A Spitzer Space Telescope Image of Messier 81, a grand design spiral

A grand design spiral galaxy is a type of spiral galaxy with prominent and well-defined spiral arms, as opposed to multi-arm and flocculent spirals which have subtler structural features. A spiral galaxy is a Galaxy belonging to one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work “The Realm of the The spiral arms of a grand design galaxy extend clearly around the galaxy through many radians and can be observed over a large fraction of the galaxy's radius. The radian is a unit of plane Angle, equal to 180/ π degrees, or about 57 Approximately ten percent of spiral galaxies are classified as grand design type spirals[1], including M81 and M51, the Whirlpool Galaxy. Messier 81 (also known as NGC 3031 or Bode's Galaxy) is a Spiral galaxy about 12 million Light-years away in the Constellation The Whirlpool Galaxy (also known as Messier 51a, M51a, or NGC 5194) is an interacting Spiral galaxy located at a distance of

The origin of Grand Design structure

Density wave theory is the preferred explanation for the well-defined structure of grand design spirals[2]. Density wave theory or the Lin-Shu density wave theory is a theory proposed by C According to this theory, the spiral arms are created inside density waves that turn around the galaxy at different speeds from the stars in the galaxy’s disk. Stars are clumped in these dense regions due to gravitational attraction towards the dense material, though their location in the spiral arm may not be permanent. When they come close to the spiral arm, they are pulled towards the dense material by the force of gravity. However, as they travel through the arm, they are slowed from exiting by the same gravitational pull. This causes material to clump in the dense regions.

References

1. Mihos, Chris (2002-01-11), Spiral Structure, <http://burro.cwru.edu/Academics/Astr222/Galaxies/Spiral/spiral.html>. Retrieved on 30 May 2007 

2. [|Masters, Karen] (2002-09), What is the Origin of Spiral Structure in Galaxies, <http://curious.astro.cornell.edu/question.php?number=199>. Retrieved on 30 May 2007