'The problem,' he continued, 'is to identify what the thing could be. It's apparently slicing through the earth l& the proverbial knife through butter. That seems to call for something significantly denser than the densest parts of dm mantle and core, denser than anything occurring naturally on earth or made in any laboratory.'

'I don't see where you're going,' said Leems sceptically 'Are you talking about some superheavy element?'

Runyan glared at him. He could see the answer so clearly Was Leems being deliberately obtuse?

'In a sense,' he replied, Godly. 'My thoughts go to stellar examples, where high densities naturally result from huge gravitational fields.' He glanced at Fletcher who gave a brief nod. 'White dwarf matter, which is crushed until atoms blur into one another, exists at densities from million to a billion grams per cubic centimetre. Neutron star material is even more extreme. Matter is squeezed until atomic nuclei dissolve at densities greater than a hundred trillion grams per cubic centimetre. If you could drop a chunk of either kind of matter on earth, it would meet virtually no resistance and plunge to the centre and pass through to the opposite side as it performed an essentially free orbit.'

'Are you suggesting a neutron star is orbiting inside the earth?' asked Gantt incredulously.

'No,' Runyan replied, frowning. 'A full-sized white dwarf would be as large as the earth and have as much mass as the sun. A neutron star would only be a few miles across, but again would have the mass of the sun. The earth's orbit hasn't been appreciably affected since the astronomers haven't raised an uproar, so whatever we are dealing with can't have much mass.'

'Then you're talking nonsense, aren't you?' It was a statement more than a question from Leems.

Runyan ignored him. 'We might consider a small piece of a neutron star or a white dwarf, but we understand the physical processes involved there reasonably well. Freed from the gigantic self-gravity, a small piece would explode under its own outward pressure. What we need is something which will remain at high densities even though it has relatively low mass. Although I can list reams of practical objections, I can only think atone possibility which fits the picture we now have.'

Leems was exasperated. 'Honest to god, Alex,' he said in a disgusted voice, 'you're not making any sense at all. What in the hell are you getting at?'

Runyan's resolve to proceed dispassionately dissolved.

'Oh, for chrissake, Harvey !' he stormed. 'Can't you see it?' He was suddenly angry that the responsibility for the message was his. He aimed his fear and frustration a Leems.

'It's a black hole!' he raged. 'The earth's being eaten b; a goddamned black hole!'

Danielson recoiled back against the cushion of the sofa a Runyan's outburst, her face draining of colour. Black holes! Her mind reeled at his vehemence, the radical leap of hi! argument. Black holes had to do with stars, space, galaxies Not downtown Dallas , Nagasaki. What in god's name was he talking about?

'Oh, bullshit!' blurted Leems. He locked eyes with Runyan and then looked down and away to a neutral pain in the room.

'What?' demanded Noldt. 'What did he say?' Fletcher: leaned over to him and began an intense reprise of Runyan'! arguments.

Runyan continued to glare at Leems and made m attempt to respond to the commotion. He felt the first wisp: of relief that the burden was no longer solely his to bear.

Good god! Have I blundered? Isaacs thought to himself as he sat upright in his chair. With a sinking sensation, hl looked quickly from Runyan to Leems, and back t< Runyan. Was coming to Jason a grievous error? Was hi innate distrust of these far-out academics finally justified He could feel his months of work and risk slipping away What a disaster, if all he had to take back to Drefke was some harebrained idea. He turned to Plumps with a look o dismay.

Phillips saw the startled concern on Isaacs's face. As he stood and moved to the front of the room beside Runyan he surveyed the others. Leems was red-faced, as if he'd picked up the colour Danielson had lost. Fletcher was still explaining, waving a finger back and forth, tracing trajectory in front of the nose of a bewildered Ted Noldt. Gantt and Zicek were attempting a disjointed analysis across the length of the room, their voices ringing with surprise. Phillips motioned for quiet.

'Gentlemen,' Phillips said firmly, 'let's see if we can have an orderly and objective discussion of this remarkable suggestion Dr Runyan has made.' Turning to Runyan he continued, 'Alex, you'll have to forgive our collective scepticism, but this notion strains all credibility. From where could such a thing have come? What could it be doing in the earth? Surely, there's a simpler explanation.'

