Image description: A composition of galaxy photographs taken with the Hubble Space Telescope and the Sloan Digital Sky Survey. The galaxies are arranged according to the Hubble sequence classification (E: elliptical galaxies; S0: lenticular galaxies; Sa_b_c_d: spiral galaxies, and Pec: irregular galaxies). Credits: HST, SDSS, GEPI.
Image description: Spiral galaxies are further subdivided based on the structure of their arms. Sa galaxies have loosely defined spiral arms and a larger central bulge, while Sc galaxies have more distinct arms and a smaller bulge. Elliptical galaxies are classified from "E0" to "E7" depending on their degree of flattening. "E0" represents a nearly spherical shape, while "E7" is significantly flattened.
The Hubble sequence is a galaxy classification system proposed by astronomer Edwin Hubble in 1926. It organizes galaxies based on their shape and morphological characteristics. This classification has been pivotal in understanding galaxy evolution and the universe.
The Hubble sequence divides galaxies into four main categories:
The Hubble sequence is sometimes interpreted as an evolutionary progression. For instance, spiral galaxies can become elliptical after major mergers. However, this is not a strict rule, as galaxy formation depends on complex factors like gravitational interactions, local environments, and gas reserves.
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