A leading researcher in astronomy and astrophysics, who elucidated the structure and dynamics of the Galaxy through radio observation of the 21cm hydrogen line, derived the position of the galactic center and other basic parameters of galactic rotation, and thus revealed the overall picture of the spiral structure of the Galaxy.
＊This field then was Field of Earth Sciences and Astrophysics.
Dynamics of the galactic system in the vicinity of the Sun (Oort, J. H.), Bulletin of the Astronomical Institutes of the Netherlands, 4, 1928.
Note on the structure of the inner parts of the Galactic System (Oort, J. H.), Bulletin of the Astronomical Institutes of the Netherlands, 9, 1941.
The structure of the cloud of comets surrounding the solar system, and a hypothesis concerning its origin (Oort, J. H.), Bulletin of the Astronomical Institutes of the Netherlands, 11, 1950.
The spiral structure of the outer part of the Galactic System derived from the hydrogen emission at 21-cm wave length (van de Hulst, H. C., Muller, C. A., & Oort, J. H.), Bulletin of the Astronomical Institutes of the Netherlands, 12, 1954.
Polarization and composition of the Crab Nebula (Oort, J. H. & Walraven, T.), Bulletin of the Astronomical Institutes of the Netherlands, 12, 1956.
High-latitude, High-velocity Clouds (Oort, J. H.), Transactions of the International Astronomical Union, 12B, 1966.
Evidence for the location of quasars in superclusters (Oort, J. H., de Ruiter, H., & Arp, H.), Astronomy and Astrophysics, 95, 1981.
Dr. Jan Hendrik Oort will receive the Kyoto Prize 1987 for Basic Sciences for his long standing contributions to astronomy and astrophysics, particularly for his elucidation of the structure and dynamics of the Galaxy. He found that the Milky Way is a large stellar system of disk shape and rapid rotation, in which the sun is located about two-thirds of its radius away from the center, as we now find in text books. This structure was first derived from his optical observation of the velocities of stars in the late 1920s and was later quantified by the radio observation with the 21cm hydrogen line performed in the 1950s by he and his students. The galactic rotation is characterized by a pair of parameters, called the “Oort constants,” and the motion perpendicular to the galactic disk is dictated by the “Oort mass limit” which is the maximum permissible surface mass density in the solar neighborhood.
One of his important contributions to astronomy was the development of radio astronomy. He initiated the 21cm observation independently of Purcell, and designed radio telescopes including interferometers. Using these radio telescopes, he found high velocity hydrogen clouds falling on the Galaxy, expanding features in the galactic center, and various interesting properties of external galaxies. He has also derived the distance to the galactic center, referring to radio and optical data.
The name of Dr. Oort is also found in the solar system study. In 1950 he showed there is a nest of comets, called the “Oort cloud,” at 100,000 AU from the sun, and comets are supplied from this cloud when disturbed by passing stars. He has also devoted himself to the study of supernovas. One of the most striking discoveries was the polarization of light from the Crab Nebula, a remnant of supernova 1054. This proved the theoretical prediction that the electromagnetic emission is due to the synchrotron radiation by relativistic electrons in magnetic fields.
Through these scientific works and as Professor of Leiden University and Director of Leiden Observatory, he has brought up many astronomers and astrophysicists who are now playing leading roles at various institutions throughout the world. There are many more who feel themselves to be Dr. Oort’s students, though he might not know them. All astronomers and astrophysicists owe greatly to his leadership in scientific research and in the organization of research activity, and are strongly impressed by his enthusiasm. He continues research work even today. His scientific achievements have been recognized with several prizes, the memberships of several academies, honorary degrees and so forth.
An account is given of the development of our view of the world from the time when as children we saw it bounded by our horizon, up to the era of the expanding Universe, when the horizon has receded to the “Big Bang”, at a distance of roughly thirteen billion light-years.
The first scientific models of the outside world were conceived by the ancient Greeks. Their models were extremely ingenious, and formed the standard of our astronomical knowledge for almost two thousand years. They were primarily concerned with the Solar System. It is only through the enormous technical developments of the 19th century, which permitted the construction of large telescopes, that the world outside the Solar System became accessible. One of the principal pioneers of the exploration of this larger world was J.C. Kapteyn in Groningen, who directed the entire work of his institute to the investigation of the huge swarm of stars surrounding us.
My relation with astronomy started when I began my study in Groningen. Under the inspiring influence of Kapteyn I became involved in the early phase of the exploration of the Galaxy. One special aspect of the investigations was the apparent contradiction between the so-called Kapteyn System based on star counts in Kapteyn’s “Selected Areas” and the model based on the distribution of globular clusters as suggested by Shapley. The controversy was solved by the discovery of the galactic rotation by Lindblad and Oort in 1925-27. This showed that the real Galaxy was different from both the Kapteyn System and Shapley’s conception. The discovery of the rotation led to better insight into several longstanding problems, such as the “star streams” which had been discovered by Kapteyn in 1902, and the motions of the high-velocity stars.
A principal feature of the new Galaxy was a thin disk of stars and interstellar clouds of gas and dust. By far the largest part of the disk was hidden from our view through the obscuration by the dust. It only became accessible by the advent of radio-astronomy, the radio waves penetrating unhindered through the dust. The first radio map showing the large-scale structure of the galactic disk was produced in Holland in 1954. It proved that our Galaxy had a spiral structure, like many of the “nebulae” that populate the Universe outside our Galaxy.
These nebulae, or “galaxies”, are now the principle objects by which the structure and evolution of the Universe is being investigated. They have yielded two major discoveries: 1. That the Universe is expanding, and must have started roughly 13 billion years ago from a small volume; 2. That it is filled with isotropic radiation which had an extremely high temperature in the far past, but has now cooled to 3 above absolute zero, and has actually been measured.
The principal “experimental” problems which are presently being studied are how galaxies, clusters of galaxies, and the huge structures that are called superclusters have formed and evolved. Much is still enigmatic.