Just a few days ago, the ESA released this Hubble image of a pair of barred spiral galaxies some 350 million light years away in the process of merging, their two galactic nuclei still separated by a massive distance but throwing out clouds of hot gas and mid-formation stars.
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NGC 1300 in infrared light. Spiral arms are regions of stars that extend from the center of spiral and barred spiral galaxies. These long, thin regions resemble a spiral and thus give spiral galaxies their name. Naturally, different classifications of spiral galaxies have distinct arm-structures.
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Messier 58 (also known as M58 and NGC 4579) is an intermediate barred spiral galaxy with a weak inner ring structure located within the constellation Virgo, approximately 68 million light-years away from Earth. It was discovered by Charles Messier on April 15, 1779 and is one of four barred spiral galaxies that appear in Messier's catalogue.The other barred spiral galaxies in Messier's catalogue are Messier 91, Messier 95 and Messier 109 M58 is one of the brightest galaxies in the Virgo Cluster. From 1779 it was arguably (though unknown at that time) the farthest known astronomical object until the release of the New General Catalogue in the 1880s and even more so the publishing of redshift values in the 1920s.
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However, recent studies show they are not possible only for edge-on galaxy but for galaxies with inclination less than 70°, with type S0 and Sb, like NGC 1532, also in Fornax Cluster. This bulges are found in other galaxies, with much less inclination. Examples for this are barred spiral galaxies NGC 3049 and IC 676.
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NGC 7098 NGC 2573 (also known as Polarissima Australis) is a faint barred spiral galaxy that happens to be the closest NGC object to the South Celestial Pole. NGC 7095 and NGC 7098 are two barred spiral galaxies that are 115 million and 95 million light-years distant from Earth respectively. The sparse open cluster Collinder 411 is also located in the constellation.
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NGC 7742 also known as Fried Egg Galaxy is a face-on unbarred spiral galaxy in the constellation Pegasus. The galaxy is unusual in that it contains a ring but no bar. Typically, bars are needed to produce a ring structure. The bars' gravitational forces move gas to the ends of the bars, where it forms into the rings seen in many barred spiral galaxies.
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The distribution of the neutral hydrogen in Dwingeloo 1 is typical one for barred spiral galaxies—it is rather flat with a minimum in the center or along the bar. The total mass of the neutral hydrogen is estimated at 370–450 million Solar masses. Dwingeloo 1 is a molecular gas-poor galaxy. The total mass of the molecular hydrogen does not exceed 10% of that of neutral hydrogen.
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At the time, it was believed that 1% of spiral galaxies are Seyferts. By 1977, it was found that very few Seyfert galaxies are ellipticals, most of them being spiral or barred spiral galaxies. During the same time period, efforts have been made to gather spectrophotometric data for Seyfert galaxies. It became obvious that not all spectra from Seyfert galaxies look the same, so they have been subclassified according to the characteristics of their emission spectra.
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Two of our closest cosmic neighbours, the Large and Small Magellanic Clouds, are barred, indicating that they may have once been barred spiral galaxies that were disrupted or torn apart by the gravitational pull of the Milky Way. 50px Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License. Something similar might be happening with IC 3583. This small galaxy is thought to be gravitationally interacting with one of its neighbours, the spiral Messier 90.
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In the French astronomer Gérard de Vaucouleurs' revised Hubble Sandage (VRHS) system of galaxy morphological classification, the Triangulum galaxy is classified as type SA(s)cd. The S prefix indicates that it is a disk-shaped galaxy with prominent arms of gas and dust that spiral out from the nucleus—what is commonly known as a spiral galaxy. The A is assigned when the galactic nucleus lacks a bar-shaped structure, in contrast to SB class barred spiral galaxies. American astronomer Allan Sandage's "(s)" notation is used when the spiral arms emerge directly from the nucleus or central bar, rather than from an inner ring as with an (r)-type galaxy.
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Our galaxy also appears unusually favorable in suffering fewer collisions with other galaxies over the last 10 billion years, which can cause more supernovae and other disturbances. Also, the Milky Way's central black hole seems to have neither too much nor too little activity.Scharf, 2012 The orbit of the Sun around the center of the Milky Way is indeed almost perfectly circular, with a period of 226 Ma (million years), closely matching the rotational period of the galaxy. However, the majority of stars in barred spiral galaxies populate the spiral arms rather than the halo and tend to move in gravitationally aligned orbits, so there is little that is unusual about the Sun's orbit.
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A majority of spiral galaxies, including our own Milky Way galaxy, have a linear, bar- shaped band of stars that extends outward to either side of the core, then merges into the spiral arm structure. In the Hubble classification scheme, these are designated by an SB, followed by a lower-case letter (a, b or c) which indicates the form of the spiral arms (in the same manner as the categorization of normal spiral galaxies). Bars are thought to be temporary structures that can occur as a result of a density wave radiating outward from the core, or else due to a tidal interaction with another galaxy. Many barred spiral galaxies are active, possibly as a result of gas being channeled into the core along the arms.
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Galaxy harassment is a type of interaction between a low-luminosity galaxy and a brighter one that takes place within rich galaxy clusters, such as Virgo and Coma, where galaxies are moving at high relative speeds and suffering frequent encounters with other systems of the cluster by the high galactic density of the latter. According to computer simulations, the interactions convert the affected galaxy disks into disturbed barred spiral galaxies and produces starbursts followed by, if more encounters occur, loss of angular momentum and heating of their gas. The result would be the conversion of (late type) low-luminosity spiral galaxies into dwarf spheroidals and dwarf ellipticals.Galaxy Harassment Evidence for the hypothesis had been claimed by studying early-type dwarf galaxies in the Virgo Cluster and finding structures, such as disks and spiral arms, which suggest they are former disk systems transformed by the above-mentioned interactions.
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The corotation circle takes on particular importance in reference to dark matter. In barred spiral galaxies (our Milky Way could be a galaxy of this type according to the most recent studies), the stars arranged along the bar structures rotate faster than those arranged along the arm structures, due to gravitational attraction. It has been calculated that if the radius of corotation were placed at a distance from the center of the galaxy greater than 1.4 times the length of the bar, this would constitute evidence that the rotation of the galaxy is curbed by dark matter halos, which are supposed to permeate space around the galaxy. All the measurements made, where galaxies have made it possible, have so far placed the circles of corotation at distances of less than 1.4, which would lead to the conclusion that dark matter does not significantly influence galactic rotation.
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