The diagram shows three populations of stars. The remains of supernovas may be neutron stars whereas dwarf stars remain dwarf and may not share their synthesized metals with the interstellar medium that breeds the next generation of stars. This highly simplified diagram shows the flow of material as giant stars evolve into supernovas which enrich molecular clouds with metals that they synthesized which are then inherited by the next generation of stars. Populations of stars co-evolve with the interstellar medium in which they form. The spiral arms of galaxies are very bright because massive short-lived high luminosity stars form there and die before leaving the arms. Metals by definition include any element other than hydrogen or helium, even oxygen, nitrogen, and carbon.Īrtistic image of the spiral arms of the Milky Way. Most of the volume is occupied by warm or hot gases that range from 6000 K to several million degrees, too hot to condense into clouds. Despite their evolutionary importance, the clouds occupy less than 1% of the volume of the medium. The interstellar medium is home to the cool dense molecular clouds that breed stars including massive short-lived stars that enrich the metal content of the medium when they explode. Table of composition of the interstellar medium from Wikipedia. Density form factors are models that approximate the distribution of stars and dark matter in the galaxy. The supermassive black hole has about four million solar masses, a huge number, but only a small fraction of the stellar or galactic mass. About 1% of the stellar mass is in the stellar halo. Most of the rest are distributed fairly uniformly among the thick disk, bulge, and interstellar medium. Nearly 70% of the ordinary baryonic matter is in the young stars in the thin disk. Nearly 90% of the mass of the galaxy is in the dark matter halo. The table shows the mass, dimensions, density, and density form function of the structures of the Milky Way galaxy. The spiral arms are regions of high density of interstellar gas and dust where giant stars continue to form and live very brief lives before recycling their metal-enriched gas back into the “empty space” of the interstellar medium. Much smaller black holes are scattered throughout the galaxy. The galactic center is a supermassive black hole. Population I stars are concentrated in the younger thin disk, but are also found in the bulge. Population II stars are found in a nearly spherical stellar halo, a central bulge and a thin disk. The galaxy includes a distribution of stars and intragalactic medium. The diagram identifies the primary features of the Milky Way galaxy not counting the massive nearly spherical dark matter halo that has three times the diameter and nearly 30 times the volume of the stellar halo shown in the diagram. All images of the disk and spiral arms are diagrams or drawings by artists based on detailed observations within the galaxy from our location.ĮdgeonphotographofMilkyWayseenfromNevadashowinglocalterrainatbottomofimage NASA image published by TBD The Milky Way Galaxy that we see in the sky at night is a view from our location within the thin disk inside the galaxy. A linear timeline best depicts this domain. Heat transport may involve thermal conduction, convection, and radiation. Transformations of energy and matter in the interior of stars involve gravitational, electromagnetic and nuclear forces. The 12 billion year history of the Milky Way Galaxy involves the formation and evolution of dark matter halos, a stellar halo, a stellar bulge, a thick disk, a thin disk with spiral arms, a supermassive black hole, and interstellar medium. This webpage is still under construction. You cannot see disks of the galaxy from inside the disk. Artist's conception of the Milky Way Galaxy and our location within it.
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