Ultimate map to stars’ homes
It’s fair to say that Dan Long has seen more of the universe than anyone but God.
Month after month, year after year, Long has sat in a windowless room atop a windy mountain peak, watching the heavens scroll by on 12 monitors connected to the Apache Point Observatory’s 98-inch telescope.
He saw stars, galaxies and clusters of galaxies banded together like giant herds of animals on an unending savanna roll by. Less frequently, exotic denizens of deep space would pop up -- blinding quasars and supernovae, flaring up as brightly on the bank of TV screens as entire galaxies.
“You get a sense of how big it is out there,” said Long, a genial 46-year-old astronomer. “If you didn’t already feel small, this would do it.”
This summer, after eight years of charting the cosmos, Long and his colleagues completed the deepest, most comprehensive map of the heavens ever produced.
Known as the Sloan Digital Sky Survey, it is a remarkable three-dimensional model of the universe that allows an observer to travel, as if by rocket ship, from the dwarf galaxies hugging the skirts of the Milky Way to the frontier campfires of the most distant quasars, blazing billions of light-years away.
In its 5 terabytes of data are 217 million individual objects, including 800,000 galaxies (which themselves contain billions of stars and planets) and 100,000 quasars -- creatures once so rare and strange that they weren’t even detected until 1962.
“Nobody’s ever done anything like this before,” said Bruce Gillespie, administrator of the Astrophysical Research Consortium, made up of 300 astronomers who helped carry out the $100-million sky-mapping project. “They’ll still be looking at this data in 50 years.”
Among the survey’s notable achievements has been helping to confirm the existence of dark energy, the mysterious force believed to be causing the universe’s expansion. The survey also has shown that the universe is flat and has lent weight to the big-bang theory that the universe began with a single explosion, followed by rapid inflation that continues to this day.
But perhaps its greatest achievement has been to bring a sense of order to the seemingly undefined vastness of the universe.
Like the great cartographers of the past who turned apparently limitless seas and unknown continents into familiar terrain, the Sloan astronomers have struggled to make that most unfathomable of places -- the universe -- as navigable as the local shopping mall.
“The joke we’ve always had is that if you rotate the galaxies in just the right way,” Gillespie said, “you’ll see the face of Elvis.”
The Sloan telescope is about 100 miles from the nearest big city, El Paso, atop a paradise of soaring ponderosa pines and Douglas firs.
The Sacramento Mountains rise like brilliant green drapery out of the gray carpet of the New Mexican desert. Below, a desert expanse as large as Massachusetts stretches to the horizon. On one side is the White Sands Missile Range; on the other, the town of Roswell, home to the modern UFO movement. At night, a deep blackness descends.
About half of the project’s observers have left over the years. “For the observers who haven’t lasted long, isolation is a major reason,” said Stephanie Snedden, who spent nearly as many nights at the telescope controls as Long.
The Sloan survey was the brainchild of Jim Gunn, a 69-year-old astrophysicist at Princeton University and one of the world’s leading experts on galaxy formation.
Before Sloan, the most authoritative map of the heavens in visible light was the Palomar Observatory Sky Survey, which from 1950 to 1957 mapped the Northern Hemisphere’s night sky with the 48-inch Samuel Oschin Schmidt telescope. The result was a master reference work for amateur and professional stargazers alike.
But by the mid-1980s, it was out of date. Radio, X-ray and infrared astronomers had launched their own sky surveys, some of which surpassed Palomar in breadth and detail.
“There was a little embarrassment” among optical light astronomers, Gunn said. “We were decades behind.”
Another motivating factor, Gillespie said, was a seminal discovery in the 1980s: Galaxies, once thought to be the largest structures in the universe, sometimes formed clusters. “This was a hint of larger structures in the universe,” Gillespie said.
It was unclear what those gigantic structures might be, but the hope of finding them gave impetus to Gunn’s plans.
With grants from the Alfred P. Sloan Foundation, the National Science Foundation, NASA and the Department of Energy, Gunn began designing a new telescope capable of capturing four times as much light as the Oschin instrument at Palomar.
Gunn’s goal was to map 1 million galaxies.
