Classification system of galaxies according to morphology
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Galaxy inshape, composition and stellar motion.American astronomer Hubble made a lot of observations on galaxies and put forward the first classification system of galaxies according to their morphology in 1926, which was continuously improved and completed the famousHubble classificationThis is a galaxy classification widely used by astronomers.
The basis of current galaxy classification is derived from the classification proposed by Hubble.After observing many galaxies, Hubble tried to classify them according to their morphology.After he proposed the first classification in 1926, he revised it again and again, and finally formed the classification.Only elliptical galaxies (E0-E7 type) were classified in 1926,Spiral galaxy(Type S) andBarred spiral galaxy(SB type), but the consistency from E type to S type is poor, so it was added in 1936Lenticular galaxy(SO type).Later, in 1950, he subdivided spiral galaxies and barred spiral galaxies into A, B and C types according to the size of the nuclear sphere and the winding mode of the vortex, and irregular galaxies into Irr type, llrr type and ll type.
Elliptical galaxy
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brief introduction
Elliptical galaxyThe shape is round or oval, the center is bright, the edge is gradually dark, there is a dense core of stars, and there are many outsideGlobular cluster。Generally, elliptical galaxies look yellow or red, which is quite different from spiral galaxies with hot young stars on their spiral arms emitting light blue tones.Elliptical galaxies can be huge or dwarf.The supergiant elliptical galaxy with the largest mass has a diameter of 500000 light-years, contains 10 trillion stars, and is the largest star system in the universe.And the smallestDwarf elliptical galaxyIt is only 3000 light-years in diameter and only consists of millions of stars, about the size of a globular cluster.
This is the spiral galaxy:
features
The movement of stars is dominated by irregular movement, which is different from that dominated by rotationspiral galaxy The stars inside.
Most stars are old and belong to the second star family.
Expressed by the English letter EEllipticityThe size is divided into eight subtypes: E0, E1, E2, E3, E4, E5, E6, E7. E0 is a circular galaxy, and E7 is the flattest elliptical galaxy.
Spiral galaxy
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Spiral galaxyThey account for about 30% of the total number of star systems. They have a relatively round core, from which two or more spiral arms extend.The degree of tightness of spiral arms of each spiral galaxy is slightly different.There is also a class of spiral galaxies. From the front, their spiral arms seem to extend from both ends of a rod like structure passing through the center of the nuclear sphere, called spiral rod galaxies.
features
The center is round and bulges like a biconvex lens, and several spiral arms extend from the core. The spiral arms include stars, gas and dust, and the shape is like a vortex
name
Ordinary spiral galaxies are represented by the letter S,Barred spiral galaxyIt is indicated by the English letter SB.
All spiral galaxies use a, b, c after S or SB to indicate the tightness or looseness of the spiral arms.
Irregular galaxy
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Irregular galaxyThere is no nuclear sphere and no rotating arm structure.Many irregular galaxies have small mass and strange shape, often leaving traces after the disappearance of spiral arms.Irregular galaxies only account for 5% of the total number of galaxies, but this estimate may not be objective because galaxies are far away from us. Astronomers often observe elliptical galaxies with larger luminosity, and some irregular galaxies with smaller luminosity may be ignored.
features
Irregular shape, usually without symmetry
name
It is indicated by the English letter Irr
Lenticular galaxy
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Lenticular galaxyIs that the Hubble classification isElliptical galaxyandspiral galaxy Between galaxies.Lenticular galaxyyesDisk galaxyMost of the interstellar matter has been exhausted or lost, and only a few stars are forming in the galaxy in progress, mainly old stars.Most of the dust in lenticular galaxies is only in the area near the core, and there is only a trace of dust in the appearance of the nuclear sphere.Since lenticular galaxies have no well-defined spiral arms, it is difficult to distinguish them from elliptical galaxies when they are facing us in the front.
features
Lenticular galaxies have prominent dust lanes, bright silver halos and globular clusters
