The Heart of a Black Hole

(Originally posted Dec 2013)

There is a reason why you cannot see the “Heart” of a black hole, but first I will explain what it really is.

A black hole is a region of spacetime from which it’s gravity force prevents anything, light, etc escaping. It is predicted in the theory of general relativity that a sufficient amount of mass compacted will create a black hole. They are incredibly small with a huge amount of mass.

Around a black hole you have what is called an event horizon. This is more commonly known as the point of no return, as once you get past that there is no way (without travelling faster than light) you can escape.

At the centre of black hole there is something known as spacetime singularity. This is a point in spacetime where the quanitities used to measure the gravitational field become infinite.

Time Dilation

This is the reason why we can’t see the heart, time dilation.

It all comes down to large quantities of mass warping space-time, causing the gravitational field becoming stronger, slowly pulling objects towards the center. Meanwhile, bending spacetime in a way that time appears different to observers outside of the field to those closing in on the event horizon.

As time is all realtive, we interpret time different than each other. Meaning one person can measure time in a certain point in space, but someone else can be travelling through a part of time that is warped can be measuring time as well. But if they observed each other, time would seem different.

Scenario

Imagine you had 2 people, one person was at a safe distance watching the black hole, the other was slowly approaching the black hole.

For the onlooker, the person travelling towards the black would be gradually travelling slower and slower. The person moving towards the event horizon will see time relative to his position in time and space, meaning time will seem normal to him and not appear to have slowed at all.

When the traveller reaches the point of no return (event horizon), he will first be broken down to the atomic level (see “Spaghettiication”), and then from on lookers time will appear to have stopped. After that, because no light can escape the black hole, he will appear to be paused on the event horizon.

So while, the onlooker will forever see the man paused at the edge of a black hole. The man will have actually broken down and compacted into the singularity of the black hole. And relative to him (or whats left) time will appear to passing normally.

If you want to learn more about this, Brian Cox explains it in the recent BBC programme “The Science of Doctor Who”, which can be viewed here.

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