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It is also important to consider the morphology of the galaxy when attempting to measure its size – an issue that has been raised by the Russian astrophysicist B.A. Vorontsov-Vel'Yaminov in 1961, which considers separate determination methods in measuring the sizes of spiral and elliptical galaxies. [2]
A spiral galaxy is a type of galaxy characterized by a central bulge of old Population II stars surrounded by a rotating disc of younger Population I stars. A spiral galaxy maintains its spiral arms due to density wave theory.
Size (left) and distance (right) of a few well-known galaxies put to scale. There are an estimated 100 billion galaxies in all of the observable universe. [1] On the order of 100,000 galaxies make up the Local Supercluster, and about 51 galaxies are in the Local Group (see list of nearest galaxies for a complete list).
Halo stars may be acquired from small galaxies which fall into and merge with the spiral galaxy—for example, the Sagittarius Dwarf Spheroidal Galaxy is in the process of merging with the Milky Way and observations show that some stars in the halo of the Milky Way have been acquired from it.
An example of a spiral galaxy (Pinwheel Galaxy). This category contains galaxies in the S (de Vaucouleurs for indeterminate) category or any galaxy where it is indeterminate whether the galaxy is SA, SB or SAB in its spiral nature. SA, S (Hubble) galaxies should be categorized under Category:Unbarred spiral galaxies
Sizes can range from only a few thousand stars (dwarf irregulars) to 10 13 stars in giant ellipticals. Elliptical galaxies are spherical or elliptical in appearance. Spiral galaxies range from S0, the lenticular galaxies, to Sb, which have a bar across the nucleus, to Sc galaxies which have strong spiral arms.
Messier 100 (also known as NGC 4321 or the Mirror Galaxy) is a grand design intermediate spiral galaxy in the southern part of the mildly northern Coma Berenices. [5] It is one of the brightest and largest galaxies in the Virgo Cluster and is approximately 55 million light-years [ 3 ] from our galaxy , about 166,000 light-years in diameter.
UGC 2885 (Rubin's Galaxy, [10] nicknamed "Godzilla galaxy" [11]) is a large barred spiral galaxy of type SA(rs)c in the constellation Perseus.It is 232 million light-years (71 Mpc) from Earth and measures 463,000 ly (142,000 pc) across, making it one of the largest known spiral galaxies.