Gerhard Elwert

Gerhard Elwert (born May 15, 1912 in Hohengehren near Esslingen , † June 25, 1998 ) was an astrophysicist at the University of Tübingen .

Teaching and Research

Gerhard Elwert studied physics , mathematics and astronomy in Tübingen and Munich . It was in 1938 by Arnold Sommerfeld with a thesis on the X-ray bremsstrahlung doctorate . Parts of his dissertation , including the Elwert factor named after him , have been included in Volume II of Sommerfeld's famous work Atomic Structure and Spectral Lines . In 1939 Elwert passed the scientific examination for teaching at grammar schools and then worked at Telefunken in Berlin on topics relating to low and high frequency technology during the Second World War .

After the end of the war, Elwert returned to Tübingen and initially went to higher education, from where Heinrich Siedentopf brought him to the University of Tübingen's Astronomical Institute as an assistant in 1950. There he completed his habilitation in 1953 with the work The radiation of the solar corona in the area of ​​soft X-rays and its importance for the formation of the ionospheric E-layer .

In his scientific research, Elwert mainly turned to questions from the field of theoretical astrophysics. He dealt with the synchrotron radiation of relativistic electrons in cosmic magnetic fields, with radio astronomy and with the celestial mechanics of the Milky Way and neighboring galaxies.

With his groundbreaking work on the theory of X-ray and ultraviolet radiation from the solar corona, Gerhard Elwert found worldwide recognition. Because of the discovery of X-rays on the sun, he was nominated for the Nobel Prize and almost got it. At the beginning of the 1950s he was particularly interested in the X-rays of the undisturbed sun. Elwert calculated both the continuous and the line radiation of a hot plasma of a few million degrees. To do this, he needed a large amount of atomic physical data, and this resulted in his work on ionization and recombination processes in a plasma , the well-known ionization formula of the solar corona and the formation of the yellow corona line.

In the following years the number of observations of solar X-rays with the help of balloons, rockets and satellites increased rapidly, and so it became possible to make comparisons between theory and measurements. The theoretical predictions of Elwert were confirmed. The preoccupation with short-wave radiation from the sun inevitably led to solar-terrestrial relationships. In his habilitation thesis , Elwert examined the influence of X-rays from the solar corona on the formation of the ionospheric E-layer.

In 1968 he was appointed to the newly created chair for theoretical astrophysics at the University of Tübingen. In addition to the theory, Elwert was particularly interested in its experimental testing. At his suggestion, the first coincidence measurements on the elementary process of X-ray bremsstrahlung were carried out in the University's Physics Institute. With his active participation, a research group from the Astronomical Institute developed zone plate cameras for X-ray imaging of the sun, with which a large number of interesting X-ray images were made of rocket ascents from Sardinia and White Sands in 1971 and 1972 .

In the 1960s, a number of satellites were used to study the sun's X-rays so that the sun could be observed over long periods of time. Therefore, many measurements of the hard X-rays emitted by solar flares could be carried out. Gerhard Elwert then turned to research into the electrons accelerated by solar flares and their propagation in the coronal plasma. He was the first to point out that the X-rays generated by the non-thermal electrons must be anisotropic and polarized . To measure the anisotropy, he proposed an experiment with two satellites , one of which orbits the earth, while the other describes an orbit around the sun (Solar Polar Mission). This project was only realized much later in the form of the Ulysses satellite , which was launched in October 1990.

In addition, Elwert, in collaboration with American scientists, was involved in the evaluation of measurements obtained during the manned Skylab missions in 1973 and 1974. With Giacconi - Wolter telescopes , X-ray images of the sun were taken with a spatial resolution that was previously unattainable. When analyzing these images, Elwert's main interest was in the magnetic fields in the solar atmosphere, which play a key role in the interpretation of solar activity and the heating of the corona. Among other things, an extensive computer program was created to calculate these fields from the component of the photospheric magnetic field measured in the direction of the line of sight.

Even after his retirement in 1980, Gerhard Elwert continued to work scientifically. As a visiting scientist, he took part in the evaluation of X-ray images of the sun that were recorded with the Hard X-Ray Imaging Spectrometer (HXIS) on board the Solar Maximum Mission (SMM). In addition, he dealt with the acceleration of plasma electrons in an electric field. In recent years, however, his state of health did not allow him to continue his research. Nevertheless, he took an active part in the work in the institute right up to the end and received reports on the latest results in the field of astrophysics.

Private life

Gerhard Elwert was interested in all of nature, not just astrophysics. To experience them, he went on extensive hikes until the time of his serious illness - preferably in the Tübingen area, the Swabian Alb and the Black Forest . But not only the closeness to nature gave him life, he was also musically gifted and interested. He was good at drawing, painting and doing handicrafts. There was a self-made model of a theater with interchangeable sets, self-made figures and electric lighting, in which he played passages from well-known plays to visitors.

In some cases, Gerhard Elwert was considered closed and unapproachable. But some also experienced him as a very warm, witty and funny counterpart who could also laugh heartily. He was very helpful and let students in need live with him for free. He would never have been capable of any intrigue towards other people.

Gerhard Elwert died unmarried and childless. He found his final resting place in the grave of his parents in the Tübingen city cemetery .

Individual evidence

1. ↑ Eberhard Haug: A word of remembrance and thanks to Prof. Dr. Gerhard Elwert
2. ↑ Mitteilungen der Astronomische Gesellschaft, No. 82, pp. 9-10, bibcode : 1999MitAG..82 .... 9H .
3. ^ ^{A b c} Dorothee Elwert-Pillwein: Gerhard Elwert - the private man.
4. ^ Gerhard Elwert and Eberhard Haug: Anisotropy of solar hard X-radiation during flares. In: Solar Physics. Volume 20, No. 2, pp. 413-421, doi : 10.1007 / BF00159773