When he answered, Runyan's voice was still too loud, his normally avuncular tone replaced by a hint of righteousness.

'Simple? What we all crave is a less radical solution. We've striven for that and come away empty-banded. I submit we won't find a simple solution in the sense you mean, Wayne. Only an orbit fits the odd trajectory. Only an orbit would have a fixed period and a direction anchored in space, independent of the earth's rotation about its axis and revolution about the sun. Can anyone deny that a simple orbit fits the picture?'

The rhetorical question was greeted with silence. Runyan paced back and forth in a tight little orbit of his own. Danielson's thoughts were awash with the idea he had thrust upon them. Her eyes watched the muscles flexing in his sun-tanned legs. His tone became calmer.

'I ask myself what sort of thing can be orbiting through the earth, and I see no alternative to the conclusion that it is very dense. Ordinary, even extraordinary matter can't exist in small quantities at extreme densities, so I'm forced to conclude that we are dealing with a small, but very deadly, black hole. Don't get the idea I'm happy with this idea. On the contrary. It scares the hell out of me.'

He continued to pace, thinking.

'Here's more support for it,' Runyan said. 'Look at the holes drilled in solid concrete with no sign of searing or scorching. That's one of the singular pieces of evidence and very hard to understand any other way. It's just what a small black hole would do. A black hole will pull in matter from a volume much bigger than itself as it moves, the gravitational force sucking the material in from the immediate vicinity.' He made a crushing motion with his fist. 'A black hole will carve a tunnel as it goes, but leave no other sign of its passage, not like a laser beam or any other such device, as Dr Danielson was quick to see.' He smiled at her for a moment. 'In fact, from the size of the holes left behind, I can estimate the mass of the thing.'

Runyan paused and dug into a pocket of his cutoffs and brandished the napkin. The numbers Matched irregularly where the ink from Danielson's pen had run in the porous material. He did this more from a sense of drama than from a need to refresh his memory. He recalled the result perfectly well. He made an abbreviated OK sign with index finger and thumb and peered through the small hole at his audience.

'The holes drilled are about this size,' he said, 'a few millimetres to a centimetre. Depending on the tensile strength of the material through which the hole passes, I would guess the mass to be comparable to a small mountain and its size to be about that of an atomic nucleus.'

'But would a small black hole do what we are observing?' Gantt asked. 'That is, if it knifes through the earth as if it were butter, how does it generate the acoustic signal?'

Runyan pondered for a moment. 'Well,' he began, 'as I've said, it would exert a force sucking in matter from the immediate vicinity. It would carve a tunnel as it went. Does that suggest anything?'

'I suppose,' replied Gantt. 'At least in subsurface rock the ambient pressure would prevent such a tunnel from existing except momentarily. I can imagine the collapse of such a thing generating acoustic waves, depending on the size.'

'That's a good point,' Runyan aimed a blunt finger at him, 'the size of the tunnel is related to the mass of the object and the rate at which the tunnel forms and collapses should give an estimate of the acoustic power — which we know! Can we check to see if the picture is self-consistent?'

Gantt joined Runyan at the board and they began a crude, but rapid calculation. They stood in front of their figures and symbols to the consternation of those in the room trying to follow the arguments. After a few minutes of gesticulation and occasional cursing, Gantt returned to his seat.

'With some uncertainty,' Runyan announced, 'the acoustic signal is consistent with the idea of a small tunnel continuously being drilled at the orbital velocity and then collapsing.'

'I'm sorry,' Isaacs said, his voice polite, but firm. 'This is very important because you're talking about the basic data that led to this thing.' If Runyan were off base, Isaacs wanted to nail him quickly. He also recognized that the notion of a black hole and its implications were too foreign to him to be absorbed rapidly. If it turned out to be more than a crackpot idea, he didn't want to miss details that would aid his ultimate understanding. 'Could you explain to me a bit more clearly what you just did.' Isaacs gestured at the board.

