There are traces and iirc there was one we were able to see around 30 or so years ago. Don't quote me on it but I'm fairly certain they did observe it. It was way before we had the ability to record it. Either than that it's largely hypothetical theoretical estimation and studying dust patterns and different stars in different parts of the galaxy.

There's a lot we havnt seen. Gravity, time, supernova and black holes, God and spirit creatures. Just because we can't witness them acting directly and irrefutably in modern times doesn't mean they don't exist and exert power. We base our beliefs on the things we can see. How these things interact with the world around us and from there we come to our conclusions.

A lot of science is based on faith. Faith in the accuracy of our mathematics. Faith in our laws of physics. Faith that the laws of nature will not be broken. It's one of those things we choose to believe in because It makes sense, you know?

Then again once you start realizing how much science is based on faith, religion doesn't seem like such a laughable idea to many scientific minded people after all