More than fifty years ago, the NRAO had its genesis in a conference organized by Associated Universities, Inc. (AUI) President Lloyd Berkner. Convened at AUI’s New York City office on May 20, 1954, this seminal meeting grew out of informal discussions among scientists from Harvard University, the Massachusetts Institute of Technology, the United States Naval Research Laboratory, Columbia University, and the Franklin Institute on what was perceived as an urgent need for a radio astronomy research facility. Attended by 37 scientists and engineers from 28 U.S. institutions, this conference led to the signing of a contract for a national radio astronomy facility just two and a half years later, on November 17, 1956. The signers were National Science Foundation Director Alan T. Waterman and AUI President Berkner, who became the Acting Director of the Observatory.
This contract formally launched the NRAO, and events proceeded quickly. Groundbreaking took place at Green Bank on October 17, 1957; the Howard E. Tatel 85 Foot Telescope was dedicated just a year later; the 300 Foot Telescope began astronomical observing on September 21, 1962; and Sebastian von Hoerner made the first scientific observations with the new 140 Foot Telescope in May 1965. We have never looked back, and the official NRAO history now includes five decades of service to the community alongside our world-class facility development and operations at these telescopes and the Green Bank Interferometer, the 36 Foot / 12 Meter Telescope, the Very Large Array, the Very Long Baseline Array, and the Green Bank Telescope. Through five decades of research, the NRAO telescopes and instrumentation have enabled astronomers from all over the world to contribute to progress in virtually every field of modern astronomy. For example, the NRAO telescopes along with their sensitive receivers played a pivotal role in unveiling the importance and pervasiveness of the molecular phase of the interstellar medium. The detection of the first interstellar organic molecule, H2CO, with the 140 Foot Telescope in Green Bank and the first detection of the CO molecule in the Milky Way and external galaxies, with the 36 Foot Telescope on Kitt Peak in the early and late 1970’s, respectively, led to the discovery of molecular clouds and the eventual recognition of their importance to star formation and galaxy formation. ALMA is being built to explore this “Molecular Universe.”
The NRAO played an important role in the development of Very Long Baseline Interferometry, which led to the discovery of superluminal expansion in compact radio sources due to relativistic outflows from active galactic nuclei, which is important evidence for the super-massive black hole paradigm. The NRAO Very Long Baseline Array (VLBA) enabled measurements of the relativistic phenomenon of gravitational bending with unprecedented accuracy. Imaging of water mega-maser emission in the nucleus of the Seyfert galaxy NGC 4258 by the VLBA provided the first direct observational evidence for a Keplerian thin accretion disk rotating about a supermassive black hole and an independent determination of the distance to NGC 4258. A project to determine the Hubble Constant to < 3 percent accuracy has recently been proposed using the VLBA which has a remarkable, but perhaps under-appreciated, astrometric precision at the few micro-arcsecond level. A high precision Hubble Constant is the one of the most important measurements that can help constrain the equation of state of Dark Energy.
The sensitivity of the Green Bank 100m Telescope has helped to drive the recent resurgence of exciting pulsar research, such as precise measurements of the new double-pulsar, and the discovery of the fastest millisecond pulsar among the 33 pulsars discovered in a single globular cluster, Terzan 5. Other GBT observations have tested whether Nature’s fundamental constants vary with time, uncovered remarkable small scale structure in the Galactic HI halo, discovered multiple biologically-significant molecules, and a water giga-maser from a Type II quasar at z = 0.66. The measurement of distances to galaxies at z ~ 1, using such giga-masers, would help to determine the rate of expansion of the Universe, which is a very strong science case for the Square Kilometer Array (SKA).
The unprecedented sensitivity and resolution at centimeter wavelengths brought by the VLA ushered in a new era in which pictures of radio sources are comparable in resolution to optical images, giving astronomers the capability to discover the remarkable spiral-shaped plasma falling towards the Galactic center, enigmatic stellar pairs that are micro-quasars, and unmatched details in the structure of radio galaxies. The VLA, by pinpointing and measuring the spectral energy distribution of the after-glow radio emission of gamma-ray bursters (GRB), helped unravel the nature of both the long and short duration GRBs, a major scientific puzzle for more than three decades. Observations of neutral hydrogen with NRAO telescopes permitted the exploration of individual galaxy rotations curves to large radii, yielding one of the early hints of dark matter’s existence in galaxies.
Using the VLA at a frequency well beyond its design goal, astronomers have been able to image the distribution of CO molecules surrounding a quasar at z = 6.42, currently the highest redshift quasar known, revealing the physical conditions of gas surrounding a quasar in the earliest epoch of structure formation in the Universe. The study of galaxies and quasars in the earliest stages of formation will become more practical with the completion of the Atacama Large Millimeter / Sub-millimeter Array (ALMA) and the Expanded Very Large Array (EVLA).
In the near-term, the ALMA will be used by astronomers from around the world. Providing extraordinary sensitivity and resolution in the millimeter and sub-millimeter wavelength range, ALMA will probe the origins of stars and planets, and image the earliest galaxies. At longer wavelengths, the EVLA will extend the VLA’s research capabilities across its entire radio spectrum through a ten-fold increase in continuum sensitivity, or a 100-fold increase in speed, vastly improved spectral resolution and coverage, and sub-arcsecond angular resolution. The NRAO will strive to support the astronomy community by providing more than simply telescope time. We will collaborate with research groups in the community on new instruments and projects. We will endeavor to help train the next generation of astronomers, especially those who would be proficient with instrumentation, via student, co-op, postdoctoral and Fellowship programs. And, as part of our drive to make the Observatory more user-friendly, a coherent data management system is being built by the NRAO so that its data products are available community-wide for research and educational purposes to every user of the National Virtual Observatory.
The NRAO will continue to enable transformational research, supporting our users in their quest to explore new scientific frontiers, as well as operating and maintaining NRAO’s facilities as world-class tools that will serve the research of astronomers from the U.S. and the world for decades to come.
Fred K. Y. Lo