Astronomy   View all facts   Glossary   Help

physical object > natural object > celestial body > collection of stars > galaxy > spiral galaxy

spiral galaxy
subject			fact

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
	has definition A galaxy with a prominent nuclear bulge and luminous spiral arms of gas, dust, and young stars that wind out from the nucleus.
	is a kind of galaxy
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

Kinds of spiral galaxy :

• barred spiral (3 kinds, 9 facts) - (in Hubble's (1936) classification, SB: in Morgan's classification, B) A spiral galaxy whose nucleus is in the shape of a bar, at the ends of which the spiral arms start.
• Milky Way (9 facts) - System of approximately 100000 million stars, of which our Sun is one. It is a normal spiral galaxy of class Sb, with a diameter now reckoned to be probably less than 100,000 light-years, and a strong but obscure energy source at the center (emitting infrared radiation). It is undergoing galactic rotation. Possibly one tenth of the galaxy's total mass - estimated at 1.8 × 10¹¹ solar masses - comprises interstellar gas and dust., The galaxy to which the Sun belongs. Our Galaxy is about 10¹⁰ years old and contains about 10¹¹ stars. Its mass is at least 10¹¹ M_sun, about 5-10 percent of which is in the form of gas and dust. Diameter ~ 30 kpc; thickness of nuclear bulge about 4 kpc; thickness of disk about 700-800 pc; distance between spiral arms about 1.4 kpc. M_v = - 20.5. Mean density about 0.1 M_sun per cubic parsec. Magnetic field about 3-5 × 10^-6 gauss. Total luminosity about 10⁴⁴ ergs s^-1, Our own galaxy, the second largest in the local group., A softly glowing band of light that bisects the skies of Earth, produced by light from stars and nebulae in the galactic disk.
• Sa spiral (4 facts) (early-type spiral) - Spiral galaxy with arms tightly wound around the nucleus., In Hubble's classification, a spiral with a large nuclear bulge and closely coiled arms.
• Sb spiral (2 kinds, 25 facts) - Spiral galaxy with arms spread out from the nucleus.
• Sc spiral (3 kinds, 36 facts) - Spiral galaxy with arms widely spread out from the nucleus.
• Seyfert galaxy (2 kinds, 16 facts) - 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., 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.
• Sombrero galaxy (7 facts) (M 104, NGC 4594) - A spiral galaxy in the constellation Virgo. It was the first galaxy whose rotation was detected.