Resultado de búsqueda
Types of Galaxies. Scientists sometimes categorize galaxies based on their shapes and physical features. Other classifications organize galaxies by the activity in their central regions – powered by a supersized black hole – and the angle at which we view them.
- Types of Galaxies | NASA Space Place – NASA Science for Kids
Types of Galaxies. A galaxy is a huge collection of gas,...
- Galaxies - NASA Science
Galaxies consist of stars, planets, and vast clouds of gas...
- Types of Galaxies | NASA Space Place – NASA Science for Kids
31 de ene. de 2024 · Types of Galaxies. What Kinds of Galaxies Are There? Astronomers classify galaxies into three major categories: elliptical, spiral and irregular. These galaxies span a wide range of sizes, from dwarf galaxies containing as few as 100 million stars to giant galaxies with more than a trillion stars.
- Overview
- Principal schemes of classification
- S0 galaxies
- Sa galaxies
- Sb galaxies
- Sc galaxies
- SB galaxies
Almost all current systems of galaxy classification are outgrowths of the initial scheme proposed by the American astronomer Edwin Hubble in 1926. In Hubble’s scheme, which is based on the optical appearance of galaxy images on photographic plates, galaxies are divided into three general classes: ellipticals, spirals, and irregulars. Hubble subdivided these three classes into finer groups.
In The Hubble Atlas of Galaxies (1961), the American astronomer Allan R. Sandage drew on Hubble’s notes and his own research on galaxy morphology to revise the Hubble classification scheme. Some of the features of this revised scheme are subject to argument because of the findings of very recent research, but its general features, especially the coding of types, remain viable. A description of the classes as defined by Sandage is given here, along with observations concerning needed refinements of some of the details.
Almost all current systems of galaxy classification are outgrowths of the initial scheme proposed by the American astronomer Edwin Hubble in 1926. In Hubble’s scheme, which is based on the optical appearance of galaxy images on photographic plates, galaxies are divided into three general classes: ellipticals, spirals, and irregulars. Hubble subdivided these three classes into finer groups.
In The Hubble Atlas of Galaxies (1961), the American astronomer Allan R. Sandage drew on Hubble’s notes and his own research on galaxy morphology to revise the Hubble classification scheme. Some of the features of this revised scheme are subject to argument because of the findings of very recent research, but its general features, especially the coding of types, remain viable. A description of the classes as defined by Sandage is given here, along with observations concerning needed refinements of some of the details.
These systems exhibit some of the properties of both the ellipticals and the spirals and seem to be a bridge between these two more common galaxy types. Hubble introduced the S0 class long after his original classification scheme had been universally adopted, largely because he noticed the dearth of highly flattened objects that otherwise had the properties of elliptical galaxies. Sandage’s elaboration of the S0 class yielded the characteristics described here.
S0 galaxies have a bright nucleus that is surrounded by a smooth, featureless bulge and a faint outer envelope. They are thin; statistical studies of the ratio of the apparent axes (seen projected onto the sky) indicate that they have intrinsic ratios of minor to major axes in the range 0.1 to 0.3. Their structure does not generally follow the luminosity law of elliptical galaxies but has a form more like that for spiral galaxies. Some S0 systems have a hint of structure in the envelope, either faintly discernible armlike discontinuities or narrow absorption lanes produced by interstellar dust. Several S0 galaxies are otherwise peculiar, and it is difficult to classify them with certainty. They can be thought of as peculiar irregular galaxies (i.e., Irr II galaxies) or simply as some of the 1 or 2 percent of galaxies that do not fit easily into the Hubble scheme. Among these are such galaxies as NGC 4753, which has irregular dust lanes across its image, and NGC 128, which has a double, almost rectangular bulge around a central nucleus. Another type of peculiar S0 is found in NGC 2685. This nebula in the constellation Ursa Major has an apparently edge-on disk galaxy at its centre, with surrounding hoops of gas, dust, and stars arranged in a plane that is at right angles to the apparent plane of the central object.
These normal spirals have narrow, tightly wound arms, which usually are visible because of the presence of interstellar dust and, in many cases, bright stars. Most of them have a large amorphous bulge in the centre, but there are some that violate this criterion, having a small nucleus around which is arranged an amorphous disk with superimposed fa...
This intermediate type of spiral typically has a medium-sized nucleus. Its arms are more widely spread than those of the Sa variety and appear less smooth. They contain stars, star clouds, and interstellar gas and dust. Sb galaxies show wide dispersions in details in terms of their shape. Hubble and Sandage observed, for example, that in certain Sb galaxies the arms emerge at the nucleus, which is often quite small. Other members of this subclass have arms that begin tangent to a bright, nearly circular ring, while still others reveal a small, bright spiral pattern inset into the nuclear bulge. In any of these cases, the spiral arms may be set at different pitch angles. (A pitch angle is defined as the angle between an arm and a circle centred on the nucleus and intersecting the arm.)
