So I’m trying to understand a bit more about the structure of the universe and I keep running across all these “if you think that’s strange wait until you hear this” moments and they almost always cause me an almost painful paradigm shift (without a clutch). Here is the latest. I was always comfortable with the idea of the coldness of space. At about five molecules per liter of volume and so damn cold. Then I learn about the center of our galaxy and the super black hole lurking there and that the same type of thing is also lurking in most if not all of the other galaxies and that because of Hawking radiation that part of our neighborhood is blinding hot. So not all of space is dead cold but certainly the space between galaxies is as cold as space should be in my mind at least and I was pleased to understand that – yes between galaxies is a cold place. But what about the space between collections of galaxies like our own dear Local Group; the thirty of more galaxies like our own Milky Way and then next one over - the M81 group? Is it hot between them again? Filled with plasma of gamma rays or other such nasty surprises or is it cold as space? Anyone know?