The lower limit on the estimate of the Milky Way's diameter is 100000 ly.
The Milky Way is a barred spiral galaxy some 100,000–120,000 light-years in diameter, which contains 100–400 billion stars. The Solar System is located within the disk, about 27,000 light-years away from the Galactic Center, on the inner edge of one of the spiral-shaped concentrations of gas and dust called the Orion Arm.
The Milky Way is the galaxy that contains our Solar System. Its name “milky” is derived from its appearance as a dim glowing band arching across the night sky in which the naked eye cannot distinguish individual stars.
From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610.
Up until the early 1920s, most astronomers thought that all of the stars in the universe were contained inside of the Milky Way. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis,[21] observations by Edwin Hubble definitively showed that the Milky Way is just one of many billions of galaxies.[22]
Surrounded by several smaller satellite galaxies, the Milky Way is part of the Local Group of galaxies, which forms a subcomponent of the Virgo Supercluster, which again forms a subcomponent of the Laniakea supercluster.[27][28]
[1] Milky Way
Source: Wikipedia
URL: http://en.wikipedia.org/wiki/Milky_Way
Public License: < CC Attribution-ShareAlike 4.0 International >
[2] How Large is the Milky Way
Source: NASA
URL: http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980317b.html