Pioneers of Dark Matter

The term 'dark matter' was coined a century ago this month. Govert Schilling selects seven scientists who shed light on astronomy's biggest mystery

- By Govert Schilling. Photographs by NASA, ESA, Johns Hopkins University, Science Photo Library, Alamy

Dark matter is what makes the Universe tick. It represents 85 per cent of the material content of our cosmos. Through its gravity, it has enabled the formation of cosmic structure, and it keeps galaxies and galaxy clusters from flying apart.

Astronomers have mapped dark matter's distribution by studying gravitational lensing - the bending of starlight by massive objects in space - but no one has ever seen the mysterious stuff, as it doesn't emit, absorb or reflect light. In this article we take a look at seven of the leading voices who helped progress the quest to understand dark matter.

JACOBUS KAPTEYN (1851-1922)

The originator of the term 'dark matter'

Dutch astronomer Jacobus Kapteyn made an early mention of the term 'dark matter' in his Astrophysical Journal paper on the structure of our Milky Way Galaxy. The paper was published on 1 May 1922, a few weeks before Kapteyn died.

One of 15 children, young Jacobus was raised in a private boarding school run by his parents. In 1878, he was appointed professor of astronomy at the University of Groningen, but he lacked the money to buy a proper telescope. Instead, he joined forces with Scottish astronomer David Gill, who photographed the southern sky from Cape Observatory in South Africa.

Using a manual plate-measuring machine, Kapteyn spent five-and-a-half years meticulously measuring the positions of 454,875 individual stars - an impressive undertaking that led to the Cape Photographic Durchmusterung (CPD) – the largest and most accurate stellar catalogue of the time.