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This is a side view of a picture perfect CME, or a prominence that probably became a CME. The arch is a magnetic tube of relatively cool gas, mostly hydrogen just like the sun. The magnetic field coils around the gas like a cotton filled streched slinky and the ends of the tube are "attached to the solar surface.

Just like a Tokamak or VASIMR is supposed to work, magnetic fields can act like a barrier for plasma (ionized gas) and contain it or hold it back.

The dark hole of a sunspot is a cool region of the photosphere kept empty by the same kind of magnetic flux tube and
it's then no suprise that sunspots and CME's are sometimes directly related.

As with any chaotic system, that isn't always the case and you can get similar phenomea from the combination of different conditions and regions on the sun.