As ambitious as it was, the new survey would contain blind spots. The great river of stars in the Milky Way galaxy cut through the night sky, obscuring a chunk of the universe behind it. Further, the telescope’s location in the Northern Hemisphere meant that most of the sky in the Southern Hemisphere would remain terra incognita.
The most daunting part of the survey was determining the distances to objects, so that the map could be constructed in three dimensions.
Astronomer Edwin Hubble discovered nearly 80 years ago that the farther away a star or galaxy, the more its light is shifted toward the red end of the spectrum. But determining the red shifts of millions of objects? Gunn and his collaborators realized that could take hundreds of years.
Gunn’s team came up with a simple solution. By feeding the image of the sky through aluminum plates with holes drilled to match the placement of stars and galaxies, the team could analyze 640 objects at a time.
Each morning, scientists at the University of Chicago sent orders for the objects they wanted measured. The physics lab at the University of Washington drilled the holes and sent the plates to Apache Point, where a team of plate-pluggers connected light-sensitive fibers to each hole.
To make the work more manageable, the team chose about 1.4 million of the most interesting objects in what Gunn called “the relatively near universe” -- within 2 billion light-years of Earth.
Metaphorically, Sloan was designed to take the study of the cosmos from the age of Herodotus and Marco Polo, with their tales of fabulous creatures and strange lands, to the modern era, when the careful cartographers traveling with Magellan and Da Gama marked the true dimensions of our planet.
If the telescope at Apache Point is a ship on a voyage of discovery, then Long has been its chief helmsman, steering through the endless eddies and currents of stars.
The son of an artist for Hallmark cards, Long was a typical science geek who dug for fossils as a child in the 300-million-year-old rocks near his home in Overland Park, Kan.
He started work at Apache Point in 1992, and grew accustomed to the endless routine.
From two hours before sunset to an hour past dawn, two observers sat in the control room, monitoring weather and conditions in the telescope. They were known as the pilot and copilot, or, more sardonically, the warm observer and cold observer, so named because when any work needed to be done at the telescope, it was the cold observer who went outside and did it.
Snedden, 58, was still finishing her doctorate in astronomy at the University of Nebraska when she joined the team at Apache Point in 1999. She took to the solitary life of a telescope observer as if born to it.
“You’re sitting there and these images are drifting by,” said Snedden, a former cabdriver and karate instructor. “You see a fuzzy blob and you know it’s another galaxy like ours, and it’s never been seen before. I call them God’s dust bunnies. It just sends a chill down your spine.”
Workers from other parts of Apache Point would often stop in for a peek.
“Everybody on the project who sat in the control room has felt that sense of awe, that we were part of something that had never been done before,” Snedden said. “Basically, it was the universe looking at itself.”
The list of discoveries by scientists using Sloan data include the most distant quasar ever found, as well as evidence that the Milky Way was formed by cannibalism in neighboring galaxies. Sloan also uncovered many more dwarf galaxies around the Milky Way than were thought to exist.
Large-scale cosmological discoveries include great expanses of nothingness, known as voids. The survey also found large numbers of galaxies clustered together, as if seeking companionship. The most massive structure of all is the “Great Wall,” a huge collection of galaxy clusters strung out in a huge filament arcing across the night sky, about 600 million light-years away.
In March, the last of the 3,000 or so aluminum plates was plugged. In July, the entire Apache Point team assembled for prime rib at the Lodge, a turn-of-the-century inn just down the road in Cloudcroft.
For Gunn, it was the culmination of two decades of labor. Seeing the project come to a successful conclusion has been “enormously rewarding,” he said.
But even as the Sloan collaboration prepares to launch the project’s next phase -- a six-year survey looking more deeply at galaxy clustering and the chemistry of the Milky Way -- Gunn has been wrestling with an unsettling mystery.
Despite all of the Sloan discoveries, none has challenged the prevailing theories about how the universe got started and how it operates today, he said.
Could it be that humankind actually understands the structure of the universe? Or could all the labor and thought behind Sloan still be too primitive to pierce the real mysteries of the cosmos?
The questions haunt him.
“We discovered lots of things, but I don’t think we found much that we didn’t expect,” he said. “I’m not sure what that says.”
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