Science

Donald Lynden-Bell: A Legacy of Astronomical Excellence

He is best known for his work on the idea that galaxies contain massive black holes at their centres.

Donald Lynden-Bell. Source: Twitter

Donald Lynden-Bell. Source: Twitter

On February 5, Donald Lynden-Bell, a household name in the circles of theoretical astrophysics, passed away, aged 82. Though his work encompassed diverse areas of study, he is probably known for his work on the idea that galaxies contain massive black holes at their centres, and that such black holes are the principal sources of energy in quasars. Lynden-Bell had suffered a stroke before Christmas 2017 and never fully recovered. He is survived by Ruth Lynden-Bell, an eminent chemist and a fellow of the Royal Society, and two children.

He was also a member of a group of astronomers known as the ‘Seven Samurai’, who postulated the existence of concentrated clumps of matter in certain regions of the cosmos whose presence could explain the peculiar motion of some galaxies.

Lynden-Bell was born in Dover in 1935. He studied astrophysics at the University of Cambridge and spent his entire personal and professional life there.

Many scientists and colleagues in the astrophysics community remember him as a man of high intellect with a grounded personality, and taking great pleasure in interacting with younger students and scientists. He was the first director of the Institute of Astronomy at the University of Cambridge. He was also the president of the Royal Astronomical Society, London, from 1985 to 1987. Asteroid 18235 Lynden-Bell is named after him.

In recent years, Lynden-Bell continued to publish actively. One of his frequent collaborators was Jiri Bicak of the Charles University, Prague. He and Bicak wrote over 20 papers on general relativity and cosmology. Their most recent paper was out in November 2017.

Following his passing, this author spoke to a few scientists who recollected their fond memories of Lynden-Bell and his work. Their notes are reproduced below, edited for clarity.

Peter Coles, cosmologist, Cardiff University, the UK

What was most remarkable about him was the creativity he brought to a huge range of disparate topics, from data analysis to telescope design, and from thermodynamics to general relativity. Donald refused to be pigeonholed and worked on whatever took his fancy. He brought unique imagination and insight to everything he did.

I first encountered him when I was an undergraduate at Cambridge. He taught a first year mathematics course for natural sciences students on how to solve ordinary differential equations. I wouldn’t say he was the most organised lecturer I’ve ever had, but he was enormously entertaining and his remarkably loud voice meant you could never doze off! That was in 1983. I remember being terrified to see he was in the audience when I gave a talk at a conference in Cambridge as a PhD student a few years later, in 1987. He asked a question at the end that completely wrong-footed me, but I soon realised that he had a habit of doing that and it wasn’t at all malicious. He just had an unexpectedly different way of looking at things. It was quite extraordinary in that he stayed that way all through his career. It’s also remarkable how little he seemed to change in the 30-odd years I knew him. In fact, in pictures of him taken in the 1960 he looks much the same as he did last year. I think that’s at least partly why his death was such a shock. He seemed timeless. One assumed he would live forever.

I find then when I know someone a bit personally, no matter how much I admire them as a scientist, it’s often other things about them that I remember better than their scientific work. My most vivid memory of Donald is from a visit to India over 20 years ago. I ended up playing croquet with him on the lawn of the director’s house at the Inter-University Centre for Astronomy and Astrophysics, Pune. Donald seemed entirely unconcerned with his own progress in the game but concentrated fiercely on sending his opponents’ balls into the shrubbery whenever the rules allowed. That is, of course, a major part of the game but I didn’t expect a distinguished Cambridge professor to take such impish delight. The game was a blast but had to be called off in the deepening twilight, with bats circling overhead, as we could no longer see well enough to continue. But I’ll remember Donald’s constant laughter. A very serious and brilliant scientist he may have been, but he also had an intensely human capacity for having a bit of fun.

Luke Dones, solar system dynamicist and chair, Division of Dynamical Astronomy, American Astronomical Association

When I started grad school in astronomy in 1980, I knew little about the subject, having majored in physics. I quickly learned of two theorists whose names were spoken in hushed tones: Peter Goldreich and Donald Lynden-Bell. A major focus of course on accretion disks at the University of California, Santa Cruz, was Lynden-Bell’s and Pringle’s 1974 paper titled ‘The evolution of viscous discs and the origin of the nebular variables’, where “nebular variables” refers to what we now call T Tauri stars.

This paper identified a source of the excess infrared emission from a T Tauri star as dissipation within an accretion disk surrounding the star. This process releases gravitational energy as mass is fed inward towards the star and angular momentum is transported outward. Our Sun and most stars are thought to go through an early T Tauri phase, so the theory of Lynden-Bell and Pringle is still relevant to our own Solar System.

The 1974 paper is one of five papers with more than 1,000 citations in the NASA Astrophysics Data System on which Lynden-Bell was first or second author. His most-cited paper [from 1962] … showed that the most metal-poor, or older, stars in the Milky Way followed plunging, nearly radial orbits, while the most metal-rich stars followed near-circular orbits.

The only time I met Lynden-Bell was in 1991 or so when I was a postdoc at the Canadian Institute for Theoretical Astrophysics (CITA). Scott Tremaine, CITA’s first director, hosted him. Lynden-Bell had invented the term ‘violent relaxation’ in a 1967 paper to describe the process by which the distribution of energies of stars in a time-changing potential (i.e. within a collapsing galaxy or star cluster) approaches equilibrium. Tremaine had worked with Michel Henon and Lynden-Bell on violent relaxation, which is a subject of active research even now. The main thing I remember is that we went out to lunch in Toronto’s nearby Chinatown after Lynden-Bell’s seminar, and he was very nice! I don’t think I was the only one to be relieved that his big brain didn’t come with a huge ego.

Robert Massey, astronomer and deputy executive director, Royal Astronomical Society, London

Donald Lynden-Bell was one of the giants of 20th century astrophysics. The RAS recognised his work with our Gold Medal, and he served as President from 1985 to 1987. He remained active until very recently, asking pertinent questions at our scientific meetings, and featured in ‘Star Men’, a documentary film about him and three peers who looked back on a lifetime in astrophysics. Donald was kind enough to come to our screening, taking questions and making the (slightly sad) point that it was time for people like him to ‘get out of the way’ to allow younger scientists to take over. We’ll miss him!

Aswin Sekhar is an Indian astrophysicist based at CEED, University of Oslo, Norway.

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