galaxy is a gravity bound star system, the rest of stars, interstellar gas, dust, and dark matter. The word galaxy comes from the Greek galaxias ( ???????? ), literally "milky" , a reference to the Milky Way. Galaxy of various sizes from dwarfs with just a few hundred million stars to a giant with a hundred trillion (10 14 ) stars, each orbiting the galactic mass center.
Galaxies are categorized according to their visual morphology as elliptical, spiral, or irregular. Many galaxies are thought to have black holes in their active centers. The central black hole of the Milky Way, known as Sagittarius A *, has a mass four million times larger than the Sun. In March 2016, the GN-z11 is the oldest and most distant galaxy that is observed at a distance of 32 billion light-years from Earth, and is observed because it is only 400 million years after the Big Bang.
The latest estimate of the number of galaxies in the observable universe ranges from 200 billion ( 2 ÃÆ' - 10 11 ) to 2 trillion ( 2 ÃÆ' - 10 12 ) or more, contains more stars than all the grains of sand on the planet Earth. Most galaxies have a diameter of 1,000 to 100,000 parsecs (about 300 to 300,000 light-years away) and are separated by distances on the order of millions of parsecs (or megaparsecs). By comparison, the Milky Way has a diameter of at least 30,000 parsec (100,000 LY) and is separated from the Andromeda Galaxy, its nearest large neighbor, by 780,000 parsec (2.5 million LY).
The space between galaxies is filled with a gassing gas (intergalactic medium) which has an average density of less than one atom per cubic meter. The majority of galaxies are gravitatively organized into groups, groups, and superclusters. The Milky Way is part of the Local Group, which is dominated by it and the Andromeda Galaxy. On the largest scale, these associations are generally arranged into sheets and filaments surrounded by very large cavities. The largest structure of unrecognized galaxies is a group of superclusters who have been named Laniakea.
Video Galaxy
Etimologi
The origin of the word galaxy is derived from the Greek term for Milky Way, galaxias ( ??? "milky one"), or kyklos galaktikos ("milky circle") because of its emergence as a milky band of light in the sky. In Greek mythology, Zeus places his son who is born by a mortal woman, baby Heracles, in Hera's chest when he sleeps so that his baby will drink his divine milk and thus will be immortal. Hera wakes up while breastfeeding and then realizes that she is breast feeding an unknown baby: she pushes her baby away, some spills milk, and produces a faint ribbon of light known as the Milky Way.
In the astronomical literature, the capital letters "Galaxy" are often used to refer our galaxy, the Milky Way, to distinguish it from other galaxies in our universe. The English term Milky Way can be traced back to a story by Chaucer c. 1380 :
"Look there, lo, GalaxyÃÆ'«
Which man cut the Milky Wey ,
To hit is why. "
The galaxy was originally discovered telescopically and is known as the spiral nebula . Astronomers from the 18th century through the nineteenth century regarded it as an insoluble star or anagalactic nebula, and were only considered part of the Milky Way, but their true composition and natureness remained a mystery. Observations using larger telescopes from several nearby light galaxies, such as the Andromeda Galaxy, began to solve them into conglomeration of large stars, but based only on the pain and real star populations, the actual distance of these objects placed them far beyond the Milky Way Magic. Way. For this reason they are popularly called the islands of the universe , but the term is quickly becoming unused, because the word the universe implies whole existence. Instead, they are known only as galaxies. Maps Galaxy
Nomenclature
Tens of thousands of galaxies have been cataloged, but only a few have established names, such as the Andromeda Galaxy, the Magellanic Cloud, the Whirlpool Galaxy, and the Sombrero Galaxy. Astronomers work with figures from certain catalogs, such as Messier catalogs, NGCs, IC (Catalog Index), CGCG (Galactic Catalog and Galaxy Cluster), MCG (Galactic Catalog Catalog) and UGC (Uppsala General Catalog of Galactic ). All the famous galaxies appear in one or more of these catalogs but each time under different numbers. For example, Messier 109 is a spiral galaxy that has number 109 in the Messier catalog, but also code NGC3992, UGC6937, CGCG 269-023, MCG 09-20-044, and PGC 37617.
Observation history
The realization that we live in a galaxy that is one of the many galaxies, a huge parallel discovery made about the Milky Way and other nebulae.
