Question: What is the most interesting part of space that you have ever seen>

Guy Rixon answered on 14 Mar 2018:

Probably the gravitational lenses, like this rather pretty one: https://en.wikipedia.org/wiki/Einstein_ring#/media/File:A_Horseshoe_Einstein_Ring_from_Hubble.JPG
This is a thing that happens when a nearby galaxy gets in front of a distant galaxy and the gravity of the closer one distorts the light from the distant one. It’s interesting because it can only happen if gravity is a space-bending effect as described by general relativity. You could say that it proves that general relativity is “right”, even the weird bits.
Full lenses like this are rare, but there are “microlensing” events where stars in our galaxy get in front of each other. These are particularly interesting, because sometimes the star in front is too faint to see directly. Scientists think there are a lot of these “brown dwarfs” – very small stars, only a little bigger than a large planet – that we will only ever be able to find by their gravity, never by their light. We’re trying to find them in the Gaia data.