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Theory of the Fireball

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6. Sinrinkage <strong>of</strong> Isotnemal Sphere<br />

We denote <strong>the</strong> 'tmass'' <strong>of</strong> <strong>the</strong> iso<strong>the</strong>rmal sphere, as defined by (6.1)~<br />

by 5, Then this mass will decrease, due to <strong>the</strong> progress <strong>of</strong> tne coding<br />

wave inward, according to<br />

d"l<br />

dt= - PO Rf<br />

Note <strong>the</strong> po 5n <strong>the</strong> denominator and <strong>the</strong> absence <strong>of</strong> <strong>the</strong> factor &fly both<br />

due to <strong>the</strong> definition (6.1) The density <strong>of</strong> <strong>the</strong> iso<strong>the</strong>rmal sphere is<br />

nearly uniform and vi11 be denoted by p<br />

is<br />

Initial values at time tar<br />

will be denoted by a subscript a. The iso<strong>the</strong>rmal sphere expands adia-<br />

bat ically, hence<br />

and <strong>the</strong>refore at any time t<br />

The speed <strong>of</strong> <strong>the</strong> cooling wave is given by (5 .LO), thus<br />

u=<br />

5<br />

- Hl<br />

(6.4)<br />

where J has been set equal to zero because <strong>the</strong>re is no appreciable flow<br />

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