Milky Way
The Greek philosopher Democritus (450-370 BC) proposed that the bright ribbon in the night sky known as the Milky Way may consist of distant stars. Aristotle (384-322 BC), however, believes the Milky Way will be caused by "the ignition of the fiery breathing of several large, numerous and adjacent stars" and that "ignition occurs at the top of the atmosphere, in the continuous regions of the World "The young Olympic theoretical philosopher criticized this view, arguing that if the Milky Way is a sublunary (the abbreviation of the ' lies between the Earth and the Moon) will look different at different times and places on Earth, and that it must have parallaxes, which are not. In his view, the Milky Way is celestial.
According to Mohani Mohamed, the Arab astronomer Alhazen (965-1037) made his first attempt at observing and measuring the Milky Way's parallax, and he then "decided that since the Milky Way has no parallax, it must be far from Earth, not belonging to the atmosphere." al-BÃ ¢ r? N? (973-1048) proposed the Milky Way galaxy to be "a collection of countless fragments of nebulous stars." Astronomer Andalusia Ibn BÃÆ' Â ¢ jjah ("Avempace", d. 1138) proposes that the Milky Way consists of many nearly touching stars and appears to be a continuous image due to the refracting effects of sublunary material, citing his observations about Jupiter and Mars conjunctions as evidence of this happening when two objects are close. In the 14th century, the Syrian-born Ibn Qayyim proposed the Milky Way galaxy to be "a myriad of small stars packed together within the sphere of the fixed stars."
The true evidence of the Milky Way consisting of many stars came in 1610 when the Italian astronomer Galileo Galilei used the telescope to study the Milky Way and found that it consisted of a large number of dim stars. In 1750 the English astronomer Thomas Wright, in his book An original theory or new hypothesis of the universe, speculated (correctly) that the galaxy may be the rotating body of a large number of stars united by the force of gravity. , similar to the Solar System but on a much larger scale. The resulting star disk can be viewed as a band in the sky from our viewpoint on the disc. In a treatise in 1755, Immanuel Kant described Wright's ideas about the structure of the Milky Way.
The first project to describe the shape of the Milky Way and the position of the Sun was done by William Herschel in 1785 by counting the number of stars in various regions of the sky. He produced a galaxy form diagram with the Solar System close to the center. Using an enhanced approach, Kapteyn in 1920 arrived at the image of a small elipsoid galaxy (about 15 kiloparsec in diameter) with the Sun close to its center. Different methods by Harlow Shapley based on the catalog of spherical clusters led to very different images: flat disks diameter of approximately 70 kiloparsec and the Sun away from the center. Both analyzes failed to account for the absorption of light by interstellar dust in the field of galaxies, but after Robert Julius Trumpler measured this effect in 1930 by studying open clusters, the present picture of our master galaxy, Milky Way, emerged.
Differences from other nebula
Some galaxies outside the Milky Way are visible in the night sky to the naked eye, including the Andromeda Galaxy, the Great Magellanic Cloud, and the Little Magellanic Cloud. During the 10th century, Persian astronomers al-Sufi made the earliest identification of the Andromeda Galaxy, describing it as a "little cloud" in his Book of Fixed Stars. In 964, Al-Sufis may also mention the Great Magellanic Cloud, which referred to it as "Al Bakr of southern Arabia"; however, since the object is placed in the southern -70 declination, it is not visible from its latitude. The Great Magellanic Cloud, after it is now commonly called, was not known by Europeans until Magellan's cruise in the 16th century. The Andromeda Galaxy was later separately recorded by Simon Marius in 1612. In 1734, the philosopher Emanuel Swedenborg in his book Principia speculated that there might be a galaxy outside of our own formed into a cluster of galaxies that is a very small part of a universe that extends far beyond what we can see. This view "is very close to the present view of the cosmos." In 1750, Thomas Wright speculated (correctly) that the Milky Way is a flat star disc, and that some nebulae visible in the night sky may be separated with Milky Ways. In 1755, Immanuel Kant used the term "island Universe" to describe this distant nebula.
Toward the end of the 18th century, Charles Messier compiled a catalog containing 109 the brightest sky objects that had a vague appearance. Furthermore, William Herschel compiled a catalog of 5,000 nebulae. In 1845, Lord Rosse built a new telescope and was able to distinguish elliptical and spiral nebulae. He also managed to create an individual point source in some of these nebulae, lending credence to Kant's previous guess.
