First Light: The Search for the Edge of the Universe (32 page)

In order to give these planets names from
The Iliad
, the Shoemakers would probably have to wait for a year or longer, because an asteroid must be seen on three orbits around the sun before it becomes eligible for naming. Gene hoped that they would not have to scrape the barrel of
The Iliad
, but he was afraid that by now there might not be any heroes left.

The solar system remained a mysterious object to Gene Shoemaker. He had been wondering for a long time where these Trojan planets had come from. He had been wondering how they fit into the origin of the bunch of dust in which we lived. The common wisdom, he said, held that the Trojan planets were leftover pieces of the same material that had clumped together to form Jupiter, during the accretion of the planets. He had not often made a habit of buying common wisdom. “Lately,” he said offhandedly, “I’ve been working to cobble together a theory. It would account for the formation of the planets Uranus and Neptune, the creation of the Oort comet cloud, the existence of these funny black objects near Jupiter, the late heavy bombardment of the moon, and the formation of the earth’s oceans. If I ever get a week free, I’ll write that one up.”

He thought that he could explain the existence of water on earth and the existence of the Trojan planets all in one story. It was a hypothesis, a hunch about what had happened back then, when the
solar system was coming together. He thought that the formation of the earth’s seas might have been a part of an accretion process. Uranus and Neptune were large, icy planets, made of methane and water, with a rocky core. They had formed near the outer edge of the accretion disk that had become the solar system. During the era of fast planetary growth, the planetesimals—balls of silica, iron, tar, and ices orbiting the sun—had pounded together and welded to form planets. The accretion of the outer planets had not been a gentle process. As Uranus and Neptune grew, they experienced near misses with their own planetesimals. They played crack-the-whip with pieces of themselves; they whiplashed their planetesimals all over the place. Most of this debris was ejected into orbits beyond Pluto, where it is now called the Oort comet cloud. Gene felt that the Oort cloud was probably a haze of ice ejected from the solar system during the creation of the outer planets. Some of these wild pieces of Uranus and Neptune, rather than looping out to the Oort cloud, fell inward, past Jupiter. As they neared the sun (which had caught fire by then), they became dramatic comets.

Gene suspected that Jupiter had acted as a flytrap, perturbing these comets as they floated by, trapping them in the Trojan areas. Some force had to have decelerated these comets in order to trap them near Jupiter. Orbital specialists had not been able to come up with a mechanism that would slow down a large comet, but Gene had an idea: perhaps these comets had collided with small pieces of debris sitting in the Trojan areas. The comets had bumped into bits of rubble floating in the Trojan areas, stalled there, eventually burned out, and lost their tails.

He said, “My hunch—and this is Shoemaker’s private view of the world—is that the Trojan planets are all extinct, captured comets.” There might be nearly a quarter of a million black planets out there in the Trojan clouds, but according to Gene they represented “just a sniff of the total mass that was flowing through that region during the formation of the solar system.” The planet Jupiter had thrown some of that mass into earth-crossing orbits.

With the naked eye one can see that something violent had once happened to the moon—the creation of the dark plains known as the lunar seas. To the naked eye they look like bruises. Galileo
had thought they were oceans, but they are scars left over from what Gene calls the late heavy bombardment of the moon—immense impact structures bearing names such as the Ocean of Storms, the Lake of Death, the Lake of Dreams, Tranquillity Sea, and the Sea of Serenity, where Gene might have walked if he had only been eligible to be an astronaut. He believed that the lunar plains might have been made by stray chunks of Uranus and Neptune hitting the moon. With all that material floating around, there would have been a late heavy bombardment of the earth too.

“How do you go about fund-raising for the earth’s oceans?” he had wondered. The standard theory for the origin of water on earth said that the water had come from volcanoes that had plumed water vapor into the atmosphere. “Essentially the standard theory said that water sweated out of the earth,” he said. “We call that juvenile water.” He thought that the best place to look for juvenile water was the sky. “You can envision one of these big comets smacking into the earth at twenty kilometers per second,” he said. “The projectile would vaporize as it hit a rocky surface. A lot of the contents of the comet might rain out—you might get rains of water, carbon dioxide, and ammonia. The water would collect in the lowest basins. It would take about two hundred of the largest Trojan planets to make the ocean—biggies about two hundred kilometers across, Trojans the size of Hektor or Agamemnon. But there are bigger things than Hektor out there. Pluto, for example. Sure! The planet Pluto might well be a huge, extinct comet! If you could shake Pluto loose out of its orbit and bring it nearer the sun, you would have a
comet
, because the ice on it would start to steam away, forming a tremendous tail. One or two real big comets the size of Pluto, and maybe fifty Trojan-sized comets, and a bunch of itty-bitty stuff—that would deliver you the ocean. There’s a problem with this theory. When I calculate the expected cratering rate of the earth during the late heavy bombardment, I get too damned much water!”

