Merge pull request #3518 from cgobat/add-astrophysics-topic

Add "astrophysics" topic

Author: MikeMcQuaid

topics/astrophysics/index.md

@@ -0,0 +1,9 @@
+---
+display_name: Astrophysics
+short_description: Astrophysics is the study of the physics of astronomical objects and processes.
+topic: astrophysics
+related: astronomy, physics, cosmology
+wikipedia_url: https://en.wikipedia.org/wiki/Astrophysics
+---
+
+Astrophysics is the scientific discipline that deals with the physics of objects, phenomena, and processes in [outer space](https://en.wikipedia.org/wiki/Outer_space), including (but not limited to) stars, galaxies, compact objects, and the formation of the Universe.