 Greetings and welcome to the introduction to astronomy in today's Misconception in astronomy. We are going to talk about the idea The incorrect idea that black holes behave like cosmic vacuum cleaners sucking up anything near them So what is a black hole? Well, the answer is of course, are they cosmic vacuum cleaners? No, they are not a black hole is a very Compact mass in space, so it's a lot of material compressed into a very small amount of space But the extreme Relativistic effects of a black hole are only noted close to the black hole So only when you get close to the black hole We have what we call the event horizon here Within that no light can escape and we cannot know anything about what goes on inside outside of that Things are things can escape light can escape from outside that event horizon Now if you get close to the event horizon very strange things will happen So it you won't don't want to get too close to an event horizon But the event horizon is very small for something like our Sun if our Sun were compressed to a black hole It might be only a kilometer or so in size So it would be very small and as long as you stayed far enough away from that You could orbit around just as we do So if you are far from the event horizon Gravity behaves just as it does So when you get close to a black hole material can be pulled away So here we have a star a black hole and a star orbiting it and material can be pulled off But note how it's not just sucked in it's pulled into a disc and it orbits around the black hole Slowly spiraling in to the black hole itself So it's not that they just suck the material in or rip the star apart. They are taking some material from the star So black holes can do some unusual things But they are not the cosmic vacuum cleaners that we think about and if the Sun were to to turn into a black hole Leaving its mass exactly the same just compressing it down much smaller Earth's orbit would not change It would get rather cold and dark because we've lost our source of light and heat in the solar system But the earth would continue to orbit just as it does today as would the other planets Here we see orbits of several several stars around The central mass of the black hole so the black hole at the center of our galaxy would be here These are orbits of stars around it. We can map out those orbits as long as they don't get too close to the event horizon They can remain in stable orbits around the black hole for a long long time So let's go ahead and finish up with our summary first of all no black holes are not cosmic vacuum cleaners Objects can orbit a black hole just as they orbit any other object in the universe The strange effects of black holes are only apparent when you get close to the event horizon That's when some very strange things start to happen So that concludes this misconception on the black holes being cosmic vacuum cleaners We'll be back again next week for another misconception in astronomy So until then have a great day everyone and I will see you in class