In 1912, Vesto Slipher made a spectrographic study of the brightest spiral nebula to determine their composition. Slipher found that the spiral nebula had a high Doppler shift, indicating that they were moving at speeds exceeding the measured star velocity. He found that most of these nebulae move away from us.
In 1917, Heber Curtis observed the nova S Andromedae in the "Great Andromeda Nebula" (as the Andromeda Galaxy, the Messier M31 object, later known). Looking for a photographic recording, he found 11 more novae. Curtis notices that this novae is, on average, 10 magnitude dimmer than what happens in our galaxy. As a result, he was able to produce an approximate 150,000 parsec mileage. He became a supporter of the so-called "island universe" hypothesis, stating that the spiral nebula is actually an independent galaxy.
In 1920 the debate occurred between Harlow Shapley and Heber Curtis (Great Debate), regarding the nature of the Milky Way, the spiral nebula, and the dimensions of the Universe. To support his claim that the Great Andromeda Nebula is an external galaxy, Curtis noted the emergence of dark lanes resembling dust clouds in the Milky Way, as well as significant Doppler shifts.
In 1922, Estonian astronomer Ernst ÃÆ'â € "pik provides distance determination that supports the theory that the Andromeda Nebula is indeed a distant extrasolar object. Using Mt. The new 100 100 inch Wilson Telescope Edwin Hubble is able to finish the exterior of several spiral nebulae as a collection of individual stars and identify several Cepheid variables, allowing him to estimate the distance to the nebula: they are too far apart to be part of the Milky Way.. In 1936 Hubble produced a classification of galaxy morphology that is used to this day.
Modern research
In 1944, Hendrik van de Hulst predicted that microwave radiation with a wavelength of 21 cm would be detectable from the hydrogen gas of the interstellar atoms; and in 1951 it was observed. This radiation is unaffected by the absorption of dust, so the Doppler shift can be used to map gas movement in our galaxy. This observation leads to the hypothesis of a rotating rod structure in the center of our galaxy. With an improved radio telescope, hydrogen gas can also be traced in other galaxies. In the 1970s, Vera Rubin discovered a discrepancy between the observed galaxy's rotational velocity and that predicted by visible stars and gas masses. Today, the problem of galaxy rotation is allegedly explained by the presence of large amounts of unseen dark matter. A concept known as the universal spiral rotation curve, moreover, shows that the problem is ubiquitous in these objects.
Beginning in the 1990s, the Hubble Space Telescope produced better observations. Among other things, Hubble's data help establish that the dark matter lost in our galaxy can not only consist of basically faint and small stars. The Hubble Deep Field, a very long exposure of the relatively empty part of the sky, provides evidence that there are about 125 billion ( 1,25 ÃÆ' - 10 11 ) galaxies in the observed universe. Improved technology in detecting spectra that is not visible to humans (radio telescopes, infrared cameras, and x-ray telescopes) allows the detection of other galaxies undetected by Hubble. Specifically, galaxy surveys in the Avoidance Zone (the sky area blocked at the wavelength of light seen by the Milky Way) have revealed a number of new galaxies.
In 2016, a study published in The Astrophysical Journal and led by Christopher Conselice of the University of Nottingham using 3D image modeling collected over 20 years by the Hubble Space Telescope concluded that there were more than 2 trillion ( 2 ÃÆ' - 10 12 ) galaxies in the observed universe.
Types and morphology
The galaxy consists of three main types: elliptic, spiral, and symbol. A slightly wider description of galaxy types based on their appearance is given by the Hubble sequence. Because the Hubble sequence is entirely based on the type of visual morphology (shape), it may lose certain important characteristics of galaxies such as star formation levels in Starburst galaxies and activity in active galactic nuclei.
Ellipticals
Hubble classification levels of elliptical galaxies are based on their ellipticity, ranging from E0, to almost unanimous, to E7, which is very elongated. These galaxies have an ellipsoidal profile, giving them an elliptical appearance regardless of point of view. Their appearance shows little structure and they usually have relatively few interstellar materials. As a result, these galaxies also have low parts of open groups and reduced levels of new star formation. Instead they are dominated by older and more evolved stars that orbit the center of common gravity in random directions. The stars contain a low abundance of heavy elements because star formation stops after the initial explosion. In this sense they have some similarities with much smaller ball clusters.
