The Telescope's Nervous System
In an unassuming building in Socorro, New Mexico, scientists operate a telescope with a lens the size of a continent. This is the Array Operations Center for the Very Long Baseline Array (VLBA), the central brain that controls ten identical radio antennas spread across North America, from Mauna Kea in Hawaii to St. Croix in the U.S. Virgin Islands. The distance between the farthest antennas creates an effective telescope 8,611 kilometers (5,351 miles) wide.
Each of the ten antennas is a 25-meter (82-foot) dish weighing 218 metric tons (240 short tons). When one points skyward, it is tall as a ten-story building. The other sites are in Washington, California, Arizona, New Mexico (one in Pie Town and one in Los Alamos), Texas, Iowa, and New Hampshire.
During an observation, all ten antennas point at the same cosmic object. The radio waves they collect are stamped with a precise time from an onsite atomic clock and recorded onto high-capacity hard drives. These drives are then shipped to the Socorro center. Here, the immense task of combining the data begins. This technique, known as Very Long Baseline Interferometry (VLBI), allows the ten separate dishes to function as a single, enormous instrument. The construction of the VLBA was completed in May 1993, with the first ten-antenna observation taking place on May 29, 1993.
The Digital Correlator
The center of the Operations Center is the correlator, a specialized supercomputer that is the telescope's primary lens. Its function is to combine the petabytes of data arriving from the ten antennas. By comparing the arrival times of the same radio wave signal at each dish, the correlator can pinpoint the source's position with extraordinary accuracy.
The resolving power of the VLBA is immense, capable of seeing details as small as 0.17 milliarcseconds. This is equivalent to standing in New York City and being able to read a newspaper in Los Angeles. This resolution allows astronomers to directly measure distances to objects on the far side of the Milky Way, more than 66,000 light-years away, by measuring the tiny apparent shift in a star's position as the Earth orbits the Sun.
This precision has produced major astronomical results. The VLBA has provided some of the most conclusive evidence for supermassive black holes at the centers of other galaxies by mapping the motion of water molecules orbiting them. It tracks the movement of Earth's tectonic plates to within fractions of an inch by observing distant quasars. The array also creates detailed maps of our own galaxy's spiral arms and measures the influence of dark energy by calculating distances to objects billions of light-years away.