Composition of Stars | klokkenluideronline.info
The Sun is a main sequence star and its chemical composition mainly When the temperature reaches million Kelvin, helium fusion becomes possible. A star is type of astronomical object consisting of a luminous spheroid of plasma held together A plot of the temperature of many stars against their luminosities produces a . This allowed the chemical composition of the stellar atmosphere to be determined. Stardust: Supernovae and Life – The Cosmic Connection. The effective temperature of a star is the temperature of a black body with the luminosity depend on the chemical composition of a star.
Overall, since the core and the mantle comprise most of the atoms of the Earth, the chemical composition of our planet is dominated by iron, oxygen, and silicon. The chemical composition of the stars In the early days of astrophysics, scientists thought that the stars were probably similar to the Earth in chemical composition.
When they passed starlight through a prism and examined the resulting spectrum, they found absorption and occasionally emission lines of many elements common here on Earth. Now, different stars have spectra which look very different click on image to see larger version: Does this mean that the chemical composition of stars varies wildly?
Initially, scientists thought the answer was "yes. She concluded that the atmospheres of stars were NOT made up of the same mix of elements as the Earth NOT wildly variable in composition but in fact, almost entirely hydrogen, in almost all stars This was so surprising that scientists ignored or rejected the idea for several years.
Eventually, after further study confirmed Payne's work, the astronomical community had to concede that the stars were, in fact, very different from the Earth. Some glow brightly, lit up by nearby stars: Other clouds appear dark, because they absorb and scatter the light which tries to pass through them: It is often easier to determine the composition of nebulae than of stars, since we can see into the center of the nebula.
The spectra of these objects show that they, too, are almost completely made of hydrogen and helium, with tiny amount of other elements. When we look at different galaxies, we find some variation in the amount of heavy elements. We believe that heavy elements can be created by the fusion of light elements at the centers of stars. Astronomers use the letters X, Y and Z to denote the fraction of material by mass which made up by hydrogen, helium, and everything else: Inthe IAU defined the astronomical constant to be an exact length in meters: Stellar evolution Stars condense from regions of space of higher matter density, yet those regions are less dense than within a vacuum chamber.
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These regions—known as molecular clouds —consist mostly of hydrogen, with about 23 to 28 percent helium and a few percent heavier elements. One example of such a star-forming region is the Orion Nebula.
Such feedback effects, from star formation, may ultimately disrupt the cloud and prevent further star formation. All stars spend the majority of their existence as main sequence stars, fueled primarily by the nuclear fusion of hydrogen into helium within their cores. However, stars of different masses have markedly different properties at various stages of their development.
The ultimate fate of more massive stars differs from that of less massive stars, as do their luminosities and the impact they have on their environment. Accordingly, astronomers often group stars by their mass: Therefore, they never undergo shell burning, never become red giantswhich cease fusing and become helium white dwarfs and slowly cool after exhausting their hydrogen.
Low mass stars including the Sunwith a mass between 0. Intermediate-mass stars, between 1. After exhausting the hydrogen at the core these stars become supergiants and go on to fuse elements heavier than helium.
They end their lives when their cores collapse and they explode as supernovae. Star formation Main article: Star formation The formation of a star begins with gravitational instability within a molecular cloud, caused by regions of higher density—often triggered by compression of clouds by radiation from massive stars, expanding bubbles in the interstellar medium, the collision of different molecular clouds, or the collision of galaxies as in a starburst galaxy. As the cloud collapses, individual conglomerations of dense dust and gas form " Bok globules ".
As a globule collapses and the density increases, the gravitational energy converts into heat and the temperature rises. When the protostellar cloud has approximately reached the stable condition of hydrostatic equilibriuma protostar forms at the core.
The period of gravitational contraction lasts about 10 to 15 million years.
Stellar composition - Department of Physics and Astronomy - Uppsala University, Sweden
A cluster of approximately young stars lies within the nearby W40 stellar nursery. These newly formed stars emit jets of gas along their axis of rotation, which may reduce the angular momentum of the collapsing star and result in small patches of nebulosity known as Herbig—Haro objects. Less massive T Tauri stars follow this track to the main sequence, while more massive stars turn onto the Henyey track.
Most stars are observed to be members of binary star systems, and the properties of those binaries are the result of the conditions in which they formed. The fragmentation of the cloud into multiple stars distributes some of that angular momentum. The primordial binaries transfer some angular momentum by gravitational interactions during close encounters with other stars in young stellar clusters.
These interactions tend to split apart more widely separated soft binaries while causing hard binaries to become more tightly bound. This produces the separation of binaries into their two observed populations distributions. Main sequence Main article: Such stars are said to be on the main sequenceand are called dwarf stars. Starting at zero-age main sequence, the proportion of helium in a star's core will steadily increase, the rate of nuclear fusion at the core will slowly increase, as will the star's temperature and luminosity.
For most stars, the mass lost is negligible. The time a star spends on the main sequence depends primarily on the amount of fuel it has and the rate at which it fuses it.
Composition of Stars
The Sun is expected to live 10 billion years. Massive stars consume their fuel very rapidly and are short-lived.Making My Own Makeup
Low mass stars consume their fuel very slowly. Stars less massive than 0. The combination of their slow fuel-consumption and relatively large usable fuel supply allows low mass stars to last about one trillion years; the most extreme of 0.
Red dwarfs become hotter and more luminous as they accumulate helium. When they eventually run out of hydrogen, they contract into a white dwarf and decline in temperature.
Besides mass, the elements heavier than helium can play a significant role in the evolution of stars. Astronomers label all elements heavier than helium "metals", and call the chemical concentration of these elements in a star, its metallicity.
A star's metallicity can influence the time the star takes to burn its fuel, and controls the formation of its magnetic fields,  which affects the strength of its stellar wind. Over time, such clouds become increasingly enriched in heavier elements as older stars die and shed portions of their atmospheres.
Post—main sequence Main articles: SubgiantRed giantHorizontal branchRed clumpand Asymptotic giant branch As stars of at least 0. Their outer layers expand and cool greatly as they form a red giant.