How Much Longer Can the Sun Continue to Generate Energy by Nuclear Reactions in Its Core?

 
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The Dominicus�s Structure and Nuclear Fusion

The proton-proton concatenation. This is the principle fusion reaction in the Lord's day. Mass, in the form of hydrogen atoms, is converted to energy as described by Einstein's formula: E = mc².

What kind of burn down is burning on the Dominicus? And what keeps it burning steady?

The power generator in the Dominicus is in its centre, buried deeply within it. It is chosen "the core", with a radius close to 1 fourth of that of the star (see the effigy in a higher place). In the core, pressures and temperatures are high enough to force fusion, that is, nuclear reactions whereby some nuclei merge to make others. It is the type of reaction that powers a hydrogen bomb. The well-nigh important reaction within the core of the Sun is the process chosen the "proton-proton cycle."

photons In the proton-proton chain reaction, hydrogen nuclei are converted to helium nuclei through a number of intermediates. The reactions produce high-energy photons (gamma rays) that move through the "radiative layer" surrounding the core. This layer takes upwardly 60 percent of the radius of the Dominicus. It takes a million years for energy to get through this layer into the "convective layer", because the photons are constantly intercepted, absorbed and re-emitted. In the cadre, the helium nuclei brand up 62% of the mass (the rest is still hydrogen). The radiative and convective layers have most 72% hydrogen, 26% helium, and 2% heavier elements (by mass). The energy produced past fusion is then transported to the solar surface and emitted as calorie-free or ejected as loftier-energy particles.

Past the time the energy reaches the surface of the Sun, things have cooled down to 6000 degrees Kelvin, a temperature that corresponds to the sunlight nosotros run into. By now most of the hydrogen is in the diminutive state and the density of the gas is low, similar to that of the gas in neon lights. The energy emitted from the hot surface, on average, is near 230 million watts per square meter. (On Earth'due south surface, nosotros typically get about a millionth of that, to warm us.)

The solar surface showing active regions and magnetic loops. (Courtesy of SOHO/EIT Consortium)

Nuclear fusion, the source of all the energy so generously radiated by the Sun, does two things: it converts hydrogen into helium (or rather, makes helium nuclei from protons) and it converts mass to free energy.

The mass-to-energy conversion is described by Einstein's famous equation: E = mc², or, in words, energy equals mass times the square of the velocity of light. Considering the velocity of low-cal is a very large number, this equation says that lots of energy can be gained from using up a minor amount of mass.

The energy created past the fusion processes inside the core of the Sun (or whatsoever other star) exerts an outward pressure level. Unless contained, such pressure would produce an explosion (as happens in the hydrogen flop, on a much smaller calibration). The inwards pressure that keeps a star from exploding is the gravitational attraction of the gas mantle surrounding the core (which is most of the book of the Dominicus, and is very hot merely does not burn itself).

The force per unit area of the energy generated in the solar core pushes outward and would cause the Sun to expand if it were not exactly balanced by the gravitational force per unit area of the Dominicus's outer layers.

The outward force per unit area from the fusion reactions keeps the stars from collapsing. The in pressure from gravitation keeps the stars from exploding. If the fusion reactions in the cadre go likewise weak, a star can and does collapse. Such plummet tin provide new weather condition in a core that outcome in new types of fusion reactions, so that expansion follows. If fusion reactions in the core become too strong, a star can and does explode. Such events tin exist observed. When a star explodes it shines with extreme effulgence for a while; it turns from an unnoticed to a "new" star, a "nova". Stars, like our Sun, where inward pressure level and outward pressure is nicely balanced, fluctuate but little in effulgence and give off a steady stream of free energy. The balance is achieved past self-regulation: a slight decrease in fusion free energy would result in contraction that would heat up the core and increase fusion rate, and vice versa. Other stars, where the balance is non so well tuned, pulsate noticeably. Living on a planet circling a pulsating star presumably would exist difficult or impossible.

The Crab Nebula. This is remnant of a supernova that occurred in the year 1054. When nuclear reactions in the core of a star no longer generate enough pressure to offset its weight, the star may explode, as happened here. (Courtesy: VLT)

Thus, the reason that the Sun neither expands (from the ongoing explosion within) nor collapses (from its own weight) is that the ii forces keep the residuum. In the distant future, when this rest is disturbed because virtually of the hydrogen is used upwardly, the Sun will expand. This volition be the terminate of the solar organisation equally we know it.

Photo of the Sun, demonstrating sunspots, dark areas of irregular shape on the surface. They are often large plenty to come across with the naked eye. (Courtesy: NASA)

Thus, on the whole, our star shines with a steady lite. However, it has changed its output over geologic time. Also, it varies a flake on a number of cycles. The most obvious manifestation of this is the and then-called "sunspot cycle" which describes periodic changes in the abundance of spots on the face of the Sun. The affluence of spots is related to the brightness of the Sunday (more spots, more than brightness). The variation is less than one percentage, and the mechanisms are poorly understood. It has to practice with changes in the magnetic field of the Lord's day and with convection within the outer layer of our star (non with processes in the core). Sunspot activeness is closely in stage with ejection of solar plasma (protons mainly) and the ensuing atmospheric fireworks in the polar regions of World called "aurora".

The Aurora Borealis Charged particles from the solar air current collide with atoms in the Globe's atmosphere to produce the "Northern Lights". (Source: NASA)

 

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Source: http://earthguide.ucsd.edu/virtualmuseum/ita/07_2.shtml

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