'Oh, sure.' Runyan was loath to halt the flow of ideas, but recognized his responsibility to Isaacs. 'The picture is that a small black hole will move without resistance through the rock of the earth's core. It's like a little vacuum cleaner, sucking up particles that it gets too close to. The mass of the black hole dictates the strength of the gravitational pull it exerts. Close to the black hole that gravitational force is overwhelming, but at larger distances the tensile forces of the rock which make it solid are stronger than the gravity of the black hole. The quantitative question is to determine the distance from the black hole at which the internal forces in the rock are stronger than the gravitational pull of the hole. Further than that, the rock remains intact. Closer than that, the suction of gravity is dominant. If you were somehow to hold the hole still, it would eat out a cavity the size of which is proportional to the gravity of the black hole and hence to its mass. If the hole has a mass comparable to a small mountain, as I said, then it will carve a hole of about the diameter that you've reported in the foundation of those buildings.'

'Okay,' Isaacs replied, 'I guess I see that. And you get a tunnel rather than single hole if this black hole moves along a path sucking up everything out to a certain distance.' He pinched an imaginary particle between thumb and forefinger and moved it methodically in a line at arm's length.

'Exactly,' Runyan confirmed.

'Then where does the seismic signal come from?'

'Ah!' Runyan exclaimed. 'Now picture this hole falling freely through the rock at a speed which is determined by the gravitational acceleration of the earth. That speed determines the rate at which this little tunnel is carved.

'But what happens to the tunnel?' Runyan proceeded to answer his own question. 'After the black hole moves on, the tunnel can't just sit there. The huge pressure in the surrounding rock will crush it. So there's a continuous process by which the hole carves the tunnel and then moves on leaving the pressure forces to collapse it. The seismic signal is very plausibly the continuous noise made by the collapsing tunnel.'

'That can't be the whole picture,' Isaacs was thinking hard. 'At the surface, in normal rock, you should just get a hole drilled, just as we've seen in these concrete foundations.'

'Good, good. That's very perceptive.' Runyan was a little condescending, but he looked at Isaacs with new respect. 'In the mantle the pressure forces are not as great and the wound of the tunnel should remain unhealed. I remind you that the strength of your seismic signal falls as the influence nears the surface. Pat said there was no detectable signal from the upper mantle. This could be exactly the reason!'

'What about the acoustic signal in the water?' Isaacs inquired.

'Probably a similar idea with cavitation.'

'Cavitation? You mean like with a motorboat propeller?'

'Right. The hole should consume a surrounding volume of water just as it does rock. After it moves on, the water will rush into the vacuum in its wake creating thousands of tiny popping bubbles. Cavitation, and acoustic noise.'

'It looks to me,' Fletcher pointed at the board, 'as if you've assumed the hole moves subsonically. What if it moves faster than the material can respond. What if it moves supersonically?'

'I don't think that's a problem except maybe in the liquid iron core of the earth where the hole would be moving at its highest speed,' Runyan replied. 'Whatever this is seems to move relatively slowly at the surface — fast, but slower than the speed of sound in rock, water, or even air. There could be shock waves near the earth's centre, though. I'll have to think some more about that.'

'Gentlemen,' cut in Plumps from the side of the room where he had been standing, 'I'm impressed with the virtuosity of your arguments, but I'm still very disturbed at the nature of your conclusions. Doesn't anyone have an alternative suggestion?'

The question was greeted with silence. Runyan stood mute. His eye rested on, but barely registered, a dollop of coffee on the desk, spilled from a cup Gantt had brought in after lunch. His fixation was broken by Ted Noldt who stirred and said, 'I have a question which bears on the possibility of a black hole.'

Runyan lifted his eyes and looked at the speaker. 'I don't know much about black holes,' Noldt said, 'but I thought the small ones, about which you are talking, were supposed to radiate away their mass and energy at a great rate, causing them to evaporate and explode. Doesn't that rule out such a black hole?'

'We're going to have to consult a real expert on the subject, which I'm surely not,' replied Runyan. 'That question has been very much on my mind.' He paused a moment and then continued. 'Here's a possibility. The theory of evaporating black holes was worked out in the context of idealized, empty space, whereas this one's in the real world!' He caught himself. 'Sorry. A grotesque pun. Unintentional. Anyway, maybe the fact that this one is surrounded by matter changes things.'

'That may be right,' mused Fletcher, picking up the argument. 'If it's consuming matter, the infall may squelch the outflow. Let's see, didn't you and Ellison estimate the rate of consumption just now?'

