existence of black holes is widely accepted by the scientific community, but ongoing research and debate is helping to further improve our understanding of these phenomena.


Supermassive black holes


Supermassive black holes are found at the center of almost every galaxy and have a major impact on them. They have millions to billions of times the mass of our sun and influence the distribution of stars. It is not yet known what causes them to form, but it is assumed that the merging of several black holes contributes to their growth.


What is known, however, is that this can occasionally lead to true luminous signals from X-rays and jet bursts.


Primordial black holes


Some scientists assume the existence of primordial black holes. These are hypothetical black holes that are said to have been created during the Big Bang as “space-time distortions”. Even though their existence is still controversial, primordial black holes are an interesting field of research that may shed light on the development of the early universe.


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