Black holes are of primary focus among cosmologists today, and ever since the first photo of a black hole was taken in April 2017, interests have peaked higher than ever before. If you are reading this now, you might know that there is so much more to black holes than we know currently- and the rest remains a mystery. But what do we actually know already?

 

Once a star with a mass lower than the Chadrasekhar limit of 1.4 solar mass runs out of elements to fuse, it will reach the end of its 'life' and collapse into a white dwarf- held up by electron degeneracy pressure where the electrons can resist the inward crush of gravity. If the stars core mass is between 1.4 and 3 solar masses, the, as it collapes, electron degeneracy pressure is too weak to create an equilibrium with gravity, and so the electrons combine with the protons to make neutrons, and these neutrons are now able to resist this strong gravitational push because of what is called neutron degeneracy pressure. Now, after 3 solar masses, it gets interesting. In a star with a mass of the core being 3 times that of our sun, both electron and neutron degeneracy pressure is insufficient to uphold the strength of gravity exerted on this star, and continues further collapse until the centre is an infinitely dense and infinitely small (size 0) object alled a singularity. Note that we should no think of it as a 3D object as such- because it has a size of 0; an infinitely small and dense object- but a point in time where time itself stops, and the laws of physics as we know it cease. After this black hole has formed, stellar matter in the near proximity of this massive gravitational influence accelerates towards and into the black hole, and so the black hole forms an accretion disc, while also shooting out two jets of positrons.

 

You might take a look at what happens when stellar matter accelerates around the accretion disc, and ask yourself what might happen if someone like you ended up inside one. Well, astrophysicists aren't completely sure at the moment- we have never sent an astronaut into one of course. Despite this, there are still theories surrounding the idea.

First of all, in the Penrose diagram, the singularity is located in the infinite future region,so, as a point in time, it is in the infinite future. If you were to fall into a black hole, you would have to be falling forever to reach this singularity, as it is a point in time and not an object that can be touched. This is because the singularity is extremely dense- the gravitational curve it causes means that you can never reach the end because it extends towards infinity. What we can conclude from this is that we can only approach the singularity. As you are approaching, the gravitational curve is extremely strong, which makes the difference in gravitational influence huge at different points. As you cross the event horizon, more pressure is being exerted on one side of the body than the other, and so you get stretched and elongate in a process known as spghettification.