



Be the first pioneers to continue the Astronomy Discussions at our new Astronomy meeting place... The Space and Astronomy Agora 
Re: Finite Matter, Infinite Density...
Forum List  Follow Ups  Post Message  Back to Thread Topics  In Response To Posted by John/">John on March 2, 1999 19:36:06 UTC 
: : : : According to theory, Black Holes have infinte mass and infinte gravity. : : : : How then, can there be an event horizon? If the force of gravity from the Black : : : : Hole is infinite, then it would not dissipate with distance and therefore would be : : : : the same everywhere, for an infinite distance. If my understanding of infinity is : : : : correct, then Black Holes must have a finite mass and gravity if there is to be an : : : : an event horizon.....right? : : : actually I think you have the theory off a bit. : : : BH have (at their singularities) infinite density, : : : not infinite mass; for the reason you state in the : : : latter portion. : ) : : : this is why there are different sizes of BH as well. : : : For instance the gravitational field surrounding a : : : BH may as well be the mass of 50 of our suns, and : : : the event horizon be 1500 feet across. : : Thanks, the finite mass aspect clears a few things up. : : It still doesn't deal with the infinite gravity though. : : How is it possible to measure the dimensions of a : : gravitational field under conditions of infinite gravity? : A BH does not have infinite gravity whatsoever. : I'm not sure where you heard this from. : Let me give you an example... : Take for instance a massive star in its dying phase. : As the nuclear fusion begins to slow, the equalibrium : balance of the force of fusion expelling outwards falls : below the force of gravity collapsing inwards. : As the crushing force is creating a denser mass, keep : in mind the mass does not change, thus the gravitational : field has not changed. : Now, imagine the star has collapsed to the critical size : called the, "Schwarzchild radius". This is the diameter : of the star where space has become "potentially" infinitely : curved. Thus light cannot even escape this boundary. : IOW, the escape velocity required to escape this event horizon : becomes infinitely close to the speed of light. : Now, lets take a step back and look at this BH. Has : its gravity increased? No... In fact, imagine this : particular BH side by side with its earlier form as : the star. The BH and star have exactly the same mass (accounting : the BH hasn't drawn anything in) as the star does. (in its early, : precollapse stage) The only thing that has increased : is the density. If you measured the gravity attraction : of the BH at a given distance, you would measure the : same gravity measurement of the same star at the same : distance... : nåte Thanks nate, you obviously know alot more about this than I. I got the infinity thing from a show on the Discovery Channel. The guy who was their "expert" described a BH as having infinite mass and infinite gravity. The logic of that didn't seem to fit, thus the posting on here. Infinite space, I can almost deal with, but infinite mass seemed to have much graver implications. 

Additional Information 

About Astronomy Net  Advertise on Astronomy Net  Contact & Comments  Privacy Policy 
Unless otherwise specified, web site content Copyright 19942024 John Huggins All Rights Reserved Forum posts are Copyright their authors as specified in the heading above the post. "dbHTML," "AstroGuide," "ASTRONOMY.NET" & "VA.NET" are trademarks of John Huggins 