The biggest galaxy is a giant ellipse. Many elliptical galaxies are believed to be formed due to galaxy interactions, resulting in collisions and mergers. They can grow to a very large size (compared to galactic spirals, for example), and giant elliptical galaxies are often found near large galaxy cluster cores.
Starburst galaxies are the result of galaxy collisions that can result in the formation of elliptical galaxies.
Shell galaxy
Shell galaxies are a type of elliptical galaxy in which stars in galaxy circles are arranged in concentric shells. About one tenth of the elliptical galaxies have shell-like structures, which have never been observed in a spiral galaxy. Shell-like structures are thought to develop when larger galaxies absorb smaller companion galaxies. As the two galactic centers approach, the center begins to oscillate around the central point, the oscillations creating a gravitational ripple forming a star shell, similar to the ripples that spread in the water. For example, the NGC 3923 galaxy has more than twenty shells.
Spirals
Spiral galaxies resemble spiral pinwheels. Although the stars and other visible matter contained in such galaxies are mostly located on an airplane, the majority of the mass in spiral galaxies exist in a dark circle of dark matter extending beyond the visible component, as shown by the concept of the rotation curve universal.
Spiral galaxies consist of rotating spherical disks and interstellar mediums, along with generally older central star bulges. Extending out of the bulge is a relatively bright hand. In the Hubble classification scheme, spiral galaxies are listed as type S , followed by letters ( a , b , or c ) indicating the level of firmness of the spiral arm and the size of the central bulge. The Galaxy Sa has a tight wound, an arm that is not clear and has a relatively large core area. At the other extreme, the Sc galaxy has an open, well-defined arm and a small core area. Galaxies with unclear arms are sometimes referred to as flocculent spiral galaxies; in contrast to large spiral design galaxies that have prominent and well-defined spiral arms. The speed at which the spinning galaxy is deemed to be correlated with the flatness of the discs because some spiral galaxies have thick bulges, while others are thin and dense.
In spiral galaxies, the spiral arms have an approximate logarithmic spiral shape, a pattern that can theoretically be shown as a result of disturbances in the rotating star mass evenly. Like the stars, spiral arms revolve around the center, but they do so at constant angular velocity. The spiral arms are considered regions with high density matter, or "density waves". As the star moves through the arm, the space velocity of each star system is modified by the gravitational force of higher density. (Speed ​​returns to normal after the stars appear on the other side of the arm.) This effect is similar to a "wave" of deceleration that travels along a highway full of moving cars. The arms are seen because high density facilitates star formation, and therefore they store many bright and young stars.
Infinite spiral galaxy
The vast majority of spiral galaxies, including our Milky Way galaxy, have a linear star-shaped ribbon extending outward to both sides of the core, and then fused with the structure of the spiral arms. In the Hubble classification scheme, this is set by SB , followed by lowercase letters ( a , b or c ) shows the shape of the spiral arms (in the same way as the normal spiral galaxy categorization). The bar is considered a temporary structure that may occur as a result of a wave of density emanating out of the nucleus, or else due to tidal interaction with other galaxies. Many spiral galaxies are barred active, possibly as a result of the gas being passed to the nucleus throughout the arm.
Our own galaxy, the Milky Way, is a large spiral disk-shaped galaxy that is about 30 kiloparsec in diameter and kiloparsec thick. It contains about two hundred billion (2ÃÆ' â € "10 11 ) stars and has a total mass of about six hundred billion (6ÃÆ' â €" 10 11 ) times the mass of the Sun.
Super-bright spiral
More recently, the researchers described a galaxy called super-glowing spiral. They are very large with an upper diameter of 437,000 light-years (compared to the diameter of 100,000 light-years of the Milky Way). With a mass of 340 billion solar masses, they produce large amounts of ultraviolet and mid-infrared light. They are thought to have a star-formation rate that increases about 30 times faster than the Milky Way.
Other morphologies
- Weird galaxies are galaxy formations that develop unusual properties due to tidal interactions with other galaxies.
- Ring galaxies have structures such as the star ring and the interstellar medium surrounding the bare nucleus. Ring galaxies are thought to occur when smaller galaxies pass through the spiral galaxy nuclei. Such events may affect the Andromeda Galaxy, as it displays a multi-ring structure as if viewed in infrared radiation.
- The lenticular galaxy is a transitional form that has the properties of elliptical and spiral galaxies. These are categorized as Hubble type S0, and they have an obscure spiral arm with an elliptical star (a patented lenticular galaxy accepting Hubble SB0 grouping.)
