The four spiral arms of the Milky Way

A research team developed the first complete map of the Milky Way galaxy's spiral arms. The diagram shows the inner part of the Milky Way consisting of two symmetrical spiral arms, extending outside the galaxy where they split into four spiral arms.

Martin Pohl, Iowa State University's professor of physics and astronomy, said: 'For the first time these arms are shown across the entire Milky Way galaxy. Bifurcation of the arms can explain why previous studies - primarily using the interior or primarily the outer part of the galaxy - have given different results'.

This new chart was developed by Pohl, Peter Englmaier of the University of Zurich, Switzerland and Nicolai Bissantz of Ruhr University in Bochum, Germany.

Because the sun and other stars circle around the center of the Milky Way, researchers cannot observe these arms directly, but must rely on indirect evidence to find them. In ordinary light, the Milky Way looks like a dense pair of stars that don't follow any rules . Dust clouds cover the center of the galaxy so it cannot be observed with ordinary light.

The National Aeronautics and Space Administration's space exploration satellite was able to observe the Milky Way in infrared light using a device called the Diffuse IR Background Experiment.Infrared light is almost transparent dust clouds.

This picture shows the spiral arms of the Milky Way in red. The color shade shows the density of the gas researchers used to graph the spiral arms of the galaxy. (Photo: Iowa State University).

Englmaier and Bissantz used infrared data from satellites to develop gas flow models inside the galaxy. Poh uses the model to reconstruct the distribution of gas molecules in the galaxy. And those efforts lead to a map of the Milky Way's spiral arms.

The Milky Way is the most studied galaxy in the universe because other galaxies are too far away to be seen in detail. And studies of galaxies are important references when studying other galaxies.

Astrophysicists know that stars in the Milky Way are distributed as a disk with the central region consisting of long star bands. Outside this central area, stars are distributed along spiral arms.

In addition to the two spiral arms within the galaxy, two weaker arms also exist. These arms last about 10,000 light-years from the center of the galaxy. (The Sun is located 25,000 light-years from the center of the galaxy.) One of these arms has been known for a long time, but has always been a mystery because of the large deviation in its movement. The new model explains this inclination as a result of gravitational orbital change. Another arm on the far side of the galaxy was recently discovered in gas data.

Englamaier spoke about this second arm discovery: 'Finally it is clear that the model's predictions for symmetry are correct and the inner part of the galaxy has a balanced structure'.

Other scientific groups are also interested in using this new chart for their research. A group from France hopes to use it in the search for dark matter.