Nice survey of dark matter candidates. I had not heard about the primordial black hole option.
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Known Dark Matter Isn't Enough
11–19 of 19 posts
Re: Known Dark Matter Isn't Enough
#12Nice survey of dark matter candidates. I had not heard about the primordial black hole option.
The next part, linked now at the end, is also informative: http://briankoberlein.com/2014/08/20/already-know-quite-bit/
Especially for the graph taken from http://arxiv.org/abs/1112.1320
Re: Known Dark Matter Isn't Enough
#13Earlier quoted context omitted.
if you don't consider the effects of quantum mechanics then all objects have an event horizon.
No- if you think about a 'classical' particle (that is, ignore quantum effects), once you are inside the particle the gravitational pull is proportional to the distance from the center. In other words, if you are outside a spherical mass the pull of gravity gets stronger as you get closer (~1/r^2). But once you are inside the mass, the pull gets weaker. Hence there is no black hole at the center of the earth, for exa…
you are correct. But what about objects moving past me at near light speeds? Would they see my mass increase to the point that I have an event horizon?
Re: Known Dark Matter Isn't Enough
#14Earlier quoted context omitted.
No- if you think about a 'classical' particle (that is, ignore quantum effects), once you are inside the particle the gravitational pull is proportional to the distance from the center. In other words, if you are outside a spherical mass the pull of gravity gets stronger as you get closer (~1/r^2). But once you are inside the mass, the pull gets weaker. Hence there is no black hole at the center of the earth, for exa…
you are correct. But what about objects moving past me at near light speeds? Would they see my mass increase to the point that I have an event horizon?
Apparently not, but to be honest the reasons are beyond my full understanding.
Re: Known Dark Matter Isn't Enough
#15Earlier quoted context omitted.
No- if you think about a 'classical' particle (that is, ignore quantum effects), once you are inside the particle the gravitational pull is proportional to the distance from the center. In other words, if you are outside a spherical mass the pull of gravity gets stronger as you get closer (~1/r^2). But once you are inside the mass, the pull gets weaker. Hence there is no black hole at the center of the earth, for exa…
you are correct. But what about objects moving past me at near light speeds? Would they see my mass increase to the point that I have an event horizon?
No, because gravitational mass is not the same as (apparent) relativistic mass. I wrote a post on it a while back, but I'm not sure of the protocol regarding comment links.
Re: Known Dark Matter Isn't Enough
#16Earlier quoted context omitted.
you are correct. But what about objects moving past me at near light speeds? Would they see my mass increase to the point that I have an event horizon?
No, because gravitational mass is not the same as (apparent) relativistic mass. I wrote a post on it a while back, but I'm not sure of the protocol regarding comment links.
I would love to read it.
Re: Known Dark Matter Isn't Enough
#17Earlier quoted context omitted.
you are correct. But what about objects moving past me at near light speeds? Would they see my mass increase to the point that I have an event horizon?
No, because gravitational mass is not the same as (apparent) relativistic mass. I wrote a post on it a while back, but I'm not sure of the protocol regarding comment links.
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Re: Known Dark Matter Isn't Enough
#18Earlier quoted context omitted.
No, because gravitational mass is not the same as (apparent) relativistic mass. I wrote a post on it a while back, but I'm not sure of the protocol regarding comment links.
I would love to read it.
Re: Known Dark Matter Isn't Enough
#19Earlier quoted context omitted.
I wouldn't worry myself with that. Since a black hole behaves exactly like a normal star at a large distance, the chance is very small, even if there are many of them. For example, when our galaxy merges with Andromeda there will be only ~1 star collision. Normal black holes are really small, much smaller than a planet, which we can barely detect now. And those planets must be orbiting a star and in the correct incli…
Stellar mass black holes are small in size, but supermassive black holes can be larger than our solar system. Fortunately for us they only exist in the centers of galaxies. The closest supermassive black hole to us is 30,000 light years away.
Also even small (stellar) black holes are very massive — 5x sol and up — (since they tend to occur from the collapse of very large stars) so having one pass near or through the solar system could be catastrophic.
Primordial black holes are posited to be possibly so small as to be able to pass through the earth without interacting with more than a few atoms, which would make visiting them both difficult and not enormously interesting.
Edit: clarification and added info on primordial black holes which I looked up.