- Irregular galaxies are galaxies that can not be classified into elliptical or spiral morphology.
- The Irr-I galaxy has several structures but is not parallel to the Hubble classification scheme.
- Irr-II galaxies do not have structures that resemble Hubble classification, and may have been disrupted. The closest examples of (dwarfed) irregular galaxies include the Magellanic Cloud.
- The ultra-diffuse (UDG) galaxy is a very low density galaxy. The galaxy may have the same size as the Milky Way but it has the number of stars seen only 1% of the Milky Way. The lack of luminosity is due to the lack of star-forming gases in the galaxy that produce the old star population.
Dwarf
Despite the prominence of elliptical galaxies and large spirals, most of the galaxies in the universe are dwarf galaxies. These galaxies are relatively small compared to other galaxy formations, being about one hundredth of the Milky Way size, containing only a few billion stars. An ultra-compact dwarf galaxy has recently been discovered that is only 100 parsecs across.
Many dwarf galaxies may orbit one larger galaxy; The Milky Way has at least a dozen such satellites, with an estimated 300-500 not yet discovered. Dwarf galaxies can also be classified as elliptical, spiral, or irregular. Since small dwarf ellipses have a small similarity with large elliptical, they are often called dwarf spheroidal galaxies instead.
A study of 27 Milky Way neighbors found that in all dwarf galaxies, the central mass is about 10 million solar masses, regardless of whether the galaxy has thousands or millions of stars. This leads to the suggestion that galaxies are largely shaped by dark matter, and that the minimum size may indicate a warm dark matter form incapable of a gravity blend on a smaller scale.
Other types of galaxies
Interact
The interactions between galaxies are relatively frequent, and they can play an important role in the evolution of galaxies. Near misses between galaxies lead to warping distortions due to tidal interactions, and can cause some exchange of gas and dust. Collisions occur when two galaxies pass directly to one another and have enough relative momentum to not join. Interacting galaxy stars will not normally collide, but gas and dust in two forms interact, sometimes triggering star formation. Collisions can greatly damage the shape of galaxies, forming bars, rings or structures like a tail.
At the extremes of interaction is a galactic merger. In this case the relative momentum of the two galaxies is not enough to allow galaxies to pass through each other. Instead, they gradually merge to form a larger single galactic. Mergers can produce significant changes in morphology, compared to the original galaxy. If one of the galaxies that joins is much more massive than other combined galaxies then the result is known as cannibalism. The larger larger galaxies will remain relatively undisturbed by the merger, while smaller galaxies are torn apart. The Milky Way Galaxy is currently in the process of abandoning the Dwarf Ellipse Galaxy Sagittarius and the Main Dwarf Galaxy of Canis.
Starburst
Stars are created in galaxies from cold gas reserves that form giant molecular clouds. Several galaxies have been observed to form stars at an extraordinary rate, known as star explosions. If they continue to do so, they will consume their gas reserves in the span of time less than the galactic lifetime. Starburst's activity therefore usually only lasts about ten million years, a relatively short period in the history of galaxies. Starburst galaxies are more common during the early history of the Universe, and, presently, still contribute about 15% to total star production levels.
Starburst galaxies are characterized by dusty gas concentrations and the emergence of newly formed stars, including large stars that ionize nearby clouds to create H II regions. These massive stars produce supernova explosions, producing widespread remains that interact strongly with the surrounding gas. This explosion triggered a chain reaction from the star building that spread throughout the gas region. Only when available gas is consumed or dispersed, Starburst activity ends.
Starburst is often associated with the incorporation or interaction of galaxies. An example prototype of such star-forming interactions is M82, which encounters closer to the larger M81. Irregular galaxies often show spotted star activity nodes.
Active galaxies
Some observable galaxies are classified as active galaxies if the galaxy contains an active galactic nucleus (AGN). Most of the total energy output of the galaxy is emitted by the active galactic nucleus, not the stars, dust and interstellar galactic medium.
The standard model for active galactic nuclei is based on the accretion of disks that form around supermassive black holes (SMBH) in the galactic core region. Radiation from the active galactic nucleus results from the gravitational energy of matter when it falls into the black hole of the disk. About 10% of these galaxies, a pair of energetic jets that are diametrically reject particles from the galactic nucleus at speeds close to the speed of light. The mechanism for producing this jet is not well understood.
