Correction

RETROSPECTIVE Correction for “ (1931–2018),” by Harvey Tananbaum, Ethan J. Schreier, and Wallace Tucker, which was first published June 4, 2019; 10.1073/pnas.1902399116 (Proc. Natl. Acad. Sci. U.S.A. 116,12587–12589). The authors note that on page 12587, right column, first full paragraph, line 4, “June 12, 1962” should instead appear as “June 18, 1962.” The online version has been corrected.

Published under the PNAS license. Published online August 26, 2019.

www.pnas.org/cgi/doi/10.1073/pnas.1913677116

18148 | PNAS | September 3, 2019 | vol. 116 | no. 36 www.pnas.org Downloaded by guest on September 27, 2021 RETROSPECTIVE

Riccardo Giacconi (1931–2018) RETROSPECTIVE

Harvey Tananbauma,1, Ethan J. Schreierb, and Wallace Tuckera

Riccardo Giacconi, the “Father of X-ray Astronomy,” experience and the failure of Nobel laureate, and one of the most influential figures other groups to detect X-rays in over the past 60 years, died on Decem- from beyond the Solar System ber 9, 2018, at the age of 87. With a career spanning led him to consider ways to the electromagnetic spectrum, Riccardo opened up concentrate weak X-ray sig- new windows for observing the universe and revolu- nals (i.e., how to build an X-ray tionized “big astronomy.” Many in the astronomy telescope). Drawing from previ- community continue to base their research on data ous considerations of potential from observatories that he conceived, built, and/or X-ray microscopes by Hans directed. Wolter (2), Riccardo quickly Riccardo’s outstanding scientific capabilities were concluded that a parabolic Riccardo Giacconi at the rostrum of the well matched by his extraordinary leadership and mirror could focus X-rays im- Chandra Symposium held in Huntsville, management skills. He had a deep belief in a scientific pinging at near-grazing inci- Alabama on September 16, 2003. Image courtesy of NASA/Marshall Space Flight approach to problem solving and to establishing sys- dence angles, while Rossi Center. tematic processes. He insisted that instruments and added the notion of nesting observatories be built to answer driving scientific surfaces to increase the col- questions. Another key to his success was the legend- lecting area (1). Riccardo undertook a research pro- ary dedication and drive of the research teams that he gram using two reflecting surfaces to design and assembled, which could be traced directly to Riccardo’s build a fully imaging X-ray telescope. deep commitment to establishing an environment of Meanwhile, in work with Frank Paolini and Herbert intellectual honesty and trust. Gursky, he developed detectors with a much wider Born in Genoa, , on October 6, 1931, Riccardo field of view and about 50 times more sensitivity than received his doctorate in 1954 from the University of ones flown previously. On June 12, 1962, their rocket Milan. At that time, the only practical way to study payload detected a strong source in the direction of high-energy nuclear reactions was through the de- the constellation Scorpius, which they named Scorpius tection and analysis of the interaction of high-energy X-1. They also discovered an all-pervasive X-ray cosmic rays, primarily protons, with atomic nuclei in background radiation. the atmosphere. For his thesis research, he spent Riccardo moved quickly to exploit this new window about two years at the Testa Grigio Observatory for exploring the universe, proposing with Gursky a (elevation: 3,500 meters) in the Italian Alps and bold five-year X-ray astronomy program that included obtained 80 high-energy cosmic ray detection events. more rocket flights, an X-ray satellite to survey the Although he learned much about the conception, entire sky, and eventually, an X-ray telescope. Apply- design, and building of detectors, Riccardo was ing his strong conviction and remarkable persistence, frustrated by the lack of “action.” Riccardo persuaded NASA to support the initial A Fulbright fellowship brought Riccardo to the phases of the program. , where he worked at Indiana and With funding from NASA, Riccardo’s group devel- Princeton before joining American Science and Engi- oped and operated the first X-ray satellite, Uhuru, neering (AS&E) in Cambridge, Massachusetts, in Sep- launched on December 12, 1970. Riccardo continued tember 1959. Shortly thereafter, AS&E Board Chair to refine what he termed a science systems engineer- and Massachusetts Institute of Technology Professor ing approach. Engineers and scientists worked side by suggested at a party that Riccardo look side to establish requirements, develop a design, con- into the possibility of developing a program to search struct and test the hardware, and plan the operations for sources of cosmic X-rays. Riccardo’s thesis research for the satellite. Even before launch, the team (which

