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To create a star you need hydrogen and helium. Therefore, you need a gas giant, not a terrestrial planet, to let it turn into a brown dwarf, and eventually into a hydrogen-burning star. You write of accretion of Jupiter-sized objects, but are these gas giants? Universe Sandbox features some exoplanets whose composition is unknown well. When I make Jupiter ...

2

In case you are interested in "apparent shrinkage", then you might want to know that the Earth is moving away from the Sun by about 15 centimeters per year, while the Sun itself is growing by about 5 centimeters per year. However, as the Earth-Sun distance is about 100 times the Sun's diameter, apparent growth (between these two factors) easily ...

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A black hole does not necessarily suck in everything around it. Something that is outside $r = 2GM/ c^2$ radial distance (Schwarzschild radius) from the black hole, behaves in a similar way as if the black hole were a normal gravitating object. Here is a Schwarzschild radius calculator online For a mass equal to that of the earth, the Schwarzschild radius is ...

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I will try to generalize your question to 'why does any object not become a black hole?'. It is indeed true that the center of mass of an object pulls the mass around it, so why does it not collapse? We need to see, what force is balancing the force of gravity. If you press an object (let's say: Iron), as hard as you can, why does it not get destroyed ...

50

Is the sun shrinking currently? It's the other way around: The Sun is slowly growing hotter and thus is slowly expanding. The Sun accumulates ever more helium in its core as it ages. This growing amount of fusion ash results in the core getting hotter, which in turn results in the Sun expanding in volume. This completely overwhelms what one would expect ...

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Sun's mass is almost $M_\odot = 1.9*10^{30}$ kg. The mass-loss scale you are talking about is around $\delta M \approx 10^{10}$ kg/s. I'm guessing this mass-loss is due to both stellar winds and nuclear fusion. So, if the Sun evolves only using this mass-loss, it will last for $t=\frac{M\odot}{\delta M} = 10^{20} seconds.$ This time scale is almost 3 ...

2

If you have a spherical ball of matter, then outside that ball of matter, the gravitational field is the same as if all them mass were concentrated at a point (as a black hole) But inside the ball of matter, some of the mass of the ball is behind you and acts in the opposite direction. This means that the gravitational field is at a maximum on the surface ...

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