When I run a minimal JavaFx application, my laptop's fan starts to activate and the computer heats up.
This usually happens when the CPU is very high, so I check the CPU but it is almost 0%.

My conclusion is that it is overusing the graphics card GPU, it does not happen when I use the integrated graphics card.
When other programs make use of the high-end graphics card, do not exhibit this behaviour (except maybe games).

It is something that should be taken care of, if JavaFX is going to be of mainstream use. It can be a serious drawback for adopting a JavaFX application.