They were looking for eclipses - when something blocks the signal they’re observing. In this case, they noticed the X-rays they were looking at were blocked fo

They were looking for eclipses - when something blocks the signal they’re observing. In this case, they noticed the X-rays they were looking at were blocked for a few hours. There’s more to it, but the article actually does a good job of explaining it all. There’s not really any way for us to prove if it exists or not today, that information is still quite far away. The best we can do is try to understand the system and make predictions about that.