Once just a theoretical concept based on physics and Einstein’s theories of general relativity, black holes are now accepted as real things – and the subject of intense study. Not only do scientists believe there is a supermassive black hole at the centre of our own galaxy (and many others) but suggest there could be as many as 10,000 smaller black holes swarming around the galactic centre.
DEATH OF A STAR
Black holes are formed when a star exhausts all of its fuel. When the energy of the nuclear fusion isn’t enough to keep the force of gravity at bay, it simply collapses under its own weight. This triggers a supernova explosion with the remnant being either a neutron star or, if the original star was massive enough, a black hole.
Black holes vary in size, theoretically as small as a single atom containing the same amount of matter as a large mountain, to, well, unimaginably vast. The largest black hole on record, S5 0014+81, has the same mass as 40 billion suns and is 236.7 billion km in diameter – or 47 times the distance from the sun to Pluto. You might want to let that sink in for a second.
HEART OF DARKNESS
The mass of a black hole is concentrated at its centre – known as the singularity – where its density and gravitational field become infinite. The black hole is then bounded by a surface known as the event horizon, within which nothing can escape – not even light, hence the name. The event horizon is, literally, a point of no return; once you pass it, your journey into the black hole – and certain excruciating death – is inevitable.
On your journey into a black hole, the first thing you see is a glowing band of dust and gas, known as the accretion disc. Like planets orbiting the sun, this is all the cosmic debris that has been drawn into the black hole’s influence, spinning inwards at ever-increasing speeds and heated to billions of degrees. While much of this material is absorbed, in the case of rotating black holes, some of it is accelerated to near the speed of light and ejected as streams of high-energy rays and particles along the axis of rotation. It would be a majestic, if somewhat deadly, sight.
And because a light source shines more brightly as it’s approaching you, if you view the accretion disc from an angle, it would appear crescent shaped, brighter on one side than the other.
THROUGH A LENS, DARKLY
While you can’t see the black hole itself, you can see how its gravity bends the light around it, a phenomenon called gravitational lensing. The effect means you can see stars and galaxies behind the black hole, which accumulate as bright ring around its edge.
The intense gravity also has another side effect, that of time dilation. As you fell towards the event horizon, anyone watching your journey would see your progress become slower and slower until you simply seemed to stand still, approaching but never quite reaching the event horizon itself. Your image would grow red, due to the Doppler effect, and then gradually fade from view.
BEYOND THE HORIZON
Sadly, you’d never be able to see what was beyond the event horizon; at close proximity to a black hole the gravitational effects are so extreme that the difference between one end of your body and the other causes you to be ripped apart, atom by atom. Scientists call this spaghettifcation – which happily conjures up an image of what would happen should you stray too near to the most complex and exotic bodies in the known universe.