- Seyfert galaxies or quasars, classified by luminosity, are active galaxies that emit high-energy radiation in the form of x-rays.
Blazars
Blazar is believed to be an active galaxy with relativistic jets pointing toward Earth. A radio galaxy radiates radio frequencies from relativistic jets. The integrated model of this active galaxy type explains the difference from the observer's point of view.
LINERS
Perhaps related to the active galactic nuclei (as well as the Starburst region) are areas of low ionisation nuclear emissions (LINERs). Emissions from LINER-type galaxies are dominated by weakly ionized elements. Excitation sources for weak ionized lines include post-AGB, AGN, and shock star. About one-third of nearby galaxies are classified as containing LINER nuclei.
Seyfert Galaxy
The Seyfert Galaxy is one of the two largest groups of active galaxies, along with quasars. They have nuclei such as quasars (very bright, distant and bright sources of electromagnetic radiation) with very high surface brightness but unlike quasars, their master galaxies can be detected clearly. The Seyfert Galaxy accounts for about 10% of all galaxies. Seen in visible light, most Seyfert galaxies look like normal spiral galaxies, but when studied under other wavelengths, their core luminosity is equivalent to the luminosity of the entire galaxy of the Milky Way.
Quasar
Quasars (/'kwe? Z? R/) or quasi-star radio sources are the most energetic members and away from the class of objects called active galactic nuclei (AGN). Quasars are very luminous and were first identified as a source of high red electromagnetic energy shifts, including radio waves and visible light, which looked similar to stars, rather than extended sources similar to galaxies. Their luminosity can be 100 times larger than the Milky Way.
Luminous infrared galaxy
Luminous infrared galaxies or LIRGs are galaxies with luminosity, brightness measurements, above 10 11 L ?. LIRGs are more abundant than starburst galaxies, Seyfert galaxies and quasi-star objects in comparable total luminosity. Infrared galaxies emit more energy in the infrared than any other combined wavelength. LIRG luminosity is 100 billion times that of our Sun.
Properties
Magnetic field
Galaxies have their own magnetic fields. They are strong enough to be important dynamically: they drive the mass flow to the galactic centers, they modify the formation of spiral arms and they can affect the rotation of gases in the region beyond the galaxy. The magnetic field provides the angular momentum transport necessary for the collapse of the gas cloud and hence the formation of a new star.
The typical average equipartition strength for spiral galaxies is about 10 GG (microGauss) or 1 nT (nanoTesla). By comparison, the Earth's magnetic field has an average power of about 0.3 G (Gauss or 30? T (microTesla).Very radio-clusters like M 31 and M 33, our Milky Way's neighbors have a weaker field (about 5 G), while gas-rich galaxies with high star formation rates, such as M 51, M 83 and NGC 6946, have an average of 15 G On a spiral arm that stands out field strength can reach 25 G in areas where gas cold and dust are also concentrated, the strongest total equipartition field (50-100? G) is found in starburst galaxies, for example in M ​​82 and Antennae, and in nuclear Starburst regions, for example at NGC 1097 centers and other prohibited galaxies.
Formation and evolution
The formation of galaxies and evolution is an active area of ​​research in astrophysics.
Formation
The current cosmological model of the early universe is based on the Big Bang theory. About 300,000 years after this event, hydrogen and helium atoms begin to form, in an event called recombination. Almost all hydrogen is neutral (not ionized) and easily absorbed by light, and no stars are formed. As a result, this period is called the "dark ages". It comes from density fluctuations (or anisotropic anomalies) in this primordial case so that larger structures begin to emerge. As a result, the mass of baryonic material begins to condense in a dark dark circle of cold. This primordial structure will eventually become the galaxy we see today.
Initial galaxy
Evidence for the early sighting of galaxies was discovered in 2006, when it was found that the IOK-1 galaxy has a remarkably high red shift of 6.96, corresponding to only 750 million years after the Big Bang and making it the furthest and primordial galaxy yet to be seen. While some scientists have claimed other objects (such as Abell 1835 IR1916) have a higher red shift (and therefore seen in the early stages of the evolution of the Universe), the age and composition of IOK-1 have been more reliable. In December 2012, astronomers reported that UDFj-39546284 is the most distant object known and has a redshift value of 11.9. The object, estimated to have been around "380 million years" after the Big Bang (about 13.8 billion years ago), is about 13.42 billion miles of light travel distance away. The existence of such early protogalax suggests that they must have grown in the so-called "dark ages". On May 5, 2015, the EGS-zs8-1 galaxy is the earliest and most measurable galaxy measured, forming 670 million years after the Big Bang. The light from EGS-zs8-1 has taken 13 billion years to reach Earth, and is now 30 billion light years away, due to the expansion of the universe for 13 billion years.
