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In astrophysics, the questions of galaxy formation and evolution are: Cosmology, as a branch of astrophysics, is the study of the large-scale structure of the universe and is concerned with fundamental questions about its formation and evolution. ...
Image File history File links Download high resolution version (2198x1274, 1278 KB)WMAP map of CMB anisotropy, from NASA.gov File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...
The age of the universe, according to the Big Bang theory, is defined as the largest possible value of proper time integrated along a time-like curve from the Earth at the present epoch back to the Big Bang. The time that has elapsed on a hypothetical clock which has...
According to the Big Bang, the universe emerged from an extremely dense and hot state (bottom). ...
The comoving distance or conformal distance of two objects in the universe is the distance divided by a time-varying scale factor representing the expansion of the universe. ...
In cosmology, the cosmic microwave background radiation (most often abbreviated CMB but occasionally CMBR, CBR or MBR, also referred as relic radiation) is a form of electromagnetic radiation discovered in 1965 that fills the entire universe. ...
In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and has strong negative pressure. ...
In astrophysics, dark matter is matter that does not emit or reflect enough electromagnetic radiation to be detected directly, but whose presence may be inferred from its gravitational effects on visible matter. ...
The Friedmann-Lemaître-Robertson-Walker (FLRW) metric describes a homogeneous, isotropic expanding/contracting universe. ...
The Friedmann equations relate various cosmological parameters within the context of general relativity. ...
Hubbles law is the statement in physical cosmology that the redshift in light coming from distant galaxies is proportional to their distance. ...
Astronomy and cosmology examine the universe to understand the large-scale structure of the cosmos. ...
A pie chart indicating the proportional composition of different energy-density components of the universe. ...
The metric expansion of space is a key part of sciences current understanding of the universe, whereby space itself is described by a metric which changes over time. ...
In cosmology, Big Bang nucleosynthesis (or primordial nucleosynthesis) refers to the production of nuclei other than H-1, the normal, light hydrogen, during the early phases of the universe, shortly after the Big Bang. ...
The observable Universe is a term used in cosmology to describe a ball-shaped region of space surrounding the Earth that is close enough that we might observe objects in it. ...
Redshift of spectral lines in the optical spectrum of a supercluster of distant galaxies (right), as compared with that of the Sun (left). ...
The shape of the Universe is a subject of investigation within cosmology. ...
It has been suggested that this article or section be merged into Large-scale structure of the cosmos. ...
A graphical timeline is available here: Graphical timeline of the Big Bang This timeline of the Big Bang describes the events that have occurred and will occur according to the scientific theory of the Big Bang. ...
This timeline of the Big Bang shows the sequence of events as predicted by the Big Bang theory, from the beginning of the Planck Epoch to the end of the Epoch of Nucleosynthesis (and beginning of the Epoch of Galaxies). ...
The timeline of cosmology lists the sequence of cosmological theories and discoveries in chronological order. ...
The ultimate fate of our universe is a topic in physical cosmology. ...
The deepest visible-light image of the cosmos, the Hubble Ultra Deep Field. ...
Spiral Galaxy ESO 269-57 Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature, and chemical composition) of celestial objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ...
General relativity (GR) is the geometrical theory of gravitation published by Albert Einstein in 1915. ...
Thousands of particles explode from the collision point of two relativistic (100 GeV per nucleon) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ...
Quantum gravity is the field of theoretical physics attempting to unify the theory of quantum mechanics, which describes three of the fundamental forces of nature, with general relativity, the theory of the fourth fundamental force: gravity. ...
Spiral Galaxy ESO 269-57 Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature, and chemical composition) of celestial objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ...
NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light years in diameter and approximately 60 million light years distant. ...
- How, from a homogeneous universe, did we obtain the very heterogeneous one we live in?
- How did galaxies form?
- How do galaxies change over time?
The formation of galaxies is still one of the most active research areas in astrophysics; and, to some extent, this is also true for galaxy evolution. Some ideas, however, are now widely accepted. The Cartwheel galaxy CREDIT: Kirk Borne (STScI) and NASA. SOURCE: http://hubblesite. ...
The Cartwheel galaxy CREDIT: Kirk Borne (STScI) and NASA. SOURCE: http://hubblesite. ...
