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Home , Leon Mestel, Maarten Schmidt

RETROSPECTIVE RETROSPECTIVE

Donald Lynden-Bell (1935–2018)

Martin J. Reesa,1

Donald Lynden-Bell was lucky in his heredity and his film-maker, Alison Rose, accompanied them and created environment. His great-grandfather knew the famous a movie called Star Men,inwhichtheprotagonists(all astronomer John Herschel. His father, an army Colo- elderly) reminisced about life, the universe, and every- nel, inherited a telescope and introduced Donald to thing. Donald, a keen mountaineer in his youth, enjoyed the wonders of the sky. At his school, Marlborough making this movie and spoke at several special showings. College, Donald was exceedingly well taught. He came But the most important event for Donald in his up to Clare College to read mathematics. In his second postdoctorate years was his marriage to Ruth in 1961. year, he was supervised by the great physicist Abdus She moved to California to finish her chemistry doctor- Salam, who advised him to divert for a year to study ate, but they both returned to in 1962. physics, which Donald did before returning to mathe- Donald then became an assistant lecturer in matics for his fourth year. He thereby had a superb mathematics and a Fellow of Clare College. I attended launching-pad for research. his course on statistical mechanics. It was one of his Donald’s doctoral supervisor was Leon Mestel, a favorite subjects and he gave spirited performances. world expert on cosmic magnetism. But Donald found But Donald felt his teaching obligations didn’t leave Leon’sproblems“too intractable,” so instead he began to enough time for research, so he soon moved to the forge his lifetime interest in stel- Royal Observatory at Herstmonceux in Sussex. lar dynamics: how swarms of It was there that Donald’s most-quoted paper ges- stars configured into the distinc- tated (2): his prescient idea that massive black holes tively shaped clusters and galax- lurk in the centers of , and shine brightly ies that populate the cosmos. because gas gets heated by viscous friction as it swirls At that time the British had down into them. This was a key to understanding the no access to world-class opti- mysterious , discovered a few years earlier by cal telescopes; California was Maarten Schmidt at the California Institute of Technology. the mecca for astronomers. So Forty years later, Donald and Schmidt shared the first after Donald got his doctorate Kavli International Prize in astronomy. in 1960, he spent 2 formative In 1972 Donald moved back to Cambridge to direct years in Pasadena, California, the new Institute of Astronomy, which merged where he had the luck to “click” Cambridge’s long-established Observatory with the with Allan Sandage, the high adjacent theoretical institute founded 5 years earlier by priest of astronomy at that time. . This was a challenging period because Their joint project led to Donald’s Hoyle’s funding had expired and it was hard to pay first really famous paper (1): infer- the staff. ring how our I was then at Sussex University, but a year later was formed from a primordial spin- elected to the other Chair in the Institute. This couldn’t ning gas cloud, and what we have happened without Donald’s approval and it was could learn about its history from a privilege and pleasure to be his colleague. For more the orbits of the oldest stars. than 20 years we alternated harmoniously as director. WhileinCalifornia,Donald Our discussions on administration were generally met other British astronomers. enlivened by zany digressions into whatever scientific Fifty years later, four of them puzzle was on his mind. Donald Lynden-Bell. Image courtesy of had a reunion: they retraced a Donald cared about all of the staff and students ’ Amanda Smith and the Institute of mountain hike they dmade and about ensuring a friendly atmosphere. He cared Astronomy, . as postdoctorates. A talented about the physical environment as well; in the early

aInstitute of Astronomy, CB3 0HA Cambridge, Author contributions: M.J.R. wrote the paper. The author declares no conflict of interest. Published under the PNAS license. 1Email: [email protected]. Published online March 16, 2018.

3510–3511 | PNAS | April 3, 2018 | vol. 115 | no. 14 www.pnas.org/cgi/doi/10.1073/pnas.1803355115 Downloaded by guest on October 1, 2021 days, Donald had an allotment in the grounds. And it’s must have been a special pleasure when Ruth became thanks to him that there are now so many spring flow- a Fellow of the Royal Society too. ers around the Institute. Those who founded the Royal Society in 1660 were Donald admired the great and described as “ingenious and curious gentlemen.” Don- would have appreciated retracing his career path to ald joined more than 300 years later, but it strikes me the Royal Observatory and then to Cambridge. Like that this phrase fit him well. Eddington, he engaged with fundamental questions. Donald was ingenious: his inventive ideas spanned a As a student, Donald thought about the origin of mass huge range. He never minded being unconventional... and inertia: Mach’s principle. His last paper, written indeed, he preferred being unconventional. He was cu- with Kumar Chitre, was a highly original conjecture on rious. Right until last year—15 years after his official re- where the entropy came from after the big bang (3). tirement—Donald regularly attended Institute colloquia But Donald’s view was that we shouldn’t spend all and coffee-time discussions. He always had lively ques- of our time groping at fundamental problems. We tions. He really wanted to understand what we were should mainly do “bread and butter” science: straight- doing. Donald said, “I’m not ashamed to ask questions forward extensions of what is known. That’s the mod- that others claim are nonsensical.” est way he would have described much of his work. And Donald was a gentleman: absolutely not in the But what made Donald special was his versatility. He “entitlement” sense of that word—he was allergic to proposed new designs for telescopes; he explained extravagance, to formality, and to badges of status— how Jupiter’s radio bursts could be triggered by one but through his courtesy and concern for everyone. of its moons; above all, he published extensively on Staff, students, and especially foreign visitors appreci- stars, galaxies, quasars, and the entire cosmos, even— ated the hospitality that Donald and Ruth offered at to Leon Mestel’s pleasure—developing neat ideas on their home. And it was perhaps his traditional back- magnetic fields. ground that deepened his commitment to serve insti- Donald worked with a diverse range of collabora- tutions, not only Cambridge but also the Royal tors, hailing from all over the world, but intensively, one Astronomical Society. at a time. Each paper normally had only one coauthor. We will all have our memories of Donald, and our But in the 1980s he joined a bigger collaboration, as personal reasons to be grateful to him. What’sremark- the gadfly and mathematician in an international group able is how little he changed, physically and mentally, that became known as the “Seven Samurai.” They ob- over his 45 years at the Institute. However, just the day served hundreds of galaxies and found that these were after he’d celebrated Ruth’s 80th birthday, a devastating all being pulled by the gravity of a huge hidden mass stroke snuffed him out so suddenly that we never had they dubbed “the Great Attractor.” the chance to convey our admiration and gratitude. Donald received many honors, including a CBE Donald left an enduring scientific legacy as one of from the government of the United Kingdom. He the great astronomers of his generation. And, more received the Gold Medal of the Royal Astronomical broadly, through those he mentored, through his Society (and served a term as its President). He was a influence on United Kingdom astronomy, and the Fellow of the Royal Society for almost half his life; it friendships he forged around the world.

1 Eggen OJ, Lynden-Bell D, Sandage AR (1962) Evidence from the motions of old stars that the Galaxy collapsed. Astrophys J 136:748–766. 2 Lynden-Bell D (1969) Galactic nuclei as collapsed old quasars. Nature 223:690–695. 3 Lynden-Bell D, Chitre SM (2017) Does viscosity turn inflation into the CMB and Λ. arXiv:1707.07566.

Rees PNAS | April 3, 2018 | vol. 115 | no. 14 | 3511 Downloaded by guest on October 1, 2021