Imagine a space faring civilization hurtling between galaxies at speeds fast enough to travel from Earth to the moon in seven minutes! They are being propelled by the gravitational energy of a black hole. And, their "spaceship" has resources for supporting a population of several billion.
This sounds like far out science fiction fantasy, but it's within the realm of plausibility.
It turns out that the supermassive black hole in the center of our Milky Way galaxy hits a star "out of the ballpark" about every 100,000 years. Astronomers have clocked these runaway stars as having enough velocity to escape the galaxy.
Though as yet there is no definitive evidence that traces their trajectories straight back to the central black hole, there is no other conceivable mechanism for imparting so much kinetic energy onto a star — not a supernova blast, nor a gravitational "billiard ball" game among multiple star systems.
That is, unless the central 4 million solar mass black hole becomes one of the players. The theory is that a star could be slingshot out of a binary star system if the stellar duo swung close to the central black hole. The hole's gravitational tidal forces would break apart the pair's gravitational embrace.
The companion star orbiting in the direction of the black hole would pick up momentum and plunge toward the black hole. In accordance with Newton's third law of motion — action-reaction — the other binary companion would go whizzing off with the same velocity but opposite direction away from the black hole.
In just a few thousand years the star would ascend out of the galactic plane and hurtle deep into intergalactic space. The persistent tug of our Milky Way's dark matter halo would slow it down but the star would never fall back into the Galaxy.
So far at least 16 of these so-called hypervelocity stars are known. They were first hypothesized in 1988. But the first one wasn’t detected until 2005. Hot and bright blue short-lived stellar runaways have been picked out because they are not native to the old stellar galactic halo population, they had to travel there. Also, the torturous Milky Way core — a stellar Monster Truck assembly plant — favors making massive stars in binary pairs.
However, it is not impossible that a sun-like star in a binary system could get the boot too. It would carry along any planetary system.
Now imagine an intelligent civilization arises on the surface a habitable planet in the runaway system. Their astronomers would gaze out into an inky black starless sky. True, there are stars in the Milky Way’s halo, but they are so faint that only a chance nearby passing star would become visible. Globular star clusters in the Milky Way’s halo would pepper the sky, looking like tiny cotton balls.
The bright nucleus of the Milky Way would look like a fuzzy headlamp. The ghostly faint tentacles of the spiral arms could be seen winding out from the nucleus. They would sprawl across a huge swath of sky.
Alien sky lore would have no constellations in the absence of stars. All mythology would be built around the nighttime wispy pinwheel with its cycloptic "glowing eye." Alien sky watchers would duly note the appearance of brilliant star-like novae and supernovae in the spiral disk. These might as first be construed as omens or messages from the gods, or fuel other superstitions. But fireworks in the galactic disk would be dutifully recorded.
The development of telescopic astronomy would allow star clusters and nebulae to be resolved. It would be as big a revelation as when Galileo first observed the Milky Way in 1609. Bright blue stars would be seen sprinkled across in the Milky Way’s spiral arms. Spectroscopy would show that the pinpoints are made of the same stuff the alien’s parent star is. But it would take a great leap of imagination to connect the tiny pinpoints to the brilliant glowing orb of their star.
Only the alien equivalent of an Einstein, Newton, and Galileo rolled together might have the conceptual breakthrough that their system is the oddball outcast in a universe of myriad stars. This might get the scientist burned at the stake as a heretic.
Inevitably larger telescopes would yield a view of the universe that revealed myriad other pinwheel structures. Spectroscopy would show they are racing away too. Still the aliens literally wouldn’t know if they’re coming or going. A long-lived civilization’s science archive would note the shrinking and dimming of the Milky Way over geologic time. They might conclude that the eerie pinwheel is speeding away from them. And without a cosmological or stellar framework, they would have no idea of cosmic evolution. They would not even be able to calibrate the vast distance to the Galaxy.
It would be easy for them to conclude that their great yellow star was the center of the universe. Ironically, the alien scientists would remain pre-Copernican even though they had a panoramic view of the Galaxy that any earthbound astronomers would envy.
Photo Illustration: Ray Villard