Professor James M Moran - Inspec Ruby Author

Harvard Smithsonian Center for Astrophysics

I think about half of the faculty members in Harvard's Department of astronomy have been publishing for more than forty years, and I am sure you have captured them all. It is perhaps an unfortunate demographic!

I have an idea that may interest you. The technique of Very Long Baseline Interferometry(VLBI) was developed in radio astronomy in 1967, which almost corresponds to your 40 year window. In this technique, signals from very compact astronomical sources are carefully recorded on tape (now disk storage) with coherence maintained by atomic frequency standards. These data were later cross-correlated to determine the size of the source and to build up its image.

In 1969 the techniques was done by ad hoc collaborations of up to 6 antennas and the recording bandwidth was 750 kHz. The technology has steadily improved. Now there is a dedicated array known as the VLBA, which is augmented by extra stations sometimes for as many as 18 stations. The detector sensitivities are 2 orders of magnitude better and bandwidths have gone to more than 1 GHz. That is an overall sensitivity improvement of over 104 in 40 years.

More importantly, the technique has been used to measure the mass and rotation rate of our galaxy through very precise astrometric measurements (a few tens of microarcseconds). Just last year an experiment at 230 GHz gave an unprecedented angular resolution of 50 microarcseconds (1000x finer than Hubble), and produced the first crude image of the emission from the immediate environment of the black hole in the center of our galaxy (see Nature, Doeleman et al., 455, 78, 2008 ("Event horizon scale structure in the super massive black hole candidate at the galactic centre").

I have worked on developing VLBI as a technique and participated in many scientific research programs over the past 42 years. There is a lot of visual material at the Center for Astrophysics in Cambridge MA, and at nearby Haystack Observatory, where much of the technical work was pioneered.