From cosmic ray physics to cosmic ray astronomy: Bruno Rossi and the opening of new windows on the universe

Abstract

Bruno Rossi is considered one of the fathers of modern physics, being also a pioneer in virtually every aspect of what is today called high-energy astrophysics. At the beginning of 1930s he was the pioneer of cosmic ray research in Italy, and, as one of the leading actors in the study of the nature and behavior of the cosmic radiation, he witnessed the birth of particle physics and was one of the main investigators in this fields for many years. While cosmic ray physics moved more and more towards astrophysics, Rossi continued to be one of the inspirers of this line of research. When outer space became a reality, he did not hesitate to leap into this new scientific dimension. Rossi's intuition on the importance of exploiting new technological windows to look at the universe with new eyes, is a fundamental key to understand the profound unity which guided his scientific research path up to its culminating moments at the beginning of 1960s, when his group at MIT performed the first in situ measurements of the density, speed and direction of the solar wind at the boundary of Earth's magnetosphere, and when he promoted the search for extra-solar sources of X rays. A visionary idea which eventually led to the breakthrough experiment which discovered Scorpius X-1 in 1962, and inaugurated X-ray astronomy.

EUROGRAV 1986–1989: the first attempts for a European Interferometric Gravitational Wave Observatory

“…The Italian longstanding tradition in cosmic ray studies was a fertile ground for new ideas concerning the detection of still unobserved cosmic messengers. The physics of cosmic rays, at first aimed at the study of particles and of their interactions, had been gradually becoming an instrument for probing the phenomena of the cosmos originating them [3,4]. Furthermore, it is worth noting that by the second half of the 1980s, Italy was at the frontier of astroparticle physics with the beginning of operation of Gran Sasso labs, hosting the MACRO facility (Monopole, Astrophysics and Cosmic Ray Observatory), a general-purpose probe which appeared as a natural extension of the Italian tradition of cosmic ray physics [8].…”

“…With four or more detectors there would be a unique intersection region. 3 In a note drafted in September 1987, Bernard Schutz, a major contributor in the field of GW research and at the time professor at Cardiff University, Wales, pointed out: 4 More detectors mean capturing more gravitational wave events. This is partly because of greater sky coverage, but mainly because the decreasing risk of 'random' coincidences caused by noise allows one to operate with lower thresholds and therefore to see a greater volume of space.…”

“…If the GW signal has an electromagnetic counterpart, the source may be pinpointed by ground-based and space-based astronomical observatories, as occurred on August 17, 2017, for the Kilonova event GW170817. It was the very first time that an astrophysical event was observed both in the gravitational and electromagnetic channels 4. Note by Bernard Schutz, Outline case for building 3 laser interferometric detectors in Europe, September 1987.…”

Stellar structure and compact objects before 1940: Towards relativistic astrophysics

“…According to his prediction there should be an azimuthal asymmetry in the intensity of cosmic rays that would depend on the sign of the charge of the primary particles. Both the charged nature of cosmic rays (also verified by the latitude effect) and the sign of the charge, were determined by such experiments [Bonolis 2014]. Research on cosmic rays was already becoming strongly related to the emerging field of elementary particle physics, and the problem of their origin was gradually less investigated, at least up to the 1940s, when it was possible to establish the nature of the primary radiation.…”