In this artificial galaxy, there is a trinary of quasar stars at the center, each one 1.5 trillion times as massive and 995 trillion times as bright as our sun, each one having its own ring of mirrors, which further raises the luminosity.

Far outside the quasars, there is a quaternary solar system. The first binary is a pair of artificially immortal blue hypergiants, each one 200 times as massive and over six million times as bright as our sun, each one having its own ring of mirrors, which further raises the luminosity. Orbiting the first binary from a distance of three-and-a-half parsecs (over 11 light-years) is the other binary, a pair of artificially immortal red supergiants, each one 17 times as massive, 1500 times as wide and 300,000 times as bright as our sun, each one having its own ring of mirrors, which further raises the luminosity.

The red supergiant binary has a habitable zone from 400 to 800 AUs away. There are plenty of Earth-like planets within this HZ, and they share the following characteristics:

  • Axial tilt: Varying from 19.01 to 28.28 degrees on a cycle exceeding 200,000 years
  • Atmosphere: While some would have an atmosphere of 300 degrees, as thick as Earth's, others would have the average of 370 miles, and maximum thickness would be 480 miles (160% as thick as Earth's)
  • Size: Identical to Earth
  • Rotation: 30 hours, which means three extra hours of daylight followed by three extra hours of night

The axial tilt suggests that all of the habitable worlds have seasons, but in this system, there is a second definition of "season", and that is because orbiting a supergiant binary orbiting a hypergiant binary affects the planet's orbital shape. In short, it elongates the orbit until it resembles a cucumber. "Summer" is where the quasar ternary and the blue hypergiant binary dominate the sky during the day and the red supergiant binary are the "second" and "third moon", each one being 250 times brighter than a full moon. "Winter" is where the red supergiant binary dominates the sky during the day and the other five stars are dimmed down to as much as 250 times as bright as Venus.

None of the planets in the red supergiant binary HZ have any life, not even microbial, so it seemed feasible to seed them with Earth species of plant, animal, fungi, microbe and even soil. But is it really? With the information provided above, would the seasons of these habitable worlds be too extreme for Earth life to thrive in?

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    $\begingroup$ Note that for a planet orbiting the red supergiants pair at 400 AU, a year will last about 1371 Earth years. For the blue/red supergiant pairs rotation, the period would be a mind-boggling 29 million years. $\endgroup$
    – Alexander
    Oct 22, 2021 at 0:57
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    $\begingroup$ @Alexander From "How to Create the Galactic Habitable Zone": "So, suppose that the Engineers build a fleet of light-pressure-supported mirrors above and below the plane of the galactic core to reflect axial light back into the plane of the galaxy. Supposing that we restrict the light to, say, a 10 degree-wide beam; that will make the radial light about 17 times brighter" $\endgroup$ Oct 22, 2021 at 2:04
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    $\begingroup$ Can't the engineers just make the seasons less extreme, then? $\endgroup$
    – Cadence
    Oct 22, 2021 at 6:28
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    $\begingroup$ Well, their giant mirror array sounds like a good place to start. $\endgroup$
    – Cadence
    Oct 22, 2021 at 14:50
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    $\begingroup$ I would agree with @Alexander, the orbital periods are pretty far out there. though calculating the HZ, assuming a combined L of 3000 the suns and a Teff of 10500K (thats basically as high as i can go) the HZ would span around 145 to 297 AU. I am not sure what these mirrors will do, and doubt the blue hypergiants will have any effect at their distance. You should look at depts.washington.edu/naivpl/sites/default/files/… for a good idea where HZ should be $\endgroup$
    – Sonvar
    Oct 22, 2021 at 21:36

3 Answers 3


At 400-800 AU away from the star, the orbital period would be so long that the transition between the seasons would occur very slowly. There would likely be a small extinction event between each season but many organisms could adapt to the changing environment quickly enough to avoid going extinct.

