Was Bedeutet Cluster Hauptnavigation
Cluster (englisch für ‚Traube', ‚Bündel', ‚Schwarm', oder ‚Ballung') steht für: Informatik und Mathematik: Cluster (Datenträger), logische Zusammenfassung von. Cluster beim Online Wöirenewbraceletreview.co: ✓ Bedeutung, ✓ Definition, ✓ Synonyme, ✓ Übersetzung, ✓ Herkunft, ✓ Rechtschreibung. d) Externe Dimension: In ihr kommt zum Ausdruck, dass die Offenheit eines Clusters nach außen von substanzieller Bedeutung ist. Die kontinuierliche. Was bedeutet CLUSTER? Das Scrabble online Wörterbuch liefert Dir Synonyme, Definitionen und Wortbedeutungen von CLUSTER. Bei Fehlern oder in. Singular, Plural. Nominativ, der Cluster, die Cluster. Genitiv, des Clusters, der Cluster. Dativ, dem Cluster, den Clustern. Akkusativ, den Cluster, die Cluster.
bedeutet Büschel oder Anhäufung.“ [1a] „Die Aufgaben sind für alle Cluster verschieden, sie gehen jeweils von einem Kontext aus und decken mit ihren Items. Cluster ist ein Anglizismus, auf deutsch bedeutet es Gruppe, Haufen oder Zusammenballung. Cluster (englisch für ‚Traube', ‚Bündel', ‚Schwarm', oder ‚Ballung') steht für: Informatik und Mathematik: Cluster (Datenträger), logische Zusammenfassung von.
Hence the proportion of metals can be an indication of the age of a star, with older stars typically having a lower metallicity.
The Dutch astronomer Pieter Oosterhoff noticed that there appear to be two populations of globular clusters, which became known as Oosterhoff groups.
The second group has a slightly longer period of RR Lyrae variable stars. These two populations have been observed in many galaxies, especially massive elliptical galaxies.
Both groups are nearly as old as the universe itself and are of similar ages, but differ in their metal abundances.
Many scenarios have been suggested to explain these subpopulations, including violent gas-rich galaxy mergers, the accretion of dwarf galaxies, and multiple phases of star formation in a single galaxy.
In the Milky Way , the metal-poor clusters are associated with the halo and the metal-rich clusters with the bulge. In the Milky Way it has been discovered that the large majority of the low metallicity clusters are aligned along a plane in the outer part of the galaxy's halo.
The difference between the two cluster types would then be explained by a time delay between when the two galaxies formed their cluster systems.
Globular clusters have a very high star density, and therefore close interactions and near-collisions of stars occur relatively often. Due to these chance encounters, some exotic classes of stars, such as blue stragglers , millisecond pulsars , and low-mass X-ray binaries , are much more common in globular clusters.
Astronomers have searched for black holes within globular clusters since the s. The resolution requirements for this task, however, are exacting, and it is only with the Hubble Space Telescope that the first confirmed discoveries have been made.
They are the first black holes discovered that were intermediate in mass between the conventional stellar -mass black hole and the supermassive black holes discovered at the cores of galaxies.
The mass of these intermediate mass black holes is proportional to the mass of the clusters, following a pattern previously discovered between supermassive black holes and their surrounding galaxies.
Claims of intermediate mass black holes have been met with some skepticism. The heaviest objects in globular clusters are expected to migrate to the cluster center due to mass segregation.
As pointed out in two papers by Holger Baumgardt and collaborators, the mass-to-light ratio should rise sharply towards the center of the cluster, even without a black hole, in both M15  and Mayall II.
The Hertzsprung-Russell diagram HR-diagram is a graph of a large sample of stars that plots their visual absolute magnitude against their color index.
Large positive values indicate a red star with a cool surface temperature , while negative values imply a blue star with a hotter surface.
When the stars near the Sun are plotted on an HR diagram, it displays a distribution of stars of various masses, ages, and compositions.
Many of the stars lie relatively close to a sloping curve with increasing absolute magnitude as the stars are hotter, known as main-sequence stars.
However the diagram also typically includes stars that are in later stages of their evolution and have wandered away from this main-sequence curve.
As all the stars of a globular cluster are at approximately the same distance from the Earth, their absolute magnitudes differ from their visual magnitude by about the same amount.
The main-sequence stars in the globular cluster will fall along a line that is believed to be comparable to similar stars in the solar neighborhood.
The accuracy of this assumption is confirmed by comparable results obtained by comparing the magnitudes of nearby short-period variables, such as RR Lyrae stars and cepheid variables , with those in the cluster.
