3.4.4 Evolution of Galaxies
Around 1956, Hatanaka became interested in the study of galaxies and joined a study
group on galactic evolution composed of Taketani Mitsuo (武谷三男), Hayakawa
Sachio (早川幸男), Obi Shin’ya (小尾信也), and others. They were widely interested in the origin of stellar populations and in the early evolution of galaxies.
3.4.4.1 Origin of Stellar Population
In galaxies, stars are globally separated into two populations: Population I: the
groups of young stars distributed in the disk, and Population II: the group of old
stars distributed in galactic halo and globular clusters.
Maartin Schwarzschild and Lyman Spitzer (1953) considered the existence of
white dwarfs and metal-poor stars in Population II stars. Both of these stars were the
remnants of primordial galaxies. White dwarfs were originally massive stars. They
were the cores of massive stars that remained after their supernova explosions. The
ejected gas, containing metal components, was mixed with primordial interstellar
matter. Population I stars were formed from such metal-rich interstellar matter
(Schwarzschild and Spitzer 1953).
In 1956, Taketani and Hatanaka’s group extended Schwarzschild and Spitzer’s
scenario, based on the recalculations of nuclear reaction rates converted from helium
to carbon. Their arguments are as follows (Taketani and Hatanaka 1956):
(a) Protogalaxies are composed of primordial elements (mostly hydrogen and
helium) in the form of turbulent gas and dust.
(b) Stars of the first generation were formed from their dense interstellar clouds.
(c) Low-mass stars, less than about one solar mass, remained Population II stars due
to their long evolutionary time as a result of their slow nuclear burning rate.
Fig. 3.7 Brightness
distribution of a solar radio
spot appearing in active
solar region observed on
June 20, 1955 (Hatanaka
et al. 1955)
3.4 Hatanaka Takeo and Astrophysics
57
Around 1956, Hatanaka became interested in the study of galaxies and joined a study
group on galactic evolution composed of Taketani Mitsuo (武谷三男), Hayakawa
Sachio (早川幸男), Obi Shin’ya (小尾信也), and others. They were widely interested in the origin of stellar populations and in the early evolution of galaxies.
3.4.4.1 Origin of Stellar Population
In galaxies, stars are globally separated into two populations: Population I: the
groups of young stars distributed in the disk, and Population II: the group of old
stars distributed in galactic halo and globular clusters.
Maartin Schwarzschild and Lyman Spitzer (1953) considered the existence of
white dwarfs and metal-poor stars in Population II stars. Both of these stars were the
remnants of primordial galaxies. White dwarfs were originally massive stars. They
were the cores of massive stars that remained after their supernova explosions. The
ejected gas, containing metal components, was mixed with primordial interstellar
matter. Population I stars were formed from such metal-rich interstellar matter
(Schwarzschild and Spitzer 1953).
In 1956, Taketani and Hatanaka’s group extended Schwarzschild and Spitzer’s
scenario, based on the recalculations of nuclear reaction rates converted from helium
to carbon. Their arguments are as follows (Taketani and Hatanaka 1956):
(a) Protogalaxies are composed of primordial elements (mostly hydrogen and
helium) in the form of turbulent gas and dust.
(b) Stars of the first generation were formed from their dense interstellar clouds.
(c) Low-mass stars, less than about one solar mass, remained Population II stars due
to their long evolutionary time as a result of their slow nuclear burning rate.
Fig. 3.7 Brightness
distribution of a solar radio
spot appearing in active
solar region observed on
June 20, 1955 (Hatanaka
et al. 1955)
3.4 Hatanaka Takeo and Astrophysics
57