A worker sets up the mold for LSST's huge main mirror.
Image courtesy of LSST Corporation
The heart of LSST is a main mirror 8.4 meters (about 28 feet) in diameter, which will, in a matter of seconds, register vanishingly faint objects in distant galaxies over an area spanning about 50 full moons. That huge bite will enable the telescope to scan the heavens far more quickly and deeply than any other previous research instrument, so rapidly that it will compile a set of digital sky images—a complete map of the half of the universe in its field of vision—in just three days. (To capture the other half of the universe would require an identical telescope halfway around the world.) By repeating this sequence over and over, LSST will record a nearly continuous movie of the heavens.
As Tyson and his colleagues envision it, LSST will keep a systematic record of everything it captures, effectively transferring the entirety of it to computer memory for posterity (hence synoptic, meaning “allowing to see the whole”). All of the pictures it takes will be available to anyone who wants them in a matter of minutes, and access will be as simple as leafing through a photo album. The technology—a kind of anytime, anywhere machine—could transform the practice of astronomy in a fundamental way. Instead of traveling to the site of a telescope, an astronomer will be able to call up the region of interest from a database whenever he or she wants. LSST will even mine data on its own: By scanning images automatically and comparing them with pictures of the same region taken earlier, it will recognize the sudden brightening of a star or an object in motion from frame to frame.
Unraveling the Mysteries of the Universe
Casting its unblinking gaze to the heavens, LSST will capture a wide sweep of cosmic events and unravel mysteries that have long gone unsolved. Take the inexplicable flashes of light that sporadically illuminate the night sky. On April 20, 2006, two small sky-monitoring cameras thousands of miles apart—one in Chile, the other in the Canary Islands—both recorded a bright starlike spot of light that rotated with the heavens for about 10 minutes before vanishing. Such flashes have been reported in the past by naked-eye observers and occasionally recorded on observatory images. Even so, some astronomers have hesitated to consider the flashes real; others, while granting their reality, have been reluctant to assign them deep significance. Yet soon enough, LSST’s remarkable imaging ability may tell us whether the flashes result from mundane local events—like sunlight glinting off a bit of satellite debris in orbit around Earth—or by a new and exotic type of stellar explosion halfway across the galaxy.
Cosmologists, meanwhile, say that LSST will help them measure the expansion of the universe, which seems to be propelled by an unseen force, a kind of “dark energy” that works against the force of gravity. Cosmic expansion and the dark energy thought to drive it can be studied by tracking the trajectory of light coming from faraway supernovas, extremely powerful stellar explosions. Most of the time observers do not see supernovas simply because no one is looking in the right direction, and cosmologists today “have just a few thousand of them on which their calculations can be based,” Ivezic says. “But LSST will give us 10 million supernovas to work with, vastly increasing the precision of that work.”
LSST will also help map the distribution of matter throughout the universe. This task is far more complicated than just taking a picture and counting all the bright things out there, because 90 percent of the material in the universe is in the form of mysterious dark matter that does not shine. Shiny or not, dark matter still exerts a gravitational force that bends light rays passing near it. As a result, light coming from a distant galaxy will be deflected by otherwise invisible globs of dark matter, causing it to appear stretched and deformed. The extent of the distortion indicates how much unseen matter is out there, pulling on the light.
With current telescopes, such subtle distortions are drowned out by far more intense distortions on the ground: the flexing of the telescope’s mirror as the temperature changes, for instance, or blurring caused by turbulent air above the observatory. As it stands, astronomers have found it difficult to sort the distant, cosmic distortions from the local events. LSST would solve the problem by taking several thousand pictures of the same area of sky. Distortions produced in the telescope itself will change from picture to picture, so by averaging the pictures in a computer—finding the distortions common to all—scientists can tease out the subtle effects and produce an accurate dark-matter map.
