Das Weltkulturerbe 2024
Free English translation on 15 November 2021.
I had to take the following passages from a book in order to make it easier for everyone to understand what is going on.
The book says that it is assumed that the universe was originally concentrated in a single point and only began to expand with the so-called big bang.
This is concluded from the fact that the universe is still expanding today, i. e. the distances between the galaxies are increasing. Consequently, there must have once been a starting point.
According to the generally accepted theory, there was no "before the big bang", since time also only came into being with the big bang. And since it has only existed since the Big Bang, there can also be no "before".
According to current cosmological models, there was a phase shortly after the Big Bang in which the universe expanded very strongly in an unimaginably short time - and at a speed that was significantly greater than the speed of light.
Surprisingly, this does not contradict the law that nothing in space can move faster than light, since no matter was moved in the process, but space itself expanded.
Will the Universe expand forever?
The latest theories say that the expansion of the universe - driven by "dark energy" - is even accelerating. However, to this day no one knows exactly what this dark energy is.
Scientists all over the world are feverishly searching for an explanation. The only thing that can be measured so far is its effect on the speed of the expansion of the universe.
What is a Black Hole?
"What is now known about black holes and what conclusions can be drawn on the matter as a result of the new findings?" https://youtu.be/1kYN4xoBa5k
Image calculated from radio images of the Event Horizon Telescope showing the supermassive black hole of the galaxy M87. The black disk in the center of the image is about 2.5 times the size of the event horizon (Schwarzschild diameter about 38-1012 m) of the supermassive black hole in the center..
A black hole is a region of spacetime where gravity is so strong that nothing — no particles or even electromagnetic radiation such as light — can escape from it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of no escape is called the event horizon. Although it has an enormous effect on the fate and circumstances of an object crossing it, according to general relativity it has no locally detectable features. In many ways, a black hole acts like an ideal black body, as it reflects no light. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is on the order of billionths of a kelvin for black holes of stellar mass, making it essentially impossible to observe directly.
Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. The first modern solution of general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916, and its interpretation as a region of space from which nothing can escape was first published by David Finkelstein in 1958. Black holes were long considered a mathematical curiosity; it was not until the 1960s that theoretical work showed they were a generic prediction of general relativity. The discovery of neutron stars by Jocelyn Bell Burnell in 1967 sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality. The first black hole known as such was Cygnus X-1, identified by several researchers independently in 1971.
Black holes of stellar mass form when very massive stars collapse at the end of their life cycle. After a black hole has formed, it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses (M☉) may form. There is consensus that supermassive black holes exist in the centers of most galaxies.
The presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light. Matter that falls onto a black hole can form an external accretion disk heated by friction, forming quasars, some of the brightest objects in the universe. Stars passing too close to a supermassive black hole can be shred into streamers that shine very brightly before being "swallowed." If there are other stars orbiting a black hole, their orbits can be used to determine the black hole's mass and location. Such observations can be used to exclude possible alternatives such as neutron stars. In this way, astronomers have identified numerous stellar black hole candidates in binary systems, and established that the radio source known as Sagittarius A*, at the core of the Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses.
On 11 February 2016, the LIGO Scientific Collaboration and the Virgo collaboration announced the first direct detection of gravitational waves, which also represented the first observation of a black hole merger. As of December 2018, eleven gravitational wave events have been observed that originated from ten merging black holes (along with one binary neutron star merger). On 10 April 2019, the first direct image of a black hole and its vicinity was published, following observations made by the Event Horizon Telescope (EHT) in 2017 of the supermassive black hole in Messier 87's galactic centre. In March 2021, the EHT Collaboration presented, for the first time, a polarized-based image of the black hole which may help better reveal the forces giving rise to quasars.
As of 2021, the nearest known body thought to be a black hole is around 1500 light-years away (see List of nearest black holes). Though only a couple dozen black holes have been found so far in the Milky Way, there are thought to be hundreds of millions, most of which are solitary and do not cause emission of radiation, so would only be detectable by gravitational lensing.