A grand design spiral galaxy is a type of
spiral galaxy
Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''[flocculent
Flocculation, in the field of chemistry, is a process by which colloidal particles come out of suspension to sediment under the form of floc or flake, either spontaneously or due to the addition of a clarifying agent. The action differs from pr ...]
spirals which have subtler structural features. The spiral arms of a grand design galaxy extend clearly around the galaxy through many
radian
The radian, denoted by the symbol rad, is the unit of angle in the International System of Units (SI) and is the standard unit of angular measure used in many areas of mathematics. The unit was formerly an SI supplementary unit (before that c ...
s and can be observed over a large fraction of the galaxy's radius. As of 2002, approximately 10 percent of
all currently known spiral galaxies are classified as grand design type spirals,
including
M51 M51 or M-51 may refer to:
* M-51 (Michigan highway), a state highway in Michigan
* M51 highway (Russia)
* M51 (Cape Town), a Metropolitan Route in Cape Town, South Africa
* M51 Skysweeper, an anti-aircraft gun
* M51 MACI mine
* M51 SLBM, a Fre ...
,
M74,
M81,
M83, and
M101.
Origin of structure
Density wave theory
Density wave theory or the Lin–Shu density wave theory is a theory proposed by C.C. Lin and Frank Shu in the mid-1960s to explain the spiral arm structure of spiral galaxies. The Lin–Shu theory introduces the idea of long-lived quasistatic s ...
is the preferred explanation for the well-defined structure of grand design spirals,
first suggested by Lin and Shu in 1964.
The term "grand design" was not used in this work, but appeared in the 1966 continuation paper,
Lin
(along with Yuan and Shu
) is usually credited with coining of the term.
According to the density wave 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 and gas 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 toward the dense material by the force of gravity; and as they travel through the arm, they are slowed from exiting by the same gravitational pull. This causes the gas in particular to clump in the dense regions, which encourages gas clouds to collapse, producing
.
References
{{Galaxy
*
Galaxy morphological types