Initial galaxy formation
The detailed process in which the early galaxies formed was an open question in astrophysics. Theory can be divided into two categories: top-down and bottom-up. In a top-down correlation (eg Eggen-Lynden-Bell-Sandage [ELS] model), protogalaxies are formed in large-scale simultaneous collapse that lasts for about a hundred million years. In bottom-up theory (such as the Searle-Zinn model [SZ]), small structures such as globular clusters form first, and then some such bodies accumulate to form larger galaxies.
After protogalaxies begin to form and contract, the first halo star (called the Population III Stars) appears in it. It is composed almost entirely of hydrogen and helium, and may be very large. If so, these big stars will quickly consume their fuel supply and become supernovae, releasing heavy elements into the interstellar medium. This first generation star ionizes the surrounding neutral hydrogen, creating a widespread air bubble in which light can easily travel.
In June 2015, astronomers reported evidence for the Third Population star in the Cosmos Redshift 7 galaxy at z = 6.60 . Such stars may have existed in the very early universe (ie, at high redshifts), and may have started production of heavier chemical elements than the hydrogen necessary for planetary formation and subsequent life as we know it.
Evolution
Within a billion years of galactic formation, key structures began to emerge. Globular cluster, central supermassive black hole, and the protrusion of a poor metal star II galaxy. The creation of supermassive black holes seems to play a key role in actively regulating the growth of galaxies by limiting the total amount of additional material added. During this early period, the galaxy experienced a massive explosion of star formation.
Over the next two billion years, accumulated matter settles into galactic disks. The galaxy will continue to absorb infalling materials from high-speed clouds and dwarf galaxies throughout its lifetime. It is mostly hydrogen and helium. The cycle of star birth and death slowly increases the abundance of heavy elements, finally allowing the formation of planets.
Galaxy evolution can be significantly affected by interactions and collisions. Galactic mergers are common during the early days, and most of the galaxies are strange in morphology. Given the distance between stars, most of the star systems in the colliding galaxy will not be affected. However, the gravitational extraction of the interstellar gas and the dust that forms the spiral arms produces a long train of stars known as the tidal tail. An example of this formation can be seen in NGC 4676 or Antennae Galaxies.
The nearby Milky Way and Andromeda galaxies are moving toward each other at about 130 km/sec, and - depending on lateral movement - they may collide in about five to six billion years. Although the Milky Way has never collided with the galaxy of Andromeda before, evidence of the Milky Way's past collisions with smaller dwarf galaxies is increasing.
Such large-scale interactions are rare. Over time, the merger of two systems of the same size became less common. Most bright galaxies have remained unchanged over the last few billion years, and the net rate of star formation may also reach about ten billion years ago.
Future trends
Spiral galaxies, like the Milky Way, produce a new generation of stars as long as they have a cloud of interstellar molecules of interstellar hydrogen in their spiral arms. The ellipse galaxy is largely devoid of this gas, and it forms several new stars. The supply of star-forming materials is limited; once the star has turned the hydrogen supply into a heavier element, the new star formation will end.
The era of star formation is now expected to continue for a hundred billion years, and then the "age of stars" will end after about ten trillion to one hundred trillion years (10 13 -10 14 Ã, year), as the smallest and longest star in our universe, the small red dwarf, begins to fade. At the end of the star's age, the galaxy will consist of solid objects: brown dwarfs, cold or cold white dwarfs ("black dwarfs"), neutron stars, and black holes. Finally, as a result of gravitational relaxation, all stars will fall into the central supermassive black hole or are thrown into intergalactic spaces as a result of collisions.
Larger-scale structure
Deep sky surveys show that galaxies are often found in groups and groups. A solitary galaxy that does not interact significantly with other galaxies with comparable masses over the last billions of years is relatively rare. Only about 5% of the galaxies surveyed have been found completely isolated; However, these isolated formations may have interacted and even joined other galaxies in the past, and may still be orbited by smaller satellite galaxies. The isolated galaxies can produce stars at a higher level than usual, because their gas is not stripped by other nearby galaxies.
