I can help you with the question. White Dwarfs are not invisible, in-fact they are among one of the shiniest objects. But they dont have hot inner core to heat them. They are shiny because they are already very hot. These white dwarfs cool down too, but it takes them about 100s of billions of years. Universe itself is just 13.7 billion years old. A cooled downed white dwarf would be called black dwarf. We cant observe them because our universe is simply not old yet. Still after that, it wouldn't be invisible.

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Nice Post by the way and your children are so cute :D