Presentation Speech by professor Hans Wilhelmsson of the Royal Academy of Sciences

Translation from the Swedish text

Your Majesty, Your Royal Highnesses, Ladies and Gentlemen,

The subject of the Nobel Prize in Physics this year is the science of Astrophysics, the Physics of the stars and galactic systems.

Problems concerning our Universe on a large scale, its constitution and evolution, play an essential role in present day scientific discussions.

We are curious about the behaviour of our Universe. In order to draw reliable conclusions regarding cosmological models it is necessary to gather detailed information about conditions in the remote parts of the Cosmos.

Radio-astronomy offers unique possibilities for studying what is taking place, or in reality what occurred very long ago, at enormous distances from Earth, as far out as thousands of millions of lightyears from us. The radio waves now reaching us have been travelling for thousands of millions of years at the speed of light to reach our Earth from those very remote sources.

It is indeed a thrilling fact that the radio signals we record today here on Earth left their cosmic sources at a time when hardly any flowers or living creatures, and certainly no physicists, existed on Earth.

New and epoch-making discoveries have been made in the field of Radioastrophysics during the last decade, discoveries that are also exceedingly important contributions to modern Physics, for example in establishing through radio-astronomical observations the presence of matter in a superdense state. One single cubic centimeter of this superdense matter has a weight of thousands of millions of tons. It consists of tightly-packed neutrons. A neutron star appears as a consequence of a star explosion, a so-called supernova event. Neutron stars, with a diameter of about 10 kilometers, are from a cosmic point of view extremely small objects. They represent the final state in the evolution of certain stars.

This year’s Nobel Prize winners in Physics, Martin Ryle and Antony Hewish, developed new radio-astronomical techniques. Their observations of cosmic radio sources represent extremely noteworthy research results.

In order to collect radio waves from cosmic radio sources one utilizes radiotelescopes. It is important that a radio-telescope should have a large area, both for highest possible sensitivity and for the high angular resolution that is needed to discriminate among the various cosmic sources of radio radiation.

For observation of exceedingly small sources it is, however, no longer possible to build a single radio-telescope of sufficient size. Ryle and his collaborators therefore developed the method of aperture synthesis. Instead of making one huge aerial, a number of small aerials are used in this method, and the signals received by them are combined in such a way as to provide the necessary extreme accuracy.

Instead of many small aerials, Ryle in fact made use of a few aerials that could be moved successively to different positions on the ground. Ryle also invented the extremely elegant and powerful technique utilizing the rotation of the Earth to move his radio-telescopes. With this technique he obtained a resolution in his observations that corresponded to an aerial of enormous size. Ryle’s measurements enable us to conclude that a steady-state model of the Universe can not be accepted. The Cosmos on a large scale has to be described by dynamic, evolutionary models.

In his latest construction in Cambridge, Ryle obtained an angular resolution permitting the mapping of cosmic radio sources with an error less than one second of arc!

The radio-astronomical instruments invented and developed by Martin Ryle, and utilized so successfully by him and his collaborators in their observations, have been one of the most important elements of the latest discoveries in Astrophysics.

Antony Hewish and his collaborators in Cambridge, in the Autumn of 1967, made a unique and unexpected discovery that has revolutionized Astrophysics. They had constructed new aerials and instruments to study the influence of the outer corona of the Sun on the radiation detected from remote point sources. A special receiver capable of extremely rapid response had been built.

The fast receiver provided a result quite different from its intended purpose. By chance the receiver detected short pulses of radio signals that were repeated periodically about every second, and with exceedingly high precision in the pulse repetition rates.

It was concluded that the radiation originated from cosmic sources of previously unknown type. These sources were subsequently named pulsars.

One has come to the conclusion that the central part of a pulsar consists of a neutron star. The pulsars are also accompanied by magnetic fields many millions of times stronger than those found in laboratories on Earth. The neutron star is surrounded by an electrically-conducting gas or plasma. Each pulsar rotates and emits beams of radiation in the Universe, resembling those from a light-house. The beams strike the Earth periodically with high precision.

These pulsars are indeed the world clocks which our Nobel Prize winner Harry Martinson mentions in his poetry.

Allow me to quote this poet of space:

“World clocks tick and space gleams
everything changes place and order”.

Early in the history of pulsar research it was suspected that neutron star matter existed in the centres of supernovas. Radio-telescopes were aimed towards the centre of the Crab nebula, a magnificent glaring gaseous remnant of a supernova event that is known, from Chinese annals, to have occurred in 1054 A.D., and indeed, they detected a pulsar! This pulsar emits not only radio pulses, as expected from a pulsar, but pulses of light and x-rays as well. It is comparatively young, rotates rapidly and is in fact exceptional among pulsars.

Antony Hewish played a decisive role in the discovery of pulsars. This discovery, which is of extraordinary scientific interest, opens the way to new methods for studying matter under extreme physical conditions.

The contributions of Ryle and Hewish represent an important step forward in our knowledge of the Universe. Thanks to their work new fields of research have become part of Astrophysics. The gigantic laboratory of the Universe offers rich possibilities for future research.

Sir Martin,

Some of the most fundamental questions in Physics have been elucidated as a result of your brilliant research. Your inventions and observations have brought new foundations for our conception of the Universe.

Professor Antony Hewish,

The discovery of pulsars, for which you played a decisive role, is a most outstanding example of how in recent years our knowledge of the Universe has been dramatically extended. Your research has contributed greatly to Astrophysics and to Physics in general.

On behalf of the Royal Academy of Sciences I wish to express our admiration and to convey to you our warmest congratulations.

The Royal Academy of Sciences regrets that Sir Martin Ryle is not here today.

May I now ask you, Professor Hewish, to receive your prize and also the prize awarded to Sir Martin Ryle from the hands of His Majesty the King.