When a star dies or any kind of gas at the center of the galaxy is tightly packed enough into a small region the force of gravitational pull becomes so great that nothing can escape out of it not any kind of electromagnetic fields neither the light. This forms a “Black Hole” which refers to no point of escape or return. The distance around the black hole where nothing can escape is known as the event of the horizon. Black holes are really difficult to observe due to their property of no light escaping from them yet we are lucky that we still have a way when any matter falls into it the matter emits a wave of light that can escape it and can be observable. When a star passes very close to the Black hole it destroys the star and the gravitational pull of the Black hole attracts the matter toward itself which then accelerates and starts emitting X-rays or Gamma rays into space which are observable through special telescopes and satellites. Astronomers have yet almost no knowledge about the black hole but at least they come to know about the formation of it.
Discovery of Black Hole:
Since the Discover of Black holes scientists have been wondering over many aspects of it including what’s inside the black hole, its formation, and how the matter’s energy is released when anything falls into it.
John Michell first proposed the idea of a body same as sun density in which light cannot escape in a letter which got published in 1784. After that wave nature of light was discovered in 19 century. This modern approach rejects the Michell statement of the light ray coming out of a massive star which later slowed down and fall back.
1915, the Einstein approach that gravity does influence the light’s motion is presented in form of the Theory of Relativity. Inside of the event horizon, the escape velocity of the matter to get out of the gravitational field of this cosmic object exceeds the speed of light in this way light rays cannot get out. Schwarzschild characterized the black hole later in 1916 by using this theory. The radius of the event horizon is named after him as Schwarzschild radius which is proportional to the total mass of collapsing star. Johannes Droste, later on, gave the same solution but more extensively. In 1967, the discovery of neutron stars later on further develop interests in the collapsed objects by gravity.
Gravitational waves were discovered along with the very first Black hole merger observation later on by the collaboration of LIGO Scientific Collaboration (LSC) and Virgo in Feb11, 2016.
Till December 11, 2018. Almost 11 gravitational wave events and 10 merging black hole events were observed. It was April 2019 when the first clear image of the Black hole and its event horizon got published. Event Horizon Telescope used to observe the Black hole in Messier 87 galactic center.
Creation of Black Hole:
There are several theories by scientists which describe the creation of a black hole. One is proposed by the famous Stephen Hawking who compares the formation of the black hole to the piling up of books in the library which at last reaches a point where adding more and more books led the library to collapse and form a black hole.
Another one is the theory which says that when two stars meet they merge into each other and a black hole is formed. The third one is that when a star burns it uses all of its fuel and starts shrinking a point reaches when it becomes so compact that it leads to “Singularity”.
Size of Black hole:
Black holes form when massive stars die due to that reason the number of these stars describes the size of the black hole yet black holes are so massive that they can have the size of billions of times of our sun.
We characterize black holes in four different types as Stellar, Supermassive, miniature, and intermediate ones. Among them stellar are the most common ones. . Black holes can be really small as the size of an atom but can acquire the mass of a whole mountain and can be as large as having mass more than 20 times than sun which is stellar black holes. Death of a big star compress to such an extent that it creates a stellar black hole. These kinds of Black holes consume so much gas and dust from their surroundings that they keep on growing. According to the research group of Harvard Astrophysics, our milky way could contain a few hundred million such black holes.
The largest black holes can have the size of more than 11 million suns all together which are known as Supermassive Black holes. These are considered to be at the center of the Galaxy of the Milky Way and one is known as Sagittarius A which has a mass of approximately a total of four million suns and can acquire millions of Earth in it. These kinds of Black holes could be formed by merging several little black holes.
There is a possibility of middle-sized black holes too which are not larger neither too small. For case, there’s a course of object called ultra-luminous X-ray sources (ULXs). These objects radiate more X-ray light than known stellar processes. One model is that ULXs harbor an intermediate black hole; however, advanced study of these objects has favored substitute models for most of them.
Intermediate Black Holes could form when clusters of several stars collide in such a way that they initiate a chain reaction. These middle-sized black holes could also join together to give rise to the supermassive ones. Astronomers are interested in this special type of black hole and in 2014 they succeeded to find out such IMBHs (Intermediate mass black holes) in the spiral galaxy. According to recent research of 2018 by the Sloan Digital Sky survey that such type of black holes could be found in the middle of small galaxies. X-Ray activity revealed such black holes ranging from solar masses of 36000 to 316000.
