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Dive into the fascinating world of stars in the Milky Way galaxy, from exploring the different types of stars to understanding globular and open clusters, as well as the intricacies of gas regions in space.
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Types of Stars Population I – Second generation stars containing elements heavier than Helium ( the Sun is population 1 ) Population II – first generation ( primordial ) stars consisting of only Hydrogen and Helium Variable Stars – Horizontal branch stars whose luminosity ( and hence their distance ) can be determined by measuring the period of their cycle of brightening/dimming
Types of Clusters Globular – tightly bound elliptically-shaped systems of 10,000 to 1,000,000 old population II stars, typically found orbiting outside the disk of a spiral galaxy Open – loosely bound irregularly-shaped systems of population I stars typically found in the galactic disk
Types of Gas • H I regions • very cold hydrogen gas giving off light at 21 cm due to transitions involving flipping electron spin • Typically found in the disk of a spiral galaxy far removed from stars
Types of Gas • H II regions • Heated ionized Hydrogen gas surrounding young stars or protostars • Emits light characteristic of atomic transitions. Protons capture electrons in an excited state , a photon is emittted when the electron drops into the ground state • Typically found in the spiral arms of a spiral galaxy
Elliptical Galaxies • Elliptical galaxies are not flattened into a disk • The three dimensional configuration is very efficient in producing stars • S0 …. • Ellipticals contain very little dust • Almost all the stars are old population II stars • Stellar orbits are approximately random ( no rotation curves )
Bulge: • Many RR Lyrae stars • A little gas & dust • Halo: • Old metal-poor stars • Globular clusters • RR Lyrae Stars • Dark Matter ! • Thick disk of Stars (~1000 pc thick) • Open Clusters & loose Associations of stars • Mix of young & old stars • Cepheid Stars in young clusters • Thin disk of Gas & Dust (~100 pc thick) • Mostly cold atomic Hydrogen gas • Dusty Giant Molecular Hydrogen Clouds
Interpretation of Rotation Curves • The velocity of rotating stars is a probe of the distribution of mass within the galaxy • The wiggles indicate the presence of spiral arms, where the matter density is higher than average • Rotation curves for spiral galaxies are typically flat out to distances beyond where any stars can be seen. This indicate the presence of DARK MATTER • The data is consistent with spherical Halos of dark matter extending far beyond the visible part of the galaxy
