Galactic astronomy

Galactic astronomy is the study of our own Milky Way galaxy and all its contents. This is in contrast to extragalactic astronomy, which is the study of everything outside our galaxy, including all other galaxies.

Galactic astronomy should not be confused with galaxy formation and evolution, which is the general study of galaxies, their formation, structure, components, dynamics, interactions, and the range of forms they take.

Our own Milky Way galaxy, where our solar system belongs, is in many ways the best studied galaxy, although important parts of it are obscured from view in visible wavelengths by regions of Cosmic dust. The development of radio astronomy, infrared astronomy and submillimeter astronomy in the 20th Century allowed the gas and dust of the Milky Way to be mapped for the first time.

Galactic astronomy

Our solar system orbits within the Milky Way, a barred spiral galaxy that is a prominent member of the Local Group of galaxies. It is a rotating mass of gas, dust, stars and other objects, held together by mutual gravitational attraction. As the Earth is located within the dusty outer arms, there are large portions of the Milky Way that are obscured from view.

In the center of the Milky Way is the core, a bar-shaped bulge with what is believed to be a supermassive black hole at the center. This is surrounded by four primary arms that spiral from the core. This is a region of active star formation that contains many younger, population II stars. The disk is surrounded by a spheroid halo of older, population I stars, as well as relatively dense concentrations of stars known as globular clusters.^[34][35]

Between the stars lies the interstellar medium, a region of sparse matter. In the densest regions, molecular clouds of molecular hydrogen and other elements create star-forming regions. These begin as irregular dark nebulae, which concentrate and collapse (in volumes determined by the Jeans length) to form compact protostars.^[36]

As the more massive stars appear, they transform the cloud into an H II region of glowing gas and plasma. The stellar wind and supernova explosions from these stars eventually serve to disperse the cloud, often leaving behind one or more young open clusters of stars. These clusters gradually disperse, and the stars join the population of the Milky Way.

Kinematic studies of matter in the Milky Way and other galaxies have demonstrated that there is more mass than can be accounted for by visible matter. A dark matter halo appears to dominate the mass, although the nature of this dark matter remains undetermined.^[37]