French astronomer Pierre-Simon Laplace predicted the existence of black holes way back in 1796, but we’ve yet to capture one on camera. The Event Horizon Telescope will bring together astronomy’s greatest radio telescopes in an attempt ‘photograph’ the supermassive black hole at the heart of the Milky Way
Where would science fiction be without black holes? As a plot device they are without equal. They can imperil our plucky hero as his spacecraft is sucked like a spider down a plughole to (almost) certain doom and they provide a handy shortcut to the past, or future, in the form of a wormhole. But despite their ubiquity in TV and film, astronomers have never actually seen one.
In fact, everything we know of black holes comes from theory and indirect observations of the effects they have on the space around them. But now scientists are getting ready to take their first picture of these enigmatic phenomena.
To tackle this monumental task they will create a global network of some of the planet’s greatest radio telescopes to create a colossal virtual telescope the size of planet Earth.
Astronomers and scientists from across the world met last week to discuss the project, which has been dubbed ‘The Event Horizon Telescope’. They hope to enlist the talents of telescopes in Arizona, Hawaii, California, Europe, Mexico, Chile and the South Pole. In all 50 radio telescopes will be involved. A technique called interferometry will allow the Earth-size network to act like a single Earth-size telescope.
Its task will be to capture an image of the black hole that hides at the centre of our galaxy, the Milky Way. But that isn’t as easy as it sounds.
Even though it is classed as a supermassive black hole that weighs in at an impressive four million times the mass of our Sun, it is extremely compressed and is almost 26,000 light-years away. Its very nature, which prevents anything (including light) from escaping, makes it impossible to image the black hole directly.
Instead, the Event Horizon Telescope will aim to photograph the swirling disk of matter and energy that surrounds the black hole. By looking for the point at which the black hole’s gravity becomes so intense that it prevents anything from escaping (called the event horizon) scientists will get an outline of this most enigmatic of cosmic phenomena.
But best of all, it's given me an excuse to talk about black holes and (as we all know) black holes rock!
The weird and wonderful black hole: A most singular singularity...
Black holes are birthed in the death throes of a large star (about 25 times the mass of our Sun is perfect). Stars rely on the heat created by nuclear fusion to remain stable. When their hydrogen fuel supply is exhausted, they throw off their remaining gases in a supernova explosion – leaving behind only their super-dense core. The core remnant then collapses under the force of its own gravitation
The core remnant keeps collapsing until it is smaller than an atom. In fact, it will become smaller than the smallest piece of all the impossibly small things that make up an atom – known as a singularity. If you imagine that a grain of salt might measure in at 0.0001 metres, to describe the size of the singularity you would have to stick 35 zeros in front of that number one... which looks like this 0.00000000000000000000000000000000001 metres – and remember, that impossibly small speck has the mass of several Suns squashed up inside it
Although the singularity is the gravitational engine of a black hole, it doesn’t define it. A black hole is defined by the region around the singularity where its gravity is felt so strongly that not even light can escape its pull. The point at which light can longer escape is called the event horizon and this defines the limits of the black hole
At the centre of a black hole, spacetime is infinitely curved and matter is crushed to infinite density under the pull of 'infinite' gravity. At a singularity, the laws of physics (as we know them) break down and space and time cease to exist
Just like planets, galaxies and pretty much everything in the universe, black holes spin. Black holes are formed from stars and all stars rotate. When a star’s core starts to collapse, the star’s rotation speeds up (think of a spinning ice-skater tucking his arms in to speed up the spin). As the star’s core shrinks to become a black hole its spin get faster and faster. Unfortunately, we can’t know how fast a black hole spins, but you can guess that its pretty fast – a neutron star (which is star that has collapsed to a few miles in diameter) can spin up to 1,000 times a second. So imagine how fast a star that has collapsed to a singularity is spinning.
The easiest way to describe how a black hole works is to imagine a very heavy ball sitting on a sheet of rubber. Just as a heavy ball makes an indent in the rubber, so a black hole makes an indent in the fabric of spacetime. Less massive objects fall into the indent – like water falling down a plug hole
But that’s a two-dimensional view of a black hole. In reality, spacetime isn’t a two-dimensional sheet – it is multidimensional – and gravity interacts with all these dimensions. This means that a black hole is more like a sphere, with a central point where spacetime is drawn to a focal point (the singularity) in the centre.
But it gets even more complicated than that. If the singularity is spinning, it twists the fabric of space around it (imagine a sheet getting caught up in drill bit)
Black holes aren’t fixed into one position in space – they wander around the universe. As they wander, they can blunder into other black holes and, if they get close enough, their mutual gravitational attraction causes them to begin orbiting each other. As they get closer, the speed of their orbit increases until they smash together – creating a much larger black hole. Black holes can also devour stars by stripping them of matter. Eventually a black hole will absorb enough of its brethren and other stars to become a supermassive black hole - one with millions or even billions of times the mass of our Sun
According to Newton’s Laws, gravity depends on distance – the closer you get to an object, the stronger you feel the effect of its gravity. This effect is exaggerated near a black hole. If you were able to get close enough to a black hole, the difference in gravity felt between your feet and you head would be colossal. In fact, the difference is so extreme that your feet would feel many hundreds of millions of times more gravity than your head. This would result in you becoming stretched into a long, thin strand (imagine holding a lump of Blu-Tack with both hands and pulling as hard as you can). This is called ‘spaghettification’