NASA Insignia Listen to this article · (info) This audio file was created from an article revision dated 2005-09-01, and does not reflect subsequent edits to the article. ...
The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble for his discovery of galaxies outside the Milky Way and his creation of Hubbles Law, which calculates the rate at which the universe is expanding. ...
The Cartwheel Galaxy (also known as ESO 350-40) is a lenticular galaxy about 500 million light-years away in the constellation Sculptor. ...
NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light years in diameter and approximately 60 million light years distant. ...
After the Big Bang, the universe had a period when it was remarkably homogeneous, as can be observed in the Cosmic Microwave Background, the fluctuations of which are less than one part in one hundred thousand. According to the Big Bang, the universe emerged from an extremely dense and hot state (bottom). ...
The deepest visible-light image of the cosmos, the Hubble Ultra Deep Field. ...
In physics, homogeneity is the quality of having all properties independent of the position. ...
WMAP image of the CMB anisotropy,Cosmic microwave background radiation(June 2003) The cosmic microwave background radiation (CMB) is a form of electromagnetic radiation that fills the whole of the universe. ...
The most accepted view today is that all the structure we observe today was formed as a consequence of the growth of primordial fluctuations. The primordial fluctuations caused gas to be attracted to areas of denser material, and star clusters and stars. One consequence of this model is that the location of galaxies indicates areas of higher density of the early universe. Hence the distribution of galaxies is closely related to the physics of the early universe. Primordial fluctuations are density variations in the early universe which are considered the seeds of all structure in the universe. ...
A great deal of the research in this area is focused on components of our own Milky Way, since it is the easiest galaxy to observe. The observations which must be explained in, or at least not at odds with, a theory of galactic evolution, include: The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias), sometimes referred to simply as the Galaxy), is a barred spiral galaxy of the Local Group. ...
- the stellar disk is quite thin, dense, and rotates
- the stellar halo is very large, sparse, and does not rotate (or has perhaps even a slight retrograde rotation), with no apparent substructure
- halo stars are typically much older and have much lower metallicities than disk stars (there is a correlation, but there is no absolute connection between these data)
- some astronomers have identified an intermediate population of stars, variously called the "metal weak thick disk", the "intermediate population II", et al. If these are indeed a distinct population, they would be described as metal-poor (but not as poor as the halo stars), old (but not as old as the halo stars), and orbiting very near the disk, in a sort of "puffed-up", thicker disk shape.
- globular clusters are typically old and metal-poor as well, but there are a few which are not nearly as metal-poor as most, and/or have some younger stars. Some stars in globular clusters appear to be as old as the universe itself (by entirely different measurement and analysis methods)!
- in each globular cluster, all the stars were born at virtually the same time (except for a few globulars that show multiple epochs of star formation)
- globular clusters with smaller orbits (closer to the galactic center) have orbits which are somewhat flatter (less inclined to the disk), and less eccentric (more circular), while those further out have orbits in all inclinations, and tend to be more eccentric.
- High Velocity Clouds, clouds of neutral hydrogen are "raining" down on the galaxy, and presumably have been from the beginning (these would be the necessary source of a gas disk from which the disk stars formed).
The galactic plane is the plane in which the majority of a flattened galaxys mass lies. ...
The galactic halo is a region of space surrounding spiral galaxies, including our galaxy, the Milky Way. ...
Prograde motion is the motion of a planetary body in a direction similar to that of other bodies within its system, and is sometimes called direct motion, especially in astrology. ...
The Pleiades, an open cluster of stars in the constellation of Taurus. ...
The English word metal is derived from the Latin word metallum, in turn derived from the Greek metallon, meaning a mine or quarry, as well as ore or metal. ...
The Globular Cluster M80 in the constellation Scorpius is located about 28,000 light years from the Sun and contains hundreds of thousands of stars. ...
The Galactic Center is the rotational center of the Milky Way galaxy. ...
Inclination in general is the angle between a reference plane and another plane or axis of direction. ...
In astrodynamics, under standard assumptions any orbit must be of conic section shape. ...
Interstellar cloud is the generic name given to an accumulation of gas, plasma and dust in our and other galaxies. ...
Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interactions. ...
General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ...
