Beyond the horizon

It is time to go beyond the limits of human experience. Beyond the limits of modern physics. Beyond the point of no return. It’s a cool place.

Black holes are weird. Black holes are sort of the itchy spot that modern physics can’t scratch. Apart from the Big Bang, dark energy, dark matter, antimatter and gravity. Modern physics should really buy a back scratcher.

I would like to take this minute to point out that black holes are entirely hypothetical and we’re not actually sure that they exist. They probably do. If they don’t, this research was a waste of time.

So. The probably-not-fictional black hole.

Black holes are hecka weird. They are literally holes in spacetime. Nothing can escape them. Black holes are objects that are so dense that they slightly break the universe.

When a massive star dies, it collapses. It emits the most massive wave of energy that we know of in the universe. A hypernova.

Don’t get in the way of this.

When the hypernova ceases, what is left is the barest core of a star. And because the star is massive, it is a massive core. And without the pressure of the nuclear fusion holding the star in shape, it collapses.

(It’s actually more complicated than that, but that sums it up pretty well and I don’t feel confident enough in my knowledge to explain any more than that.)

Once the star begins to collapse, a number of things can happen. The star can stop collapsing and form a brown dwarf, the burnt-out husk of a star. It can go a bit further and form a neutron star, a star made entirely of neutrons. These are tiny, stars the mass of the Sun with a radius of only 10-20km. Neutron stars are pretty weird, But not as weird as the next logical progression of this sequence.

A black hole is what happened when a mass becomes so dense, it passes its Schwarzschild radius. The Schwarzschild radius (try spelling that without a dictionary) is the size at which a star goes through a stage change and becomes a black hole. It requires the object to be extremely, extremely dense. The Schwarzschild radius of the Earth is 9mm, the Sun’s is 3km. And once an object passes that size, some very interesting/scary things start happening.

For one thing, time and space dilate. According to the Theory of General Relativity, matter can warp spacetime the same as high speeds. As you approach a black hole, time will slow down. The closer you get, the slower time will run. When you kiss the very edge of the black hole, the event horizon itself, time stops.

The next thing: gravitational lensing. We like to think that light goes in straight, pretty lines so we can draw nice reflection lines. That is generally right. But under high gravities, things are weird. Light can bend and arc and stretch and warp. And what that means is, we can use supermassive objects as cosmic-scale telescopes.

Let’s get in a little closer.

As clouds of gas and dust (plus any unfortunate stars) are pulled towards the black hole, they spiral into a disc. That disc would become superheated as it fell, glowing brilliantly. But not as bright as the very inner edge of the disc. As the gas and dust particles touch the edge of the black hole, they are vaporised in a massive burst of radiation. This is what those jets being emitted from drawings of black holes are.

Closer.

The very edge of the black hole is a little-understood place. It is exactly the size of the Schwarzschild radius of the black hole, and acts as the cloak that hides the singularity itself from view. Exactly on the surface of the event horizon is a disc of photons, perpetually in orbit. Orbiting light. If a photon is just a nanometre above the horizon, it will escape the black hole. A nanometre below, it will be pulled in.

On the event horizon of a black hole, time stops. Not for you, falling faster downward. For us outside observers, we would see you stop moving. Time has stopped for you, relative to use. Plus, the light carrying the image of you falling in would never reach us. It too would fall victim to the black hole.

And that is where modern physics ends – the event horizon of a black hole. What lies beyond is anybody’s guess.

Probably not bookshelves, Interstellar.

Not a black hole.

Our best guess is that at the direct centre of the black hole is the singularity, the point at which spacetime itself is punctured. That’s the source of all of the effects, and the unbelievable gravity.

In fact, argument about what the inside of a black hole is like is a little pointless, given how it would be virtually impossible to get anywhere near it. As you get closer, the difference in gravitational forces between your head and feet would tear your body apart almost instantly. So unless we have spectacular breakthroughs in both interstellar travel and ultra-strong metamaterials, we will likely never know what even the area around the event horizon is actually like, let alone beyond that.

So really, who knows? Maybe, beyond the horizon of the most powerful force in the universe, is an empty space. And a glowing sign saying ‘Start of Level 2’.

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One thought on “Beyond the horizon

  1. FW says:

    Really enjoyed reading this…. you put it all together very well. Black holes have always fascinated me and it’s mind boggling to think what they can be like.

    Like

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