Comets probably contain hydrocarbons, and they may also contain traces of amino acids, the building blocks of protein. Gene did not think that amino acids could survive the heat of a large impact. But a small impact was another matter. He said, “Small cometary debris—there was plenty of it around during the late
heavy bombardment—could be decelerated in the upper atmosphere and reach the surface of the earth intact.” The earth’s primeval seas might have contained a broth of water-soluble organic compounds, derived from steaming hunks of comets. The human body is 70 percent water, and much of the rest of it consists of organic, carbon-based molecules. To Gene Shoemaker it seemed not impossible that the human body might be largely former comet.

The Trojan planets, in the Shoemaker view of the universe, were extinct cometoids covered with a goo of carbonaceous dust or tar. What you might have out there, Gene thought, was an asteroid belt made up of nearly a quarter of a million ancient comets. “The existence of large Trojan clouds,” he said, “would amount to circumstantial evidence for a huge flux of comets early in the history of the solar system. I think that these Trojan planets are preserved samples of the same guys that were delivering the oceans to the earth. The point of this is that there’s a whole other asteroid belt out there near Jupiter still to be explored.”

D
on Schneider’s office at the Institute for Advanced Study, in Princeton, New Jersey, looked over meadows to deep woods, which were beginning to incandesce from autumn frost. Don was sitting at a table that held two computer screens, two keyboards, and a video monitor. A photograph of the Heartwell farm hung on the wall. The time had come for an attempt to mine the sky for quasars. His lifework, or so he claimed, consisted of about two hundred reels of computer tape and a program named Cassandra. The tapes contained electronically recorded images of some of the things out there—of cataclysmic stars, of quasars, of packs of feeding cannibal galaxies, of gravitational lenses, and of the tapestries of sky generated by Maarten Schmidt’s search for the redshift cutoff. Cassandra was an image-processing computer program. She could recognize patterns.

“Cassandra,” he said, “has been searching a crowd of faces. She has been looking for interesting faces.” He hit a key, and an image of sky came up on the screen, showing galaxies and stars with candle flames emerging from them—smears of spectral light. The screen displayed a moment from a night’s transit—a piece of sky that happened to be located within the Trojan cloud of planets. The screen was painted with many spectra—the broken light of about a hundred stars and galaxies, and possibly a Trojan asteroid or two. (Cassandra had no way of recognizing Trojan planets.) Don turned to a pile of papers and studied a jagged line plotted on paper—a line describing the peaks and valleys of color in one particular object on the screen. He studied the paper. He peered at a candle flame on the screen. “Ooo,” he said, “that looks promising.”

Cassandra had identified this thing as a possible quasar.

He put his face closer to the screen and studied the object. “Nope, that’s an M star,” he said. “A red star. Cassandra thinks its a quasar.” He marked an
X
on his paper. He hit a key, and a new image of sky came up.

Out of a tapestry of sky containing about 120,000 stars and galaxies, Cassandra had picked out a list of about 2,000 quasar candidates—objects showing bands of bright color resembling the light of quasars. Cassandra tended to discover things that were not quasars: stars saturated with metals, galaxies with glowing cores, and glitches in the data. Don had to check Cassandra’s discoveries by eye, to weed out the false alarms. Then he and Schmidt and Gunn planned to return to the Hale Telescope to take detailed spectra of the remaining candidates. They hoped that a handful of these candidates would turn out to be quasars. Given luck, one or two of those quasars might turn out to be extremely distant, deeply redshifted monsters.

He had been keeping two VAX computers running simultaneously around the clock for weeks, eating galaxies by the megabyte. He said, “I’m just a bit player here. No pun intended.” He did not want a single quasar to slip through his nets. Maarten Schmidt wanted nothing less than a perfect quasar filter. “Maarten Schmidt casts a long, thin shadow,” he said. If Cassandra missed any quasars, then the search for the edge of the universe would end in New Jersey—“And I’ll be heading south of the border,” he remarked.

