On Wed, Dec 4, 2013 at 8:12 PM, LizR <lizj...@gmail.com> wrote:
>> The earliest reference I can find is 1783 by John Michell, he called
>> them "dark stars", however it had very different properties from a modern
>> Black Hole. If I was far from one of Michell's Newtonian dark stars I could
>> not see it, but unlike a real Black Hole, I could obtain a picture of it
>> and print it in the newspaper, I'd just have to get closer in a powerful
>> spaceship. I could even land on the classical dark star, get a sample of it
>> and then return it to Earth, that sort of thing would be impossible with a
>> real Einsteinian Black Hole.
> > That's the one. It was used in a story by Brian Aldiss, I guess before
> black holes became widely known about in SF circles (which was probably
> thanks to Larry Niven). Of course one could only "land" on it if one could
> withstand the gravity,
If it was large enough the surface gravity on one of Michell's "dark stars"
could be a earth like 1g or even less. The escape velocity from the surface
of a object depends on BOTH its surface gravity and how big the object is
because that determines how fast the gravity weakens with distance from the
surface, with big objects even a long way away the gravity is almost as
strong as it is on the surface. Actually if it were big enough even with
Einstein's Black Hole the gravity at the event horizon could be 1g,
although after passing that point of no return you would find the gravity
increasing continually until it reached infinity at the singularity at the
center of the hole.
> and only take off if one could travel faster than light
No, a continuously thrusting rocket could escape from one of Michell's
"dark stars" as slowly as you'd like just like you can from the Earth, but
not so with Einstein's Black Hole, from that there is no way out.
John K Clark
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