Origin of Structure
Density wave theory is the preferred explanation for the well-defined structure of grand design spirals. 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; and 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. At the center of these galaxies are super-massive black holes.
Read more about this topic: Grand Design Spiral Galaxy
Famous quotes containing the words origin of, origin and/or structure:
“Someone had literally run to earth
In an old cellar hole in a byroad
The origin of all the family there.
Thence they were sprung, so numerous a tribe
That now not all the houses left in town
Made shift to shelter them without the help
Of here and there a tent in grove and orchard.”
—Robert Frost (1874–1963)
“Someone had literally run to earth
In an old cellar hole in a byroad
The origin of all the family there.
Thence they were sprung, so numerous a tribe
That now not all the houses left in town
Made shift to shelter them without the help
Of here and there a tent in grove and orchard.”
—Robert Frost (1874–1963)
“One theme links together these new proposals for family policy—the idea that the family is exceedingly durable. Changes in structure and function and individual roles are not to be confused with the collapse of the family. Families remain more important in the lives of children than other institutions. Family ties are stronger and more vital than many of us imagine in the perennial atmosphere of crisis surrounding the subject.”
—Joseph Featherstone (20th century)