  • $\begingroup$ Not if the orbital mass is high enough. $\endgroup$ Oct 25, 2021 at 21:07
  • $\begingroup$ @JohnWDailey - T ∝ r^1.5 / sqrt(m). To get 1 year orbits at 600AU would require about 200 million solar masses ((600^1.5)^2). This is a supermassive black hole all by itself... $\endgroup$
    – TLW
    Oct 30, 2021 at 2:09

Earth life has evolved to thrive in Earth conditions, so simply plopping them down on a distinctly different planet wouldn't work. It would take time for life to evolve to deal with those conditions. However, you do say that the galaxy is artificial, meaning that humans have very advanced technology in your universe. Since that is the case, the same people who are doing this could help the Earth life to adapt, possibly ease them into living on the new planet. So your answer is: No, not without help.


There’s a lot of missing information here, so I took some guesses.

the ‘cucumber’ orbit

From the question it must have a pericenter within the effective habitable zone of the red super pair while the apocenter must be in the combined habitable zone of the blue hypers and the galactic core quasars. For now, let's set the quasars aside.

Ignoring the mirrors, the red supers combine to act like a star with 34 solar masses and 600k solar luminosity (not exactly correct due to occultations, etc. but close enough). Plugging this into the formulas for habitable zone start/end, we get:

  • HZ start = sqrt(L/1.1) = 740 AU
  • HZ end = sqrt(L/0.53) = 1070 AU

Adding in the mirrors requires a lot of math I’m not feeling like doing so I’ll use the 17x value from the comments. That increases luminosity to 10.2M solar luminosity and changes to habitable zone a lot:

  • HZ start = 3050 AU
  • HZ end = 4390 AU

On the other end, the blue hypers combine to act like a star with 400 solar masses and 12M solar luminosity:

  • HZ start = 3300 AU
  • HZ end = 4760 AU

Scaled up with mirrors, we get 204M solar luminosity. Plugging that in:

  • HZ start = 13,620 AU
  • HZ end = 19,620 AU

The distance between the red supers and blue hypers is given as 3.5 parsecs. Converting that to AUs gives us 721,930. Subtracting the outer edge of the blue hyper’s HZ, we find that getting within 19,620 AUs of the blue hypers means being 702,310 AUs from the red supers.

let’s build a ‘cucumber’ orbit…

Setting the semi-major axis to 300,000 AUs and the eccentricity to 0.99 (i.e., just short of parabolic), we can calculate pericenter and apocenter:

  • pericenter = (1-eccentricity)*semi-major axis = 3000 AU
  • apocenter = (1+eccentricity)*semi-major axis = 597,000 AU

Ok, it looks like keeping the pericenter inside the zone means we can’t stretch the apocenter far enough. Which is actually ok. This is an unhinged orbit anyway so we’re pretty frantically handwaving already. We’ll just pretend this orbit will work because it gives us a rough order of magnitude on the period for the real orbit: 28 million years.

This planet will have relatively brief period (a few million years) of livable temperatures at pericenter and again at apocenter. It will spend the 10 million or so years in between in deep freeze. Nothing survives.

but wait! what about the quasars?!

I’m glad you asked. It all depends on how far away they are.

Per the question, this quaternary system is ‘far outside the quasars’. That, unfortunately, isn’t a number. Working backwards, let’s see where they’d have to be to warm this planet up during the long transit. Here’s what we know:

  • quantity = 3
  • mass = 1.5x10^12 solar masses each
  • luminosity = 9.95x10^14 solar luminosity each
  • they have those same 17x mirrors

Again, we can treat them like a single object with a luminosity of 2.985x10^15. Calculating a habitable zone:

  • HZ start = 52M AU = 822 light years
  • HZ end = 75M AU = 1185 light years

All we need to do it keep our planet in range and everything’s fine.


If this planet is inside the quasar habitable zone, the stars are just overkill. We’d actually need to avoid getting too close to each star to avoid overheating.

Maybe that’s the answer: ‘summer’ is the few milling years nearest to each star and ‘winter’ is the time in between. Of course, this will mess with your view. Those quasars aren’t going to change in apparent size if they go from 1150 light years away to 1160 light years away.


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