In the 1950s, astronomers produced the map of our galaxy based off radio observations of gas. Such studies suggest that the Milky Way is made of four major spiraling arms.
The four major arms were Norma, Scutum-Crux, Sagittarius, Persues, while our Solar System is located on a "small, partial" arm called the Orion. For decades, astronomers have produced the structure of the milky way based only on radio signals.
By the 1990s, the use of infrared telescopes became the accepted form of mapping the Milky Way since infrared could penetrate dust and thus have better resolution in crowded sectors of our galaxy. However, such use of infrared observations have overthrown many preconceptions of the structure of the galaxy!
In 2008, A team of scientists using the Spitzer Infrared Space Telescope showed that the Milky Way had two major arms instead of four!
"These major arms, the Scutum-Centaurus and Perseus arms, have the greatest densities of both young, bright stars, and older, so-called red-giant stars. The two minor arms, Sagittarius and Norma, are filled with gas and pockets of young stars. Benjamin said the two major arms seem to connect up nicely with the near and far ends of the galaxy's central bar."
For additional information and curiosity of the minor arms, Far/Near 3kpc, please view this link.
However, that was what NASA said in 2008. In 2009, another group of scientists used Very Long Baseline Array (VLBA) and revitalized the previous concepts that the Milky Way Galaxy has four arms instead of two.
VLBA is "a system of 10 radio-telescope antennas stretching from Hawaii to New England and the Caribbean, provides the best ability to see the finest detail, called resolving power, of any astronomical tool in the world. The VLBA can routinely produce images hundreds of times more detailed than those produced by the Hubble Space Telescope," and thus making the claim these scientists are trying to assert, as the most recognized idea of the structure of the Milky Way Galaxy yet.
To more understand this competing theory, please click here.
Yet, another group of scientists based off Brazil by 2010 are starting to claim that the Milky Way Galaxy may in fact be a square instead of the circular shape previous scientists have conceived of its structure as.
Their data which is built upon the 2008 VLBA study shown above, indicates that many parts of the 'spirals' didn't neatly circle the galactic center, but were in fact straight.
Although not the first group of scientists to claim this, this group of scientists also believe that their data shows that the Milky Way Galaxy is composed of not two or four arms, but three!
To understand more about these Brazilian scientist's standpoints, click on this link.
This long, messy pursuit of knowledge of how our galaxy looks like from another galaxy's point of view illustrates science perfectly, as competing theories continue to grow to seek more support until one theory is agreed upon by the majority of astronomers. Unfortunately for the time being, it would seem that the shape and size of the Milky Way Galaxy, our own tiny backyard within the almost infinite universe, remains uncertain.