Spiral galaxies
 A spiral galaxy warped as a result of colliding with another galaxy. After the other galaxy is completely absorbed, the distortion will disappear. The process typically takes millions of years. The earliest modern theory of the formation of our galaxy (known by astronomers as ELS, after the initials of the authors of that paper, Olin Eggen, Donald Lynden-Bell, and Allan Sandage[1]) describes a single (relatively) rapid monolithic collapse, with the halo forming first, followed by the disk. Another view published in 1978 (known as SZ for its authors, Leonard Searle and Robert Zinn[2]) describes a more gradual process, with smaller units collapsing first, then later merging to form the larger components. An even more recent idea is that significant portions of the stellar halo could be stellar debris from destroyed dwarf galaxies and globular clusters that once orbited the Milky Way. The halo would then be a "new"er component made of "recycled" old parts! Image File history File links Download high resolution version (1435x732, 1231 KB) This image is take from NASAs hubble website. ...
Image File history File links Download high resolution version (1435x732, 1231 KB) This image is take from NASAs hubble website. ...
Olin Jeuck Eggen (July 9, 1919 – October 2, 1998) was an American astronomer. ...
Donald Lynden-Bell (born Dover, England April 5, 1935 – ) is a British astrophysicist, best known for his theories that galaxies contain massive black holes at their centre, and that such black holes are the principal source of energy in quasars. ...
Allan Rex Sandage (Born June 18, 1926) is an American astronomer. ...
In geometry, a disk is the region in a plane contained inside of a circle. ...
In recent years, a great deal of focus has been put on understanding merger events in the evolution of galaxies. Rapid technological progress in computers have allowed much better simulations of galaxies, and improved observational technologies have provided much more data about distant galaxies undergoing merger events. After the discovery in 1994 that our own Milky Way has a satellite galaxy (the Sagittarius Dwarf Elliptical Galaxy, or SagDEG) which is currently gradually being ripped up and "eaten" by the Milky Way, it is thought these kinds of events may be quite common in the evolution of large galaxies. The Magellanic Clouds are satellite galaxies of the Milky Way that will almost certainly share the same fate as the SagDEG. A merger with a fairly large satellite galaxy could explain why M31 (the Andromeda Galaxy) appears to have a double core. MILSTAR:A communication satellite A satellite is any object that orbits another object (which is known as its primary). ...
The Sagittarius Dwarf Elliptical Galaxy (Sag DEG) is a satellite galaxy of the Milky Way Galaxy. ...
The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias), sometimes referred to simply as the Galaxy), is a barred spiral galaxy of the Local Group. ...
The two Magellanic Clouds are irregular dwarf galaxies orbiting our Milky Way galaxy, and thus are members of our Local Group of galaxies. ...
This image is a Galaxy Evolution Explorer observation of the large galaxy in Andromeda, Messier 31. ...
M31 in a small telescope The Andromeda Galaxy (IPA: , also known as Messier 31, M31, or NGC 224; older texts often called it the Andromeda Nebula) is a spiral galaxy approximately 2. ...
The SagDEG is orbiting our galaxy at almost a right angle to the disk. It is currently passing through the disk; stars are being stripped off of it with each pass and joining the halo of our galaxy. Eventually, only the core of SagDEG will exist. Although it will have the same mass as a large globular cluster like Omega Centauri and G1, it will appear rather different, as it has far lower surface density due to the presence of substantial amounts of dark matter, while globular clusters appear, mysteriously, to contain very little dark matter. This article is about angles in geometry. ...
The Globular Cluster M80 in the constellation Scorpius is located about 28,000 light years from the Sun and contains hundreds of thousands of stars. ...
A small region at the heart of Omega Centauri, containing some 50,000 stars (NASA/STScI) Omega Centauri or NGC 5139 is a globular cluster of stars orbiting our galaxy, the Milky Way. ...
Mayall II, G1, SKHB 1, or HBK 0-1 is a globular cluster in M31, the Andromeda Galaxy. ...
In astrophysics, dark matter is matter that does not emit or reflect enough electromagnetic radiation to be detected directly, but whose presence may be inferred from its gravitational effects on visible matter. ...
Further examples of satellite dwarf galaxies that are in the process of merging with the Milky Way are the Canis Major Dwarf Galaxy, discovered in 2003 and thought to be responsible for the Monoceros Ring, and the Virgo Stellar Stream, discovered in 2005. The Canis Major Dwarf Galaxy is located in the same part of the sky as the constellation of Canis Major. ...
