Galaxy Morphology and Classification
Terms you will need
- spiral galaxyA spiral galaxy is a galaxy with a flat disk shape and spiral arms that wind out from a central bulge of stars.
- elliptical galaxyAn elliptical galaxy is a galaxy that has a smooth, oval shape and lacks the spiral arms or disk structure seen in other galaxies.
- irregular galaxyAn irregular galaxy is a galaxy that does not have a regular shape or structure, unlike spiral or elliptical galaxies.
- hubble tuning fork diagramThe Hubble tuning fork diagram is a classification system for galaxies that looks like a tuning fork, with elliptical galaxies on one side and spiral galaxies on the other.
- galactic bulgeThe galactic bulge is the central, dense region of a spiral galaxy where many stars are concentrated.
- disk componentThe disk component is the flat, rotating part of a spiral galaxy where spiral arms and most of its stars are located.
How this topic runs
Galaxy morphology and classification involve organizing galaxies based on their visual appearance, structure, and light distribution. The most famous classification scheme is the Hubble sequence, introduced by Edwin Hubble in 1926. It divides galaxies into three main categories: ellipticals, lenticulars, and spirals, with irregular galaxies as a fourth class. Elliptical galaxies have smooth, featureless shapes and are denoted by the letter 'E' followed by a number indicating their ellipticity. Lenticular galaxies, labeled 'S0', have a central bulge and a disk but lack spiral arms. Spiral galaxies, marked 'S', have a central bulge and spiral arms, with a subset having a bar-like structure, denoted 'SB'. The Hubble sequence is often depicted as a tuning-fork diagram, with ellipticals on the left and spirals on the right. Later, Gérard de Vaucouleurs expanded this system to include more detailed classifications based on bars, rings, and spiral arm tightness. These classifications are crucial for studying galaxy evolution, star formation, and the distribution of matter in the universe.
Figures (10)
Galaxy morphology and classification is about grouping galaxies based on how they look. Ellipticals are on the left, with the most circular on the far left. Lenticulars sit in the middle, and spirals branch off to the right.
It considers bars, rings, and how tightly wound the spiral arms are. For example, SAB(r)c means a weakly barred spiral with a ring and loosely wound arms. They lack a clear shape and are labeled Irr I or Irr II.
The Hubble sequence is still widely used, even though it has some flaws. Still, it helps scientists study galaxy properties like star formation and structure.
Key Points
- A spiral galaxy consists of a flattened disk, with stars forming a (usually two-armed) spiral structure, and a central concentration of stars known as the bulge.
- An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image.
- An irregular galaxy is a galaxy that does not fit into the Hubble sequence because it has no regular structure (either disk-like or ellipsoidal).
- The Hubble tuning fork diagram is a morphological classification scheme for galaxies, often represented in the form of a two-pronged fork, with the ellipticals on the left and the barred and unbarred spirals forming the two parallel prongs of the fork on the right.
Terms
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Sources & licensing(4)
- Wikipedia contributors — en.wikipedia.org/wiki/Galaxy_morphological_classification (Creative Commons Attribution-ShareAlike 4.0)
- Wikipedia contributors — en.wikipedia.org/wiki/Hubble_sequence (Creative Commons Attribution-ShareAlike 4.0)
- Wikipedia contributors — en.wikipedia.org/wiki/Barred_spiral_galaxy (Creative Commons Attribution-ShareAlike 4.0)
- Wikipedia contributors — en.wikipedia.org/wiki/Elliptical_galaxy (Creative Commons Attribution-ShareAlike 4.0)