Despite the tiny reach of our space programmes, and even the Voyager I probe having only recently left our solar system, we know a remarkable amount about our galaxy and the universe. One of the most fascinating and still puzzling astronomical phenomena are ‘black holes; though we do not fully understand them, study of the universe has taught us some incredible things…
1. Black Holes Are NOT Empty
One popular misconception about black holes is that they are just that: holes, containing no matter whatsoever. The truth is very different, however, as black holes are in fact a huge amount of matter which is packed into a tiny space, as if the Sun were compressed until it were just three kilometres wide. This isn’t a fixed size, however, as black holes can be larger or smaller depending on their mass, which is directly proportional to the radius of its event horizon (Schwarzschild radius).
2. They Make Time Stand Still
The concept of time not being a constant is admittedly quite difficult to get one’s head around, and we’re not going to get into the precise details here, so you’ll have to trust us or check Wikipedia when we say that the speed at which time passes is directly affected by gravity. Because of the huge gravitational pull of a black hole, time passes more slowly the closer one is to it (relative to observers further away), causing time to effectively stop within its event horizon.
3. There’s One At The Centre Of The Galaxy
You probably know that our home galaxy, the Milky Way, is laid out in the shape of a spiral, with all of its stars rotating around a dark central point. Well, this dark central point is in fact a black hole so huge that its mass is the equivalent of around four million of our suns. Known as a supermassive black hole (because of its super mass, duh), this huge phenomenon is located 26,000 light years away in a region known as Sagittarius A*.
4. They Are Formed By Dead Stars
It’s no secret that eventually, even such huge balls of gas as our own sun will eventually run out of fuel and die, and the same is true of stars even bigger and brighter than our own. However, when stars with a mass at least 10 to 15 times greater than the sun burn out, they can explode in a supernova which leaves behind the burned-out core of the dead star. This core, known as a stellar remnant, is generally packed full of dense elements, so much so that its own gravitational forces will cause it to collapse in on itself to the point where it has zero volume and infinite density, creating a singularity: a black hole.
5. It’s Very Difficult To Get Sucked In
Despite the popular myth, the chances of any interstellar traveller being unlucky enough to be unwittingly sucked into a black hole is very slim. The Schwarzchild radius, which we referred to earlier, is the boundary that marks the point at which even light cannot escape from the gravitational pull of the black hole. Compared to the overall mass that would have led to the black hole’s formation, this radius is extremely small: for example, compare the 700,000km radius of our sun with the 3km Schwarzchild radius that a black hole with the mass of our sun would have.
6. If You Did Get Sucked In, You Wouldn’t Know It
Sorry to break it to any budding space adventurers out there, but even if it were possible to send manned craft to the nearest black hole (V4641 Sgr, about 1600 light years away), the idea of embarking on a one-way trip to see what might be inside is simply out of the question. The gravitational forces at work at even the smallest black hole are incredibly intense, and they get stronger as you get closer to the point of no return: the event horizon. The trouble is, you’d be dead long before you reached this boundary from beyond which not even light can escape – if you were going feet first, the gravity at your toes would be stronger than that at your head, causing you to be torn apart, no matter what protective gear you might be wearing.
7. We Find Black Holes Using X-Rays
More precisely, we find them by detecting the emission of x-rays by super-heated, electrically-charged atoms which make up any matter that is being pulled toward the black hole. The kinetic energy built up by these atoms reaches temperatures of several million degrees, causing them to emit x-rays into space at a speed fast enough to escape from the black hole’s gravitational pull. These sources of x-rays are picked up by space-based telescopes and analysed to determine whether they originate from a black hole or other astral body, such as a neutron star.