Structure
Spiral galaxies consist of four distinct components:
- A flat, rotating disc of (mostly newly created) stars and interstellar matter
- A central stellar bulge of mainly older stars, which resembles an elliptical galaxy
- A near-spherical halo of stars, including many in globular clusters
- A supermassive black hole at the very center of the central bulge
The relative importance, in terms of mass, brightness and size, of the different components varies from galaxy to galaxy.
Read more about this topic: Spiral Galaxy
Famous quotes containing the word structure:
“There is no such thing as a language, not if a language is anything like what many philosophers and linguists have supposed. There is therefore no such thing to be learned, mastered, or born with. We must give up the idea of a clearly defined shared structure which language-users acquire and then apply to cases.”
—Donald Davidson (b. 1917)
“I really do inhabit a system in which words are capable of shaking the entire structure of government, where words can prove mightier than ten military divisions.”
—Václav Havel (b. 1936)
“Each structure and institution here was so primitive that you could at once refer it to its source; but our buildings commonly suggest neither their origin nor their purpose.”
—Henry David Thoreau (1817–1862)