'Right,' said Runyan, turning to the board once more. 'I don't remember all the formulae for the evaporation rate, but maybe I can piece something together.' He doodled for a minute while the others looked on and listened to the scratching chalk. 'Yes!' he looked up. 'That's probably it: there seems to be a comfortable margin. As long as the hole bores through the earth, it will eat the matter and grow. You'd have to stop the consumption to get it to evaporate.'

'Wait a minute,' said Noldt, punching a finger in the air. 'That's not really relevant, is it? This flung must have come from space somehow, so it must be massive enough not to have evaporated before it got caught in the earth. Isn't that right?'

Runyan beetled his brows at Noldt and paced along the narrow corridor in front of the blackboard a couple of tunes. Then he turned to face him again.

'No,' he said, 'I'm not sure that is right. It's true that the cosmologists have told us about the possibility of such mini— black holes created in the turbulence of the Big Bang. But there are two problems. In the first place, though my estimates are crude, I don't believe this object is massive enough to have survived since the beginning of time. Secondly, there is a great difficulty with the curious fact that it moves with the earth.'

'What's that?' Noldt was puzzled.

'If this were a black hole born in space,' Runyan explained, 'there is little chance that it could get trapped in the puny gravity of the earth. For that to happen, it would have to be moving very slowly with respect to the earth. But what with the earth's motion around the sun and the sun's motion around the galaxy and the galaxy's motion off to god knows where, the relative speed between the earth and any random astronomical body would be much greater than the escape velocity from the earth. The earth could not possibly attract and hold anything moving past it so rapidly.

'Do you remember the Tungus event?' he asked Noldt. Noldt had to think for a second, "fungus? Russia. Siberia ! Big explosion?'

'Right,' Runyan replied. 'Still rather mysterious. Some explosion in Siberia in 1919. Burned and flattened trees for miles around. But no crater. That ruled out a large meteorite. Any piece of space rock big enough to do the damage done would have to have left a crater rivalling the old one in Arizona. The best idea seems to be a comet. Comets are thought to be very loose fragmentary icy structures. Such a thing could deliver a hell of an impact but be sufficiently diffuse not to gouge a crater.'

'So?' Noldt did not see the point.

'Well, whenever something strange happens somewhere, someone is going to suggest a black hole.' He broke off and looked at Leems scowling at him. 'I know what you're thinking, Harvey. If the shoe fits... But hear me out.

'There was a suggestion that the Tungus event was caused by a small black hole. Then it would just dig a small tunnel as I've described, not make a large crater.

'This idea was quickly ruled out though, for just the reason I said. Any black hole coming in from space would have to be moving at a huge velocity, at least a hundred times greater than we're dealing with here. The question earl raised a minute ago is pertinent. Such velocities are supersonic and the hole arrives with a large shock wave. That's what was supposed to cause the Tungus blast itself. But then when the hole went through the earth it would have generated seismic waves that would have pinned seismographs all over the earth, and while the 'Fungus event itself was registered, nothing like the passage of a supersonic black hole occurred.

'Finally, you can trace the angle of impact from the pattern of flattening of the trees. Any such black hole should have reemerged in the Baltic Sea and blown Norwegian fishing boats out of the water. From all reports, they fished peacefully that day.

'So the hypothesis of a black hole from space ultimately made no sense there.' Runyan looked directly at Noldt again. 'And it makes no sense here either for the same reasons. The velocity would be too high. But whereas a low speed black hole would not have caused the Tungus event, a low speed black hole fits what we've seen here.' He nodded towards Isaacs and Danielson.

Noldt thought for a moment. 'Well,' he said, 'suppose the universe is littered with these things, and we just happened to have the bad luck to finally overtake one slowly, and it settled in.'

'We don't know anything about the distribution of such holes in space, of course,' said Runyan. 'No evidence for them has ever been observed. To have enough small black holes to make the interaction you describe probable, I would think they would have to be so densely distributed that we would have noticed many other astronomical effects.'

'I don't understand what you are saying,' stated Noldt.

'What is the alternative? Surely such a thing doesn't occur spontaneously on earth?'

'No, I don't see how it possibly could,' agreed Runyan.

'I don't see how it could have occurred naturally on or off of the earth.' He paused, unable to avoid sounding portentous, and somewhat embarrassed at doing so. He was determined not to speak next.

