Alfred E. Glassgold

Alfred Glassgold, an atomic and nuclear physicist who became an astrophysicist and astrochemist, died in San Francisco on 4 January 2019. His work progressed from atomic nuclei and superfluidity, to interstellar clouds and circumstellar envelopes, to winds from young stars and the birthplaces of planets, illuminating our understanding of these regions of the cosmos. A versatile physicist who was active in teaching and research well into his 80s, he was also a treasured colleague and mentor.

Born 20 July 1929 and raised in Philadelphia, Al was an accomplished clarinetist who initially considered a career in music but ultimately chose physics as his lifelong pursuit. As an undergraduate, he majored in physics at the University of Pennsylvania. He later studied theoretical nuclear physics with Victor Weisskopf’s group, obtaining his PhD from MIT in 1954. For his postdoctoral studies, Al moved to UC Berkeley, where he worked on problems in statistical mechanics with applications to atomic physics, superfluidity, and nuclear physics. For a few years, he taught physics courses to UC students with Edward Teller.

In 1963 Al moved with his wife and two children to New York, where he joined the physics faculty at NYU. He was an integral member of the university for 36 years, serving as head of the academic senate as well as chair of the physics department during an important period when the department was growing rapidly and its new building was planned and constructed.

Although his initial background was in atomic and nuclear physics, Al’s research interests turned to astrophysics in the early 1970s, as a result of the detection of interstellar molecules made by the Charles Townes group using microwave techniques, as well as UV observations of interstellar molecules made from space. Simple interstellar molecules had been detected in absorption as early as 1937. However, the detection of molecular emission and the discovery of polyatomic molecules (e.g., ammonia, water) opened up many new avenues of study.

Inspired to use his knowledge of atomic physics to understand the physical conditions in the interstellar medium, Al went to UC Berkeley for a summer to work with Townes, who shared his interest in this topic. It was the beginning of Al’s career as an astrophysicist and an astrochemist. Throughout the 1970s and 1980s, Al and his collaborators, students, and postdocs studied the thermal, chemical, and ionization structure of interstellar clouds and the circumstellar envelopes of late-type stars.

In 1990 Al spent a sabbatical year at UC Berkeley, and his research interests changed direction once again. At the time, Berkeley was a lively focal point for studies on the origins of stars and planets. Al’s astrochemistry expertise complemented the theoretical and observational interests of the star and planet formation group, and he began long-term collaborations with Frank Shu and others. Al’s insights contributed to our understanding of the important role atomic winds play in driving molecular outflows and solving a star’s “angular momentum problem,” i.e., understanding how stars remove enough angular momentum to allow their assembly to proceed.

Al’s work on winds also led to studies of protoplanetary disks, the rotationally supported structures around young stars that are the birthplaces of planets. Over the past two decades, he led fundamental work on the ionization structure of disks as well as the molecular and atomic diagnostics that are used to understand their chemical and dynamical nature. These studies demonstrated that stellar x rays, not cosmic rays, are primarily responsible for disk ionization. The ionization structure of disks governs how they interact with magnetic fields and how they evolve dynamically. Further studies on disk chemistry illustrated how water and other simple molecules can be synthesized in disk atmospheres, and how atmospheres can be heated enough to produce observable emission features, i.e., the signposts that provide clues to their nature.

Much of this later work was carried out after 2000, when Al retired from NYU and joined the UC Berkeley astronomy faculty. He continued to teach and advise students and postdocs until just a few years ago. Throughout his life, Al read widely on all subjects and enjoyed music, art, and food. Since moving to San Francisco, he had also been closely involved in the political life of the city.

Al is remembered not only for his research accomplishments but also as a treasured mentor and colleague. Unfailingly polite and with a playful sense of humor, he welcomed and encouraged colleagues of diverse backgrounds, including many women astronomers. He is survived by his wife, Irene, and children, Judith and Eric Glassgold. He is much missed.