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Encyclopedia > Hubble sequence
It has been suggested that this article or section be merged with Galaxy classification. (Discuss)


The Hubble sequence is a classification of galaxy types developed by Edwin Hubble in 1936. It is also called the tuning-fork diagram as a result of the shape of its graphical representation. Galaxy types are divided as follows: Wikipedia does not have an article with this exact name. ... Astronomers classify galaxies based on their overall shape (elliptical, spiral or barred spiral) and further by the specific properties of the individual galaxy (for example degree of ellipse, number of spirals or definition of bar). ... Astronomers classify galaxies based on their overall shape (elliptical, spiral or barred spiral) and further by the specific properties of the individual galaxy (for example degree of ellipse, number of spirals or definition of bar). ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light years in diameter and approximately 60 million light years distant. ... Edwin Hubble Edwin Powell Hubble (November 20, 1889–September 28, 1953) was an American astronomer, noted for his discovery of galaxies beyond the Milky Way and the cosmological redshift. ... 1936 (MCMXXXVI) was a leap year starting on Wednesday (link will take you to calendar). ...

Tuning-fork style diagram of the Hubble sequence
Tuning-fork style diagram of the Hubble sequence
  • An elliptical galaxy (E0-7) has an ellipsoidal form, with a fairly even distribution of stars throughout. The number gives the degree of eccentricity: E0 galaxies are nearly round, while E7 are greatly flattened. The number indicates only how the galaxy appears on the sky, not its true geometry.
  • A lenticular galaxy (S0 and SB0) appears to have a disk-like structure with a central spherical bulge projecting from it, and does not show any spiral structure.
  • A spiral galaxy (Sa-d) has a central bulge and an outlying disk containing spiral arms. The arms are centered around the bulge, and vary from tightly wound (Sa) to very loose (Sc and Sd). The latter also have less pronounced central bulges.
  • A barred spiral galaxy (SBa-d) has a similar sort of spiral structure to spiral galaxies, but instead of emanating from the bulge, the arms project out from the ends of a "bar" running through the bulge, like ribbons on either end of a baton. Again, SBa to SBd refer to how "tightly wound" these arms are.
  • An irregular galaxy (Irr) can be of type Irr-I, which shows spiral structure but is deformed in some way, and Irr-II for any other galaxy that does not fit into another category.
Known Properties of Galaxies
Galaxy Type Mass (Solar Masses) Luminosity (Solar Luminosity) Diameter (kpc) Stellar Populations Percentage of Observed Galaxies
Spiral /
Barred Spiral
109 to 1011 108 to 1010 5-250 disk: Population I
halo:Population II
77%
Elliptical 105 to 1013 105 to 1011 1-205 Population II 20%
Irregular 108 to 1010 107 to 109 1-10 Population I 3%

Hubble based his classification on photographs of the galaxies through the telescopes of the time. He originally believed that elliptical galaxies were an early form, which might have later evolved into spirals; our current understanding suggests that the situation is roughly opposite, however, this early belief left its imprint in the astronomers' jargon, who still speak of "early type" or "late type" galaxies according to whether a galaxy's type appears to the left or to the right in the diagram. A tuning-fork diagram of the Hubble galaxy classification scheme. ... A tuning-fork diagram of the Hubble galaxy classification scheme. ... An elliptical galaxy is a type of galaxy in the Hubble sequence characterized by the following physical properties: The giant elliptical galaxy NGC 4881 (the spherical glow at upper left) lies at the edge of the Coma Cluster of Galaxies. ... The Spindle Galaxy (NGC 5866), a lenticular galaxy in the Draco constellation. ... A spiral galaxy is a type of galaxy in the Hubble sequence which is characterized by the following physical properties: Spiral Galaxy M74 presents a face-on view of its spiral arms. ... NGC 1300, viewed nearly face-on. ... NGC1427A, an example of an irregular galaxy. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... The Sun is the star at the center of Earths solar system. ... Metal-poor is a term that is used to describe the chemical make up of an astronomical object. ... Metal-poor is a term that is used to describe the chemical make up of an astronomical object. ... A sepia-tinted photograph of an English couple, taken in 1895. ... 50 cm refracting telescope at Nice Observatory. ...


More modern observations of galaxies have given us the following information about these types:

  • Elliptical galaxies are generally fairly low in gas and dust, and are composed mostly of older stars.
  • Spiral galaxies generally have plentiful supplies of gas and dust, and have a broad mix of older and younger stars.
  • Irregular galaxies are fairly rich in gas, dust, and young stars.

From this, astronomers have constructed a theory of galaxy evolution which suggests that ellipticals are, in fact, the result of collisions between spiral and/or irregular galaxies, which strip out much of the gas and dust and randomize the orbits of the stars. See galaxy formation and evolution. REDIRECT [[ --68. ...

Elliptical Galaxies examples
Name Right Ascension Declination Hubble Type
M49 (NGC 4472) 12h 29.8m 8° 00' E4
M59 (NGC 4621) 12h 42.0m 11° 39' E3
M60 (NGC 4649) 12h 43.7m 11° 33' E1
M84 (NGC 4374) 12h 25.1m 12° 53' E1
M86 (NGC 4406) 12h 26.2m 12° 57' E3
M89 (NGC 4552) 12h 35.7m 12° 33' E0
M110 (NGC 205) 00h 40.4m 41° 41' E6

Elliptical Galaxy M49 (also known as Messier Object 49, Messier 49, M49, or NGC 4472) is an elliptical galaxy in the Virgo constellation. ... M59, courtesy of NOAO. Elliptical Galaxy M59 (also known as Messier Object 59, Messier 59, M59, or NGC 4621) is an elliptical galaxy in the constellation Virgo. ... M60, courtesy of NOAO Elliptical Galaxy M60 (also known as Messier Object 60, Messier 60, M60, or NGC 4649) is an elliptical galaxy in the constellation Virgo. ... The Lenticular Galaxy M84 (also known as Messier Object 84, Messier 84, M84, or NGC 4374) is a lenticular galaxy in the Virgo constellation. ... The Lenticular Galaxy M86 (also known as Messier Object 86, Messier 86, M86, or NGC 4406) is a lenticular galaxy in the Virgo constellation. ... Elliptical Galaxy M89 (also known as Messier Object 89, Messier 89, M89, or NGC 4552) is an elliptical galaxy in the Virgo constellation. ... The Elliptical Galaxy M110 (also known as Messier Object 110, Messier 110, M110, or NGC 205) is an elliptical galaxy in the Andromeda constellation, a satellite of the Andromeda Galaxy, and a member of the Local Group galaxies. ...

See also


  Results from FactBites:
 
Hubble sequence - Wikipedia, the free encyclopedia (406 words)
The Hubble sequence is a classification of galaxy types developed by Edwin Hubble in 1936.
It is also called the tuning-fork diagram as a result of the shape of its graphical representation.
Hubble based his classification on photographs of the galaxies through the telescopes of the time.
  More results at FactBites »

 
 

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