Gravitational collapse happens when the density of the matter is so high that the force of gravity overcomes the other fundamental forces that keep matter together.
At the core of the black hole is the singularity. A point in space-time where the density of a mass becomes infinite. This point is so massive that it bends the whole space-time around it which curvature so deep even the light can't escape it. Yes , the light, which doesn't actually have any mass isn't actually prevented from escaping the black hole due gravity itself, but the space itself being so twisted that the light is unable to find it's way out of there.
While scientists are just starting to think about the ways how we could find the miniscule black hole that might be circling the Sun at the edge of the solar system another black hole has been found. What makes it remarkable is that it's the closest one found so far. The scientists who found it said (I kid you not) it's just 1000 light years away.
It's one of those regular sized ones. Not the supermassive kind that can be found at the center of the galaxy or the small, primordial one like the suspected one in our own system.
Not only do black holes defy common sense and understanding they also defy the laws of physics. They are the only non-quantum sized objects we know that don't abide with the classical physics. Sure, one could argue about the size of singularity and it's relative size to anything at the quantum level. But still, unlike the individual quantum particle that doesn't have any effect on the macro scale the effects of the black holes are definitely measurable even in the cosmic scale.
Isn't it amazing that sun is almost exactly 400 times further from earth than moon and the moon is also 400 times smaller? What are the odds of that happening.
Over the billions of years of these objects existence, it's actually 100. Billions years ago when the moon formed it started to orbit our planet at much closer distance. Over the years it has slowly been distancing from us so that currently it just happens to be at around that 1/400 times the distance of sun away from us.
There was yet another supermoon earlier this week. Lately these occurrences have been widely marketed around the media giving them each some obscure unique name as if mere super- preposition wouldn't be enough.
So there have been planets that have been reclassified, planets that, if the theories hold true, have been destroyed or hurled out of the solar system and theoretical planets to explain anomalies in the behaviour of other celestial objects. After all those, we are left with the eight planets we know of today.
There are however unexplained behaviour of different objects in our solar system that suggest there might be more planets to be found.
In addition to actual objects that have just been demoted from planet status there has been multiple supposed planets astronomers have been trying to locate throughout history.
Vulcan was a speculated planet that was expected to reside between Mercury and the Sun. The perturbations in Mercury's orbit suggested there should be something there. These anomalies were however later explained by Einstein's theory of general relativity.
Everybody remembers Pluto's demotion to dwarf planet in 2006. This reclassification was triggered by the discovery of Eris, an object far out beyond Pluto's orbit that was found to be 27% more massive than Pluto. So either it had to be the tenth planet, or Pluto shouldn't classify as planer either.
I hope you are sitting down firmly as I'm about to tell you how fast you are actually going around just sitting there in place.
First of all, your on the surface of this planet, rotating around it's axis. The rotation takes you around the circumference of the planet in one day. To accomplish that, we are spinning around at around 1700km/h (or 0,5km/s).