Are galaxies net importers or exporters of mass/energy?

[UltrafastPED]

Galaxies radiate energy from their stars, but there is also flows of matter into a galaxy.

Is the net energy produced by these flows of matter (evaluated as E=mc^2 under the assumption that it will be processed by stars as nuclear fuel) occurring at a greater or lesser rate than the radiative losses from the stellar population of our galaxy?

If anyone is aware of a good study on this topic that would be appreciated.

 

[phinds]

I have no hard facts or even specific knowledge but it seems to me that galaxies by themselves must be net exporters of energy in the form of radiation. If this were not the case then Olber's Paradox would have a different outcome.