Dyothelite Posted November 9, 2006 Report Share Posted November 9, 2006 Does the escape velocity and gravitational force of a star change exponentially as it collapses or is it constant? Quote Link to comment Share on other sites More sharing options...
Buffy Posted November 9, 2006 Report Share Posted November 9, 2006 The gravitational force does not change because the mass is constant, all its doing is "redistributing" itself to concentrate the mass in a smaller volume. No matter how big though, its going to throw off some mass into the space around it....This is true of stars that end up as everything from brown dwarfs to black holes, so its not realy a black hole question.... At the event horizon,Buffy Quote Link to comment Share on other sites More sharing options...
Dyothelite Posted November 9, 2006 Author Report Share Posted November 9, 2006 Again, sorry for my ignorance, but doesn't the escape velocity increase therefore the gravitational force increases? Quote Link to comment Share on other sites More sharing options...
Buffy Posted November 9, 2006 Report Share Posted November 9, 2006 The "escape velocity" is the speed required to to move away from an object without additional force being required to not get pulled back into it. The key factor is that the velocity is dependent upon *how close you are* to the object. The reason that black holes have an event horizon--beyond which nothing can escape--is that there is a point at which that escape velocity must be greater than the speed of light in order to get away, which of course is an impossibility. Since the black hole is so small phyiscally, you can get really close to its huge mass. If you start with the giant star before in collapses into a black hole, how "close" you would have to be to it--and this is an absurdism, but colloquially it gets the point across--would be a point *inside* the star, but at that point, since most of the mass would be *away* from you, there's no problem escaping (if you don't burn up from being inside a fusion reactor). So its really all about the distribution and the distance. The force F of gravity of a mass is dependent solely upon the size of the masses and the distance between their centers of gravity. This is why Dark Matter has such a huge gravitational effect although it has a density that is equivalent to what we call a vacuum.... This is not really all that simple to grok, so continue to ask questions for clarification... Gravitationally challenged,Buffy Quote Link to comment Share on other sites More sharing options...
Dyothelite Posted November 9, 2006 Author Report Share Posted November 9, 2006 "Gravitationally challenged" hahaha I like that. Well ok, but from the surface of the star as it collapses, the escape velocity gradually increases, right? So does it increase constantly or exponentially? Quote Link to comment Share on other sites More sharing options...
Buffy Posted November 9, 2006 Report Share Posted November 9, 2006 Well ok, but from the surface of the star as it collapses, the escape velocity gradually increases, right?This is a loaded statement that I need to interpret. If you mean, you're standing on the surface as it collapses, and as it collapses you stay in contact with that surface, then what's really happening is that you are moving closer to the center of gravity of the star. So....So does it increase constantly or exponentially?Since Newton says that the Gravity increases as the square of the distance, yes, the escape velocity for you is increasing geometrically, which means that you'd better move quick because these suckers don't collapse at any sort of "gradual" pace!!! Conversely if you were able to *maintain*your distance from the center of the star as it collapsed below you, the force of gravity would be *constant*! On the surface of a star going nova is *not* a place I'd wanna be! Get me outta here,Buffy Quote Link to comment Share on other sites More sharing options...
Dyothelite Posted November 9, 2006 Author Report Share Posted November 9, 2006 Thanks Buffy, I appreciate your patience with me. This pursuit is very important to me. Quote Link to comment Share on other sites More sharing options...
infamous Posted November 9, 2006 Report Share Posted November 9, 2006 Again, sorry for my ignorance, but doesn't the escape velocity increase therefore the gravitational force increases?Yes to the first question and no the the second. With the progression of collapse, a point is reached where the radius of the body shrinks to the Schwartzchild Limit. At this stage of collapse, photon energy can no longer overcome the gravitational force present within the body. So yes, escape velocity increases to ©, the speed of light. However, the gravitational force of the body has not changed because this force is a function of the total mass of the body in question. What has happened is, as Buffy has already explained, the surface of the body has now shrunk closer to the gravitational center and at this stage, the gravitational force has only become more focused. Think of it this way; A magnifying glass collects sunlight and focuses it on to a smaller point, same amount of light energy only it's been focused to within tighter constraints................................Infy Quote Link to comment Share on other sites More sharing options...
Dyothelite Posted November 9, 2006 Author Report Share Posted November 9, 2006 What if say an object is a mile from the surface of the star and falls at a certain rate, then the star collapses and you place an object a mile a way from the collapsed star. Will the object fall at the same rate as the first object? Quote Link to comment Share on other sites More sharing options...
infamous Posted November 9, 2006 Report Share Posted November 9, 2006 What if say an object is a mile from the surface of the star and falls at a certain rate, then the star collapses and you place an object a mile a way from the collapsed star. Will the object fall at the same rate as the first object?Both objects will fall at an accelerated rate dependant upon the mass of both the object and the star and also the distance between them..........................Infy Quote Link to comment Share on other sites More sharing options...
Buffy Posted November 9, 2006 Report Share Posted November 9, 2006 As both Infy and I have said, but is an *extremely* subtle issue: what's important is the distance *to the center of the mass*. So "one mile away" in your question is actually very misleading because the *surface* moved, but the center of mass did not. If I were to restate your question, after the collapse, "one mile away from the surface" is now *much* closer to the center of mass, therefore, in this particular situation, the force would be "greater" but that's because (to mix in your SR thread) your frame of reference--the physical surface--*has moved*... It really all does depend on your point of view! I'm late,Buffy Quote Link to comment Share on other sites More sharing options...
Dyothelite Posted November 9, 2006 Author Report Share Posted November 9, 2006 Yeah I have other reasons for asking this. I'm struggling with a multi-dimensional model of the universe, and basically I'm wondering if accelaration can ever be seen as changing. accelaration is a change in velocity, I'm wondering if there is such a thing as changing acceleration on a natural level... like could the gravitational acceleration of a star chnage during collapse, so that during collapse the gravitational acceleration actually increases... Probably not but it woulda made my day easier. hahahaha Quote Link to comment Share on other sites More sharing options...
arkain101 Posted November 9, 2006 Report Share Posted November 9, 2006 I havnt been able to understand how those mass and energy jets are capable to blast out of the poles of a black hole. As I understand they happen periodically and matter and energy is blasted from the proximity of a black hole near the speed of light. It either escapes from inside, which doesnt make sense, right?Or It is material that has not yet entered the event horizon and in the mix of the powerful gravity is chucked out at the poles. Quote Link to comment Share on other sites More sharing options...
arkain101 Posted November 9, 2006 Report Share Posted November 9, 2006 I dont mean to take away this thread. It just seemed pointless to start an entire thread for a quick question. apologies. Quote Link to comment Share on other sites More sharing options...
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