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Model of the Solar Interior The theoretical data presented here is the basis of the Two–Layer Model of Stars: Core & Envelope Traditional models of the Solar Interior present three regions: The Core, The Radiative Zone and the Convective Zone I will present evidence that suggests that a Two-Layer Model of the Sun may be more useful for us in understanding how stars operate. Standard Solar Model Standard Solar Model (references) Reactions (description, from [ref]). Predicted spectrum (postscript file, 21K) Predicted fluxes, from Bahcall and Pinsonneault. The page reproduced to the left is just for cosmetics. You do not need to read it. It is a visual reminder that if an astronomer understands the reactions that go on within the Sun and the pressure and temperature conditions that control those reactions, they can calculate the properties of the interior of the Sun with great precision even though they have never “seen” into the solar interior directly. The Sun’s internal structure is displayed in the following four slides that show how the luminosity, mass, temperature, and density vary with the distance from the Sun’s center. These internal structure (L, M, T and ρ) parameters are from the Standard Solar Model. A solar radius (the distance from the Sun’s center to the photosphere) equals 696,000 km. Solar Interior Structure Cumulative Luminosity Energy production is the basis of the Two-Layer model 1 of the Sun. One layer – the 95% This The How region graph big is the displays shaded core? inthe red coreproduces energyas and by cumulative represents that luminosity portion ofathe Since it is about 1/5’th the its thermal supports 0.75 function Sun located of pressure solar within radius. 0.2 solar solar radius, the volume of the the envelope against further CORE ENVELOPE Notice radii orhow 1/5’th the the luminosity solar radius. core is 1/5’th cubed the collapse. Without the core the climbs toward 1 Solar Notice volume that ofwould the about Sun 95% or, of the 0.5 envelope collapse. The Luminosity as the fractional We will call the volume of the entire equivalently Sunsolar beyond less than solar 1% is the second layerluminosity is0.2 the envelope radius increases. radii the envelope. The envelope generated volume produces of the within Sun. 0.2 energy Let solar me that produces nono energy but 0.25 (almost) and occupies 99% emphasize radii ofrequired the ofSun’s the center. this volume. result. Isn’t The is to maintain core this interesting? 99% of thecore Sun’s ofconditions. the volume Sun has that produces fusion We shall call this region the nothing to do with energy production almost all the – orenergy does it? In 0 core. Almost all the energy Lets fact, the envelope is essential occupies forexamine energy onlysome production 1% ofother the Sun’s 0 0.1 0.2 0.3 0.4 produced 0.5 0.6 0.7 0.8 0.9 1 by the Sun occurs properties of the core and because its weight on the core volume. maintains What the does core the other in the core. envelope. pressures so that fusion can 99% continue. Without do? the R/RSunof the Sun envelope that core would explode! Solar Interior Structure 1 Cumulative Mass 0.75 0.5 33% 0.25 0 0 Let’s think About 33% 1/3 or about this. 1/3 of the of the Sun’s How much of Sun’s mass is mass is mass the Sun’s the core.into squeezed isin contained 2/3’rds of the 1% ofthe the within Sun’s Sun’s mass volume. core? are the must Thein core envelope. be very dense! 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 R/RSun 1 Density, g/cm3 Halfway What Imagine Thus,isthe athrough that How characteristic core you about ofthe had thethe envelope Sun andensity envelope? iron How is extremely bar the about ofthe the density 100 size core? high of is Solar Interior3Structure 3! and down a loaf in density toofabout ordinary while 1 gm/cm white the envelope g/cm bread or equivalent Remember is low justto in like the white you density. could of water! squeeze that ironthat hasiron a 1000 bread density bar density theofsize about of a8 100down to a ball of about 3. So tennis ball, just like you g/cm could dothe to white core of 10 bread.1 That squished iron thebar Sun would is over still10 not 100 g/cm be as dense as the core timesofas the dense Sun. as 0.1 1 g/cm Pressures are so great in the cores iron. of stars 0.01 CORE we thinkENVELOPE that material of as sturdy can be 0.001 squished like white bread! 3 3 0.0001 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 R/RSun 1 Solar Interior Structure 15 Million K 100,000,000 3 Million K Temperature, K 10,000,000 1,000,000 CORE ENVELOPE 100,000 10,000 1,000 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 R/Rhot Sun (10’s Million K) conclude that the core is very We What What The How isthe aSun isHow characteristic aenvelope about characteristic is about cool a bit only a over few temperature attemperature Million 10 itscooler very Million Kelvins. outer in Kelvins. in thesurface. the Envelope? core? while is much (Millions of K). Just This However, as balanced thethe this Weight will be Currently Sun, maintained balance Lifter willWeight must eventually like Lifter, Let’sour compare the throughout eventually tire, so give Sun the Main way, will a is “happy” because Sun to athe Weight Sequence as eventually it must with run lifetime out our of balance exists Lifter. The Weights the Weight fuel Sun. to sustain Lifter, core the between the represent the as Sun hydrogen runs out burning. of Sun downward weight of envelope of the energy Then the indown inevitable its core. the “envelope” and pushing on the will happen. the force from coreupward represented by the “core”. Weight Lifter. Envelope Core The Gravity Sun, details never just of like gets what our tired! We will explore next Weight Sooner happens or tolater stars will allas be stars how theLifter, crushing of a crushed meet their the by same are the crushed weight fate – to star’scores core can cause of be is the crushed envelope. by intotheir Units thedescribed envelope swell64 envelopes. & 66. creating a Giant star. The Sun can be functionally divided into two layers. • The core – Produces almost all the energy – Supports the weight of the envelope preventing further collapse – Contains 1/3 the mass of the Sun – Has a density of near 100 g/cm3 – Has temperatures is excess of 10 million K • The Envelope – Produces essentially no energy – Restrains the core against blowing up and maintains conditions for fusion – Contains 2/3’rds the solar mass – Has a density of around 1 g/cm3 – Has a temperature in the millions of K Please keep this Two-layer Model in mind as you study the life cycle of stars.