Hubble and Sandage noted further deviations from the standard shape established for Sb galaxies. A few systems exhibit a chaotic dust pattern superimposed upon the tightly wound spiral arms. Some have smooth, thick arms of low surface brightness, frequently bounded on their inner edges with dust lanes. Finally, there are those with a large, smooth nuclear bulge from which the arms emanate, flowing outward tangent to the bulge and forming short arm segments. This is the most familiar type of Sb galaxy and is best exemplified by the giant Andromeda Galaxy.
These galaxies characteristically have a very small nucleus and multiple spiral arms that are open, with relatively large pitch angles. The arms, moreover, are lumpy, containing as they do numerous irregularly distributed star clouds, stellar associations, star clusters, and gas clouds known as emission nebulae.
As in the case of Sb galaxies, there are several recognizable subtypes among the Sc systems. Sandage has cited six subdivisions: (1) galaxies, such as the Whirlpool Galaxy (M51), that have thin branched arms that wind outward from a tiny nucleus, usually extending out about 180° before branching into multiple segments, (2) systems with multiple arms that start tangent to a bright ring centred on the nucleus, (3) those with arms that are poorly defined and that span the entire image of the galaxy, (4) those with a spiral pattern that cannot easily be traced and that are multiple and punctuated with chaotic dust lanes, (5) those with thick, loose arms that are not well defined—e.g., the nearby galaxy M33 (the Triangulum Nebula)—and (6) transition types, which are almost so lacking in order that they could be considered irregular galaxies.
The luminosities, dimensions, spectra, and distributions of the barred spirals tend to be indistinguishable from those of normal spirals. The subclasses of SB systems exist in parallel sequence to those of the latter.
There are SB0 galaxies that feature a large nuclear bulge surrounded by a disklike envelope across which runs a luminous featureless bar. Some SB0 systems have short bars, while others have bars that extend across the entire visible image. Occasionally there is a ringlike feature external to the bar. SBa galaxies have bright, fairly large nuclear bulges and tightly wound, smooth spiral arms that emerge from the ends of the bar or from a circular ring external to the bar. SBb systems have a smooth bar as well as relatively smooth and continuous arms. In some galaxies of this type, the arms start at or near the ends of the bar, with conspicuous dust lanes along the inside of the bar that can be traced right up to the nucleus. Others have arms that start tangent to a ring external to the bar. In SBc galaxies, both the arms and the bar are highly resolved into star clouds and stellar associations. The arms are open in form and can start either at the ends of the bar or tangent to a ring.
Today, we understand that at least some galaxies have changed types over the billions of years since the universe began. As we shall see in later chapters, collisions and mergers between galaxies may dramatically change spiral galaxies into elliptical galaxies.
Types of Galaxies - Spiral, Elliptical & Irregular Galaxies. The most widely used classification scheme for galaxies is based on one devised by Edwin P. Hubble and further refined by astronomer Gerard de Vaucouleurs. It uses the three main types: Spiral. Elliptical. Irregular.
![What Are The 3 Types Of Galaxies [Full Guide] - DopeGuides](https://mx.images.search.yahoo.com/search/images?p=3+types+of+galaxies&q=Federico+I+de+Dinamarca&ei=UTF-8&fl=0&rd=r2&norw=1&age=1m&hsimp=yhs-elex_22find&hspart=Elex&fr=yhs-Elex-elex_22find&th=123.2&tw=164.5&imgurl=https%3A%2F%2Fdopeguides.com%2Fwp-content%2Fuploads%2F2020%2F10%2F3-types-of-galaxies-galaxy-a-cluster-of-billions-and-trillions-of-stars-bound-together-by-gravity-l.jpg&rurl=https%3A%2F%2Fdopeguides.com%2F3-types-of-galaxies%2F&size=58KB&name=What+Are+The+3+Types+Of+Galaxies+%5BFull+Guide%5D+-+DopeGuides&oid=2&h=355&w=474&turl=https%3A%2F%2Ftse1.mm.bing.net%2Fth%3Fid%3DOIP.ccnY2fKfRnp5-85qPBeIcgAAAA%26pid%3DApi%26rs%3D1%26c%3D1%26qlt%3D95%26w%3D164%26h%3D123&tt=What+Are+The+3+Types+Of+Galaxies+%5BFull+Guide%5D+-+DopeGuides&sigr=fTKvtVxWOCh1&sigit=NyfScmw7PN_e&sigi=mdYWAE5kDykx&sign=YberREFVigtu&sigt=YberREFVigtu "What Are The 3 Types Of Galaxies [Full Guide] - DopeGuides")
