“So what was the big new idea she had?” Celine asked. “Even if it’s hard to understand, you have to be able to explain it to me. If I don’t get it, I guarantee that not many others around here will.”

“Best you ask Star about that.” Wilmer paused in his steady munching. “You give her a drink or two, get her loosened up, and she’ll talk. Do I hear her clogs out there? What’s she doing?”

The footsteps on the hard polished floor of the corridor had an odd cadence. They clopped forward half a dozen paces, paused for five seconds, advanced, and paused again.

“I think she’s looking at the pictures,” Celine said. “It’s a portrait gallery of the Presidents.” She suspected from Wilmer’s expression that he had walked along the same corridor three minutes earlier and never noticed the walls at all. She moved across to the side table and said as Star came in, “Here you are. How about a drink, then?”

“Yer better believe it.” Astarte was carrying a single bag. Like Wilmer, she apparently believed in traveling light — the travel bag was for both of them. She walked forward to the table, picked up a bottle of vodka, and sniffed at it. As she poured two tumblersful she said, “Lot of ugly old buggers out there in the hall. Yer the only woman, and the only one of the whole lot who looks halfway human.”

If you tried really hard, you could take that as a compliment. Celine pointed to the ice bucket as Astarte handed one of the tumblers to Wilmer. Star shook her head. “Dilutes the goodness out.” She raised her glass, took a big gulp, and breathed in deeply through her nose. “Not bad. Better than at the convent. Tastes a bit turpid, though. D’yer make it yerself?”

“In the basement,” Celine said, and saw Star’s accepting nod. Another joke fallen down dead. She made a decision and poured herself a glass of chilled white wine. In politics it often helped to be the only one sober, but tonight was not politics.

Though what it was, Celine was not sure. Not the end of the world, but perhaps the beginning of the end?

“Come and sit. down.” She nodded at the server, and it began to rotate the loaded tureens slowly to each place.

Astarte brought her tumbler and the bottle with her, set them down in front of her, and watched the action of the server. “Smart little bugger,” she said after a while. The server was pausing only at places where someone was sitting. “How’s it know where we are?”

“Thermal sensor. Help yourself.”

“Yeah. We do it that way at the convent in Weipa. Only they got people to serve food for yer at Wilmer’s institute, so yer feel yer can’t take too much. How come yer don’t get served by people? Yer the President.”

“People talk more freely if there’s no one else listening.” Which was a totally bogus explanation, since Celine knew that the whole meeting was being recorded. “Just take what you want from any dish.”

“And you use a knife and fork, Star,” Wilmer added. “Same as at the institute. Or you’ll be in trouble.”

Astarte glared at him, but she nodded. She piled her plate high with meat and shrimp, ignoring all forms of vegetable. Wilmer took his turn and helped himself to a ton of everything. As he was doing so Astarte drained her glass and refilled it to the brim from the bottle of vodka.

“No worries.” Wilmer noticed Celine’s dubious look. “Star’s got a hollow leg. She’ll drink you and me under the table and then go back to work on her physics. How about a bit of chat from you, Star? I bring you all this way, and we don’t get a peep out of you. What’s Celine here going to think?”

“All right.” In spite of Wilmer’s warning Astarte was holding three large shrimp in her left hand and a juicy veal chop in her right. “What yer want me ter say?”

“It’s your theory, girl. Talk about it.”

“What about my food?”

“It can wait. We’re not going to pinch it.”

Celine added, “If you like, we can warm it for you later.”

“Oh, all right.” Astarte reluctantly put down the veal chop and the shrimp and wiped her hands on the sides of her sleeveless top. “A supernova’s — mmm — just one form of stellar — mmm — instability.”

“Chew and swallow first.” Wilmer turned to Celine. “I can’t take her anywhere. She does that all the time. You’d think she was a pelican the way she packs food into her mouth.”

Star grinned at Celine, a round-cheeked chipmunk smile, chewed, swallowed, and finally said, “He’s always on at me, but he’s all right otherwise. Let’s start with a question: When is a star unstable? Wilmer proved that yer can’t make Alpha Centauri go supernova if you work with the usual theories and continuous variables. But it did. Once you accept that, then yer have ter ask, can yer do it with discontinuous variables? Things that act like an impulse. You know what an impulse is, do you?”

“Assume I do.” Once, in the distant past, Celine had possessed a first-rate technical training. The question was, how much of it remained?

“There’s a few different ways to drive a star toward instability,” Astarte went on. “One is, you load on mass from outside until all of a sudden you have a collapse and an explosion. Another is you run out of raw material for fusion, an’ again you get a collapse an’ explosion. But those don’t work for Alpha Centauri; Wilmer proved that. So I asked myself, is there another way to cause instability, using some kind of impulsive events?

“Well, there is. Yer take a star — an’ it don’t have ter be the usual sort of star for a supernova. I mean, it don’t have to be a binary with one dwarf component, or a star many times as massive as the Sun. It can be any old star, could even be Sol. There’s something for yer to think about. So you take this star, an’ you apply a compressive pulse. A bit of a squeeze, and it don’t have to be a big squeeze, either. Yer can do it asymmetric, like on opposite poles, or you can make it work with radial squeezes, too, toward the center. Either way, yer can calculate the modes of oscillation.”

“You mean you can.”

“Yeah. Me and Wilmer.” Astarte picked up a shrimp, stared at it longingly, then put it down. “A star is stable because there’s a balance everywhere inside it between gravitational force inward and radiation pressure outward. So the star reacts ter the squeeze by contracting a bit, then the radiation pressure takes hold and pushes it back out. It overshoots a little bit, comes out a bit farther than it was ter start with, and oscillates. For some stars, like Cepheid variables, the wobble occurs naturally. But for most stars the oscillation will damp out — unless, just at the right moment, yer hit it again with another compressive pulse. And then you hit it again, and again, doing it each time at just the right moment. Then the oscillations don’t damp out at all. Yer get resonance.”

“Like soldiers,” Celine said, “marching over a bridge. They’re supposed to break step and not march together, otherwise the regular rhythm of their marching could hit the resonant frequency of the bridge and make it collapse.”

“I didn’t hear about that!” Star’s eyes widened with pleasure. “I love it. Have yer seen it happen?”

“No. Actually, I’m not sure it ever has. But people talk about it all the time as if it’s true.”

“Yer could do it. You’re the President, you’re in charge of the Army. Yer could take a whole bunch of troops, and a bridge, and tell ’em ter march over and not break step and see what happens.”

“Not if I want to stay President I couldn’t,” Celine said, and Wilmer added, “Star, unless I hear more astrophysics I’ll take that bottle away.”

“First yer tell me ter talk, and then when I’m talking you complain.” Astarte turned to Celine. “Anyway, an oscillating star’s not quite like troops walking over a bridge. It’s more like a pendulum, where if yer give it a bit of a nudge on each swing, the size of the swing gets bigger and bigger each time. But all of a sudden, instead of swinging back, the pendulum changes the way it moves.” Star made a complete revolution with her arm. “It goes right over the top and comes down on the other side. That’s what it does if it’s a pendulum. If it’s a star, it goes supernova. Like Alpha Centauri went supernova. Got it?”