Galaxies Vocab

4. An extended bulge of stars that is nearly spherical in shape and that consists primarily of Population II stars.
5. A galaxy that does not have the clearly defined shape and structure of typical elliptical, lenticular, or spiral galaxies.
6. A type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image.
8. A galaxy emitting unusually high quantities of radiation from an active galactic nucleus at its center.
10. A group of stars or galaxies forming a relatively close association.
11. A cluster with no specific shape, generally poor, and made of irregular, elliptical, spiral, and barred spiral galaxies.
12. A distribution of matter between a distant light source and an observer, that is capable of bending the light from the source as the light travels towards the observer.
16. A spiral galaxy with a central bar-shaped structure composed of stars.
17. An empirical relationship between the mass or intrinsic luminosity of a spiral galaxy and its asymptotic rotation velocity or emission line width.
19. The hot, X-ray emitting gas that permeates the space between galaxies.
20. Unseen matter that may make up more than ninety percent of the universe.
22. A galaxy in which the stars and gas clouds are concentrated mainly in one or more spiral arms.
23. A cluster that is spherically-shaped, usually rich, and one that contains many elliptical galaxies.

1. A simple method of describing the shapes of galaxies, using subdivisions of each of four basic types (elliptical, spiral, barred spiral, and irregular).
2. A law stating that the redshifts in the spectra of distant galaxies (and hence their speeds of recession) are proportional to their distance.
3. The unobserved matter required for the observed rotation of most galaxies to be consistent with their masses as inferred from luminous matter.
7. The spiral pattern rotates in a particular angular frequency (pattern speed), whereas the stars in the galactic disk are orbiting at a different speed depending their distance to the galaxy center.
9. Disc galaxies that have used up or lost most of their interstellar matter and therefore have very little ongoing star formation.
13. A cluster of galaxies which themselves occur as clusters.
14. A plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy's center.
15. The center of a galaxy, usually small, very bright, and containing a high density of stars and other objects.
18. A massive and extremely remote celestial object, emitting exceptionally large amounts of energy, and typically having a starlike image in a telescope.
21. A system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.