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What would you see in a black hole?
Something about a black hole just pulls you in. Sure, its gravity is so strong that not even light can elude its grasp. But, there's something else, something harder to pinpoint. Maybe it's a black hole's absolute darkness, a mysterious, infinite chasm that dares you – or even compels you – to venture closer. When a massive star exhausts its fuel, it collapses under its own weight and implodes into a black hole. Only stars with enough heft – those maybe about 25 times more massive than our Sun – will create one. About one out of every thousand stars in the galaxy is massive enough to make a black hole. The Milky Way has at least 100 billion stars, which means about 100 million black holes are lurking out there in the galaxy. But remember, space is big. Even if you're travelling at the speed of light, the nearest black hole will still take a few thousand years to reach. But let's say you master interstellar travel, whether via warp drive or wormholes, and you reach one of these black holes. A trip into a black hole is a one-way journey. Once you cross the event horizon – the point at which light can't escape – there's no turning back. Most likely, you'd die a violent death. If you're not deterred, let's at least explore what we might see if we were to visit one.
Circling the drain Well, nothing really. A lone black hole is, unsurprisingly, black. If you circle around it, you'll notice that it's spherical, unlike those flat, Acme portable holes in Road Runner cartoons. And if it's spinning – which is likely, as most things in the universe rotate to some degree – then the black hole will be wider around the middle, rather than a perfect circle.
For a more dramatic view, though, zip on over to the Milky Way's centre, the home of a supermassive black hole nearly four million times more massive than the Sun. The black hole's gravity has gathered lots of gas and dust, which has accumulated into a disc that's spiralling into the hole – circling the drain, so to speak. As the material gets consumed, friction heats it up to billions of degrees, producing lots of radiation, and outflows of energy and charged particles.
Bright and clear So while you can't see the black hole directly, you'd see its shadow, surrounded by a bright ring and crescent. Some researchers worried that some of the gas, dust, and charged particles spewing out of the disc might obscure this dramatic image. To envision exactly what the black hole's shadow would look like, researchers created some of the most accurate computer simulations yet that incorporate all the physics of the gas and gravity around the black hole.
It turns out that the view would remain bright and clear, says Feryal Ozel, an astrophysicist at the University of Arizona who helped produce the simulations. They make for some cool movies but more importantly, they help astronomers anticipate what they will see when they observe the shadow of the Milky Way's black hole for real.
Smashed into smithereens This spring, the researchers got seven telescopes hooked up and ready to go. By 2017, he hopes to have all of them set up, and people will be able to directly see a black hole. Indeed, getting an image is groundbreaking, he says, and it'll offer the strongest proof yet that black holes do exist (all evidence so far has been indirect, for example based on a black hole's gravitational influence of nearby stars at the galactic centre). Physicists will also be able to make the most detailed observations ever on what goes on around a black hole, allowing them to test the intricate details of Einstein's theory of gravity.
But maybe simply a view isn't enough, and you still want to go inside the black hole. Unfortunately, physicists aren't quite sure what will happen. The conventional hypothesis is that you'd get spaghettified. If you leap into the black hole feet first, your feet will feel stronger gravity than your head. As you approach the hole, the difference in gravity at your feet and your head gets bigger and bigger until you're ripped apart. Soon, this tidal gravity, as it's called, will tear every cell, molecule, and atom in your body into smithereens.
To find out once and for all what happens inside a black hole, you might simply have to go inside one. The problem is you won't then be able to tell anyone what you’ve seen.
