I am imagining a special ecosystem on a rogue planet (a planet that wanders throughout space without orbiting a star or other heavenly object) but I would need your help to fill in the gaps and realize if a world like this would be possible.
Imagine a jupiter sized gas giant: lets call it Erebus.
Erebus would have few moons orbiting around it.
One of it would be the size of Mars and would have a dense atmosphere, which would keep the heat inside. The moon would be habitable, thanks to the heat trapped, water resources and other elements that allow the construction of organic things. The moons name would be lyra.
Life could be possible and could last even longer then if Lyra orbited a basic star, because the star would "die" one day (leaving the planet to freeze). But life would last longer on a moon that orbits a rogue planet: Erebus heats Lyra because its tidal forces slowly (and relatively) stretches Lyra, causing it to produce heat. This "heat production" wouldn't wear out, because the force that causes Lyra's stretching is gravity. So thanks to Lyra's composition and Erebus's tidal forces: life is possible, but... we miss one thing. We miss light in all of this.
As Erebus wanders throught the galaxy: Lyra is enlighten by starlight. But it isn't enough to cause photosynthesis or eyesight, and won't allow a complex biodiversity to emerge. This is why I thought Erebus could be a light source. At the beginning, I thought erebus could've been a brown dwarf that slowly produces light. But a brown dwarf isn't eternal.
That is why I need your help:
Could there be a way in which Erebus radiates light just like the sun (without necessarily radiating heat and not thanks to thermonuclear fusion) thanks to a chemical or other reaction? What could it be? Or could something else (that orbits around Erebus) radiate light?
Lyra would have a day/night system like planet Earth as it wouldn't be tidally locked towards erebus because it would have an eccentric orbit so it would be able to rotate on itself while orbiting erebus. This would only happen if it was erebus emitting light but if it isn't erebus that radiates light, how could lyra sustain an day/night system?
My basic questions are: how could Erebus produce light forever (in a self sustaining way) or if not what would produce light in an eternal way? What reactions could able this process to happen?