« on: 07/12/2017 20:54:38 »
Quote from: Petrochemicals
How on gravity ! does it fight th3 gravitational pull.The Sun fights gravity with temperature. An increase in temperature produces an increase in pressure.
Pressure can be considered an expansion force which fights the compressive force of gravity.
At present, the Sun is a Hydrogen-burning star. During this process, the core shrinks, gravitational compression increases in the core, and the rate of fusion slowly increases, over billions of years. This means that radius is slowly increasing, luminosity is slowly increasing, but the temperature and color remains roughly the same.
See graph at: https://en.wikipedia.org/wiki/Sun#Main_sequence
However, in about 5 billion years (age: around 10 billion), the Sun will have run out of Hydrogen in its core (although there will still be hydrogen farther out). The radius of the Sun will reach Earth's current orbit, and the luminosity will be thousands of times higher than present - but the surface temperature will be lower (a dull red color), and the surface gravity will be much lower. The surface gravity will be so low that the Sun will shed most of its outer shell, as a planetary nebula.
A complicated sequence of events happen as helium burns into carbon - surface temperature grows to around 6 times the current temperature (a blue-white color), but radius shrinks to 10 times the current value.
But for polarisThere are highly non-linear relationships between:
- fusion fuel, reaction rates, core temperature and pressure
- surface temperature, surface area, color, and luminosity.
- mass, radius, surface gravity and core gravity.
- mass loss over time
- and all these parameters continually change over the Sun's lifetime.
So don't expect a simple relationship between the size, surface gravity and color of the Sun and another star - or even when comparing the Sun at two different ages (measuring age in billions of years).
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