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William A. Dent (1938–2020)

Dent discovered the variability of quasars and helped found the astronomy program at the University of Massachusetts, Amherst, pursuing radio astronomical studies of AGN variability.

Published onOct 02, 2020
William A. Dent (1938–2020)
<p>Bill Dent with students in 1969.</p>

Bill Dent with students in 1969.

William A. Dent died on Wednesday the 18th of March, 2020

The Astronomy Department at the University of Massachusetts, Amherst, is saddened to report the passing of retired Full Professor William A. (Bill) Dent. Professor Dent was a key founder of the observational aspect of the Astronomy Program at UMass Amherst. As a graduate student at the University of Michigan, Bill made the amazing discovery that the brightness of what were called quasi-stellar radio sources (quasars) varied with time. This required that the physical sizes of these objects be vastly smaller than had been postulated; many years later we have learned that quasars contain supermassive black holes, often with masses of billions of times the mass of our Sun.

The new astronomy program at UMass began in 1966 with the hiring of three theoretical astrophysicists. Clearly an astronomy program needed an observational component, and just as clearly New England was not a good location for traditional optical astronomy. Radio astronomy, where at most wavelengths the atmosphere is relatively transparent, was a possibility, if suitable faculty could be recruited. In 1968 two radio astronomers were hired, Bill Dent and Richard Huguenin. These two went in different directions in their research. Huguenin founded the Five College Radio Astronomy Observatory on the Prescott Peninsula in the Quabbin Reservoir, which has ultimately led to UMass participation in the Large Millimeter Telescope in Mexico.

Bill Dent instead took advantage of the university, becoming a charter member of the Northeast Radio Observatory Corporation (NEROC), founded in 1967. After its original goal of building a new, extremely large radio telescope was not successful, NEROC took over from the Air Force the operation of the 37-meter-diameter Haystack radio telescope in Westford, Massachusetts. Of the original 13 university members of NEROC, the most active universities using the telescope for many years were Harvard, MIT, and the University of Massachusetts (primarily because of the research programs of Bill Dent). In addition to the Haystack Observatory, Bill also utilized the National Radio Astronomy Observatory’s 36-foot telescope at Kitt Peak and the now-defunct 300-ft telescope at Greenbank in his frontline studies of the variations in brightness of quasars, now commonly known as Active Galactic Nuclei (AGN). He continued to publish significant research results in the major astronomical journals throughout his career, normally with funding from federal science agencies. Bill was a member of the International Astronomical Union and was active in three of its Divisions.

As a professor at UMass, Bill trained graduate students who have gone on, for example, to tenured faculty positions at American and Canadian universities and to important positions at the US National Science Foundation and the Space Telescope Science Institute. He was considered a great motivator of the graduate students, helping them relax via local swing dancing and once taking several canoeing through the Minnesota Boundary Waters. Bill was the chair of the committee for the student who was UMass’s first Black astronomy PhD recipient.

Bill’s colleagues also recall his trips to very exotic places and the very adventurous ways he traveled, including bus trips in Bolivia, a trek across northern Australia by all-terrain truck, hiking the Tonto Plateau of the Grand Canyon, a far-off-the-beaten-track portion of Canyonlands National Park in mid-summer, and a month-long trek to the Mount Everest region of Nepal.

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