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Updated November 18, 2024

The Hubble Sequence: Understanding Galaxy Classification

The Hubble Sequence

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.

galaxy classification in the Hubble sequence

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.

Galaxy Types in the Hubble Sequence

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.

Examples

Future Collision of Our Galaxy with the Sagittarius Galaxy Future Collision of Our Galaxy with the Sagittarius Galaxy
Differences between the Milky Way and the Andromeda Galaxy Differences between the Milky Way and the Andromeda Galaxy
Why are Galaxies, Unlike Stars, So Close to Each Other? Why are Galaxies, Unlike Stars, So Close to Each Other?
Galaxies of the Local Group Galaxies of the Local Group
The hidden galaxy, one of Euclid's first images The hidden galaxy, one of Euclid's first images
The Virgo Cluster spans approximately three Full Moons The Virgo Cluster spans approximately three Full Moons
Where did the dark matter in our Galaxy go? Where did the dark matter in our Galaxy go?
Merging galaxies and black holes Merging galaxies and black holes
Mirages created by gravitational lenses Mirages created by gravitational lenses
Mystery of the Big Bang, the problem of the horizon Mystery of the Big Bang, the problem of the horizon
Cartwheel Galaxy Cosmic Event Cartwheel Galaxy Cosmic Event
The first second of our history The first second of our history
A small galaxy tears apart the large NGC 6745 A small galaxy tears apart the large NGC 6745
The mystery of gamma bursts The mystery of gamma bursts
The Cigar Explosion The Cigar Explosion
Shockwaves Shockwaves
Gould's belt, a stellar fireworks display Gould's belt, a stellar fireworks display
Recombination in cosmology Recombination in cosmology
Journey to the center of our galaxy Journey to the center of our galaxy
Lyman-alpha bubbles Lyman-alpha bubbles
Andromeda in the ultraviolet Andromeda in the ultraviolet
The most beautiful galaxy clusters The most beautiful galaxy clusters
Tinkerbell merger of three galaxies Tinkerbell merger of three galaxies
A gigantic black hole A gigantic black hole
Enigma of coplanar galaxies Enigma of coplanar galaxies
The cluster of galaxies Coma in its soup The cluster of galaxies Coma in its soup
The cannonball, proof of dark matter The cannonball, proof of dark matter
El Gordo galaxy cluster El Gordo galaxy cluster
Einstein ring and cross Einstein ring and cross
How to measure distances in the Universe? How to measure distances in the Universe?
The Hubble sequence and types of galaxies The Hubble sequence and types of galaxies
The spiral shape of the galactic arms The spiral shape of the galactic arms
Even more stars, the Cigar galaxy Even more stars, the Cigar galaxy
The Universe of X-rays The Universe of X-rays
The most beautiful galaxies The most beautiful galaxies
The oldest galaxies in the universe The oldest galaxies in the universe
Quasars the nuclei of galaxies Quasars the nuclei of galaxies
Sagittarius A black hole at the center of our Galaxy Sagittarius A black hole at the center of our Galaxy
The MOND theory and its contradiction The MOND theory and its contradiction
The first image of a black hole The first image of a black hole
Central area of the Milky Way Central area of the Milky Way
Laniakea, our supercluster of galaxies Laniakea, our supercluster of galaxies

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