Stars
Stars are the most widely recognized astronomical objects, and represent the most fundamental building blocks of galaxies. The age, distribution, and composition of the stars in a galaxy trace the history, dynamics, and evolution of that galaxy. Moreover, stars are responsible for the manufacture and distribution of heavy elements such as carbon, nitrogen, and oxygen, and their characteristics are intimately tied to the characteristics of the planetary systems that may coalesce about them. Consequently, the study of the birth, life, and death of stars is central to the field of astronomy.
stars
Stars are born within the clouds of dust and scattered throughout most galaxies. A familiar example of such as a dust cloud is the Orion Nebula. Turbulence deep within these clouds gives rise to knots with sufficient mass that the gas and dust can begin to collapse under its own gravitational attraction. As the cloud collapses, the material at the center begins to heat up. Known as a protostar, it is this hot core at the heart of the collapsing cloud that will one day become a star. Three-dimensional computer models of star formation predict that the spinning clouds of collapsing gas and dust may break up into two or three blobs; this would explain why the majority the stars in the Milky Way are paired or in groups of multiple stars.
Stars are fueled by the nuclear fusion of hydrogen to form helium deep in their interiors. The outflow of energy from the central regions of the star provides the pressure necessary to keep the star from collapsing under its own weight, and the energy by which it shines.As shown in the Hertzsprung-Russell Diagram, Main Sequence stars span a wide range of luminosities and colors, and can be classified according to those characteristics. The smallest stars, known as red dwarfs, may contain as little as 10% the mass of the Sun and emit only 0.01% as much energy, glowing feebly at temperatures between 3000-4000K. Despite their diminutive nature, red dwarfs are by far the most numerous stars in the Universe and have lifespans of tens of billions of years.On the other hand, the most massive stars, known as hypergiants, may be 100 or more times more massive than the Sun, and have surface temperatures of more than 30,000 K. Hypergiants emit hundreds of thousands of times more energy than the Sun, but have lifetimes of only a few million years. Although extreme stars such as these are believed to have been common in the early Universe, today they are extremely rare - the entire Milky Way galaxy contains only a handful of hypergiants.
In general, the larger a star, the shorter its life, although all but the most massive stars live for billions of years. When a star has fused all the hydrogen in its core, nuclear reactions cease. Deprived of the energy production needed to support it, the core begins to collapse into itself and becomes much hotter. Hydrogen is still available outside the core, so hydrogen fusion continues in a shell surrounding the core. The increasingly hot core also pushes the outer layers of the star outward, causing them to expand and cool, transforming the star into a red giant.If the star is sufficiently massive, the collapsing core may become hot enough to support more exotic nuclear reactions that consume helium and produce a variety of heavier elements up to iron. However, such reactions offer only a temporary reprieve. Gradually, the star's internal nuclear fires become increasingly unstable - sometimes burning furiously, other times dying down. These variations cause the star to pulsate and throw off its outer layers, enshrouding itself in a cocoon of gas and dust. What happens next depends on the size of the core.
Starring a repository also shows appreciation to the repository maintainer for their work. Many of GitHub's repository rankings depend on the number of stars a repository has. In addition, Explore shows popular repositories based on the number of stars they have.
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Can I apply as an international student?Unfortunately, we are not accepting international students. If you are an international student and have funding, your program director may contact urstars@ucsd.edu for eligibility information.
A star is a big ball of gas which gives off both heat and light. So where do stars come from? What happens to them as they grow older? A galaxy contains clouds of dust and gas, as well as stars. It is in the clouds of dust and gas that stars are born. As more and more of the gas (which is mostly hydrogen) is pulled together by gravity into a cloud, the cloud starts to spin. The gas atoms start to bump into each other faster and faster. This creates heat energy. The cloud gets hotter and hotter. Finally, it gets so hot within the cloud that something called "nuclear fusion" happens. The cloud begins to glow. The glowing cloud of gas is now known as a protostar. Theprotostar continues to grow. Once it stops growing, it is known as a mainsequence star. A main sequence star can shine for millions of years ormore. The amount of time it lives is determined by how big it is. Medium stars In medium size stars, after the nuclear fusion has used up all the fuel it has, gravity will pull the remaining material closer together. The star will shrink. In fact, it may get to be only a few hundred kilometers wide! The star is then called a "white dwarf". It can stay like this for a long time. Eventually, it will stop producing any light at all. It is then called a "black dwarf" and it will stay that way forever.Massive stars In large size stars, nuclear fusion will continue until iron is formed. In stars, iron acts like an energy sponge. It soaks up the star's energy. This energy is eventually released in a big explosion called a supernova. The little bit of matter that used to be at the center of the star before the supernova will then be either a neutron star or a black hole. Which object it becomes depends on the size of the original star. A star that is 1.5 to 4 times larger than our Sun will become a neutron star. Stars that are even bigger than that will become black holes. Sing me part of a song about a star! Sorry, your browser does not support the audio element, please consider updating.(Words)
What type of stars will become neutron stars as they are dying out? 1) Stars smaller than our Sun. 2) Stars more than 10 times larger than our Sun. 3) Stars the same size as our Sun. 4) Stars 1.5 to 4 times larger than our Sun. Show me the Level 2 version of this page.
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The term is mostly found in science fiction, as humanity has not yet constructed such vehicles (while the Voyager and Pioneer probes have traveled into local interstellar space, they are not generally considered starships, mainly because they are both unpowered and unmanned). However, exploratory engineering has been undertaken on several preliminary designs and feasibility studies for starships that could be built with modern technology or technology thought likely to be available in the near future. For examples of such studies, see Project Daedalus, Project Orion, and Project Longshot. 041b061a72