By matching up these curves on the HR diagram the absolute magnitude of main-sequence stars in the cluster can also be determined.
This in turn provides a distance estimate to the cluster, based on the visual magnitude of the stars.
The difference between the relative and absolute magnitude, the distance modulus , yields this estimate of the distance.
When the stars of a particular globular cluster are plotted on an HR diagram, in many cases nearly all of the stars fall upon a relatively well-defined curve.
This differs from the HR diagram of stars near the Sun, which lumps together stars of differing ages and origins.
The shape of the curve for a globular cluster is characteristic of a grouping of stars that were formed at approximately the same time and from the same materials, differing only in their initial mass.
As the position of each star in the HR diagram varies with age, the shape of the curve for a globular cluster can be used to measure the overall age of the star population.
However, the above-mentioned historic process of determining the age and distance to globular clusters is not as robust as first thought, since the morphology and luminosity of globular cluster stars in color-magnitude diagrams are influenced by numerous parameters, many of which are still being actively researched.
Certain clusters even display populations that are absent from other globular clusters e. The historical paradigm that all globular clusters consist of stars born at exactly the same time, or sharing exactly the same chemical abundance, has likewise been overturned e.
One such effect is called blending, and it arises because the cores of globular clusters are so dense that in low-resolution observations multiple unresolved stars may appear as a single target.
Thus the brightness measured for that seemingly single star e. The most massive main-sequence stars will also have the highest absolute magnitude, and these will be the first to evolve into the giant star stage.
As the cluster ages, stars of successively lower masses will also enter the giant star stage. Thus the age of a single population cluster can be measured by looking for the stars that are just beginning to enter the giant star stage.
This forms a "knee" in the HR diagram, bending to the upper right from the main-sequence line. The absolute magnitude at this bend is directly a function of the age of globular cluster, so an age scale can be plotted on an axis parallel to the magnitude.
In addition, globular clusters can be dated by looking at the temperatures of the coolest white dwarfs. Typical results for globular clusters are that they may be as old as The ages of globular clusters place a bound on the age limit of the entire universe.
This lower limit has been a significant constraint in cosmology. Historically, astronomers were faced with age estimates of globular clusters that appeared older than cosmological models would allow.
However, better measurements of cosmological parameters through deep sky surveys and satellites such as the Hubble Space Telescope appear [ clarification needed ] to have resolved this issue.
Evolutionary studies of globular clusters can also be used to determine changes due to the starting composition of the gas and dust that formed the cluster.
That is, the evolutionary tracks change with changes in the abundance of heavy elements. The data obtained from studies of globular clusters are then used to study the evolution of the Milky Way as a whole.
In globular clusters a few stars known as blue stragglers are observed, apparently continuing the main sequence in the direction of brighter, bluer stars.
The origins of these stars is still unclear, but most models suggest that these stars are the result of mass transfer in multiple star systems.
In contrast to open clusters, most globular clusters remain gravitationally bound for time periods comparable to the life spans of the majority of their stars.
However, a possible exception is when strong tidal interactions with other large masses result in the dispersal of the stars.
After they are formed, the stars in the globular cluster begin to interact gravitationally with each other. As a result, the velocity vectors of the stars are steadily modified, and the stars lose any history of their original velocity.
The characteristic interval for this to occur is the relaxation time. This is related to the characteristic length of time a star needs to cross the cluster as well as the number of stellar masses in the system.
Although globular clusters generally appear spherical in form, ellipticities can occur due to tidal interactions. Clusters within the Milky Way and the Andromeda Galaxy are typically oblate spheroids in shape, while those in the Large Magellanic Cloud are more elliptical.
Astronomers characterize the morphology of a globular cluster by means of standard radii. These are the core radius r c , the half-light radius r h , and the tidal or Jacobi radius r t.
The overall luminosity of the cluster steadily decreases with distance from the core, and the core radius is the distance at which the apparent surface luminosity has dropped by half.
This is typically larger than the core radius. The half-light radius includes stars in the outer part of the cluster that happen to lie along the line of sight, so theorists will also use the half-mass radius r m —the radius from the core that contains half the total mass of the cluster.
When the half-mass radius of a cluster is small relative to the overall size, it has a dense core.
An example of this is Messier 3 M3 , which has an overall visible dimension of about 18 arc minutes , but a half-mass radius of only 1.
Almost all globular clusters have a half-light radius of less than 10 pc , although there are well-established globular clusters with very large radii i.
Finally the tidal radius, or Hill sphere , is the distance from the center of the globular cluster at which the external gravitation of the galaxy has more influence over the stars in the cluster than does the cluster itself.
