| Seyfert galaxy | has definition A type of spiral galaxy first discovered by Karl Seyfert in the 1940s. The central region of a Seyfert galaxy is distinguished by powerful radiation, much of it focused into narrow frequencies. |  |
| has definition One of a small class of galaxies (many of which are spirals) of very high luminosity and very blue continuum radiation with small, intensely bright nuclei whose spectra show strong, broad, high-excitation emission lines probably caused by discrete clouds moving at velocities that are higher than the escape velocity. Seyferts possess many of the properties of QSOs, such as the ultraviolet excess of the continuum, the wide emission lines, and the strong infrared luminosity. The energy sources in their nuclei are unexplained; presumably the energy input can be associated with some process that liberates gravitational binding energy to accelerate relativistic particles. Seyferts comprise about 1 percent of the bright galaxies. The brightest Seyfert known is NGC 1068. Weedman-Khachikian classification: class 1 Seyferts have broad Balmer line wings; class 2 have no obvious Balmer line wings. | |
| is a kind of spiral galaxy | |
| spiral galaxy | has classification criterion Subdivided according to the openness of the spiral arms as Sa spiral, Sb spiral or Sc spiral. | |
| has mass 1010 to 1012 Msun | |
| galaxy | has number of stars 106 to 1012 | |
| has catalog galaxy catalog | |
| celestial body | has spectra | |
| physical object | has location or center of gravity | |
| has angular momentum | |
| has velocity | |
| has momentum | |
| has temperature | |
| has volume | |
| has extent | |
| has material | |
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