#Barred spiral galaxy sba professional#

See also: Lenticular galaxy Spirals The Pinwheel Galaxy (Messier 101/NGC 5457): a spiral galaxy classified as type Scd on the Hubble sequence The barred spiral galaxy NGC 1300: a type SBbc Įxamples of lenticular galaxies: M85, M86, NGC 1316, NGC 2787, NGC 5866, Centaurus A.

The bulge-to-disk flux ratio in lenticular galaxies can take on a range of values, just as it does for each of the spiral galaxy morphological types (Sa, Sb, etc.). Lenticular and spiral galaxies, taken together, are often referred to as disk galaxies. Missing from the Hubble sequence are the early-type galaxies with intermediate-scale disks, in between the E0 and S0 types, Martha Liller denoted them ES galaxies in 1966. Later observations (by Hubble himself, among others) showed Hubble's belief to be correct and the S0 class was included in the definitive exposition of the Hubble sequence by Allan Sandage. Hubble believed that they were necessary as an intermediate stage between the highly flattened 'ellipticals' and spirals. When viewed edge-on, the disk becomes more apparent and prominent dust-lanes are sometimes visible in absorption at optical wavelengths.Īt the time of the initial publication of Hubble's galaxy classification scheme, the existence of lenticular galaxies was purely hypothetical. When simply looking at a galaxy's image, lenticular galaxies with relatively face-on disks are difficult to distinguish from ellipticals of type E0–E3, making the classification of many such galaxies uncertain. Unlike spiral galaxies, the disks of lenticular galaxies have no visible spiral structure and are not actively forming stars in any significant quantity. These galaxies consist of a bright central bulge, similar in appearance to an elliptical galaxy, surrounded by an extended, disk-like structure.

See also: Elliptical galaxy Lenticulars The Spindle Galaxy (NGC 5866), a lenticular galaxy with a prominent dust lane in the constellation of Draco.Īt the centre of the Hubble tuning fork, where the two spiral-galaxy branches and the elliptical branch join, lies an intermediate class of galaxies known as lenticulars and given the symbol S0. Įxamples of elliptical galaxies: M49, M59, M60, M87, NGC 4125. Observations of the kinematics of early-type galaxies further confirmed this. However, from studying the light profiles and the ellipticity profiles, rather than just looking at the images, it was realised in the 1960s that the E5–E7 galaxies are probably misclassified lenticular galaxies with large-scale disks seen at various inclinations to our line-of-sight. Observationally, the most flattened 'elliptical' galaxies have ellipticities e = 0.7 (denoted E7). It is important to note that the ellipticity of a galaxy on the sky is only indirectly related to the true 3-dimensional shape (for example, a flattened, discus-shaped galaxy can appear almost round if viewed face-on or highly elliptical if viewed edge-on). The ellipticity increases from left to right on the Hubble diagram, with near-circular (E0) galaxies situated on the very left of the diagram. By convention, n is ten times the ellipticity of the galaxy, rounded to the nearest integer, where the ellipticity is defined as e = 1 − b / a for an ellipse with a the semi-major axis length and b the semi-minor axis length.

They are denoted by the letter E, followed by an integer n representing their degree of ellipticity in the sky. Elliptical galaxies have relatively smooth, featureless light distributions and appear as ellipses in photographic images. On the left (in the sense that the sequence is usually drawn) lie the ellipticals.

#Barred spiral galaxy sba professional#

The Hubble sequence is the most commonly used system for classifying galaxies, both in professional astronomical research and in amateur astronomy.Ĭlasses of galaxies Ellipticals The giant elliptical galaxy ESO 325-G004. A fourth class contains galaxies with an irregular appearance. The tuning fork scheme divided regular galaxies into three broad classes – ellipticals, lenticulars and spirals – based on their visual appearance (originally on photographic plates). Tuning-fork style diagram of the Hubble sequence It was invented by John Henry Reynolds and Sir James Jeans. It is often colloquially known as the Hubble tuning-fork diagram because the shape in which it is traditionally represented resembles a tuning fork. The Hubble sequence is a morphological classification scheme for galaxies published by Edwin Hubble in 1926. Galaxy morphological classification scheme advocated by Edwin Hubble