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Milky Way Galaxy


Artist's conception of the Milky Way Galaxy and our location within it. You cannot see disks of the galaxy from inside the disk.

This webpage is still under construction. Stay tuned. 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. Transformations of energy and matter in the interior of stars involve gravitational, electromagnetic and nuclear forces. Heat transport may involve thermal conduction, convection, and radiation. A linear timeline best depicts this domain. 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. All images of the disk and spiral arms are diagrams or drawings by artists based on detailed observations within the galaxy from our location.




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. The galaxy includes a distribution of stars and intragalactic medium. Population II stars are found in a nearly spherical stellar halo, a central bulge and a thin disk. Population I stars are concentrated in the younger thin disk, but are also found in the bulge. The galactic center is a supermassive black hole. Much smaller black holes are scattered throughout the 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.


The table shows the mass, dimensions, density, and density form function of the structures of the Milky Way galaxy. Nearly 90% of the mass of the galaxy is in the dark matter halo. Nearly 70% of the ordinary baryonic matter is in the young stars in the thin disk. Most of the rest are distributed fairly uniformly among the thick disk, bulge, and interstellar medium. About 1% of the stellar mass is in the stellar halo. The supermassive black hole has about four million solar masses, a huge number, but only a small fraction of the stellar or galactic mass. Density form factors are models that approximate the distribution of stars and dark matter in the galaxy.

Table of composition of the interstellar medium from Wikipedia. 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. Despite their evolutionary importance, the clouds occupy less than 1% of the volume of the medium. 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. Metals by definition include any element other than hydrogen or helium, even oxygen, nitrogen, and carbon.

artistic image of the spiral arms of the Milky Way. The spiral arms of galaxies are very bright because massive short-lived high luminosity stars form there and die before leaving the arms.

Populations of stars co-evolve with the interstellar medium in which they form. 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. 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. The diagram shows three populations of stars. The first generation of stars (known as Population III) were metal free and many had masses hundreds of times greater than the sun and lived very brief lives before exploding to enrich interstellar space with the first metals in the universe. Higher metal content is essential for the formation of planets and life.

According to this representation, exploding massive stars are the primary or exclusive source of some of the most important elements for the formation of Earth-like planets and the building blocks of life.
This graph shows a model that fits observations well and indicates that star formation in terms of stellar mass per year per volume peaked when the universe was about two billion years old and is currently maybe 30 times smaller. The Milky Way formed through a seuence of mergers of smaller galaxies, mostly within the billion years following the Big Bang.




Formation of the Milky Way

Florent Renaud

Published on Oct 3, 2016

Hydrodynamical simulation of the formation of the Milky Way Dark matter in red, gas in blue, stars in yellow, iron in green.


Formation of the Milky Way and its Neighbors

djxatlanta Published on May 23, 2011

How did our galaxy form, and and when did its neighbors arrive? Researchers found all the dark matter halos in the Bolshoi simulation that had subhalos with speeds, distances and masses that matched the Magellanic Clouds, and then visualized one of them to show what the Milky Way's development may have been like. The Magellanic Clouds likely arrived together, recently! See the formation of the Milky Way and the Magellanic Clouds in this video. credit: Busha, Kaehler, Marshall & Wechsler, KIPAC/Stanford University


How was the Milky Way created?


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