Often, we call the stages of a star its “life cycle”, and I’ve been thinking about this for a bit.
Stars meet many of the requirements for living organisms: they can consume matter, they can react to stimuli (sort of, does gravity count? e.g. binary systems), they can reproduce (they expel gas clouds on death that can eventually create new stars), they can grow and change size over their lifespan, and they maintain equilibrium (between gravity and radiation pressure from fusion)
What stops stars from being considered living objects?
edit: as it turns out, the formation of new stars after death doesn’t really count as reproduction, and gravity shouldn’t count as stimuli (a rock experiences gravity too, but it doesn’t react to stimuli)
But why does it have to be unobservable? And if it is unobservable, how do you know that it is there?
We know pretty well and can observe that children inherit the DNA of their parents. And nowadays we also know that it is not only the DNA, but the epigenetic postprocessing that gets (at least partially) inherited. So according to your definition if we ever fully understood how bacteria propagate and behave, it would not be alive anymore?
Specifically, an organism has to keep latent information that’s unobservable to anything it interacts with (i.e., its ecosystem)—or at least, anything with an interest in predicting and controlling it. Otherwise, it has no guarantee of independent behavior, and it’s effectively part of a colony organism (or an organ of another organism). It also has no differential behavior for natural selection to act on, so it can’t evolve in a Darwinian sense.
To take your example of bacteria, we don’t observe and control the entirety of each individual bacterium’s behavior, but it has happened: it’s how mitochondria ceased to be independent organisms.