Dark Matter Paradox / Black Hole Runaway

[David Spain]

OK, I'll pose a problem. Time for an Original Post from me ;-)

If, as conjectured, dark matter pervades the Universe, (making up as
much as 24% of the mass in the universe) why hasn't/isn't any of this
been swallowed into the ultimate gravitational attractor. Why are there
so few black holes around and why are they so small if we are awash in
"Darth Matter"? Why are they the result only of stellar collapse? Why
don't they just form spontaneously out of the Dark Matter aether?

David

[Greg (Strider) Moore]

>"David Spain" wrote in message
>news:voidnYBcg7QTd4bM...@giganews.com...

I'd say because they've never achieved the density required. Even the early
lumpiness of the Universe probably didn't provide enough density for dark
matter objects to form. If they can't form, no "dark matter stars" no black
holes.

As for few black holes, not so much. I believe they pretty much believe
every galaxy as a decent sized one in the center.


>
>David
>
>

--
Greg D. Moore http://greenmountainsoftware.wordpress.com/
CEO QuiCR: Quick, Crowdsourced Responses. http://www.quicr.net

[David Spain]

On 2/14/2013 11:06 AM, Greg (Strider) Moore wrote:
>
>> "David Spain" wrote in message
>> news:voidnYBcg7QTd4bM...@giganews.com...
>>
>> OK, I'll pose a problem. Time for an Original Post from me ;-)
>>
>> If, as conjectured, dark matter pervades the Universe, (making up as
>> much as 24% of the mass in the universe) why hasn't/isn't any of this
>> been swallowed into the ultimate gravitational attractor. Why are
>> there so few black holes around and why are they so small if we are
>> awash in "Darth Matter"? Why are they the result only of stellar
>> collapse? Why don't they just form spontaneously out of the Dark
>> Matter aether?
>
> I'd say because they've never achieved the density required. Even the
> early lumpiness of the Universe probably didn't provide enough density
> for dark matter objects to form. If they can't form, no "dark matter
> stars" no black holes.
>
> As for few black holes, not so much. I believe they pretty much believe
> every galaxy as a decent sized one in the center.
>
>

OK that could explain why we don't see spontaneously forming black holes
out of nothing...

But if I give the existing ones 24% more mass than was previously
considered available why are they size we see? Why are their event
horizon diameters pretty much in line with theory that says its due to
mass obtained from 'non-dark'?

I call this the 'Miami-Beach Theory'. A black hole may have no hair, but
as far as dark matter is concerned it must also be wearing sunglasses,
and if its name happens to be Kerr, a significant equatorial bulge. In
other words a fat, balding 'hole', hanging around the beach with Tequila
in hand, with sunglasses on to filter out all the WIMPs leaving them
only the ability to see the bikini clad "Material Girls"...

Dave

[Brian Gaff]

Maybe they cannot collide and hence cannot form into huge masses. However,
if that was the case, then what bends the light near where it is said a lot
of it exists?

Brian

--
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"David Spain" <nos...@127.0.0.1> wrote in message
news:voidnYBcg7QTd4bM...@giganews.com...

[Brian Gaff]

The imbalance between the matter and anti matter is also a bit puzzling
could the imbalance of gravity and apparent mass with nothing solid to
create it be part of the result of the imbalance. Gravity seems to be a
force which only has one pole. You do not get anti gravity do you.

Brian

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Blind user.

"Greg (Strider) Moore" <moo...@ignorethisgreenms.com> wrote in message
news:soSdna8xPdPkloDM...@earthlink.com...

[mar...@gmail.com]

I am no expert but this is my understanding of the current theory.

When regular matter collides part of the kinetic energy in the collision is
radiated away as heat (EM radiation) which causes matter to lump together
relatively easily. This is due to electromagnetic interactions. Regular mat
ter also has other interactions, like the nuclear forces.

Unlike regular matter, dark matter is believed to only interact gravitation
ally, with itself and also with regular matter; there are no other known in
teractions. This means that when two "clouds" of dark matter collide they j
ust pass right through each other without any loss of kinetic energy. They
may later slow down by gravitational attraction and change direction for an
other pass-through. Since there is no mechanism by which kinetic energy can
be lost this cycle could go on forever (almost), like an ideal oscillator.
This is what prevents dark matter from lumping together. Same happens when
dark matter collides with regular matter.

