How big is the Milky Way REALLY in diameter?
The stellar disk of the Milky Way galaxy is approximately 100,000 light-years (9.5×1017 km) in diameter, and is believed to be, on average, about 1,000 ly (9.5×1015 km) thick. it is estimated to contain at least 200 billion stars and possibly up to 400 billion stars, the exact figure depending on the number of very low-mass stars, which is highly uncertain. Extending beyond the stellar disk is a much thicker disk of gas. Recent observations indicate that the gaseous disk of the Milky Way has a thickness of around 12,000 ly (1.1×1017 km)—twice the previously accepted value. As a guide to the relative physical scale of the Milky Way, if it were reduced to 100 m in diameter, the Solar System, including the Oort Cloud, would be no more than 1 mm in width. The Galactic Halo extends outward, but is limited in size by the orbits of two Milky Way satellites, the Large and the Small Magellanic Clouds, whose perigalacticon is at ~180,000 ly (1.7×1018 km).At this distance or beyond, the orbits of
M31 is around 140,000 light-years in diameter. Counting the sparse low luminosity stars and the red giants from the outskirts of its disk will make it 50-60,000 light-years larger. The January 2009 paper put forward to the AAPAS says that the Milky Way may be of comparable size as a giant spiral. The best estimate makes the former 100,000 light-year galaxy about 30,000 light-years in diameter larger and that is not counting the sparsely distributed stars I mentioned earlier. Pretty large, huh? I answered a similar question just a few days ago: http://answers.yahoo.com/question/index;… http://www.universetoday.com/2009/01/05/… You’ll know where my answer is. Clear skies!
