Seyfert galaxies were once considered to be a distinct class of galaxies because they:
A)are completely devoid of structure, appearing to be amorphous spheres of gas and dust.
B)are in the constellation of Seyfert in the southern hemisphere sky.
C)are very close to the Milky Way and appear to be gravitationally bound to it.
D)have hot and very bright and variable, compact central cores.

Question

Quizplus · Accepted Answer

Seyfert galaxies are characterized by their bright and variable central cores, which emit large amounts of radiation in different wavelengths. This radiation is believed to be caused by the presence of a supermassive black hole at the center of the galaxy, which is surrounded by a disk of hot gas and dust. This disk is responsible for much of the radiation emitted by the galaxy, and can give rise to strong emission lines in the spectrum of the galaxy. The other options are incorrect: Seyfert galaxies come in a variety of shapes and sizes, and are not necessarily close to the Milky Way; they are not completely devoid of structure, and can have spiral arms or other features; and the constellation of Seyfert is not particularly relevant to the definition of these galaxies.

Seyfert Galaxies Were Once Considered to Be a Distinct Class