A supermassive black hole lives next door

Despite their size, two super massive black holes have been hidden behind clouds of gas and dust in our neighbouring galaxies. The giants, described as “monsters under your bed” by Dr Annuar of Durham University, provide further evidence that there may be a supermassive black hole at the centre of every galaxy.

Any object that has a gravitational pull so great that even light is trapped inside is a black hole. The different types are the result of the mass of the object before it "turned". This is all good and well, but if all black holes mass are hidden from view and tightly packed to infinite density, how do we know a supermassive black hole is…well, massive?

The answer is the event horizon. You see.... you were right... the centre of every black hole is ultimately the same. Of infinity density. BUT, every black hole has a different size of event horizon, and it is this that can give us an indication of what that black hole was originally made from. The event horizon is the edge. The boundary. You can fly your space ship a millimetre away from it and be completely safe. But cross it and you’re sucked in to never return.

What defines the event horizon is the mass of the original object. This was discovered by a bloke called Schwarzschild. He found that every object had the potential to be a black hole. It didn’t need to be a colossal star. It could be you, a car, Jupiter…you get the idea. If you compress something enough, eventually it will turn into a black hole. Schwarzschild’s question was how small must it be before this happens. This point is now called the Schwarzschild radius and to give you an example, for Earth it is one inch. This means that if the mass of Earth was squeezed into a sphere with one inch radius, it would become a black hole, and one inch would be the radius of its event horizon. Pitiful really compared to a supermassive black holen. The point of no escape is the event horizon. But, its size is the Schwarzschild radius.

Thank you Schwarzschild. I’ll make sure I take some notes of your formula when I buy my spaceship. Until then, we can use it to determine whether our “new” neighbours are likely to pose a threat. Luckily the answer is no. The event horizons of these black holes are still too distant from Earth to be of any concern. So, don’t worry. You can still sleep at night. These monsters under your bed aren’t going to be the ones to get you.