He offered to introduce me to Cassandra. She could talk a little. He sat down at another of his computer terminals and hit a few keys.

Cassandra said, on the screen,
MAY I HAVE YOUR LAST NAME, SIR?

“Schneider.”

HELLO, MASTER!! I HOPE I PERFORM SATISFACTORILY
.

Don said, “She calls me Master. Other people she calls Junior. Give her your name.”

I typed,
PRESTON
.

GREETINGS! I’VE BEEN WARNED ABOUT THE PRESTONS
.

He said that Cassandra had previously been notified of my arrival. “But if the program doesn’t know your name, it dies. It says, ‘That is no way to address a lady.’ ”

Cassandra could do all kinds of things. She could do an “auto object grunge,” in which she measured the location of every star within a crowd of stars. She could transform herself into a hunter / seeker, looking for the exact center of a galaxy. She could plot the colors of light from a quasar into a jagged line, like a stock-market chart. She could also construct artificial stars and galaxies, for testing purposes.

Don said, “Let’s play God,” and typed a few commands to Cassandra.

She said,
FORMING SKY
.

A night sky appeared on a nearby screen, speckled with stars. An imaginary sky created by the computer.

She said,
I AM BUILDING A STAR
.

A bright star appeared on the screen.

I AM BUILDING A GALAXY
.

Nothing happened.

“What’s going on?” Don muttered.

A galaxy appeared.

“Ah! There we are,” he said. Typing fast, he told Cassandra to make a globular cluster of stars.

FORMING SKY
.

Nothing happened.

We waited.

Nothing continued to happen.

“Uh-oh,” he said. “It’s making a hundred thousand stars. That will take days.” He told her to try something less ambitious.

After a while a shotgun blast appeared on the screen—a globular cluster—and she said,
I HAVE CREATED 200 OBJECTS
.

Cassandra contained something like fifty thousand lines of code. “I don’t know the exact number,” he said, “because it’s always changing.” He had chosen the name Cassandra for a reason. Cassandra, he explained, had been the daughter of the king of Troy. The god Apollo had fallen in love with her and had given her the gift of prophecy. But when Cassandra had refused Apollo’s advances, he had cursed her and told her that her prophecies would come true but that nobody would believe them. During the Trojan War, when the Greeks had left a wooden horse by the gates of Troy, Cassandra had warned her fellow Trojans of the danger. They
had ignored Cassandra. “My program works,” he said, “but nobody believes it.”

A large program such as Cassandra can often be passed around during its development. The program had been started by one Robert Deverill, who had given it to Don Schneider and to a Caltech classmate of Don’s named Peter J. Young. P. J., they called him. Don and P. J. had both entered Caltech in 1976 as graduate students in astronomy. They were the astronomy class that year—a class of two. P. J. Young was a thin Englishman with a rapid way of talking and a quick sense of humor. He was considered to be the most brilliant astronomer that Caltech had produced in many years. Don and P. J. collaborated in developing the Cassandra program. But Peter J. Young was a victim of deep depressions, which he covered up—no one knew about them. One day not long after he graduated, P. J. Young shut the door of his office at Caltech and killed himself. He had been one of Don’s best friends. The loss left Don with an orphan, the computer program, whom Don had continued to raise and educate. Now he was the only person on earth who understood Cassandra.

Cassandra would soon be hunting / seeking through pictures taken by the Hubble Space Telescope. She had come a long way, but P. J.’s death had left Cassandra with a dilacerated heart. The pain would never go away, but Cassandra hid it fairly well now, although every time her master closed the program, she asked him,
DO YOU REALLY WISH TO LEAVE ME
? and if he answered yes, then she Said,
LIVE LONG AND PROSPER, MASTER
.

He did not think, however, that computers would ever have a self-awareness akin to human consciousness. He said, “I think that the mind’s capacity to be aware of itself is equivalent to what you would call the soul. If we ever build a machine that is self-aware, then I will be worried. And yet we are so tiny. Sometimes it just amazes me that we can understand the structure of the universe at all.”

