The Milky Way

The Milky Way in the strict sense, the band-like brightening the night sky, around a large circle as a prominent symmetry plane of the Milky Way spans the sky. The term stands in the broad sense or in the vernacular as a shorthand designation for the entire galaxy, also known as Galaxy. This star system of the type of barred spiral galaxy is the home of our Solar System. Other islands are extragalactic star galaxies genannt.Die for Population I stars of the galactic disk counting can be divided with increasing scattering around the main level and age into three sub-populations. The so-called "thin disk" in a range of 700 to 800 light-years above and below the galactic plane, in addition to the above-mentioned luminous stars in the spiral arms, which remove only a maximum of 500 light years from the plane, stars of spectral classes A and F, some giants of classes A, F, G and K dwarf stars, as well as the classes G, K and M dwarfs and some whites. The metallicity of these stars is comparable with that of the sun, but usually twice as high, her age is around one billion years.Another group is the medium of old stars (age up to five billion years). These include the Sun and other dwarf stars of spectral types G, K and M giants and some under-and red. The metal content is much lower with only about 50 to 100 percent of the sun. Also, the orbital eccentricity of galactic orbits of these stars and higher they are no more than 1,500 light-years above or below the galactic plane.Between a maximum of 2500 light-years above and below the main level extends the "thick disk". There are red K and M dwarfs, white dwarfs, and some subgiants and red giants, but also long-period variables. Their age reaches up to ten billion years and they are relatively metal-poor (about a quarter of Sonnenmetallizität).This population is also similar to many stars in the bulge.The galactic disk is not perfectly straight, through gravitational interaction with the Magellanic Clouds, it is easy gebogen.Messungen in their direction from the year 2004 showed that the Milky Way is about 13.6 billion years old. The accuracy of this assessment, which determines the age of beryllium using some globular clusters is estimated at about 800 million years ago. Since the age of the universe is 13.7 billion years ago as a fairly reliable determined, this would mean that the formation of the Milky Way in the early universe dated.In 2007, for the star HE 1523-0901 in the galactic halo determined by the ESO observatory in Hamburg, an age of 13.2 billion years ago. As the oldest known object in the Milky Way is this dating a lowest limit, which is in the range of the measurement accuracy of the estimation of 2004.By the same method, the age of the thin galactic disk where the oldest measured objects can be estimated, yielding an age of about 8.8 billion years ago with an estimated width of about 1.7 billion years ago. On this basis, a time gap would be about three to seven billion years between the formation of the galactic center and the outer disk.