A real place.
An extraordinary scale.
Look toward the constellation Sagittarius and, beyond the dust between stars, toward the center of the Milky Way. Roughly 27,000 light-years from Earth lies Sagittarius A* (Sgr A*), the supermassive black hole at that center. A light-year is the distance light travels in one year: about 9.46 trillion kilometers. Even light needs roughly 27,000 years to cross the distance between us and the Galactic Center.
Measurements of stars passing close to Sgr A* put its mass at about 4 million times the Sun’s mass. Those nearby stars reveal the black hole’s gravity through their orbits. The wider Milky Way, however, does not revolve because of the black hole alone; the gravity of its stars, gas and dark matter also shapes galactic rotation.
The boundary
light cannot cross back.
A black hole’s event horizon is a boundary: once matter or light passes inward, no signal can reach a distant observer again. It is not a solid surface. For an ideal, nonrotating black hole with a mass of 4 million Suns, the calculated horizon radius is about 12 million kilometers. The real Sgr A* may spin, so this is a scale estimate rather than a measured edge.
Gas approaching the black hole can form an accretion disk. Friction and magnetic processes heat that gas, making it radiate before it crosses the horizon. Gravity also bends light, producing a bright ring and a dark apparent shadow. The shadow seen in black-hole imaging is larger than the event horizon itself.
Einstein’s relativity predicts that clocks deeper in a strong gravitational field run more slowly when compared with clocks far away. The effect becomes dramatic close to the horizon. It does not turn the whole Galactic Center into a place where time simply stops; the amount depends on location and motion.
A star beyond
the horizon.
Now the story moves from observed astronomy to a physically constrained setting. Eldios is a K-type star: somewhat cooler than the Sun. Our reference model assigns it 0.9 solar masses and 0.6 solar luminosities. It follows a proposed orbit about 5,000 astronomical units (AU) from Sgr A*. One AU is approximately the Earth–Sun distance.
Using a rounded black-hole mass of 4 million Suns, Kepler’s law gives an Eldios orbital period of approximately 177 Earth years. That calculation is consistent with the enormous central mass and the system’s distance from it. An orbit is a model parameter, though, not evidence that Eldios has been discovered.
Distance from the black hole by itself does not establish safety. Radiation, stellar encounters and the history of the Galactic Center still matter. Eldios and its planets are worldbuilding possibilities placed inside known physics, with these environmental questions open for future chapters.
Three paths
around one light.
Verdantis, Aurelia and Caelum orbit Eldios, not the black hole directly. Their proposed distances from their star are 0.65, 0.85 and 1.05 AU, respectively. At 0.6 solar luminosities, they receive approximately 1.42, 0.83 and 0.54 times the sunlight Earth receives. Those values follow the inverse-square law for light; they do not, by themselves, tell us whether any surface is habitable.
A star’s habitable zone is the range where liquid water could exist on a planet’s surface under suitable atmospheric conditions. Verdantis may need reflective clouds or efficient heat transport; cooler Caelum needs a substantial greenhouse effect for protected liquid-water regions. Atmosphere, geology and radiation exposure remain essential parts of each world’s design.
From this physical frame come the dreamlike seas, unusual skies and, eventually, the lives and histories of these worlds. The settings and inhabitants are fiction. Their orbital arithmetic and stated physical constraints guide the story.