Since second-generation stars coalesced from such clouds, a full percent or a bit more of a second-gen's mass comes from metals — 'metals' in this context meaning elements heavier than helium.

Third-generation stars are even more recent; the suns of all the Commonwealth homeworlds are third-gens, as are all stars being born today, although, of course, some first-gens and a lot of second-gens are still around, too. Third-gens consist of about two percent metals." Jag paused for a moment, and looked from face to face in the room.

"Well," he said, "that star" — he gestured with one of his medial arms at the green orb in the holo sphere "has about eight percent of its mass as metals, four times as much as even a typical third-gen. The thing has enough iron in it that you could actually mine it."

"What about the green color?" asked Keith.

"It's not really green, of course, any more than a so-called red star is actually red. Almost all stars are white, with just a hint of color."

He gestured with his medial limbs at the starfield around them.

"PHANTOM routinely colorizes the stars in our holo bubble, assigning them colors based On their Hertzsprung-Russell categories.

The star out there just has a greenish tinge. The absorption-line blanketing due to its metal content is stronger than the backwarming, and that weakens the star's output in the blue and ultraviolet. The result is more of the star's light coming out in the green region of the spectrum." His fur danced. "I would have said a star with so much metal content would be impossible in our universe at its present age if I hadn't seen one with my own four eyes. It must have formed under very peculiar local conditions, and-"

"Forgive the interruption, good Jag," said Rhombus, "but I'm detecting a tachyon pulse."

Keith swiveled in his chair, facing the shortcut.

"Gods," said Jag, rising to his feet. "Most stars are part of multiple star systems-"

"We can't take another close passage," said Lianne.

"We'll-"

But the shortcut had already stopped expanding. A small object had popped through. The gateway had grown to only seventy centimeters in diameter before collapsing down to an invisible point.

"It's a watson," announced Rhombus. An automated communications buoy.

"Its transponder says it's from Grand Central Station."

"Trigger playback," Keith said.

"The message is in Russian," said Rhombus.

"PHANTOM, translate."

The central computer's voice filled the room. "Valentina Ilianov, Provost, New Beijing Colony, to Keith Lansing, commander, Starplex. An M-class red-dwarf star has erupted from the Tau Ceil shortcut.

Fortunately, it emerged heading away from Tau Ceil, rather than toward it. So far, no real damage has been done, although we had trouble piloting this watson past the star and into the portal. This is our third attempt to reach you. We did manage to contact the astrophysics center on Rehbollo for advice, and they had the incredible news that a star has popped out of the shortcut near them as well — a blue B-class star, in their case. I am now contacting all other active shortcuts to find out just how widespread this phenomenon is. End of message."

Keith looked around the bridge, bathed in green starlight.

"Christ Jesus," he said.

"I say we're under attack," announced Thoraid Magnor, getting up from the helm position, and walking over to the seating gallery to sit a few chairs to the right of Jag. "We've apparently been lucky so far, but dropping a star into a system could destroy all life there."

Jag moved his lower two arms in a Waldahud gesture of negation. "Most shortcuts are in interstellar space," he said.

"Even the one you call "the Tau Ceti shortcut' is still thirty-seven billion kilometers from that star, more than six times as far as Pluto is from Sol. I would say that in fifteen out of sixteen cases, the arrival of additional stars would have minor effects on the closest systems, and, since inhabited worlds are few and far between, the chances of actually doing short-term damage to a planet with life on it are quite small."

"But could these stars be, well, bombs?" asked Lianne.

"You said that the green star is very unusual. Could it be about to explode?"

"My studies of it have only begun," said Jag, "but ! would say that our new arrival has at least a two billion years of life left. And singleton M-class dwarfs, like the one that popped out near Tan Ceti, don't go nova."

"Still," said Rissa, "couldn't they disturb the Oort clouds of star systems they pass close to, sending showers of comets in toward the inner planets? I remember an old theory that a brown dwarf dubbed — Nemesis, I think it was — might have passed close to Sol, causing an onslaught of comets at the end of the Cretaceous."

"Well, Nemesis turned out not to exist," said Jag, "but even if it did, today each of the Commonwealth races has the technology to deal with any reasonable number of cometary bodies — which, after all, would take decades or even centuries to fall into the inner part of a system. It is not an immediate concern."

"But why, then?" asked Thor. "Why are stars being moved around? And should we try to stop it?"

"Stop it?" Keith laughed. "How?"

"By destroying the shortcuts," said Thor, simply.

Keith blinked. "I'm not sure they can be destroyed," he said.

The Waldahud's fur danced pensively for a moment, and when he spoke, his bark was subdued. "Yes, theoretically, there is a way." He looked up, but neither of his eye pairs met Keith's gaze. "When first contact with humans was not going well, our astrophysicists were charged with finding a way to close the Tau Ceti shortcut, if need be."

"That's outrageous!" said Lianne.

Jag looked at the human. "No, that is good government.

One must prepare for contingencies."

"But to destroy our shortcut!" said Lianne, anger bringing unfamiliar lines to her face.

"We did not do dit," said Jag.

"To contemplate it, though! If you didn't want us to have access to Rehbollo, you should have destroyed your own shortcut, not ours."

Keith turned around to look at the young woman.

"Lianne," he said softly. She faced him, and he mouthed the words "cool it" at her. He turned back to Jag. "Did you find a way to do it? To destroy a shortcut?"

Jag lifted his upper shoulders in assent. "Gaf Kandaro em-Weel, my sire, was head of the project. The shortcuts are hyperspatial constructs that extrude a nexus point into normal space. An absolute coordinate system exists in hyperspace. That's why Einsteinian speed restrictions don't apply there; it is not a relativistic medium. But normal space is relativistic, and the exit — the thing we call the shortcut portal — has to be anchored relative to something in normal space. If one could disorient the anchor point, so that it no longer could extrude through from hyperspace, the point should evaporate in a puff of Cerenkov radiation."

"And how would you disorient the anchor?" Keith asked, his tone betraying his skepticism.

"Well, the key is that the shortcut is indeed a point, until it swells up to accommodate something passing through it.

A spherical array of artificial-gravity generators assembled around the dormant shortcut could be designed to compensate for the local curvature of spacetime. Even though most shortcuts are in interstellar space, they are still within the dent made by our galaxy. But if you remove that dent, the anchor would have nothing to hold on to, and — poof! — it should disappear. Since the shortcut is so small when dormant, an array only a meter or two across should be able to do the trick, so long as it is fed enough power."

"Could Starplex provide the power required?" asked Rhombus.