Monoceros Ring is a proposed ring of stars around the Milky Way which consists of stars torn from the Canis Major Dwarf Galaxy as it merges with the Milky Way over the course of billions of years. ...
The Virgo Stellar Stream (or Virgo Overdensity) is the proposed name for a stream of stars in the constellation of Virgo which was discovered in 2005. ...
Elliptical galaxies Giant elliptical galaxies are probably formed by mergers on a grander scale. In the Local Group, the Milky Way and M31 (the Andromeda Galaxy) are gravitationally bound, and currently approaching each other at high speed. Since we cannot determine the speed of M31 perpendicular to the line from us to it, we do not know if it will collide with the Milky Way. If the two galaxies do meet they will pass through each other, with gravity distorting both galaxies severely and ejecting some gas, dust and stars into intergalactic space. They will travel apart, slow down, and then again be drawn towards each other, and again collide. Eventually both galaxies will have merged completely, streams of gas and dust will be flying through the space near the newly formed giant elliptical galaxy. Out of the gas ejected from the merger, new globular clusters and maybe even new dwarf galaxies may form and become the halo of the elliptical. The globulars from both M31 and the Milky Way will also form part of the halo; globulars are so tightly held together that they are largely immune to large scale galactic interactions. On the stellar scale, little will happen. If anybody is around to watch the merger, it will be a slow, but magnificent event, with the sight of a distorted M31 spectacularly spanning the entire sky. M31 is actually already distorted: the edges are warped. This is probably because of interactions with its own galactic companions, as well as possible mergers with dwarf spheroidal galaxies in the recent past - the remnants of which are still visible in the disk populations. An elliptical galaxy is a type of galaxy in the Hubble sequence characterized by the following physical properties: The giant elliptical galaxy NGC 4881 (the spherical glow at upper left) lies at the edge of the Coma Cluster of Galaxies. ...
A member of the Local Group of galaxies, irregular galaxy Sextans A is 4. ...
This image is a Galaxy Evolution Explorer observation of the large galaxy in Andromeda, Messier 31. ...
M31 in a small telescope The Andromeda Galaxy (IPA: , also known as Messier 31, M31, or NGC 224; older texts often called it the Andromeda Nebula) is a spiral galaxy approximately 2. ...
Intergalactic space is the physical space between galaxies. ...
Warp is to bend or twist, and this usage is the basis for the derivation of the following terms: warp drive for the propulsion device used in Star Trek, which warps space warp are the spun lengthwise threads used in weaving the Time Warp is a dance from The Rocky...
In our epoch, large concentrations of galaxies (clusters and superclusters) are still assembling. This "bottom-up" picture is referred to as hierarchical structure formation (similar to the SZ picture of galaxy formation, on a larger scale). Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. ...
Superclusters are large groupings of smaller galaxy groups and clusters, and are among the largest structures of the cosmos. ...
While we have learned a great deal about ours and other galaxies, the most fundamental questions about formation and evolution remain only tentatively answered.
References The Astrophysical Journal is one of the foremost research journals devoted to recent developments, discoveries, and theories in astronomy and astrophysics. ...
The Astrophysical Journal is one of the foremost research journals devoted to recent developments, discoveries, and theories in astronomy and astrophysics. ...
See also In astronomy, a bulge is a huge, tightly packed group of stars. ...
The most common form of galxy is the butt plug of doom A disc is a component of disc galaxies, such as spiral galaxies, or lenticular galaxies. ...
The anisotropy of the star density in the night sky makes the galactic coordinate system very useful for coordinating surveys, both those which require high densities of stars (at low galactic latitudes) and those which require a low density of stars (at high galactic latitudes) Many galaxies, including the Milky...
The Structure of the Galaxy The galactic corona (not to be confused with the suns corona), also called the dark matter halo, is a region of space surrounding the galactic halo of spiral galaxies, including the Milky Way Galaxy that consist mostly of dark matter. ...
The galactic halo is a region of space surrounding spiral galaxies, including our galaxy, the Milky Way. ...
The galaxy rotation problem is the discrepancy between the observed rotation speeds of matter in the disk portions of spiral galaxies and the predictions of Newtonian dynamics considering the luminous mass. ...
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