Okay, so imagine you are playing hide-and-seek with your friends, but you can't find them because they are hiding behind a wall or a door. That's sort of like what happened with astronomers trying to study space a long time ago - they couldn't see everything because some things were "hiding" behind clouds of gas and dust in space.
But then scientists discovered something really cool - when you shine special rays of light called X-rays at things, they can bounce off and reveal what's behind the clouds! This was kind of like having a magic flashlight that could see through walls.
So around 60 years ago, scientists started using X-rays to study space. They built instruments called X-ray telescopes, which were like regular telescopes but designed specifically to detect X-rays. These telescopes were sent on rockets and satellites up into space so that they could get a clearer view of the universe.
What did they find with these X-ray telescopes? Lots of things! They discovered all sorts of exciting and strange objects in space that they couldn't see with regular telescopes, like black holes, neutron stars, and supernova remnants. They also used X-ray astronomy to study things like galaxy clusters and star formation.
X-ray astronomy has come a long way since then - scientists are continuing to use better and better instruments to study the X-rays coming from space, and they are making new discoveries all the time. It's kind of like playing a never-ending game of cosmic hide-and-seek!