This is the distance at which the individual stars belonging to a cluster can be separated away by the galaxy.
The tidal radius of M3 is about 40 arc minutes,  or about pc  at the distance of In measuring the luminosity curve of a given globular cluster as a function of distance from the core, most clusters in the Milky Way increase steadily in luminosity as this distance decreases, up to a certain distance from the core, then the luminosity levels off.
Typically this distance is about 1—2 parsecs from the core. In this type of cluster, the luminosity continues to increase steadily all the way to the core region.
Core-collapse is thought to occur when the more massive stars in a globular cluster encounter their less massive companions.
Over time, dynamic processes cause individual stars to migrate from the center of the cluster to the outside. This results in a net loss of kinetic energy from the core region, leading the remaining stars grouped in the core region to occupy a more compact volume.
When this gravothermal instability occurs, the central region of the cluster becomes densely crowded with stars and the surface brightness of the cluster forms a power-law cusp.
The dynamical heating effect of binary star systems works to prevent an initial core collapse of the cluster. When a star passes near a binary system, the orbit of the latter pair tends to contract, releasing energy.
Only after the primordial supply of binaries is exhausted due to interactions can a deeper core collapse proceed. The different stages of core-collapse may be divided into three phases.
During a globular cluster's adolescence, the process of core-collapse begins with stars near the core.
However, the interactions between binary star systems prevents further collapse as the cluster approaches middle age. Finally, the central binaries are either disrupted or ejected, resulting in a tighter concentration at the core.
The interaction of stars in the collapsed core region causes tight binary systems to form. As other stars interact with these tight binaries, they increase the energy at the core, which causes the cluster to re-expand.
As the mean time for a core collapse is typically less than the age of the galaxy, many of a galaxy's globular clusters may have passed through a core collapse stage, then re-expanded.
The Hubble Space Telescope has been used to provide convincing observational evidence of this stellar mass-sorting process in globular clusters.
Heavier stars slow down and crowd at the cluster's core, while lighter stars pick up speed and tend to spend more time at the cluster's periphery.
The globular star cluster 47 Tucanae , which is made up of about 1 million stars, is one of the densest globular clusters in the Southern Hemisphere.
This cluster was subjected to an intensive photographic survey, which allowed astronomers to track the motion of its stars. Precise velocities were obtained for nearly 15, stars in this cluster.
A study by John Fregeau of 13 globular clusters in the Milky Way shows that three of them have an unusually large number of X-ray sources, or X-ray binaries, suggesting the clusters are middle-aged.
Previously, these globular clusters had been classified as being in old age because they had very tight concentrations of stars in their centers, another test of age used by astronomers.
The implication is that most globular clusters, including the other ten studied by Fregeau, are not in middle age as previously thought, but are actually in 'adolescence'.
The overall luminosities of the globular clusters within the Milky Way and the Andromeda Galaxy can be modeled by means of a gaussian curve.
Computing the interactions between the stars within a globular cluster requires solving what is termed the N-body problem.
The naive CPU computational "cost" for a dynamic simulation increases in proportion to N 2 each of N objects must interact pairwise with each of the other N objects , so the potential computing requirements to accurately simulate such a cluster can be enormous.
The motions are then described by means of a formula called the Fokker—Planck equation. This can be solved by a simplified form of the equation, or by running Monte Carlo simulations and using random values.
However the simulation becomes more difficult when the effects of binaries and the interaction with external gravitation forces such as from the Milky Way galaxy must also be included.
The results of N-body simulations have shown that the stars can follow unusual paths through the cluster, often forming loops and often falling more directly toward the core than would a single star orbiting a central mass.
In addition, due to interactions with other stars that result in an increase in velocity, some of the stars gain sufficient energy to escape the cluster.
Over long periods of time this will result in a dissipation of the cluster, a process termed evaporation. Binary stars form a significant portion of the total population of stellar systems, with up to half of all stars occurring in binary systems.
Numerical simulations of globular clusters have demonstrated that binaries can hinder and even reverse the process of core collapse in globular clusters.
When a star in a cluster has a gravitational encounter with a binary system, a possible result is that the binary becomes more tightly bound and kinetic energy is added to the solitary star.
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Categorie : Calcolo distribuito Calcolo parallelo. Cluster means "many things". However, saying "a cluster of" sounds more intense than just saying "a lot" It sounds like there are many, many, MANY things.
It's also more rare to hear "a cluster of" rather than "a lot of". Sorry, I wasn't clear. I meant to say that the definition is "many things", or "a lot of things".
And sure, I can help you with other things. I don't think I can use them all in one sentence lol "Hog" means two things: 1 to not share something "My brother is so mean.