The Universe at Midnight: Observations Illuminating the Cosmos - Hardcover

ONE: HIGH MIDNIGHT

Stars in my pocket like grains of sand
Radiant pinpoints, they sting my hand
I grab a fistful, a gift for the breeze
Who will carry them far and away with ease

-- WHITE WILLOW ("THE BOOK OF LOVE")

It is just before midnight, and stars spangle the sky: newborn stars emerging from magenta gas clouds, middle-aged suns dutifully towing planets through space, elderly red giants about to puff their atmospheres into the void. Every star the naked eye can see races around a giant black hole buried behind the dust clouds of the constellation Sagittarius. In the next hour, we too will dash half a million miles through space, as the Sun pursues its orbit around the Sagittarian black hole. The Sun, the Earth, and the canopy of stars all belong to the same celestial kingdom, the Milky Way, which boasts more stars than the Earth does people.

Yet most of the universe lies beyond the Milky Way. In the constellation Andromeda, a faint wisp betrays another Milky Way, another titanic empire of stars, planets, and possibly people, all anchored to one another by gravity. Call it a galaxy, after the Greek for "Milky Way." So distant is the Andromeda Galaxy that the light we see tonight set out from its spiral shores 2.4 million years ago, before the human race arose. Both Andromeda and the Milky Way belong to a flock of galaxies called the Local Group. Among Local Group galaxies, Andromeda ranks number one in size and brilliance, our own Milky Way number two -- not bad, since altogether the Local Group houses three dozen galaxies.

Yet most of the universe lies beyond the Local Group. Long ago, stargazers pictured a star pattern south of the Big Dipper's handle as a woman holding a spike of grain, and they named her Virgo. Here cluster thousands of galaxies that rule the center of a huge galactic metropolis which a maverick astronomer named the Local Supercluster. At the time, other astronomers didn't believe him, but in fact galaxies speckle the Local Supercluster the way stars do a galaxy, with the Milky Way residing near its edge. The Local Supercluster's most beautiful galaxies spin so fast that they whip up exquisite spirals and resemble celestial whirlpools. The Milky Way is a spiral, as is its partner in Andromeda. Other galaxies, less fortunate, look round or oval; they are called elliptical galaxies. And still others, less orderly, less organized, are dubbed irregular. When the light we see from the Local Supercluster's most remote galaxies set out into space, dinosaurs ruled the Earth.

Yet most of the universe lies beyond the Local Supercluster. An even larger supercluster drapes through the constellations Pisces and Perseus, and in the opposite direction a cluster of superclusters -- a superdupercluster? -- tries to pull us its way. Its name is the Great Attractor. Superclusters string the cosmos like glowing cobwebs, with vast voids of mostly empty space between. If galaxies were trees, the superclusters and the voids would be forests and meadows.

Far beyond the superclusters and voids, like the backdrop to a mighty play, shines the afterglow of the universe's creation, the redshifted remains of light that tore free of matter 300,000 years after the universe's birth. Tiny fluctuations in this light reveal that the early universe was not perfectly smooth. Instead, some regions were denser than others. The denser regions, through their gravitational force, attracted additional material, eventually conglomerating into the galaxies, galaxy clusters, and galaxy superclusters that adorn the cosmos today. The sparser regions lost material to the denser ones and became the voids.

COSMOLOGY: THE UNIVERSE AT LARGE

Beautiful though each star, galaxy, or supercluster is, cosmologists aim to understand the entire universe -- its origin, composition, evolution, and ultimate fate. This is no small task, but one that has tripped up astronomers before and will likely do so again. As one senior cosmologist said, "Cosmology and comedy, cosmic and comic, are not far apart."

Most of what cosmologists know about the universe they learned only in the last hundred years. Their observations indicate that the whole material universe -- what is now a myriad of stars, galaxies, and planets -- was once compressed into a single point that burst forth 12 to 16 billion years ago in the big bang. Relics of this primordial fireball lie close to home: the hydrogen in a glass of water -- the H in that H2O -- came from the big bang, the oxygen from brilliant stars that exploded billions of years afterward.

Ever since the big bang, the universe has been expanding. Each hour, 3 million miles of new space opens up between us and the Virgo cluster, 12 million miles of new space between us and the Pisces-Perseus supercluster. Not everything moves away, however. The Milky Way's gravity binds its stars to the homeland and even forces several smaller galaxies to revolve around it, colonies paying tribute to the Galaxy's empire. The Milky Way derives its gravitational muster from every star, every planet, every person within it: your weight contributes approximately 0.000000000000000000000000000000000000003 percent of the Milky Way's total, so if you left the Milky Way, its stars would revolve slightly more slowly, its satellite galaxies would swing around the Galaxy slightly more sluggishly, the Galaxy's grip on its farthest-flung outposts would be slightly less secure. Thank you for choosing to live in the Milky Way.

Gravity herds the entire Local Group, preventing its galaxies from fleeing the flock. Gravity might do the same to the universe itself. If the universe is dense enough, the gravity of all its galaxies will eventually halt its expansion. Then the universe will start to collapse, ending its days in a fiery inverse big bang -- a "big crunch." For decades astronomers have known that the universe harbors far more matter than meets the eye, dark material whose gravity tugs on the stars and galaxies. However, despite all this dark matter, the universe is not dense enough to collapse. Moreover, empty space seems to exert a repulsive force that speeds up the universe's expansion. If so, not only will the universe expand forever, it will expand forever faster. In only about 150 billion years, all galaxies beyond the Local Supercluster will vanish from the sky, because the space between them and us will be expanding so fast that their light can no longer reach the Earth.

These remarkable deductions come from large telescopes, some perched atop mountains, others lofted into space, that have helped decipher the tangled clues left behind in the wake of the big bang. The first cosmological observation, however, required no telescope at all. Look at the night sky: it is dark. Why?

Copyright © 2001 by Ken Croswell