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I’m working on a fantasy novel and trying to keep the underlying science internally consistent so obviously i have some questions since im not a science person.

  1. How possible is it for a planet in an S-type orbit around one star in a binary system, with the entire system orbiting a black hole to have life?

  2. Could the secondary star have a long enough orbital period (thousands of years) that environmental conditions on the planet could change slowly enough for civilizations to rise and fall between different phases?

  3. If a system like this orbits a black hole at a safe distance, could its effects vary over time, or would they be effectively constant?

  4. If the black hole has an accretion disk and the system far enough that it remains habitable, would that disk realistically be visible from the planet?

Some more context about the setting, The planet orbits a relatively cool primary star. A hotter secondary star orbits at a much grater distance and it influences the planet’s climate depending on its distance, making the environment periodically more or less habitable. During the story, the second star is at a distance where the weather is getting noticeably warmer but there is no doomsday panic yet.

The black hole isn’t really an immediate “threat”. The main driver of the conditions on the planet is the suns. I want to focus more on how living in orbit of a black hole could effect life on the planet.

I’m also fully aware that a world like this would be very unlikely to produce complex life and repeated civilizations in real life. I’m willing to assume that life somehow found a way, what I’m trying to figure out is whether the astronomy and planetary effects can be made plausible enough around that assumption.

Also keep in mind this is a fantasy story, not sci-fi. The science won’t be explicitly explained in story nor will the reality of what’s going on with the stars or the black hole ever be understood by the characters. My goal is just for the world to be built in a way that the “fantasy” could be interpreted through science and logic. So all this is really just subtext in a story where people probably don’t even know there are two suns in the sky.

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    $\begingroup$ Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. $\endgroup$ Commented yesterday
  • $\begingroup$ @AlexP couldn’t a second sun in the sky effect a planets climate without having an overwhelming gravitational influence if it’s at a certain distance $\endgroup$ Commented yesterday
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    $\begingroup$ The Sun definitely has an overwhelming gravitational influence over Neptune, but as seen from Neptune the Sun appears as a very bright star (magnitude -19.3, about 500 times as bright as the full Moon seen from Earth) with minimal influence over the environmental conditions. Yes, it does provide some light, about as much light as we have here on Earth in winter on a heavily overcast day; no, it does not provide any noticeable amount of energy. For example, our space probes can rely on solar panels for their electric power only to about the orbit of Jupiter. $\endgroup$ Commented yesterday
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    $\begingroup$ Hello @eys, welcome to Worldbuilding. For future reference, please be aware that asking more than one question is literally a reason for closing the question. Click the "close" link and read the text for "Needs More Focus." I recommend that you read the following four pages to better understand this service's expectations and limitations: tour, help center, help center and How to Ask. Thanks. $\endgroup$ Commented yesterday
  • $\begingroup$ @AlexP Could a star hotter than our sun approach close enough to affect a planet’s climate and then go further away again without completely throwing the planet off its orbit? Im wondering if in the perfect circumstances something like this could happen or is it a definite no. $\endgroup$ Commented yesterday

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  1. The stars in a binary system almost certainly move on circular orbits around their common center of mass, because tidal circularization is a thing. As a consequence, the distance between the two stars in a binary pair is constant and very very much larger than the orbit of a planet around one of the two stars.

  2. If the second star is close enough to have noticeable environmental effects then it is definitely close enough to make stable S type orbits impossible...

    Gravitationally bound systems consisting of three or more bodies are chaotic unless carefully handcrafted by God (= the Omnipotent Author), or, in practice, if the distances between the three or more bodies are such that the orbits can safely be computed pairwise. For example, the Sun-Earth-Moon system is stable only because the Sun is so very far away from the Earth-Moon system.

  3. There is nothing wrong with orbiting a black hole at a safe distance. For example, the Earth is orbiting around the Sun and the Sun itself is moving around the center of the galaxy which as it happens is home to a ginormous black hole. The black hole at the center of the galaxy has never bothered us.

  4. There is nothing unbelievable about being able to see the accretion disk of a black hole with the naked eye. While we do not have an example of a black hole sufficiently close for us be able to see it with the naked eye, we do have V404 Cygni, which is a triple system containing a black hole, and the optical fluctuations of the accretion disk of the black hole in that system can be observed with a modest 200 mm telescope. (Link goes to space.com. Many articles are available on the Internet if you don't like space.com; search for v404 cygni observations 200 mm telescope.) (A decent 200 mm telescope costs something like maybe 1000 euros, and there are millions of amateur star gazers which have such telescopes or better.)

  5. Black holes are active things so that they definitely manifest changes over time. On the other hand, if you are sufficiently close enough to a black hole that it has material effects on you then you are way too close to the black hole.

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