Now, since it interacts gravitationally, dark matter should obey General Re
lativity, in that it should radiate energy as gravitational waves, and give
n a sufficiently long time should slow down and eventually lump together. I
can’t give you an estimate for how long that would take, maybe much long
er than the age of the Universe.

Regarding black holes, I would assume that dark matter falling in should st
ay in and add to the mass of the BH, just like regular matter. I don’t th
ink there’s a way to tell what proportion of a BH’s mass comes from reg
ular or dark matter. But, per above, I don’t think dark matter itself cou
ld form a BH that wasn’t there in the first place, unless given a very ve
ry long time.

[Brian Gaff]

As people have said before though, there are problems even obn the level you
state. What started the motion of dark matter in the first place and how can
it clump if its so very low in interactablity?

I'm loathe to mention it, but since the speed of light appears to be the
same in any local frame of reference we can devise, how can anyone tell what
is moving in relation to what. there is no centre of the universe, just a
horison we cannot see beyond. Thus when talking about that other
inconvenient p issue, dark energy, nobody can say there is not a huge
enclosure to the universe that as it balloons out does not drag the space
within it with it stretching it out. All we see is red shift surely?

Brian

--
>From the Bed of Brian Gaff.
The email is valid as bri...@blueyonder.co.uk
Blind user.

<mar...@gmail.com> wrote in message
news:a7077238-7d46-4f3e...@googlegroups.com...

[Steve Willner]

Poster 'mar...@gmail.com' gave basically the right answer.

In article <khd5jo$s19$1...@dont-email.me>,

"Brian Gaff" <bri...@blueyonder.co.uk> writes:
> What started the motion of dark matter in the first place

Gravity.

> and how can it clump if its so very low in interactablity?

Gravity. Look at a globular cluster for example. The stars don't
collide or dissipate energy, but the cluster stays bound. I'm
oversimplifying a bit, but analysis show the dark matter clumpiness
grows over time, and simulations show the same thing. There's a nice
movie at
http://www.mpa-garching.mpg.de/galform/millennium/
though I fear it won't do much good if you are blind. Basically it
shows all the (simulated) dark matter particles zooming around, but
they tend to concentrate in overdense regions, and the size of the
overdense structures grows with time.

> I'm loathe to mention it, but since the speed of light appears to be the
> same in any local frame of reference we can devise, how can anyone tell what
> is moving in relation to what.

It's easy to measure relative motion. There is, so far as we know,
no absolute rest frame.

> there is no centre of the universe, just a horison we cannot see
> beyond.

Right, or at least so we think now.

I'm afraid I don't understand the rest of the post, but something
outside our horizon shouldn't have any effect on what we observe
unless that something was previously in causal contact. Dark energy
remains mysterious, but a cosmological constant is certainly one
candidate for what it might be.

--
Help keep our newsgroup healthy; please don't feed the trolls.
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Cambridge, MA 02138 USA

[David Spain]

Steve,

I'm not sure I'm buying the 'low density' argument in the vicinity of a
black hole. If a BH can form an accretion disk of ordinary matter why is
dark matter so selectively able to 'stay away'?

Well the day job is getting in the way of doing more research on this
topic today. I'll try to follow up with a better reasoned argument when
I can find the time to do so.

Dave

[David Spain]

On 3/5/2013 12:10 PM, mar...@gmail.com wrote:
> Regarding black holes, I would assume that dark matter falling in should st
> ay in and add to the mass of the BH, just like regular matter.

I would too.

> I don�t think there�s a way to tell what proportion of a BH�s mass comes from reg
> ular or dark matter. But, per above, I don�t think dark matter itself could form
> a BH that wasn�t there in the first place, unless given a very very
long time.

Well maybe, you have to define 'long time'. Esp. since we know the
Cosmic Microwave Background is not uniform, why do we think gravitation
should be?

However, my main issue is how does DM respond in the vicinity of a BH?
If it's really there, Swartzchild's calculations would have or should
have been way off.