After a moment, Leems spoke up with an edge in his voice. 'If we accept your arguments up to this point, then we're forced to the conclusion that this thing was manufactured. Is that what you're saying?'

Runyan nodded, but remained silent as all eyes shifted towards him. At last he said, 'That's the second conclusion I've reached. I think we must allow for the possibility unless it can be rigorously ruled out.'

Again Runyan became silent as he exchanged glances with his colleagues, desiring to support, but not lead the discussion at this critical juncture.

'There are two possibilities then, aren't there?' asked Fletcher. 'It's man-made or...' He paused and finally said in a flat voice, 'Or it's not.'

'Omigod!' exclaimed Noldt. 'You mean this thing could have been manufactured by extraterrestrials and... and planted here?'

Several voices were raised in simultaneous protest.

'This is getting out of hand!'

'UFO's again! That's very hard to believe!'

Isaacs had a flash of memory of the AFTAC headquarters in Florida where he had first heard of the seismic signal. He couldn't believe what he was hearing. How could that simple little rattle in the earth be related to the insanity that was being expressed in this room! Then he thought of Zamyatin. Whatever was going on, he couldn't feature explaining black holes to the KGB chief, never amid trying to convince him they were being fired by nasty little green men from outer space. He shook his head and pinched his eyes with thumb and finger. This discussion just had no connection whatever with the real world of geopolitical confrontation with which he dealt every day.

Runyan cut in. 'I'm sure we agree that the whole situation is hard to believe!'

'The energy requirements to make such a thing must be gigantic,' said Leems. 'Surely the suggestion that it's artificial is absurd.'

'It would take a lot of energy,' Runyan agreed. 'Don't you think it's fair to conclude then,' Leems pressed, 'that such a thing would be exceedingly difficult, if not impossible, to create? I have a strong suspicion we're on the wrong track altogether despite your argument here.'

'I don't deny that point,' replied Runyan. 'It's very difficult to conceive how such a thing could be done.'

'Still,' argued Noldt, 'it's not that it's impossible, just that we can't see how it could be accomplished technologically. Isn't that correct?'

'I think that's correct,' said Runyan. 'We're talking about very large amounts of energy, but not an infinite amount. In principle, it could be done. After all, we're fairly comfortable with the notion of it happening spontaneously in an astronomical context. Also, the large energy you're thinking about is based on brute force compression. There may be more elegant means to the end.'

'Then,' said Noldt with a barely suppressed excitement, 'since we see no way to do it on earth, aren't we forced to consider the possibility that such a thing was made by extra-terrestrials and put in the earth for some purpose?'

'Before we invoke some malevolent intent, terrestrial or otherwise,' Leems said with scarcely veiled sarcasm, 'I must say I'm not satisfied that we really know enough to rule out a natural origin. Even if we accept that we're dealing with a black hole, and I'm as yet far from convinced of the necessity, how can we eliminate the possibility that this thing started out exceedingly small a long time ago? Maybe the earth even condensed around it, and it took all this time, five billion years, for it to grow to its present size.'

'I have two responses to that,' Runyan said. 'One is that the universe was already quite old when the earth was born. There were no special conditions at the time to create small black holes, and any born in the Big Bang should have long since evaporated.'

'Well then, figure out a way to prevent evaporation,'

Leems said harshly. 'That still seems more likely than insisting on some intelligent plot at work.'

'Maybe so, maybe so,' Runyan said slowly. 'The other thing that bothers me is that the growth time for this thing is relatively long. I find it peculiar that this phenomenon has only just been discovered, since the technology to detect it has been around for some time.'

'Are you saying that this dung has just been put here recently?' asked Noldt. He half-glanced over his shoulder as if expecting to catch a glimpse of an alien presence.

After a moment's hesitation, Runyan spoke again. 'I'm disturbed that we're skirting a bit close to the edge of reason here with too few facts to support us.' He cleared his throat, then continued. 'Perhaps we should set aside for a while the issue of how such a dung could come to be and try to consider some other factors. We should discuss what we can do to learn more about this object.'

'I've been thinking about that,' said Fletcher, 'as a remedy for incipient hysteria.'