aHigh Energy Astrophysics Division, Smithsonian Astrophysical Observatory, Cambridge, MA 02138; and bPrivate address, Baltimore, MD 21217 Author contributions: H.T., E.J.S., and W.T. wrote the paper. The authors declare no conflict of interest. Published under the PNAS license. 1To whom correspondence may be addressed. Email: [email protected].

www.pnas.org/cgi/doi/10.1073/pnas.1902399116 PNAS Latest Articles | 1of3 the authors of this retrospective joined in the late from his X-ray group to the optical community, Riccardo 1960s) also developed software to analyze the data, recruited Ethan Schreier to oversee the Hubble opera- which enabled us to rapidly rearrange the observing tions and data system. Riccardo proceeded to build an schedule and satellite configuration to follow-up and entire new institute from scratch, assembling a core exploit discoveries. staff with expertise in the operational, engineering, On a personal level, although junior scientists, we and scientific disciplines necessary to operate Hubble. three and several colleagues received assignments Innovations introduced by Riccardo and his staff for that challenged us to our limits while providing Hubble included a formal data archive with a funded opportunities to develop technical, management, data analysis program, the distribution and archiving of scientific, and communications skills. Riccardo met calibrated data, an artificial intelligence-based planning weekly with the Uhuru science group. In these often- and scheduling system, reserved time for large and stormy sessions, there was wide-open give and take. “key” programs, and freely distributed portable data Ideas were floated with abandon and shot down analysis software. remorselessly. There was respect for one and all, but However, NASA and the telescope subcontractors no one was sacrosanct, and everyone, including Riccardo, did not conduct a prelaunch end-to-end test for Hub- had to defend his ideas based on logic and scientific ble. Shortly after launch, the well-known flaw in the merit. optical system was discovered. With NASA’s support While the all-sky catalog of more than 300 newly and Riccardo’s guidance, both near- and long-term discovered X-ray sources achieved one of the primary solutions were developed, and by the early 1990s, mission goals, the most significant result from Uhuru Hubble had become one the most productive tele- was the revelation that luminous X-ray sources (such as scopes ever. Riccardo instituted the first community- Scorpius X-1) were powered by accretion onto com- operated grants program to support Hubble users and pact stars in binary systems. One of those stars, Cyg- a “Hubble Fellows” program to support young astron- nus X-1, provided the first compelling evidence for the omers. Both of these became models for other mis- existence of black holes. sions and disciplines. Riccardo also recognized the The merging of X-ray astronomy into the main- importance of sharing scientific discoveries and beau- stream of astronomy was accelerated in the late 1970s tiful images with the public and instituted a vigorous by the launch of the Einstein Observatory, with Ric- public outreach program for Hubble. cardo as Principal Investigator. By then, he had moved In 1993, Riccardo was recruited as director gen- with a core group to the Harvard–Smithsonian Center eral of the European Southern Observatory (ESO), for Astrophysics (CfA). The Einstein Observatory’s im- where he oversaw the building of the Very Large aging capabilities revealed that essentially all types of Telescope and applied his practiced science system astronomical objects from nearby stars to distant qua- engineering to fully reorganize ESO, introducing sars radiate X-rays. Riccardo also initiated a guest modern management techniques to ground-based observer program, enabling all astronomers to use optical astronomy. He also set ESO on a path to Einstein Observatory. This model, new at the time, working with global partners on the Atacama Large has now been widely adopted. Millimeter/Submillimeter Array (ALMA), which would In 1976, cognizant of the limited lifetime projected become the world’s largest ground-based observa- for Einstein Observatory, Riccardo and Harvey Tanan- tory. In 1999, Riccardo returned to the United States baum proposed its successor, the Chandra X-ray Ob- to serve as president of Associated Universities Inc., servatory. Launched in 1999 and now in its 20th year the managing organization of the National Radio As- of operation, the Chandra X-ray Observatory remains tronomy Observatory. There, he played a leading without peer in the X-ray band for its subarc-second role in negotiating the governance structure for angular resolution and its sensitivity for studying ob- ALMA, a truly worldwide collaboration involving jects as diverse as exoplanets, neutron stars, black North America, Europe, and East Asia. Before he re- holes, clusters of galaxies, dark matter, and dark en- tired in 2004, construction was initiated on the Ex- ergy. Although Riccardo would move on to new chal- panded Very Large Array and ALMA. lenges, he remained involved with the Chandra X-ray Riccardo always set future directions before he Observatory, pursuing the soft X-ray background radi- moved on: technology work for Chandra was under- ation discovered in 1962. This research shows that the way when he left CfA, studies had been initiated for X-ray background is primarily produced by the accret- what became the James Webb Space Telescope be- ing supermassive black holes in galaxies distributed fore he left STScI, and the European Extremely Large near and far across the sky. Telescope and ALMA were being planned when he In 1981, Riccardo became the first director of the left ESO. He was able to work effectively and lead Space Telescope Science Institute (STScI) and pro- teams in a wide range of venues—industry, govern- fessor of astrophysics at . The ment/nonprofit research centers, universities, insti- scientific community had insisted that the scientific tutes run by university or multinational consortia, and operations of a large, unique, and expensive new management organizations. facility—the first major international optical observa- Before it became the norm, Riccardo encour- tory in space, later to be christened Hubble—be man- aged diversity. A number of women started their aged by the community itself (3). Recognizing the scientific careers as part of his X-ray group or at need to transfer the scientific operations philosophy STScI, and several now occupy some of the most

