Excerpt from THE UNIVERSE AT MIDNIGHT

Introduction: A GREAT ATTRACTION

Sometimes, your own Galaxy gets in the way. Between the Milky Way's glowing stars weave clouds of gas sprinkled with the dark ash of ancient suns. Although these interstellar clouds can assume fanciful shapes--eagles, horseheads, seagulls, swans--they obscure the universe beyond, cloaking a fifth of the sky in perpetual fog.

"We knew that finding galaxies behind the Milky Way would be very difficult," said Renee Kraan-Korteweg, a Dutch-born astronomer at the University of Guanajuato in Mexico. "At optical wavelengths, it was not believed possible to uncover these galaxies, because they would be so hard to see." Indeed, this daunting region which girdled the sky had long been labeled the "zone of avoidance," since galaxies seemed to shun it.

So did galaxy-seeking astronomers. In 1994, however, Kraan-Korteweg and her colleagues trespassed into the forbidden zone and took aim at the constellation Cassiopeia with a radio telescope. The radio waves zipped past the gas and dust, betraying a large galaxy, never before seen, only 10 million light-years from Earth--in astronomical terms, just around the block. It looked like the letter S, as if to say it had surrendered. Without the Milky Way's gas and dust, the galaxy would appear as one of the ten brightest in Earth's sky. Meanwhile, other astronomers dug up the wreckage of a small galaxy in Sagittarius, on the far side of the Milky Way. It proved to be the closest galaxy ever seen, a mere 80,000 light-years from Earth. It got torn apart when it strayed too close to the Milky Way's shores.

Even with these discoveries, a far mightier entity lurked behind the Milky Way. Astronomers had earlier discovered that the gravitational pull of something they christened the Great Attractor was trying to suck in all galaxies, including our own, for hundreds of millions of light-years around. The Great Attractor had accelerated our Galaxy to a speed of 1 million miles per hour, but its exact center eluded detection by concealing itself behind the southern Milky Way.

Kraan-Korteweg and her colleagues got to work, projecting magnified images of optical photographic plates onto a small screen in a darkened room. "It was a very slow process going through these plates--finding galaxies, identifying them, classifying them," she said. "They're smudges that you can't see without enlarging them." Not only did the Milky Way's gas and dust dim the galaxies, but also hordes of foreground stars speckled the photographs, raindrops on a celestial windshield, further obstructing the view.

Nevertheless, she and her colleagues persevered. "We were charting thousands and thousands of new galaxies," said Kraan-Korteweg, "and it became very clear that there was an enormous concentration of galaxies very close to the predicted center of the Great Attractor." Deploying telescopes in Chile, South Africa, and Australia, the astronomers then measured the new galaxies' distances, finding them all 250 million light-years from Earth, nestled in a dense cluster like candles lighting an immense chandelier. The cluster's galaxies dwelt in and around Norma, a forgettable southern constellation invented by an eighteenth-century astronomer best known for inventing forgettable southern constellations. Norma lies southwest of Scorpius, the striking zodiacal constellation that bears the brilliant red star Antares.

"The Norma cluster is like Manhattan in New York," said Kraan-Korteweg: "the business district with all the tall buildings." The cluster abounds with giant elliptical galaxies, the celestial equivalent of skyscrapers, which throng the richest galaxy clusters. The Norma cluster isn't the Great Attractor any more than Manhattan is New York City; it accounts for only a tenth of the Great Attractor's mass, but it does mark the monster's heart--supergalactic downtown.

Strangely, astronomers had catalogued the Norma cluster a few years earlier, but because of the Milky Way's dusty veil, they thought it only a minor affair. In actuality, the Norma cluster rivals the greatest clusters known, such as the famous Coma cluster, yet until recently no one knew it existed. "In astronomy," said Kraan-Korteweg, "there's still so much to explore."

Time after time, the universe has astonished those who explore it--offering hidden galaxy clusters, mysterious halos of dark matter, even a bizarre "antigravity" force that seems to pervade empty space. For millennia, of course, people have gazed heavenward and contemplated great cosmological questions--How did the universe begin? What is it made of? What will be its ultimate fate?--but only in the last hundred years have astronomers begun to acquire the data about the stars and galaxies that may answer these provocative questions.

The Universe at Midnight aims to tell this story of cosmological inquiry and discovery. During the day, scientists and philosophers can construct elegant theories of how they think the universe should operate; but at night, at midnight, when powerful telescopes swing toward distant galaxies, the universe delivers its verdict. Sometimes it validates existing observations and theories. Often, though, it repudiates them, forcing scientists to devise new conceptions of the cosmos. Drawing upon extensive interviews with the scientists who made the key discoveries, The Universe at Midnight tells the twisted, tangled, riveting story as it happened. It is part mystery novel, part detective story, part human drama. It is also, I hope, an up-to-date portrait of the state of cosmology today and how observers and theorists have arrived there. The book therefore proceeds chronologically, as one surprising discovery led to another. It starts with cosmology's oldest observation--of the darkness that falls every evening--and ends with the recent discovery that the universe's expansion may be speeding up.

Nearly half of The Universe at Midnight examines work from the past decade, illustrating how rapidly cosmology has progressed. But the book also sounds a note of caution, for this progress has often come at the expense of overturning previous truths. A hundred years ago, for example, astronomers thought that the universe was static, when today we know that it is expanding; forty years ago, they thought that the glittering stars within galaxies constituted the bulk of the universe, when today we think they are mere gems floating on a black velvet sea of dark matter; and ten years ago, they thought that the universe's expansion must be slowing, as the gravitational attraction of the galaxies braked its speed. Furthermore, some features of modern cosmology, such as the mysterious dark matter which sheathes the galaxies, and the repulsive force which seems to drive them apart, are so peculiar that they suggest crucial elements in cosmology remain missing. Although revolutionary discoveries add drama to the story, they also make one wonder which truths presented herein may themselves be overturned, the next time astronomers atop tall mountains point their telescopes at the heavens, at midnight.

From Ken Croswell's The Universe at Midnight. Copyright by Ken Croswell. All rights reserved.

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