Structure of Black hole:
The mass of the black hole is entirely compact at a very small point that is a singularity that is surrounded by an event horizon which is the distance at which the escape velocity becomes more than light speed. The formation of singularity is because of the compressed nature which allows no other force to escape. This doesn’t happen in stars like the sun because outer nuclear reactions pressure to balance the inner gravitational pull. At the point of singularity, the concept of time and space fails and the force of gravity becomes mysteriously strong. As we move away from the point of singularity the escape velocity decreases and a point reaches where it becomes equal to the speed of light. This point is called the Schwarzschild radius. It depends on the mass of the black hole and for a black hole as large as the sun it’s 2 miles and for extrasolar mass, it increases by 2 miles.
The event of the horizon is just an area where nothing can ever return out of the black hole and be trapped inside it forever. The black hole becomes bigger and bigger as it increases in mass when anything enters it.
The black hole is surrounded by the ergosphere which is the area in which the gravitational pull of the black hole drags all space towards itself. The gravitational effects of a rotating black hole are quite complicated than the stationary ones because it pulls space-time along with it which leads to an effect known as frame-dragging and this occurs inside the ergosphere. Cross-sectional it is oval-shaped having an influence area extending more into space at the black hole’s equator rather than on poles.
Death of Black hole:
That’s quite an interesting approach that how a Black hole dies when it made up of dead stars matter but to explain this Hawking approach of radiation is used which means that the area around it which is the event horizon composed of matter and antimatter which is continuously merging and forming energy but if antimatter reaches the end that is the singularity of the Black hole the antimatter particles destroy the matter particles the black hole completely shrinks and it would almost diminish.
“The bigger the size of a Black hole, the shorter life span it has”
- Roger Penrose awarded the noble prize for the discovery of the formation of the black hole by using the general theory of relativity prediction and Andrea Ghez along with Reinhard Genzel for the discovery of a supermassive object at the galaxy center which makes Ghez the fourth women in the history of physics to get a noble prize.
- Recently biggest Black hole collision is being reported which is between the mass of 85 times and mass of 66 times more than the sun to form a black hole of mass of 142 times by LIGO and its European counterpart Virgo in May 2020.
- LIGO and Virgo collaborated and made an announcement in April about the discovery of a crash between two black holes which were almost 2.4 billion light-years apart from each other and weighted almost 30 times more than the sun. Due to the asymmetric nature of the crash, it is considered the latest and unique because it leads to the possibility of another kind of hierarchical merges in which the remnants of the two collided black holes merge with other black holes.
- Theorists have suggested that black holes could be like fuzz balls because the collapsing of matter and energy into compact form up to the point of infinity is almost a physically impossible concept so they are trying to find a new aspect using string theories that condemns the particles and other forces in subatomic particles rather than gives a concept of vibrating strings. According to the latest study made in October show that if the neutron stars’ atoms are not dense enough that they could make a black hole. Then they might be just a collection of strings which when compressed don’t make a proper black hole but a yarn ball-like fuzzy structure. Not a lot of research has been done on this idea but it is also currently under consideration.
- Recently work has been done on the existence of primordial black holes which physicists didn’t know about in the past era and also SLAB’s ( Stupendously large Black Holes) which are almost a trillions time of Sun’s mass 10 times more than TON618 which is almost 66 sun molar masses.
- Spaghettification is a phenomenon in which an object that comes close to a black hole at a certain distance got shred into strands of materials that’s why nothing could dare to come too close to a black hole but recently a discovery has been made in May in which the cosmic Pac-Man seems to be orbiting along with HR 6819 at a safe distance which is the most closely recorded distance from a black hole. This distance is recorded more than three times concerning previous ones. HR 6819 system stars can be seen in the Southern Hemisphere by using a star chart using Pavo, the peacock in Telescopium.
The black hole has been a topic of interest for the past 100 years by various astronomers, physicists, and researchers, and a huge number of discoveries are made since today. Yet the more scientists explore the galaxy they become amazed by the data which opens up to new levels of discoveries. Previously it was just a mathematical curiosity and now with several statistical and computational pieces of research, it leads the interests of various theoretical physicists into it. With the day-by-day progression, the topic will lead to unimaginable discoveries related to birth, death, and the explanations of all the processes of the galaxy. In short, we can say that nature will continue to amaze the imaginations of people.
Article author: Maryam00000 (Fiverr.com)