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How Dangerous are Black Holes?

Black Holes are among the most mysterious objects in the sky but, how dangerous are they? I want to explore this question in this logbook entry and give you are quick summary of how I understand the topic. Please be aware that I’m not an astrophysicist and can only share my view which may have som flaws! My main inspiration is the thought of such a hole flying by our sun! I never really thought about how dangerous this seemingly innocent event could be?

First of all I find the name black hole a little misleading but it got stuck for what is essentially a black star. A star forms from collapsing gas clouds in space very similar to gas giants like Jupiter. What you see in the video above is a litte simulation I wrote based on Newtonian physics and this shall just prove that all animations - with the simulation icon to the lower right - are NOT just made up but act very similar if not identical to real planets and stars. I could in fact never control the movements of so many objects by hand and if you are still sceptical you can of course look for errors in some of the celestial body movements. They are all equal in mass and occupy a region that is roughly as big as our inner solar system. Back at a star formation the amount of gas collapsing into a single object is much bigger than that of a gas giant so that the star generates enough pressure in its core for fusion to begin.

n-body Simulation

Fusing atom cores or nuclei together requires immense forces because they repel each other as they are made of Protons and Neutrons and are therefore positively charged. Once they get close enough though, other forces that keep the Protons themselves holding together take over and the two cores snap together rapidly as if a barrier was crushed. Depending on what elements fuse this process releases a lot of energy which heats up the star’s core to many many millions of degrees Celcius. ( Life would actually be impossible near any star if there wasn’t that thousands of kilometers thick gas cloud covering the hot inner regions, which is also necessary to generate that pressure in first place. So we don’t have to fear that this cloud could be blown away off our sun anytime soon since the star would not be able to sustain such a strong fusion without it. But, at some point, as a star’s fusion gets more intense with age, the core temperature gets hotter and hotter fusing elements together even at the most outer layers. This is where a star blows up to many times its size until its core extinguishes causing the entire star to collapse.

This collapse or implosion causes some massive star clouds to bounce back exploding into outer space, a supernova. It spreads the new elements it created around the galaxy causing nearby gas clouds to collapse in a billion year chain reaction forming new stars and systems as the universe ages. Just btw. a supernova, while similar, is not directly related to a nova. The terms got a little mixed up right there since a regular nova is a star explosion caused by one star feeding from another, and not one star blowing up on its own. Anyways, the remains most commonly shrink forming a white or black dwarf star. For extremely massive stars however, this is where it gets really interesting. The dwarf they leave behind ia a Neutron Star where you couldn’t lift a single scoop of matter with the strongest of machines. A cubic meter has a mass of millions of tons. Unimaginably heavy.

Neutron Star Comparison

Such a Neutron Star is the only glimpse we have at the formation of black holes. They are essentially the last step before matter collapses into the abyss. Into nothing, a single point with zero space, the famous singularity. Full disclosure, I’m not a physicist, but to get an idea how this is possible at all one has to know that the size of matter as we know it, is only based on the fundamental forces of nature. A solid surface looks solid to us because of the way light bounces of it and it feels solid because of how the surface atoms interact with our body’s. We can’t push our hand through it because there is a force stopping us. And it is nothing but a force. The force is strong in that one. Given enough pressure you could push your hand through everything assuming that the force would not crush the hand itself. What I try to say is even the smallest of elements that take up a certain space do that based on these strange forces, that just exist with yet unknown origin. ( This hopefully helps to illustrate that when the outside pressure caused my gravity wins, they can collapse indefinitely like the hand moved through the wall. There is no known boundary or limit to how small matter or energy can be compressed by gravity. Thinking about black holes it is therefore important to know that these are giant stars, carrying the same mass, just collapsed into spaces so small that we cannot see them anymore. What we instead see or not s…not observe, is a region surrounding them where the gravity gets so intense that everything that falls behind it is trapped forever, even light.

The distance from the singularity where this region begins is the so called Schwarzschild or Schwarzschild radius and it can range from just a few kilometers for small black holes up to millions of kilometers for supermassive ones like the one holding our galaxy together in the center of our milky way. The literal translation of Schwarzschild from German btw. is Black Shield Radius which is ironically quite fitting. However, it is actually a German astrophysicist’s name: Karl Schwarzschild. So it’s not a term you would translate. While the inner workings of a black hole are unknown and matter of speculation, everything outside the Schwarzschild-Radius is very well understood. The gravity of a black hole is not different to that of stars and other bodies even ourselves. The black hole in our galaxy’s center is not sucking up the galaxy as one would maybe imagine.

The tens of billions of stars just orbit itmon peaceful and stable trajectories like our solar system does for now billions of years with a couple dozen rounds trips so far. The dangerous black holes I want to talk about are not the giant ones in the centers of galaxies. I want to talk about relatively small rogue black holes that zip around the milky way like our sun does. Unlike our sun they are invisible and they can only be observed indirectly by either a glowing disc of matter surrounding them, or the warp in spacetime they create. Gravity warps space time forming a giant 3-dimensional funnel a little like this.

This funnel is the reason for why we are glued to our planet’s surface and don’t fall off into space. So keeping track and mapping the 3D space of our surrounding stars is therefore vital to find such rogue black holes. The danger does not lie in the black hole itself though. At least according to my simulations. A direct hit with our sun or our earth is very unlikely due to their incredibly small size but that doesn’t means its harmless. Our solar system balanced itself out of billions of years and is much more fragile that one would imagine. (ww w.kN ews.spac e) To illustrate this I can again use my little simulation tool and plug in the numbers for our solar system. It now shows how the real orbiting bodies would be affected by a flyby of the most lightest of black holes, just a couple times heavier than our sun.

The camera is locked to the sun so the point it leaves behind is its origin as it gets attracted towards the incoming threat. And here it comes from the top. Woah. It really scared the hell out of me when I saw this. I never really thought about the dangers of just a seemingly innocent flyby. The black hole would fling most of the solar system’s planets into deep space and separate us from our host star or as seen here throw us directly into it. Our future friends on Mars are not much better off. I simulated it hundreds of years into the future at it will end up crashing into the sun as well as Jupiter gives it its final gravity assist. This means just moving to a neighbouring planet is not the final solution to safe humanity and possibly life for an eternity. We have to move out to different stars in the long run if we want to sustain us and our surroundings. But falling into the sun has actually a rather low chance and I use this for the dramatic effect.

Black Hole Slingshot

The by far most common outcome in all the simulations I ran is a slingshot into deep space. Black holes are multiple times more heavy than our sun so such slingshots are incredibly powerful. Now, I don’t want to leave you worrying about such a dark future. We as humans are thankfully very good at dealing with never before seen problems and science will allow us to identify such threats long before they actually put our lifes at risk. We would become the Guardians of the Earth as we’d use our knowledge of fusion power to create our own sun. Or multiple ones! Double sun power!

But seriously, we could fuse hydrogen like the sun does to warm up the planet even without a star so I am very positive that even such a worst case scenario would not be the end of all life as we know it. The foundations to this are currently laid at many places and one of them is ITER or International Thermonuclear Experimental Reactor. ( The biggest ever experimental fusion reactor that is supposed to generate power is being built in europe as I speak. But the first step would probably be to seek shelter below the ground to make use of our own planet’s heat source, the by nuclear fission driven thermal activities deep down below the earth’s crust. For that we’d need boring machines and what not which is of course also being worked on, but that’s maybe a story for another video. Have you ever thought about black holes flying by our sun? Tell me what you think!