At the centre of every galaxy, there is a supermassive black hole (a million to a billion times bigger than the Sun). But how do we even know that? There are so many scientific results that have jigsaw-pieced together throughout the past century that allow us to know that now, so join me, as I go through decade by decade and explain the significance of all the results that have built up the big picture.
And for those of you who like reading straight from the source, here are links to all the papers I mentioned throughout the video, again listed by decade (note that "et al." is Latin for "and others"):