le>HR Diagram
Hertzsprung-Russell Diagram:Readings: Schneider & Arny: devices 50, 58
In 1905, Danish astronomer Einar Hertzsprung, and also independently Americanastronomer Henry Norris Russell, noticed that the luminosity that starsdecreased native spectral kind O to M. They developed the technique ofplotting pure magnitude because that a star matches its spectral form to lookfor families of mainly type.These diagrams, dubbed the Hertzsprung-Russell or HR diagrams, plotluminosity in solar units on the Y axis and also stellar temperature on the Xaxis, as displayed below.

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Notice the the scales space not linear. Hot stars inhabit the left handside of the diagram, cool stars the ideal hand side. Bright stars atthe top, faint stars at the bottom. Our sunlight is a relatively average starand sits near the middle.A plot that the nearest stars ~ above the HR diagram is displayed below:
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Most stars in the solar community are fainter and also cooler than theSun. There are additionally a grasp of stars which are red and very bright(called red supergiants) and also a few stars that space hot, but an extremely faint(called white dwarfs). Us will check out in a later lecture that starsbegin their life ~ above the main sequence climate evolve to various partsof the HR diagram.Most the the stars in the over diagram fall on a curve the we call themain sequence. This is a region where most normal stars occur. Normal,in astronomy terms, means that they are young (a couple of billion year old)and burning hydrogen in your cores. Together time goes on, star readjust orevolve as the physics in their cores change. But for many of thelifetime of a star it sit somewhere on the main sequence.
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Several regions of the HR diagram have been provided names, return starscan occupy any portion. The brightest stars are called supergiants.Star clusters space rich in stars just off the main sequence dubbed redgiants. Key sequence stars are called dwarfs. And also the faint, hot stars arecalled white dwarfs.
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The spectral classification species were an ext accurate climate attempts to measure up the temperatureof a star by its color. So regularly the temperature range on the horizontal axis is replaced byspectral types, OBAFGKM. This had the advantage of being an ext linear 보다 temperature (nicelyspaces letters) and contained more information around the star than simply its temperature (thestate of its atoms).The HR diagram becomes a calculating tool as soon as one realizes the temperature, luminosity andsize (radius) room all related by Stefan-Boltzmann"s law. The traditional Stefan-Boltzmann legislation isfor allude sources, one idealized case. Genuine objects have actually size, which means surface area. Largeobjects cool much faster (emit power faster) than small objects, so there need to be part correlationwith radius. For stars, the luminosity, temperature and radius are connected by an expansion ofStefan-Boltzmann"s regulation that says:L = 4πR2σT4This equation deserve to be to express in terms of solar systems such that:L/Lo =(R/Ro)2(T/To)4where Lo, Ro and To space the luminosity, radius and surfacetemperature of the Sun.Knowing native laboratory measurements that Stefan-Boltzmann"s continuous is 5.67x10-8allows one to calculate the luminosity of a star in systems of watts (like a light bulb) if weknow the radius the the star in meters and also the temperature in kelvins. For example, the sunlight is6.96x108 meters in radius and also has a surface temperature that 5780K. Therefore, itsluminosity is 3.84x1026 watts.On a log-log plot, the R squared ax in the above equations is astraight heat on an HR diagram. This means that top top a HR diagram, astar"s dimension is basic to review off as soon as its luminosity and also color areknown.
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The HR diagram is a key tool in tracing the advancement of stars. Starsbegin their life top top the main sequence, however then evolve off into redgiant phase and also supergiant phase before dying together white dwarfs or somemore violent endpoint.Thermonuclear Fusion:Energy generation is the heart of stars. It offers the power thatwe watch as light, and also it additionally supplies the heat and also pressure thatsupports a stars" structure. The power source for stars isthermonuclear fusion.Normally, corpuscle with favor charges (positive-positive ornegative-negative) repel each other, this is referred to as electrostaticrepulsion. However at temperatures over 15 million degrees K, themotions of protons room high enough to get over the electrostaticforces and the nuclei deserve to ``fuse"" utilizing the solid force. The primary output indigenous a thermonuclear reactions room photons in theform of gamma-rays, however a big number of other particles areproduced together well.
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The simplest combination reaction is the proton-protonchain, typical in all key sequence stars. It has the adhering to fourstages:
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All the gamma-ray photons space scattered many, countless times as theyleave the mainly core. Every scattering exchanges power so that thephotons transform into visible, UV, IR and radio photons, too ashigh energy ones, developing a thermal, Planck curve, spectrum.The Neutrino Problem:During the proton-proton chain, number of different varieties of issue arecreated from energy and many gamma-ray photons are released. However, dueto the high densities in the main point of a star, every these objects room trappedin the center and, thus, we can not `see" what go on inside a star.However, plenty of neutrinos are likewise created, and also the neutrino is a veryspecial form of fundamental particle with no electric charge, a really smallmass, and one-half unit of spin. Neutrinos belong come the family members ofparticles called leptons, which are not topic to the strong nuclearforce, because of this not quit by the issue in the core of a star.
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Neutrinos room the many penetrating of subatomic particles since theyreact with matter only through the weak interaction. Neutrinos execute notcause ionization, due to the fact that they are not electrically charged. Only 1 in 10billion, traveling through issue a street equal to the Earth"sdiameter, reacts through a proton or neutron. However, due to the fact that neutrinos areweakly interacting, lock are additionally just as complicated to detect. Ours bestneutrino `telescopes" are large tanks that water hidden deep undergroundsuch together the SuperKamiokande in Japan. Water consists of lots of protons in the kind ofhydrogen atoms.
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Neutrinos from a supernova explosion take trip at or verynear the speed of light and carry a many energy. On rarely occasions, aneutrino will certainly hit a proton in the tank of water (the more water, thegreater the chance). This collision will produce a positron i beg your pardon recoils v suchhigh rate that it emits a brief flash of light known as Cerenkov radiation. Thedetector tank that water is hidden deep in the planet to get rid of cosmicrays and other interactions that would certainly distort the detection that theneutrinos. Only neutrinos can reach to together depths.

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Even though neutrinos room so difficult to stop, there space so countless of lock thatit is possible to architecture detectors. Unfortunately, the detectors detectonly a portion of the number neutrinos castle should. This to be a majorsource of concern and confusion for years, and also was referred to as the"neutrino problem," or "the problem with solar neutrinos." What does thismean? nobody knew because that a long time. It could have intended that our ideasabout the proton-proton chain require revising, or that there is some unknownmechanism at work that absorbs countless of the neutrinos prior to they with theEarth. It remained a an enig until relatively recently when astronomers andphysicists suggested that the neutrinos may readjust their characteristicsas castle travel toward Earth. So as soon as they obtained to the detectors on Earth,many that the neutrinos had actually changed into a different type otherthan what the detectors were looking for. Solid evidence for this wasannounced in June, 2001, and it shows up that the "neutrino problem" hasbeen solve.
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