Jun Davd’s composure was undisturbed despite the backhand swipe the cosmos had just taken at him. “It’s that black hole we’re heading toward. If you’ll keep your eye on it, you can see the process as it gets ready to toss the next one at us. The hole must be spinning very fast. It must have a very strange geometry—sliced off flat at the poles, but with the curvature of its circumference undisturbed. The gas and dismantled stars flowing into it would have a very strong magnetic field. You can’t anchor a magnetic field in a black hole, but some of the field lines would penetrate the accretion disk and attach themselves very close to the event horizon. Then it’s crack the whip—a million stars at a time.”
“Why are we heading directly toward it?” Bram asked Jao. “I thought we were on a course that gave it a wide berth.”
“We were,” Jao said, his face grim.
“We still are,” Jun Davd’s voice said. “That object you see is not the black hole at the center of the galaxy.”
“What is it, then?” Bram said, but he was afraid he already knew.
“It’s another black hole—in orbit around the galaxy’s central hypermass. The black hole at the center of the galaxy has a second black hole as its satellite.”
Except for those who were not able to leave their monitor boards, everyone on the bridge had gathered around the viewscreen showing Jun Davd’s display. Nobody was doing much talking.
Bram stared, fascinated, at the flat, double-ended funnel of fire that was sucking in the stars. You couldn’t see the black hole itself, of course. You couldn’t even see the accretion disk. But you could see those whirlpools of superheated gas by the inferno of radiation they gave off as they fell down that cosmic drain. And that intense, tiny blaze at the center was where the condensed matter crossed the static limit and doomed itself to leave the universe forever.
Jun Davd’s model of binary black holes explained a lot of things. It explained the rolling yawn of the satellite hole: that was caused by the precession of its spin axis. And it explained those fingers of fire across the bed of coals: the satellite hole was sweeping out the rotating gas cloud of its primary. The geometry of space-time must be very complicated in there. Eventually the orbit of the satellite hole would decay, and it would fall into its primary.
And that would make quite a splash! If anyone in the nearby universe was trying to prove the existence of gravity waves, it would make his day.
“How did it happen?” Bram said.
“The black hole may have been snatched from the Bonfire when the two galaxies met,” Jun Davd said. “That might help to explain why the Bonfire lost its shape.”
Jao spoke wonderingly. “That would have been quite a meal for our galaxy to digest. First it nibbles around the edges. Then it reaches in and pulls out a plum.”
Jun Davd cackled appreciatively. “The stolen hole would have fallen to the center, sweeping up stars and gas,” he went on. “By the time it took up residence as part of a binary pair, it would have been quite massive. We can assume, from the present remnants of the Bonfire, that its central black hole could not have been much more than a hundred million solar masses. However, the satellite hole appears to be three or four times that mass. In fact, I’d put it at a fourth to a third the size of its primary, which I now estimate at well over a billion solar masses—much bigger than I expected. Or…”
“Or?” Bram prompted.
“Alternatively, the orbiting black hole might have been born right here in the galactic nucleus—maybe with the help of turbulence caused by the passing of the Bonfire.”
“You don’t sound very convinced.”
“The dust is certainly thick enough and stellar collisions frequent enough to aggregate a second black hole of a few thousand solar masses. A single collision would be enough to start the process if the stars were massive enough to begin with.”
“But we’re dealing with a hole of three or four hundred million solar masses.”
Jao burst in: “Why stop at one orbiting black hole? Why not a whole planetary system of them?”
“Exactly,” Jun Davd said. “Of course, a number of additional black holes may exist. In fact, I’d be surprised if they didn’t. And two or more of them may have consolidated to form a larger hole. But nothing big enough to explain what we’re facing here.”
“What, then?”
“What we’ve got here is a binary system, not a planetary system. Both of them have a very rapid spin, they’re very close—only a few diameters apart—and one is at least a fourth the size of the other. In fact, they fit almost perfectly the picture of contact binaries.”
Bram struggled to remember his rusty astronomy. “Contact binaries. When the primordial cloud gains too much angular momentum as it condenses and relieves itself by forming a disk. And the disk condenses into a companion, not a planetary system, because it contains too much material and the lines of magnetic force aren’t strong enough to cause spin-down and the spiraling outward of the disk.” He frowned as if Jun Davd could see him. “But you’re describing the formation of stars.”
Jun Davd’s disembodied voice said, “What, essentially, are black holes?”
Outside the observation wall, the flickering tongue of ionized gas continued to rattle through the spectrum, a slice at a time. How long had Jun Davd said it was? Twenty-five light-years. It had grown another light-year while they were talking.
The viewscreen gave him a better impression of what the tongue was doing. It appeared as a mottled serpent swinging laterally away from them on its whiplash path, swallowing stars as it went.
Bram saw something that must have been a supernova—a wink of brilliant light, that was gone in an instant, on Yggdrasil’s speeded-up time scale. Then another flash and another, each of them bathing space in a cosmic instant of inconceivable radiation, each blowing most of its substance off to add more fuel to whatever was happening here in the heart of the galaxy, leaving its core behind as a neutron star.
Chain reaction!
In the galaxy outside, perhaps forty or fifty days had gone by in the last few minutes. Supernovae weren’t supposed to occur that close together. They were supposed to occur once every century or two.
Now he could see another cosmic jet forming at the hub of whirling gases that marked the central black hole. It whipped around, growing by the light-year, ready to slap Yggdrasil when it was long enough.
“Jun Davd,” Bram said, feeling sick, “how long can these jets grow?”
Jun Davd’s voice was grave. “Millions of light-years in the most extreme cases we know. More often, a few tens of thousands of light-years.”
“And in this case? From what you’ve been able to observe?”
“Long enough to reach the edge of the galaxy. That’s what you wanted to know, isn’t it?”
“And they’re growing at seventy-five percent of the speed of light?”
“They’ll slow down a bit as they proceed outward. Some of them will fall back.”
Bram grasped at a slender hope. “Then there would be time to warn the Father World, wouldn’t there? We could stop broadcasting the Message and use our radio beacon to beam a warning. We know they’re listening to the center of the galaxy. They’d have at least twelve thousand years to get ready. Maybe … maybe build a fleet of ships to migrate. Or … or set up ramjet screens for whole planets.”
“The primary threat isn’t the jets themselves,” Jun Davd said gently. “It’s the wave front of radiation coming from the events that have already begun here in the central region—and that travels at the speed of light.” He went on as if he were giving one of his lectures. “The jets themselves contribute to that wave front—relativistic aberration makes them radiate most intensely in the direction of their motion. But they’re only a part of the story. The supernovae are adding their increment of radiation. But, chiefly, it’s coming from that whirligig of black holes and their accretion disks. The soup of matter that engine is feeding on is getting progressively thicker—it’s now a self-sustaining process—and friction is causing the smaller, four-hundred-million-sun hole to spiral inward at an increasing rate.”