Author Topic: Anyone remember the recent SGU episode about dark matter/black holes?  (Read 368 times)

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Offline God Bomb

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I think the gist of it was that there are way more black holed than we thought, possibly enough to account for all dark matter, therefore new particles such as WIMPs aren't required.

WHen listening to this I wanted to ask, if this was the case, why do all the depictions of dark amtter, (based on gravitational effects, I guess) show it as a kind of halo or cloud, in and around galaxies.  If it was comprised of black holes it would be points, rather than a cloud. 

Can anyone clear this up for me?
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Offline InsanePat

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according to
"If this is correct, then all galaxies, including our own, are embedded within a vast sphere of black holes each about 30 times the sun's mass."
so i'd be like a cloud made of (relatively) small black holes. At the scale of the universe, it may be small enough nnot to be distinguishable from a cloud of smaller elements, despite, I assume, a low enough density for them not to merge and transform the universe into a single huge black hole. Or maybe the expansion and equilibrium of attractions is enough for that, i guess i'm far out of my depth here.

Offline God Bomb

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ok, thanks.  My uninformed opinion is that if it were the case that this many were out there, we would see way more lensing when looking at other galaxies.  A cloud and a collection of larger objects may have a similar gravitational effect, but lensing should be clear as it's based on curvature around what is essentially a point in space.  Also it's hard to believe none of these ever coalesce, wouldn't there be some kind of detectable artifacts in the perimeters of galaxies if some of these were to collide?  </uninformed speculation>

Maybe i just like the idea of elementary particles we still haven't discovered.  I never thought we'd reach a point in physics where black holes are the most boring explanation.
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Online The Latinist

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I posted about that in the episode thread.  It is my understanding that gravitational lensing surveys have ruled out MACHOs with masses ranging from .5 earth masses to 30 solar masses comprising any significant fraction of dark matter.  That means that primordial black holes of the type LIGO may have discovered, while probably accounting for some of the missing mass, cannot "BE" dark matter.
I would like to is undesirable to believe in a proposition when there is no ground whatever for supposing it true. — Bertrand Russell