How do black holes and galaxies project light?
Black holes do NOT project light. Hence the name black hole.
Their gravity field is so strong that nothing escapes, not even
light photons. The only way we know they exist by the bending of
the trajectory of photons passing them. Galaxies project light via
radiant energy, i.e. photons. In the same way you observe a
lightbulb, you observe a galaxy. The primary difference is that we
have developed instruments to not just observe galactic energy
within the visible spectrum, but the entire electromagnetic
spectrum, e.g. radio waves and x-rays. Those instruments would work
with a lightbulb too, but they're usually busy looking at galaxies.
Actually, black holes probably do give off light (and all other
particles). This effect is quantum mechanical in nature and was
discovered by Stephen Hawking. However, it is not at present
possible to measure this. Whether or not Hawking is right, we can
observe black holes, and not just because of light from distant
stars bending around them. The event horizon is a very violent
place, and materials are being spun around in the vortex just
outside of the horizon, and they are being torn apart before
entering the horizon as well. All of this creates a massive output
of energy that we can observe. We get hints that we are observing a
black hole by observing how nearby stars interact with it. Black
holes sometimes 'suck up' so much matter that some of it escapes.