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[[File:MilkyWay1.jpg|right|250px|thumb|Map of the structure of the Milky Way galaxy.]]

[[File:MilkyWay1.jpg|right|250px|thumb|Map of the structure of the Milky Way galaxy.]]

The Milky Way galaxy is roughly divided into three sections: The '''galaxy core''' or bulge containing the Galactic Center, the '''disk''', which contains the majority of stars and material of the galaxy and is further divided into spiral arms, and the '''halo''', a diffuse, roughly spherical region of stars around the rest of the galaxy, consisting of mainly old stars.

The Milky Way galaxy is roughly divided into three sections: The '''galaxy core''' or bulge containing the Galactic Center, the '''disk''', which contains the majority of stars and material of the galaxy and is further divided into spiral arms, and the '''halo''', a diffuse, roughly spherical region of stars around the rest of the galaxy.

===Galaxy Core===

===Galaxy Core===

The '''Galaxy Core''', also called the '''Galactic Center''' or '''Galactic Bulge''', is the rotational center of the Milky Way.  It is some 25,000 light years away from our solar system and is the densest and most compact part of our galaxy, mostly consisting of older [[Metallicity|Population II stars]].  From the vantage point on Earth, it appears as the brightest part of the Milky Way.  Much of our knowledge of this region of our galaxy is from observations through [[gamma ray]], [[X-ray]], [[radio waves|radio]], and [[infrared]] satellites.  This is because much of the Galactic Center is visibly blocked from our vantage point by intervening interstellar dust.

The '''Galaxy Core''', also called the '''Galactic Center''' or '''Galactic Bulge''', is the rotational center of the Milky Way.  It is some 25,000 light years away from our solar system and is the densest and most compact part of our galaxy, mostly consisting of [[Metallicity|Population II stars]].  From the vantage point on Earth, it appears as the brightest part of the Milky Way.  Much of our knowledge of this region of our galaxy is from observations through [[gamma ray]], [[X-ray]], [[radio waves|radio]], and [[infrared]] satellites.  This is because much of the Galactic Center is visibly blocked from our vantage point by intervening interstellar dust.

In the center of the core of the galaxy is a large, complex radio source known as '''Sagittarius A''' that is invisible in normal light due to interstellar dust.  Here a [[supernova]] remnant exists along with a region of ionized [[hydrogen]].  Towards the center of this complex is '''Sagittarius A*''', the source of the radio waves and is the location of a supermassive black hole.<ref>http://news.bbc.co.uk/2/hi/science/nature/7774287.stm</ref> <ref>http://cass.ucsd.edu/public/tutorial/MW.html</ref> The black hole itself isn't the source of the radio waves, but the large accretion disk around it.

In the center of the core of the galaxy is a large, complex radio source known as '''Sagittarius A''' that is invisible in normal light due to interstellar dust.  Here a [[supernova]] remnant exists along with a region of ionized [[hydrogen]].  Towards the center of this complex is '''Sagittarius A*''', the source of the radio waves and is the location of a supermassive black hole.<ref>http://news.bbc.co.uk/2/hi/science/nature/7774287.stm</ref> <ref>http://cass.ucsd.edu/public/tutorial/MW.html</ref> The black hole itself isn't the source of the radio waves, but the large accretion disk around it.

There appears to be no star formation currently in the core of the galaxy, which consists of mostly older, red stars and [[globular cluster|globular clusters]].  However, there is a cluster of 100-200 very young stars.  It is possible they are from a star cluster outside the galactic core and migrated inward over time and now orbit near Sagittarius A*.<ref>http://www.astro.ucla.edu/~ghezgroup/gc/publications/yso.shtml</ref>  They are sometimes collectively referred to as the '''paradox of youth''' as the presence of the supermassive black hole is thought to normally disrupt any star formation.  The area immediately surrounding the core of the galaxy though, known as the "'''5-kpc ring'''", holds a large percentage of both the galaxy's molecular hydrogen and current star formation.<ref>http://www.bu.edu/galacticring/new_introduction.htm</ref>

There appears to be no star formation currently in the core of the galaxy, which consists of mostly red stars and [[globular cluster|globular clusters]].  However, there is a cluster of 100-200 very young stars.  It is possible they are from a star cluster outside the galactic core and migrated inward over time and now orbit near Sagittarius A*.<ref>http://www.astro.ucla.edu/~ghezgroup/gc/publications/yso.shtml</ref>  They are sometimes collectively referred to as the '''paradox of youth''' as the presence of the supermassive black hole is thought to normally disrupt any star formation.  The area immediately surrounding the core of the galaxy though, known as the "'''5-kpc ring'''", holds a large percentage of both the galaxy's molecular hydrogen and current star formation.<ref>http://www.bu.edu/galacticring/new_introduction.htm</ref>

===Disk===

===Disk===

===Halo===

===Halo===

The '''halo''' is a the region that surrounds the galactic disk and holds old Population II stars and globular clusters, of which 158 have been discovered so far<ref>http://www.seds.org/~spider/spider/MWGC/mwgc.html</ref>.  The Galactic Halo itself has a diameter of at least 200,000 light years based on the locations of the globular clusters, although it may extend much further.   

The '''halo''' is a the region that surrounds the galactic disk and holds Population II stars and globular clusters, of which 158 have been discovered so far<ref>http://www.seds.org/~spider/spider/MWGC/mwgc.html</ref>.  The Galactic Halo itself has a diameter of at least 200,000 light years based on the locations of the globular clusters, although it may extend much further.   

The stars that inhabit this sparsely populated portion of the galaxy tend to have retrograde or highly inclined orbits.  Many of these stars may have been acquired from smaller galaxies that have pulled into and since merged with the Milky Way.  There is no star formation out in the halo and the region appears to be free of interstellar dust.

The stars that inhabit this sparsely populated portion of the galaxy tend to have retrograde or highly inclined orbits.  Many of these stars may have been acquired from smaller galaxies that have pulled into and since merged with the Milky Way.  There is no star formation out in the halo and the region appears to be free of interstellar dust.