Helvi Witek explica o que são buracos negros e como os podemos

Hello, everyone! My name is Helvi Witek and I was a PhD student here at the Center for Astrophysics in Lisbon. and my working project was related to black holes. What are black holes? Most people may hear about them in journals but don't have any idea of what they are. So I will try to explain to you a little bit of what we think they are. So black holes are very heavy objects, but also very small, very compact objects. So, to give you an idea, imagine you could shrink the earth to something... to some ball the size of one centimeter. So maybe, something like that. Or if you wish, something of the size of your fingernail. And because these objects are so heavy and so compact, Nothing, not even light, can escape from them. And that is the reason why scientists call them black holes. To at least have some imagination of what they are, instead of being just pure mathematical exotic objects. So now we might wonder, if they are just mathematical... Or are they just mathematical objects? Or can we actually observe them somehow? And let me tell you that we think we can. So, of course, we cannot see them directly, but we think they are in the sky, so we expect to have very, very massive black holes in the center of the galaxy. Or not so heavy black holes like our sun that live in our galaxy. So, for example, if you go out next summer at night and try to look of the constellation of Sagittarius, you would look directly to the center of our galaxy. And there, if you could see it, you would find our black hole. Our very own family black hole which has a mass that is four million times the mass of our sun. So something that is very hard to imagine. And we try to measure... or to observe them by looking at the stars and looking how the stars move around the center object. So I hope I could give you a very small idea of what black holes are and why we want to look for them.