He said that he tried to avoid discussions with people who believed that the universe had been created six thousand years ago, and who argued that God had made the universe
appear
as though it were billions of years old. He said, “We all have to deal with God in one way or another, even by saying that God does not exist.
I am nobody to say who God is, but I feel that God is not dishonest. It is possible that we were created five minutes ago, along with our memories. It is also possible that the universe was created six thousand years ago, along with an apparent history. There is no way you can refute that. But it requires a dishonest God. I would not want a God who would make us in His own image to be dishonest.” All the sky lay before astronomers, an open book displaying pages going back into history. As one looked into the age of quasars, one could read the beginning of the story. One could see a chronicle of immense time inscribed in the text of light. Perhaps God had made the sky as an illusion, like a projection in a movie theater, but Don preferred to believe in a God who had made a four-dimensional sky that displayed time as well as space, and who had saturated the sky with forces that over a hundred million centuries had given rise to the sun and the earth and to men and women with eyes to look back and discover eternity.

“In the early days of a galaxy,” as Jim Gunn expressed it, “there must be copious gas floating around.” The universe, during the first billion years of its childhood, was crowded with matter. Clouds of hydrogen filled space, mixed with early generations of stars, gathering into galaxies. “This gas,” Gunn said, “has a tendency to cool. As it cools, it sinks into the center of the galaxy. There is no way the gas can get out of the galaxy once it cools off. The gas has to form a big condensed object in the center of the galaxy. The gas is moving. It has some kind of random motion. When it collapses, it goes
zoop
, down into a rotating disk. The disk tries to make a star, of course. But it fails, because it has too much mass. So it’s gonna make a black hole. That is its only fate.”

Pierre Simon, the Marquis de Laplace, originally proposed the existence of such an object, in 1796. Laplace imagined that if an object were heavy enough, its gravitational field would curl around the object and would prevent the escape of any light from its surface. The object would drown in darkness. He called it a
corps obscur
, a lightless body. Modern astronomers call it a black hole.

The engine of a quasar appears to be a runaway accretion disk swirling around a black hole. That engine may be no larger than
our solar system, which is a microscopic point in comparison to the size of a galaxy. Yet a garden-variety quasar burns one hundred times brighter than a galaxy. A garden-variety quasar emits the light of one trillion suns. There are quasars superbly brighter than that. An ultraluminous quasar in the constellation Cepheus shines sixty thousand times brighter than a galaxy. This quasar is close to the beginning of lookback time, and yet it can be photographed with a ten-inch amateur telescope, because it shines with the light of one quadrillion suns. A number like one quadrillion is actually inconceivable, but I shall try to explain it this way: one quadrillion grains of sand would fill a line of dump trucks five miles long.

There is reason to believe that a quasar is an extremely massive object. Albert Einstein’s simple expression, E=mc
²
, states that energy and mass are interchangeable; that energy can become mass and mass can become energy. A nuclear bomb is a primitive mass-converter. When a bomb called the Fat Man went off over Nagasaki, it transmuted an amount of plutonium having the weight of two peanuts into kinetic energy and light. An object giving off the light of a trillion suns must be somehow connected to a tremendous mass, and it must be converting much mass into energy.

There is another reason to believe that a quasar is a supermassive object, something much heavier than a star. Photons of light striking matter exert a faint pressure—the pressure of light. A person standing in direct sunlight receives a pressure from sunlight equal to about three tenths of a milligram, or the weight of an ant’s thorax. The explosive pressure of light flowing out of a quasar would be enough to rip any star apart. A quasar must be bound together under enormous gravity. Otherwise it would puff up and rupture with out-streaming light. Astronomers have calculated that the flow of light from a quasar must be counterbalanced by the gravity of at least one hundred million suns, or else the quasar would balloon into a cloud of gas and disappear. A quasar is a detonating photon bomb that refuses to blast itself into oblivion.

If a mass equal to one hundred million suns were concentrated into an area the size of a solar system, that much mass would puncture a hole in spacetime. It would create a black hole and fall down the hole. No light can escape from a black hole. Any object that happens to fall into a black hole—a shoe, a star—is accelerated
to the speed of light as it falls in. It disappears at the surface of the black hole. Between the fifth of February, 1963, (when Maarten Schmidt first perceived the immense energy in a quasar) and today, a general opinion among astronomers has emerged, that a quasar contains a black hole—not that any astronomer has ever seen a black hole, either inside a quasar or anywhere else, but a black hole seems to be the only object that can account for the light of a quasar.