Can an object grow past the schwarzschild radius?
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Disclaimer: NOT a physicist, just someone who took undergrad physics.
My best understanding of the Schwarzchild Radius is that it is a solution to an equation. By rearranging a bunch of terms and solving for x, they found the number (or rather an equation that can give you the number). The argued about the number and what it means for a while, and it was originally determined to mean (or solved to mean) the radius (specifically, distance from the object’s center of mass) at which a body of a given mass has enough gravity that light cannot reach the escape velocity of the object. You probably already know all of this based on your comment.
What’s important to realize is that ABOVE the Schwarzchild radius (getting farther from the COM), the escape velocity for the object is no longer above the speed of light. Another important thing to remember is the terms on the other side of the equation giving the Schwarzchild radius: mass, the universal gravitational constant, and the speed of light. The last two are always the same, so the only thing determining a specific object’s Schwarzchild radius is its mass. In your example in your comment, adding the planet changes the mass of the star, and thus its Swarzchild radius.
“Couldn’t the star keep existing and growing just as it was before, with the exception that light is sucked back in?”
Well… this is where a trained physicist would really help me… but my best understanding of the event horizon tells me that a good answer here would be “we don’t really know, and there’s no way for us to know.” If light is sucked back in, then there is an event horizon, and there is no way for us to get information back “out” of the black hole, so there’s no way for us to study what’s happening in there. All we really know is that once an event horizon has developed, we are dealing with a black hole and can expect Hawking radiation and all that other stuff I definitely know about.
People who know more than me, please correct me…
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