Maybe they are. I don't know how much experimental/observational rigor
has been applied in trying to determine the theories accuracy. More
research I need to do that I don't have the time for right now.

Those who have knowledge in this area are always welcome to contribute
what they know! Steve?


Dave

[David Spain]

On 3/25/2013 8:27 PM, David Spain wrote:
> However, my main issue is how does DM respond in the vicinity of a BH?
> If it's really there, Swartzchild's calculations would have or should
> have been way off.
>

I'd be a lot happier with the CDM hypothesis if it were re-framed
somewhat. Rather than think of it terms of discrete "matter", I'd prefer
to think of it in terms of a space-time "contour". Seen this way CDM
only presents at very, very large scales. As you continually reduce the
scale (volume) of the Universe under observation, essentially CDM fades
away. This would eliminate the issue I have with CDM "falling" into a
BH. The contours are essentially "straight". But at the scale of a
galaxy or esp. at a universe space-time exhibits the popular bands and
strands. I'd call this a "course-structure" model, but that'd probably
confuse the issue.

What's still missing is a QM explanation for why a CDM contour would
exist. If we can ever incorporate Gravitation into QM maybe we can start
to understand why.

Dave

[Steve Willner]

In article <QMSdnZR-ZuOw-c3M...@giganews.com>,

David Spain <nos...@127.0.0.1> writes:
> If a BH can form an accretion disk of ordinary matter why is
> dark matter so selectively able to 'stay away'?

Because dark matter isn't affected by anything except gravity. A DM
particle comes in, and unless its orbit intersects the event horizon,
the particle goes right back out again, regardless of what other
particles may be nearby. (I'm over-simplifying a bit: the relevant
distance is a little larger than the event horizon but not much.) A
baryon, on the other hand, may hit another baryon, and orbits of both
get changed. In particular, motion parallel to the angular momentum
vector is damped out, forming a disk. Once a disk forms, viscosity
(baryon-baryon interaction) causes matter to flow inward, eventually
into the black hole. If baryons were collisionless, they wouldn't
form a disk or be accreted either.

An analogy for DM particles around a black hole is globular cluster
stars. Many GCs probably have black holes in the middle, but the
stars don't magically get sucked in. The stars just continue
orbiting unless (very rarely) one of the orbits is perturbed enough
to bring the star very close to the black hole.

[David Spain]

Thanks for the reply Steve, your explanation helps a great deal.
A few comments tho...

On 3/26/2013 4:57 PM, Steve Willner wrote:
> In article <QMSdnZR-ZuOw-c3M...@giganews.com>,
> David Spain <nos...@127.0.0.1> writes:
>> If a BH can form an accretion disk of ordinary matter why is
>> dark matter so selectively able to 'stay away'?
>
> Because dark matter isn't affected by anything except gravity. A DM
> particle comes in, and unless its orbit intersects the event horizon,
> the particle goes right back out again, regardless of what other
> particles may be nearby. (I'm over-simplifying a bit: the relevant
> distance is a little larger than the event horizon but not much.) A
> baryon, on the other hand, may hit another baryon, and orbits of both
> get changed. In particular, motion parallel to the angular momentum
> vector is damped out, forming a disk.

Parallel? If you are referring to angular momentum relative to the BH,
don't you mean perpendicular?

> Once a disk forms, viscosity
> (baryon-baryon interaction) causes matter to flow inward, eventually
> into the black hole. If baryons were collisionless, they wouldn't
> form a disk or be accreted either.
>
> An analogy for DM particles around a black hole is globular cluster
> stars. Many GCs probably have black holes in the middle, but the
> stars don't magically get sucked in. The stars just continue
> orbiting unless (very rarely) one of the orbits is perturbed enough
> to bring the star very close to the black hole.
>

I'm still stuck on the visualization of DM as 'particles'.
I think the problem is that DM is so 'extremely massive' it's hard to
think of it in terms of ordinary matter. I get your GC analogy (and
thanks for that as well it really helps!) however, there are several
real problems that remain. Sure DM can whiz past a BH in a
non-intersecting orbit, but there are many possible orbits. For example,
stellar pairings of stars and BH's trapped in their own mutual
gravitation are not uncommon. So why wouldn't BH's attract halo's of DM?
Especially If DM is far more common than matter? Would not this cause
measurable gravitational anomalies in the vicinity of a BH that we
should be able to observe?