At the largest scale, the universe continues to expand, resulting in an increase in the average separation between individual galaxies (see Hubble's law). Galaxy associations can overcome this expansion on a local scale through their shared gravitational attraction. This relationship is formed at the beginning of the Universe, because the dark matter clumps pull each of the galaxies together. The nearby groups then combine to form larger scale groups. This ongoing merging process (as well as the infusion of gas inflow) heats gas between galaxies in a group to a very high temperature, reaching 30-100 megakelvins. Approximately 70-80% of the mass in the cluster is dark matter, with 10-30% consisting of this heated gas and the remaining percent of the material in the form of galaxies.
Most of the galaxies in the universe are gravitated to a number of other galaxies. It forms a fractal-like, hierarchical distribution of clustered structures, with the smallest associations called groups. A group of galaxies is the most common type of galaxy cluster, and this formation contains the majority of galaxies (as well as most of the baryonic mass) in the universe. To remain gravitationally bound with such groups, each member galaxy must have a low enough speed to prevent it from coming out (see Virial theorem). But if kinetic energy is insufficient, the group may evolve into fewer galaxies through mergers.
The galaxy cluster consists of hundreds to thousands of galaxies bound together by gravity. Groups of galaxies are often dominated by single giant elliptical galaxies, known as the brightest group galaxies, which over time, tidally destroy their satellite galaxies and increase their own mass.
Superclusters contain tens of thousands of galaxies, which are found in groups, groups and sometimes individually. At the supercluster scale, galaxies are arranged into sheets and filaments around a wide empty void. On this scale, the universe looks the same in all directions (isotropic and homogeneous).
The Milky Way Galaxy is a member of an association named Local Group, a relatively small group of galaxies that has a diameter of about one megaparsec. The Milky Way and the Andromeda Galaxy are the two brightest galaxies in the group; many other galaxy members are dwarf companions of these two galaxies. The Local Group itself is part of a cloud-like structure in Virgo Supercluster, a large and extended group structure and galaxy group centered on the Virgo Cluster. And Virgo Supercluster itself is part of the Pisces-Cetus Supercluster Complex, a giant galactic filament.
Multi-wavelength observation
The peak radiation of most stars lies in the visible spectrum, so the observation of the stars forming the galaxy has become a major component of optical astronomy. It is also a beneficial part of the spectrum to observe the ionized H II region, and to examine the distribution of dusty arms.
The dust present in the interstellar medium is not transparent to visual light. It's more transparent to far-infrared, which can be used to observe the gigantic interior areas of giant molecular clouds and galactic nuclei in great detail. Infrared is also used to observe distant red rolling galaxies that formed much earlier in the history of the universe. Water vapor and carbon dioxide absorb a number of useful parts of the infrared spectrum, so high-altitude or space-based telescopes are used for infrared astronomy.
The first non-visual studies of galaxies, especially active galaxies, were made using radio frequencies. Earth's atmosphere is almost transparent to the radio between 5 MHz and 30 GHz. (Signal of the ionosphere block below this range.) Large radio interferometers have been used to map active jets emitted from active nuclei. Radio telescopes can also be used to observe neutral hydrogen (through radiation 21 cm), including, potentially, unionized matter in the early universe that then collapses to form galaxies.
Ultraviolet and X-ray telescopes can observe highly energetic galactic phenomena. Ultraviolet light is sometimes observed when stars in galaxies are far apart from tidal forces from nearby black holes. The distribution of hot gas in galaxy clusters can be mapped with X-rays. The existence of supermassive black holes in the galactic core is confirmed through astronomical X-rays.
See also
Note
References
Source
- "Uncover the Secrets of Dwarf Virgo Error". ESO. May 3, 2000. Archived from the original on 2009-01-09 . Retrieved January 3rd, 2007 .
Bibliography
External links
- NASA/IPAC Extragalactic Database (NED) (NED-Distances)
- Galaxy in In Our Time
- The Atlas of the Universe
- Galaxy - Information and amateur observation
- Discovered Oldest Galactic
- The Galaxy classification project, utilizing the power of the internet and the human brain
- How many galaxies in our universe?
- The most beautiful galaxy in Astronoo
- 3-D Video (01:46) Ã, - More Than A Million Milk Galaxies each - BerkeleyLab/animation.
Source of the article : Wikipedia
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