The Mysteries of Black Holes - Part I: How They Form and What Happens Inside Them
What is a Black Hole?
Black Holes are on of the most fascinating and mysterious objects in the universe. Black Holes are high dense objects and because of that their gravity is so strong that not even light can escape once it gets too close. According the No-Hair Theorem, Black Holes can only have three things, those are mass, electric charge and angular momentum. In this article, we'll explore how Black Holes form and what happens inside them.
How Black Holes Form
Scientists assume that the smallest Black Holes(Miniature Black Holes) formed when the universe begins. But most of other Black Holes are born from a dying star. When a star out of it' fuel(Hydrogen and Helium) it may collapse or fall into itself. The stars those up to about three times the sun's mass which are normally called small stars, the new core will become a neutron star or a white dwarf. But when a larger star which means stars those have mass three times bigger than the sun collapse, it continuous to collapse and create a Black Hole.
Types of Black Holes
According to scientists they have discovered three types of Black Holes so far. They are Stellar Black Holes, Supermassive Black Holes, Intermediate Black Holes.
Stellar Black Holes
Stellar Black Holes are created from the gravitational collapse of a star. These Black Holes have more than three times mass of the sun in a diameter of a city. Stellar Black Holes grow their sizes by consuming the dust and gas from surrounding galaxies.
Supermassive Black Holes
There are many theories about how the Supermassive Black Holes form. Some of them are, They may be the result of hundred or thousand of tiny Black Holes merging together, When a groups of stars falling together(Collapse of a Stellar Cluster) or From a large cluster of Dark Matter.
These black holes are millions, sometimes billions times massive as the sun but about the same diameter. Supermassive Black Holes dominate the universe. These are lying at the middle of the galaxies. Milky Way also have a Supermassive Black Hole in the middle of it. As the same way sun keep the planets around it by it's gravity these Black Holes keep Galaxy together.
Intermediate Black Holes(IMBHs)
In the beginning of studying Black Hole, scientists thought the sizes of Black Holes are only very small and very large. But research has reveled the possibility of midsized or Intermediate Black Holes(IMBHs) exist. In 2014 an Intermediate Black Hole was found in a arm of a spiral galaxy. Tim Roberts of University of Durham in the United Kingdom once mentioned about IMBHs. He said that "Astronomers have been looking very hard for these medium sized Black Holes. There have been hints that they exist, but IMBHs have been acting like a long-lost relative that isn't interested in being found". A research from 2018 says that IMBHs may exist in the heart of dwarf galaxies(very small galaxies)
What Happens Inside a Black Hole
What Happens inside a Black Holes is still a mystery.
So the short answer is No one knows!!!
"In some ways that's one of the most profound questions in physics," said University of Chicago Prof. Daniel Holz. "There are not many cases in physics where we simply cannot predict what happens, but this is one of them". Black Holes have two parts. They are Event Horizon and the Singularity. Event Horizon is can be considered as the surface. This is the place where gravity goes too strong for anything to scape. Then after the Event Horizon there is the center of the Black Hole which named as Singularity. Singularity is the word that use to describe a point that is infinitely dense and infinite curvature of space-time.
From the General Relativity, which describes gravity we can have an idea about what event horizon look likes. But when getting close to the Singularity laws of physics we know start to break down. "Very near the Singularity , one would expect quantum effects to become important. However, we don't yet have a quantum theory of gravity(or, at least one capable of reliably making such predictions), so we just don't know the correct description of the singularity -or even whether it really is a Singularity" said by Prof. Robert Wald of University of Chicago.
Because of the this there are many scientific and non- scientific theories and predictions about Black Holes. And there are many fictional books, movies and tv shows have created based on Black Holes and their mysteries. Some scientists assume that Black Holes are eventually explode after their life time, but it will take many many time. But scientists haven't witnessed such a event yet, which make it another mystery.
"Maybe there's a little nugget left behind containing all of the information that fell into the Black Hole, may be there's a portal to a new universe, may be the information is just gone forever; we simply don't know." said Holz.
References
https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-black-hole-k4.html
https://www.space.com/15421-black-holes-facts-formation-discovery-sdcmp.html
https://en.wikipedia.org/wiki/Stellar_black_hole
https://news.uchicago.edu/explainer/black-holes-explained#inside