I'm less unhappy if I think of DM not as 'particles' but as contours.
Contours that play out only along very very very large distances. Since
BH geometry is quite compact, it would help explain (to me anyway) why
we don't see strange BH/DM interactions.

To get a feel for what I'm talking about let's consider the problem from
a purely spacial perspective and "re-normalize". Think of the
circumference of a 'typical' BH event horizon being about the size of a
hand-held shot-put. Think of the circumference of a DM 'particle' being
the circumference of the Earth. From the BH perspective the DM
'particle' presents as a flat surface. From the Moon I can see the DM
'particle' as a discrete object and it would take mighty powerful optics
to see the shot-put at all.

Ignoring all the other differences, am I getting closer to a better analogy?

Dave

[Steve Willner]

In article <Ae2dnbolaKiXrM7M...@giganews.com>,

David Spain <nos...@127.0.0.1> writes:
> Parallel? If you are referring to angular momentum relative to the BH,
> don't you mean perpendicular?

The angular momentum _vector_ points toward the pole of rotation.
For a disk to form, the relevant angular momentum is that of the
baryons that make up the disk. Depending on the formation mechanism,
that might be close in direction to the black hole angular momentum,
but it doesn't always have to be.

> I'm still stuck on the visualization of DM as 'particles'.

Can't help you with that; it works fine for me.

It might help to think about comets approaching the Sun. They come
in from all directions and at varying speeds, but very few hit the
Sun. Mostly they just go back out where they came from. If the Sun
were replaced by a black hole of the same mass, nothing much would
change except that the cross section for "hitting" would be a lot
smaller. Is that clear?

As you say later, having multiple bodies complicates things. Some
comets are perturbed by Jupiter or other planets into Sun-
intersecting orbits. However, some that would have intersected the
Sun are perturbed into orbits that miss. I doubt there's a
substantial net effect one way or the other, but it's beyond me to do
a detailed calculation. Dark matter particles should behave the same
way (except that radiation pressure and other non-gravitational
forces are zero).

The basic point is that a black hole isn't some kind of "cosmic
vacuum cleaner" that goes around sucking in everything in the
vicinity. It's just a gravitating body like any other except very
near the event horizon. Depending on how sensitively you can measure
and how close the orbit comes to the event horizon, there may be
measureable differences, but the overall appearance of orbits is the
same whether the central mass is a black hole or any other body.

[David Spain]

On 3/13/2013 6:25 AM, Steve Willner wrote:
> There's a nice movie at
> http://www.mpa-garching.mpg.de/galform/millennium/

Thanks for posting this, I've been looking over this entire website
whenever I get a chance.

Some scholia:

1) Units of Gpc/h, Mpc/h and kpc/h not explained.

For those of us not steeped in this for a living I did a little
research. Gpc == Giga-parsecs, Mpc == Mega-parsecs kpc == kilo-parsecs.
The /h is a scalar correction in the range [0.5, 0.75] reflecting the
uncertainty in the value of the Hubble constant H for the rate of
expansion of the Universe. See Wikipedia:
http://en.wikipedia.org/wiki/Parsec

To give you a feel for the 'size' of a Mega-parsec, according to the
cited Wikipedia page, the Andromeda Galaxy is about 0.78 Mpc away from
the Earth.

2) Units of Gyr assumed to be Giga-years, i.e. 10**9 or as we say in the
US one billion years (thank your Dr. Sagan). As opposed to Phoenix
Goodyear Airports... See Wikipedia: http://en.wikipedia.org/wiki/Gyr

3) For the series of images which are taken as zoomed slices through the
density field, I'm presuming the redshift taken for each series can also
be presumed as how it would appear for various ages of the universe. For
example at a z=0 t=13.6 Gyr we are essentially looking through density
fields for the universe at its current age. At z=18.3 t=0.21Gyr we are
looking at density fields for a universe that is 'only' 210 million
years old.

Steve correct where needed.

Dave