Starplex

“No, it is not okay,” said Jag, his bark returning to its usual sharpness. “In fact, it has never made any sense. We’ve never had a good model for galactic spiral-arm formation. Most models are based on differential rotation—the fact that stars near the galactic center make several orbits around the core in the time it takes for those farther out to complete just one. But any arms that resulted because of that should be temporary phenomena, enduring at most for a billion years. Oh, we should see some spiral galaxies, but there is no way that three out of every four large galaxies should be spirals—which is the ratio we actually observe. Ellipticals should far outnumber spirals, but they do not.”

“Obviously, then, there’s a flaw with the theory,” said Keith.

Jag lifted his upper shoulders. “Indeed. We astrophysics types have been limping by for centuries with something called ‘the density-wave model’ for explaining the abundance of spiral galaxies. It proposes a spiral-shaped disturbance that moves through the medium of a galactic disk, with stars getting caught up in it—or even being formed by it—as the wave rotates. But it has never been a satisfactory theory. First, it fails to account for all the different types of spiral forms, and, second, we don’t have a good answer as to what would cause these imagined density waves in the first place. Supernova explosions are sometimes cited, but it’s just as easy to model such explosions canceling each other out as it is to get them to build up long-duration waves.” He paused. “We’ve had other problems with our galaxy-formation models, too. Back in 1995, human astronomers discovered that distant galaxies, observed when they were only twenty percent of the current age of the universe, had rotational rates comparable to what the Milky Way has today—that’s twice as fast. as they should have been rotating at that age, according to theory.”

Keith thought for a second. “But if what we’re seeing right now is correct, then spiral galaxies like ours must somehow form from simple disks, right?”

Another lift of the Waldahud’s upper shoulders. “Perhaps. Your Edwin Hubble proposed that galaxies each start as a simple sphere of stars, gradually spin out into a flat disk, then develop arms that open up more and more over time. But although we now have observational proof that that sort of evolution does indeed happen”—he gestured at the disk of stars in the glowing frame—“we still don’t have an explanation for why the evolution takes place, or why the spiral structures persist.”

“But you say three quarters of all large galaxies are spirals?” asked Lianne.

“Wellll,” said Jag, PHANTOM translating a hissing bark as a protracted word, “actually, we don’t know much directly about the ratio of elliptical to nonelliptical galaxies in the universe at large. It’s hard to make out structure in dim objects that are billions of light-years away. Locally, we see that there are many more spirals than there are ellipticals, and that spirals contain a preponderance of young blue stars, whereas our local ellipticals contain mostly old red stars. We’ve assumed, therefore, that any vastly distant galaxy that showed lots of blue light—after correcting for redshift, of course—was a spiral, and any that showed mostly red was an elliptical, but we really don’t know that for sure.”

“It’s incredible,” said Lianne, looking at the image. “So—so if that’s how it looked six billion years ago, then none of the Commonwealth homeworlds yet exists, right? Is there—do you suppose there’s any life in the galaxy now?”

“Well, ‘now’ is still ‘now,’ of course,” said Jag. “But if you’re asking if there was any life in the Milky Way hack when that light started its journey to us, I would say no. Galactic cores are very radioactive—even more so than we used to think. In a large elliptical galaxy, such as we’re seeing here, the whole galaxy is essentially the core. With stars that close together, there would be so much hard radiation everywhere that stable genetic molecules wouldn’t be able to form.” He paused. “I guess that means it’s only middle-aged galaxies that can give rise to life; young, armless ones will be sterile.”

There was silence on the bridge for a time, broken only by the gentle hiss from the air-circulating equipment and the occasional soft beep from a control panel. Each person contemplated the small fuzzy blot of light that one day would give rise to all of them, contemplated the fact that they were farther out in space than anyone had ever been before, contemplated the vastly empty darkness all around them.

Six billion light-years.