Pat Danielson had been following the discussion intently. She had felt herself becoming more edgy as the tension in the room increased. She had read some popular accounts of astronomy and their discussions of black holes and thought she was beginning to make some sense from Runyan's remarks, but the idea that he would leap from the evidence she had compiled to this conclusion still left her stunned. And now talk of manufacturing such a dung. That just couldn't be. She joined the nervous laughter after Fletcher's remark and could sense the more relaxed mood that spread through the room.

Fletcher continued, 'There should be quite a bit one could do by adopting your hypothesis as a working assumption and constructing appropriate models. If we could predict the behaviour of a small black hole, or whatever, orbiting through the earth, we could compare such predictions with the seismic data and other observations and perhaps get a much better idea of just what we are dealing with. Ideally, we should be able to prove your hypothesis true — or false.'

'Ah, a voice of reason,' said Leems, in a more lively tone. 'I don't know much about seismic waves, but it still seems to me that they should be modelled as well, to see whether the data that have been reported can be accounted for as some natural seismic phenomenon. The data are admittedly quite bizarre, but surely our seismologist friends don't know everything about the workings of the inner earth. Maybe there are special fissures or lattice works that channel waves in this special way.

'I do concede, though, Alex,' Leems continued, 'that since you have let this particular genie of yours out of the bottle, it should be pursued.'

'That's right,' agreed Noldt, 'if we are, in fact, dealing with a black hole and it originated on the earth's surface, then, if I have the picture correctly, it should return roughly to its point of origin.'

'I wish you wouldn't assume it was made on the earth's surface,' interrupted Leems.

Noldt gave him a befuddled glance and continued, gesturing towards Isaacs and Danielson. 'We already have reasonably accurate predictive capabilities. We can predict when and where the thing is due to come up and, well, of course you don't just grab it, but surely we could learn more about it then.'

'In fact,' added Fletcher, 'shouldn't an orbit tell us just where the origin was with respect to the surface?' Leems frowned again, but did not say anything.

'Yes, exactly right,' said Runyan. 'If we compare the apogee, the point farthest from the centre of the earth, to the earth's topography, that should give us some pertinent information. We already have an interesting indication from the Dallas event so nicely predicted by Dr Danielson.' He nodded at Danielson and she smiled quickly in return. 'About forty seconds elapsed from the first episode in the bar to the destruction of the building across the alley. An object in free fall could not have risen and then fallen more than a few thousand feet. So apparently apogee is somewhat above sea level, but not far. The point at which the orbit peaks will occur deep under mountains of any height, the Rockies or the Himalayas. More precise information of this sort could be most useful.'

'If we can tell where this thing comes out of the earth, what sort of test can we run?' asked Noldt. 'You can't see such a thing can you?'

'No,' answered Runyan, 'it's about the size of an atomic nucleus. You surely couldn't see it directly. It's most distinctive characteristic, of course, would be its gravitational field. That should be quite appreciable. Gravimeters set up in the vicinity should be able to tell us precisely what the mass of the object is, whether or not it comes to or through the surface. A simple seismic wave will have no effect on the local strength of gravity. A massive, orbiting object, on the other hand, should give a definite signature.

'I propose that this be our first move, and that since Gantt is our resident seismologist, he's the man to mount such an expedition.' Runyan turned to Gantt. 'What do you say, Ellison? If Dr Danielson can predict where the event will approach the surface at a given time, won't you be able to measure or set stringent limits on the fluctuations of the gravitational field?'

'That's an excellent ideal' responded Gantt with enthusiasm. 'I'll start planning immediately.'

Runyan glanced at Leems and then inquired, 'What do you think of that, Harvey ?'

Leems clasped his fingers together and stared at them for a moment. 'The gravity seems to be an effective discriminant. By all means, let's put your idea to the test.'

Gantt raised a finger and inquired, 'How well can you predict the point of surfacing? Can Dr Danielson's estimates be improved?'

'I think there's much to be done with computer models,' responded Runyan. 'I sketched a crude hypothetical orbit on the board. There will be many perturbations to an idealized orbit, but to work those out in detail can be done with sufficient effort. In addition, there may be some effect from the sun and moon, and perhaps the larger planets. With the exception of the effect of the structure of the inner earth, which is not known precisely, computation of a detailed hypothetical orbit should be possible.'