Other material such as gas and dust that is circling the galaxy runs into these slower more dense arms. This occurrence can be compared to traffic jams. Once this gas and dust collides with the slower moving material it forms new blue stars. These newborn stars are very bright, but are short-lived and they usually die out before they pass through the spiral arm. This is why the arms are so bright and distinct.
Bars are large bodies of gas, dust, and stars.
These structures are cigar shaped and are 2 times more long than they are wide. Bars rotate as a solid object. Scientists have learned through the use of infrared telescopes that the gases inside of these bars are moving very quickly. It is also thought that bars are just part of a stage in the life of spiral galaxies. Bars are fairly common structures for galaxies to have.