We are sitting in one of the majestic arms of the Milky Way Galaxy, our home, our home galaxy. Should we call ourselves Milky Wayans? At a 8-light-minute distance from our Sun, we move with the whole solar system around the Center of the Milky Way. If it was not spectacular enough, close your eyes, stretch your imagination, and realize that there are numerous galaxies scattered around the Universe, separated by vastness of space from each other.
However, there are some instances of interaction and close encounters between various galaxies.
For example, the beautiful and dramatic galactic quintet: Stephan’s Quintet .
Even more mind boggling is the fact that we discovered that each massive galaxy also has a central black hole of colossal sizes. And for a small fraction of galaxies that black hole is active.
But what activates, what ignites this central engine?
This is still a debate.
There are two main scenarios.
First scenario is based on external triggering event, such as a clash with another galaxy.
The second scenario is based on processes within the galaxy itself, such as instability in a spiral arm.
I discuss this briefly in my thesis figure, as shown in this video.
Reference: Alexander & Hickox, 2012, Fig. 2.
– Your astronomer from Helsinki
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