July 21, 2013
Top 10 Black Hole Facts
Black holes are very interesting objects. By their very nature they seem to bend, and even break, the laws of physics. As we learn more about these exotic, dynamic objects, the stranger reality becomes. To prove this point, I have compiled a list of my Top 10 Black Hole Facts for your enjoyment. Think I’ve missed one? Respond in the comments and I’ll try to follow up.
1) Black Holes are the Densest Objects In The Universe. The result of the supernova collapse of a massive star, black holes are incredibly massive, yet incredibly small in volume. In fact, the mass is so tightly packed into these objects, that the very laws of physics as we know them break down.
2) Some Black Holes Are Billions Of Times The Mass Of Our Sun. Known as Supermassive black holes, these objects are generally located at the cores of galaxies. They are responsible for much of the observed motion and evolution of galaxies, yet how exactly they come into existence is still not settled.
3) Black Holes Are NOT Cosmic Vacuum Cleaners. There is some misconception about the gravitational power of black holes. When approaching the “surface” of these dense objects, the gravitational becomes immense. In fact, light cannot escape once it crosses the event horizon – the place where the escape velocity equals the speed of light. However, if our Sun were suddenly replaced with a one solar-mass black hole, the gravitational force experienced by the Earth would not change. It is only when you get close to the black hole – in this case within a solar radius – would the difference in the gravitational force become apparent.
4) If A Person Fell Into A Black Hole They Would Be “Spagettified”… If a person were falling feet first into a black hole, the force on their feet would be stronger than the force experienced on their head. Additionally, since all of the lines of force point towards the center of the black hole, the person would also be squeezed inwards. The result is that eventually, as the person got closer and closer to the black hole, they would spagettified – turned into a single stream of particles one atom thick. Think of a single strand of spaghetti, hence the name.
5) …But A Cockroach Would Probably Survive The Initial Fall. Interestingly, while a person would be “spagettified” by the gravitational force gradient described in point 4, a cockroach would actually survive much longer. The reason is that a cockroach is much smaller, so the difference in force from its bottom to its top would be much smaller. Additionally, they have a comparatively strong skeleton. For more on this, check out my recent podcast with black hole theorist, Kelly Holley-Bockelmann.
6) Light Cannot Escape A Black Hole… As mentioned previously, once light crosses the event horizon it cannot escape from the clutches of the black hole. This is because once this point is crossed, the speed something would need to travel to escape would be greater than the speed of light. And to the best of our knowledge it is not possible to accelerate light or matter beyond the cosmic speed limit.
7) …But Information About A Black Hole CAN Escape. Things get tricky when talking about what can and what cannot escape a black hole, and there are theories abound that come to slightly different conclusions. However, it seems that as best we know, while light cannot escape crossing the black hole event horizon, information can be preserved. The reason is that particles, such as electrons and positrons, are created in pairs. If this happens near the black hole boundary and one particle falls into the black hole, while the other does not (i.e. they move off in different directions), the information about the particles is preserved, even as one falls into the singularity.
8) The Gravity From Black Holes Can Bend Light. In general, the gravitational force can bend light. In fact, it does not take the gravity of a black hole to warp the path of a light ray; our Sun, and even the Earth, do it readily. But, the effect can be magnified because of the strong gravitational fields very close to the black hole. As a result, we can use this to help us identify these mysterious objects, which leads us to…
9) Despite Being “Black” We Still Detect Their Presence, Albeit Indirectly. Since light cannot escape a black hole, we don’t have a tool to directly observe these objects. (I’ll ignore, for now, Hawking radiation. While this is certainly a widely held theory, its effect is weak and not a meaningful way of identifying black holes at this point.) All is not lost, however, because we can still find these objects lurking in our universe. We do this by looking for their effect on other objects, either by distorting their motion, or warping the light coming from the objects.
10) We May Be Living Inside A Black Hole. This is a strange one, and probably more of a fringe theory than mainstream, but physicists have long noticed that the mass-energy density of our Universe, when taken as a whole, is about right for that of a black hole. As a result, some scientists have suggested that perhaps our Universe is simply the inside of a black hole, perhaps a black hole in a whole other Universe. And black holes in our Universe? Perhaps gateways to other Universes. While this is not a widely held theory, it is certainly interesting nonetheless.
Image Credit: oorka / Shutterstock