Professor Donald Lynden-bell
Cambridge theoretical astrophysicist who defined the relationship between quasars and black holes
PROFESSOR DONALD LYNDEN-BELL, who has died aged 82, was a theoretical astrophysicist known for his work on the formation of galaxies and, in particular, for a landmark paper, “Galactic Nuclei as Collapsed Old Quasars”, published in Nature in 1969, in which he argued that quasars are young galaxies powered by supermassive black holes, and that most large galaxies still have such black holes in their centres.
For this he shared, with Maarten Schmidt, the first Kavli Prize in Astrophysics in 2008. (The Kavli Prize honours achievements in fields that have emerged since the foundation of the Nobel Prize.)
The term “quasar” (“quasi-stellar radio source”) was first coined in 1964 to describe distant sources of radiowave emission, seen in photographic images as point-like stars, which produce an astounding amount of energy – the equal, in some cases, of the combined brilliance of 100,000 ordinary galaxies.
These ultra-radiant objects had puzzled astronomers ever since they began appearing in all-sky radio surveys from the late 1950s. An early theory, the so-called “starburst” model, suggested that they were caused by bursts of birth and death among stars in the cores of young galaxies.
This model fell out of favour after 1969 when Lynden-bell proposed that quasars could be powered by black holes – objects of extreme density, with such strong gravitational attraction that even light cannot escape from inside them – far more efficient and compact sources of energy than “starbursts”. According to this theory, colliding galaxies might awaken a massive black hole lurking in the galactic core, stirring up huge quantities of gas and dust which would start falling into the centre, feeding the black hole. The extreme brightness of quasars, Lynden-bell calculated, was due to frictional heating of these gases, rotating in discs around the black holes.
A corollary was that the cores of many galaxies closer to Earth (and therefore older than more distant galaxies, due to the time it takes light to travel) might be “the graveyard of quasars’’ still harbouring black holes millions or billions of times as massive as the Sun. Later, Lyndenbell postulated the existence of black holes of various masses in the nuclei of individual galaxies, observing that their presence would account for the large amounts of infrared energy that emanate from the centre of galaxies.
Lynden-bell’s model was subsequently supported by images of relatively nearby quasars which almost invariably show them embedded in galaxy-shaped “fuzz”. His model also suggested that quasars would tend to fade over time, as each black hole finished sweeping up everything in its vicinity. This, too, has been borne out by the observation that the closer (and therefore older) a quasar is, the less likely it is to be highly luminous.
Donald Lynden-bell was born at Dover on April 5 1935, one of two children of Lt-col Lachlan Arthur Lynden-bell, MC, and his wife Monica, née Thring.
Educated at Marlborough, he went up to Clare College, Cambridge, to read Mathematics and Physics and was inspired by the writings of Arthur Eddington to pursue a career in astronomy. After graduation, he stayed at Cambridge to take a doctorate under Leon Mestel on stellar and galactic dynamics.
Elected to a research fellowship at Clare and awarded a Harkness Fellowship, he went on to study at the California Institute of Technology, where in 1962 he published research with Olin Eggen and Allan Sandage arguing that our own galaxy, the Milky Way, probably originated through the dynamic collapse of a single large gas cloud some 10 billion years ago, a discovery that still forms the basis of scientific understanding of its origins.
Returning to Cambridge in 1965, he taught mathematics, but three years later moved to the Royal Greenwich Observatory at Herstmonceux Castle, where he published his work on quasars and black holes. In 1971, with Martin Rees, he was the first to predict, in a paper entitled “On Quasars, Dust and the Galactic Centre”, that the Milky Way would be found to harbour a supermassive black hole at its centre – a theory confirmed by observation a few years later.
The following year Lynden-bell was appointed Professor of Astrophysics at Cambridge and founding director of its new Institute of Astronomy, where he worked on a variety of astrophysical problems until his retirement in 2001. Most notably, as a member of a group of astronomers nicknamed the “Seven Samurai” (the other members were Sandra Faber, David Burstein, Alan Dressler, Roger Davies, Roberto Terlevich and Gary Wegner), he proposed in 1987 the existence of a “Great Attractor” – a huge, diffuse region of material around 250 million light-years away – after observing the movement of a large number of local galaxies towards an area of space in the constellation Centaurus.
In the late 1980s Lynden-bell conceived of searching for nearby galaxies, where interstellar dust in the Milky Way often hinders observation using radio telescopes, to estimate the effect that their gravitational pull would have on the motion through space of the Milky Way. He brought together a team of seven astronomers from Britain, the Netherlands and the US who, in a paper in Nature in 1994, announced the discovery of a galaxy of about 300 billion stars close to our own.
The new galaxy, in the constellation of Cassiopeia, was named Dwingeloo 1 after the radio telescope in the Netherlands that detected it.
In retirement Lynden-bell continued to be active in astrophysical research, a recent area of his interest being the study of Mach’s principle, which claims a connection exists between local physical laws and the structure of the universe.
Elected a Fellow of the Royal Society in 1978, Lynden-bell served as President of the Royal Astronomical Society from 1985 to 1987. As well as the Kavli Prize, he was awarded the Eddington Medal (1984), the Gold Medal of the Royal Astronomical Society (1993), the Brouwer Award of the American Astronomical Society (1991), the Karl Schwarzchild Medal (1983), the Bruce Medal (1998), the US National Academy of Sciences John J Carty Award for the Advancement of Science (2000) and the Henry Norris Russel Lectureship Award (2000). He was appointed CBE in 2000. A keen hill-walker, in 2015 he appeared in Star Men, a documentary film which followed him and three fellow British astrophysicists – Roger Griffin, Nick Woolf and Wal Sargent – as they retraced a road trip taken 50 years earlier across the American South West.
In 1961 he married Ruth Truscott, an eminent chemist with whom he worked to determine the thermodynamic equilibrium in clusters of stars and galaxies.
She survives him with their son and daughter.