How can a galaxy appear to have a massive hole in the middle?
The massive hole in the middle is caused by a collision with another galaxy. However, not all galactic collisions result in gigantic holes. Only a head-on collision, similar to a ‘bullseye shot’, can produce a hole surrounded by a ring, or sometimes multiple rings. The hole is formed as the galactic ‘heart’ gets knocked off, and stars at the inner parts of the galaxy oscillate outwards in response to the gravitational disturbance. The rings are density waves that spread out from a single point.
In addition to a bullseye collision, two additional conditions must be met. Firstly it needs a thin galactic disc to serve as an ‘aiming board’ and a smaller galaxy to be the bullet, and secondly it needs a cheering cosmic environment where the ‘galactic Olympic shooting games’ can be held without any disruptions. In the current universe such conditions are easily met, and all we need is a bullseye champion.