According to physics, the universe sprang into existence from a singularity — a term physicists use to describe regions of space that defy the laws of physics. They know very little about singularities, but it's known that such regions exist in the cores of black holes. It's a region where all the mass gobbled up by a black hole gets squeezed into a tiny point, infinitely massive, but also very, very small. Imagine cramming Earth into something the size of a pinpoint. A singularity would be smaller.
That's not to say the universe began as a black hole, however. Such an assumption would raise the question of something existing before the Big Bang, which is pretty speculative. By definition, nothing existed prior to the beginning, but that fact creates more questions than answers. For instance, if nothing existed prior to the Big Bang, what caused the singularity to be created in the first place? It's a "gotcha" question astrophysicists are still trying to understand.
However, once the singularity was created (however it happened), physicists have a good idea of what occurred next. The universe was in a hot, dense state and began to expand through a process called inflation. It went from very small and very dense, to a very hot state. Then, it cooled as it expanded. This process is now referred to as the Big Bang.
Although the term implies some kind of explosion, there really wasn’t an outburst or a bang. It was really the rapid expansion of space and time. Think of it like blowing up a balloon: as someone blows air in, the exterior of the balloon expands outward.
Please follow the below links for previous chapters :-
Chapter 1 - Revealing the secrets of Black Hole
Chapter 2 - Observational history of Black Holes
Chapter 3 - If falling into a Black Hole
Chapter 4 - Death by spaghettification of Black Hole
Chapter 5 - Mystery of Monster Black Holes
Chapter 6 - Crossing a wormhole : Reality Or Science fiction
Chapter 7 - Unveiling the Secrets of Biggest Black Hole
Chapter 8 - Gravity Grasp - Exploring Time Dilation Near Black Holes
Chapter 9 - Formation and Evolution of Black Hole