2of3 | www.pnas.org/cgi/doi/10.1073/pnas.1902399116 Tananbaum et al. senior positions in astronomy. He strongly supported (with astrophysicists Raymond Davis Jr. and thefirstWomeninAstronomyWorkshopandconceived , who were honored for research of the Baltimore Charter for Women in Astronomy. on cosmic ) “for pioneering contributions to Riccardo was elected to the National Academy of astrophysics, which have led to the discovery of cos- Sciences in 1971 before his 40th birthday. He re- mic X-ray sources.” ceived the 1980 Franklin Institute Elliott Cresson In summing up his career, Riccardo said: “Iam Medal, the 1981 American Astronomical Society grateful to live in this heroic era of astronomy and to Dannie Heineman Prize for Astrophysics and Henry have been able to participate and contribute to its Norris Russell Lectureship, the 1981 Astronomical evolution” (4). Society of the Pacific , the 1982 Gold Medal of the Royal Astronomical Society, the 1987 Acknowledgments , and the 2003 National Medal of Adapted with permission from refs. 5 and 6, which were originally Science. In 2002, he shared the for published by Physics Today and Scientific American, respectively.

1 R. Giacconi, B. Rossi, A telescope for soft X-ray astronomy. J. Geophys. Res. 65, 773–775 (1960). 2 H. Wolter, Spiegelsystem streifenden Eingalls als abbildende Optiken fur Rontgenstrahlen. Ann. Phys. 445,94–114 (1952). 3 National Research Council, Institutional Arrangements for the Space Telescope: Report of a Study at Woods Hole, Massachusetts, July 19–30 (The National Academy Press, Washington, DC, 1976). 4 R. Giacconi, Secrets of the Hoary Deep (The Johns Hopkins University Press, Baltimore, 2008). 5 E. J. Schreier, H. Tananbaum, W. Tucker, Riccardo Giacconi. Phys. Today 72, 71 (2019). 6 W. Tucker, E. J. Schreier, H. Tananbaum, “Remembering Riccardo Giacconi: A titan of the heroic age of astronomy.” Scientific American (2018). https://blogs.scientificamerican.com/observations/remembering-riccardo-giacconi-a-titan-of-the-heroic-age-of- astronomy/?redirect=1. Accessed December 31, 2018.

Tananbaum et al. PNAS Latest Articles | 3of3