What types galaxies are there

Some are fated to collide, like the Milky Way and Andromeda. Olmsted STScI. 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 million stars to giant galaxies with more than a trillion stars. Ellipticals, which account for about one-third of all galaxies, vary from nearly circular to very elongated.

They possess comparatively little gas and dust, contain older stars and are not actively forming stars anymore. The largest and rarest of these, called giant ellipticals, are about , light-years across. Astronomers theorize that these are formed by the mergers of smaller galaxies. Much more common are dwarf ellipticals, which are only a few thousand light-years wide.

Spiral galaxies appear as flat, blue-white disks of stars, gas and dust with yellowish bulges in their centers. These galaxies are divided into two groups: normal spirals and barred spirals. In barred spirals, the bar of stars runs through the central bulge. The arms of barred spirals usually start at the end of the bar instead of from the bulge.

Spirals are actively forming stars and comprise a large fraction of all the galaxies in the local universe. Irregular galaxies, which have very little dust, are neither disk-like nor elliptical. Astronomers often see irregular galaxies as they peer deeply into the universe, which is equivalent to looking back in time. These galaxies are abundant in the early universe, before spirals and ellipticals developed.

Aside from these three classic categories, astronomers have also identified many unusually shaped galaxies that seem to be in a transitory phase of galactic development.

These include those in the process of colliding or interacting, and those with active nuclei ejecting jets of gas. In the late s, astronomer Vera Rubin made the surprising discovery of dark matter. She was studying how galaxies spin when she realized the vast spiral Andromeda Galaxy seemed to be rotating strangely.

Some extra non-visible mass, dubbed dark matter, appeared to be holding the galaxy together. She soon discovered that a huge halo of dark matter was present in galaxy after galaxy that she examined. Its invisible and ubiquitous presence affects how stars move within galaxies, how galaxies tug on each other and how matter clumped together in the early universe.

Some of the best evidence for the existence of dark matter comes from galaxy cluster 1E , also known as the Bullet Cluster. Elliptical galaxies are usually comprised of very old stars or stars with low mass.

They are very dim in comparison with the very bright spiral galaxies. Irregular galaxies are commonly small, and collectively they make up about a quarter of all the galaxies. They lack a distinct shape or form often having a chaotic appearance. The largest galaxies are usually giant elliptical galaxies, containing a trillion or even more stars.

They span as much as one million light-years across — 10 times as much as the Milky Way. Curious enough, the smallest galaxies are also the elliptical types. The oldest and farthest galaxy ever discovered is an irregular type of galaxy called GN-z It is estimated that the galaxy formed just around million years after the Big Bang.

Spiral Galaxies They have a flat, spinning disk with a central bulge surrounded by spiral arms. Elliptical Galaxies Elliptical galaxies have an elongated spherical shape and lack a nucleus or bulge at the center. Irregular Galaxies Irregular galaxies have no definite shape, though they are in constant motion like all other galaxies.

Until now, three major types of irregular galaxies have been established: Irr I — they feature some structure but not enough to be placed into the Hubble sequence. Irr II — they do not appear to feature any structure. DIrr III — dwarf irregular galaxy. They tend to have low metallicity and relatively high levels of gas. They are also believed to be similar to the earliest galaxies that populated the Universe. Barred Spiral Galaxies Barred spiral galaxies share the same features and functions as regular spiral galaxies, but they also have a bar of bright stars that lie along the center of the bulge and extend into the disk.

They are further divided into three categories: Barred spiral galaxy type A — abbreviation SBa — they feature tightly bound arms. Barred spiral galaxy type B — abbreviation SBb — they feature both tightly and loosely bond arms.

Barred spiral galaxy type C — abbreviation Sbc — they have loosely bound arms. Around two-thirds of spiral galaxies contain a bar structure through their center. Other types of Galaxies Some galaxies have a ring-like structure of stars and interstellar medium surrounding a bare core. Formation Modern cosmological models of the early universe are based on the Big Bang theory.

Numbers Most galaxies are between 1. Habitability Probably the most powerful argument for life to exist elsewhere besides our Solar System is the sheer vastness of the universe in its unimaginable number of galaxies. Future Recently, a number of galaxies without dark matter were discovered. Galaxies can be found by themselves, in small groups and in large clusters. It is very rare to find stars in the space in between galaxies. Galaxies sometimes collide with each other, with interesting results.

These collisions can trigger bursts of star-formation in addition to changing the shapes of the galaxies that collide. However, when galaxy collisions occur, individual stars do not collide, due to the vast distances between them. Interacting galaxies imaged by the Hubble Space Telescope.

Ford JHU , G. Galaxies are classified by shape. There are three general types: elliptical, spiral, and irregular. Just like typical spiral galaxies, barred spiral galaxies contain a disk, bulge, and halo. NGC Additionally, as noted earlier, the Milky Way is a barred galaxy! But this went unnoticed by astronomers for a while compared to other galaxies because of the smaller bar of the Milky Way compared to other barred galaxies. Because of their close proximity to Earth, both of these galaxies are pieces of two different constellations.

These elliptical galaxies are classified by their ovular shape and lack of central bulge. In contrast to their name, however, sometimes these galaxies are rather circular. The stars and gasses in these types of galaxies are spread fairly evenly throughout, however, the center is still the brightest area.

Additionally, elliptical galaxies do not contain many new stars. Rather, these galaxies are comprised of old, low mass stars. At the center of an elliptical galaxy is typically a black hole. Compared to a barred spiral or typical spiral galaxy, in an elliptical galaxy there is a black hole where the bulge of old stars should be.

This black hole may be part of the reason why new stars do not form often in elliptical galaxies. Because the central black hole of elliptical galaxies likely consumes the dust and gas necessary for new star formation, the materials necessary to make these new stars are not abundant in elliptical galaxies.

The notation for elliptical galaxies is E. Unlike the additional spiral tightness classification of barred and typical spiral galaxies, elliptical galaxies have a more specific classification of the numbers 0 through 7. As the name implies, irregular galaxies are all quite unique. These do not have any previously discussed components, such as a bulge, disk, or arms, that other galaxies are known to have. According to NASA, the uniqueness of irregular galaxies may be because of interactions they could have had in the past with other, neighboring galaxies.

Irregular Galaxy NGC Martin Pugh. Although there is nothing typical, symmetrical, or ordinary about irregular galaxies, there are two distinct types: IrrI Irr1 and IrrII Irr2. IrrI tend to have regions with an abundance of hydrogen gas as well as young stars.