The Crafoord Prize 1985 – one of the largest prizes ever – in astronomy to professor Lyman Spitzer, Jr., USA

The Royal Swedish Academy of Sciences awards the Crafoord Prize of ca. 135 000 US dollars to Professor Lyman Spitzer, Jr., Princeton, USA, for his “fundamental pioneering studies of practically every aspect of the interstellar medium, culminating in the results obtained using the Copernicus satellite”.

The Prize is one of the largest prizes in astronomy ever awarded.

Lyman Spitzer will receive the prize from the hands of His Majesty the King at a ceremony at the Royal Swedish Academy in Stockholm, Sweden, the 3rd of October 1985.

Grants totaling ca. 70 000 US dollars are awarded to Swedish Scientists within the same field of astronomy.

Professor Lyman Spitzer, Jr., Princeton University, has been awarded the 1985 Crafoord Prize for his work on the physics of the interstellar medium including star formation. This year´s prize is awarded in field of astronomy.

Based on fundamental investigation of practically all aspects of the interstellar medium (matter and light in space in between the stars). Professor Spitzer´s results have led to important progress within the field.

Lyman Spitzer stands out as the leading theoretician in interstellar medium research but he has also made or inspired important investigations in other fields. Some of the highlights in this career came with the results obtained with the Copernicus satellite in the seventies.

Until the 19th century it was thought that the space between the stars was empty. It was the realized that many of the “holes” seen in the Milky Way – regions which are poor in stars – in fact originate from extensive interstellar clouds that block the background light. Such a cloud is evident during summer and autumn evenings when one can see with the naked eye how the Milky Way breaks up into two parallel bands from the constellation of Cygnus down towards the southern horizon.

The dark lane between the bands is due to such a cloud, which is very extensive, along Milky Way. During this century it was found that these clouds contain small dust particles that absorb and scatter starlight. It was also found that interstellar space contains gas.

Today, thanks largely to Lyman Spitzer, we have a very detailed picture of the conditions in interstellar space. We now know that interstellar matter varies tremendously in density, temperature and velocity throughout our galaxy. We know the chemical composition of this material and its variations in space and time. During the last few decades it has been discovered that relatively complicated compounds are formed spontaneously in the cold clouds and that the denser clouds are centers for the formation of new stars in the galaxy. At the end of the evolution of certain stars dramatic phenomena, for instance supernova explosions, occur when gas is violently ejected into the interstellar medium. Here, instant changes take place into the physical state of the medium surrounding the stars.

A result of such events is that the chemical composition of interstellar matter is a whole slowly changes with time.

Spitzer started his research in the field in 1941-42 with three theoretical works on the dynamics of the interstellar medium. In these works he discussed the electric charges of interstellar dust grains, their velocity distribution, and the influence of stellar radiation on dust grains, protons and hydrogen atoms (radiation pressure).

After the 2nd world war Spitzer started a series of theoretical investigations into how interstellar clouds are heated and cooled. Heating is mainly due to supernova explosions, and cosmic radiation, and cooling mainly due to radiation from the interstellar gas. Spitzer was able to estimate theoretically the efficiency of the various heating and cooling mechanisms and from this to calculate the temperatures of interstellar clouds. He showed that in the cold clouds, where hydrogen is neutral, the temperature is around 100 K (-170 c) while in the warm clouds where hydrogen is ionized, the temperature is around 10,000 K.

Spitzer has also considered the interstellar magnetic fields and shown their importance in controlling the motion of charged particles in the galaxy.

Another area where Spitzer has contributed with pioneering theoretical work is the question of how stars form through contraction of interstellar cloudlets. In these studies he considered the influence of rotation, temperature, density of dust and magnetic fields. In connection with these studies he also considered the gravitational influence from interstellar clouds on stars and how hot stars may affect the motion of cloud material.

Parallel to these theoretical studies he made observations at the Mount Wilson Observatory in USA, measuring the velocity of interstellar clouds and the relative content of sodium and ionized calcium. Spitzer was able to show an interesting difference in the relative amounts of these elements in clouds of high-velocity and of low-velocity respectively. Through data obtained much later from the Copernicus satellite, it is now know that calcium in the high-velocity clouds is ejected from dust grains in them, due to collisions with atoms.

On of the highlights in Spitezer´s output occurred in 1956 when he postulated that our galaxy has a corona of hot gas with a temperature of 1 million degrees. This prediction, which came as a surprise to astronomers at the time, was based on absorption of radiation from interstellar calcium. Spitzer suggested that this radiation must originate in cold clouds in pressure equilibrium with a gas of temperature 1 million degrees. Confirmation of this proposal came with the Copernicus satellite when interstellar oxygen, stripped of 5 of its 8 electrons, was discovered. Such oxygen can exist only at temperatures of around a million degrees.

Spitzer realized early that observations from satellites and balloons were necessary for a better understanding of the interstellar medium. After Sputnik I and the establishment of NASA he contributed by having the program Orbiting Astronomical Observatory (OAO) accepted, and Princeton University became responsible for the third satellite in this program – the Copernicus satellite, which was launched in 1972 after 10 years of design work. Spitzer participated actively in all the work even on the engineering side and the success of this large project was to a large extent related to him.

Among the results that the Princeton group obtained through Copernicus observations should be mentioned the analysis of deuterium and ordinary hydrogen radiation. The radio of the number of atoms of deuterium to those of normal hydrogen was derived to 1.4 X 10 -5 , a result of cosmological interest since, on the “Big Bang” theory of the early evolution of our universe, it is an open universe. A consequence of this is that our universe must be continually expanding.

Among all Spitzer´s contributions one can mention lastly that he has actively contributed to the US government´s acceptance of plans for a large space telescope – a project which will give new data of still higher quality also for the interstellar medium.

Spitzer´s influence has been large not only as a scientist but also as a teacher. He has for instance published three works regarded as standard astronomy textbooks all over the world. Here he has clearly and distinctly summarized our present knowledge and thereby to a high degree influenced further research.

Spitzer´s principal published works are:
The physics of fully ionized gases (1956, revised edition 1962) 
Diffuse matter in space (1968) 
Physical processes in the interstellar medium (1978)