Lack of runaway black holes hints at dark matter density

Although the study's authors don't dare to challenge the orthodoxy of
Dark Matter belief, reading between the lines, one can say that this may
actually be the falsification of Dark Matter's existence. A supermassive
black hole of 5 billion Msun is approximately as massive as a whole
dwarf galaxy by itself. Such a concentrated source of mass should be
swallowing Dark Matter, and swallowing it a rate that makes it a runaway
process. Unlike Baryonic Matter, Dark Matter can't be kept in check from
falling into a black hole by electromagnetic forces, such as magnetism
or friction, so Dark Matter should be captured endlessly without
resistence. The fact that this isn't happening is very telling.

The study author's simply say that DM density must be lower than
expected. Sure that's possible, but that puts an upper limit on Dark
Matter density, making it harder still to fit models around it.

Yousuf Khan

***
Study: Lack of runaway black holes hints at dark matter density -
Science Fair: Science and Space News - USATODAY.com
"In calculations, the pair finds that if dark matter has a critical
density (above 250 solar masses per cubic parsec or about .0003
microgram of dark matter per cubic mile of space), such black holes
would have grown in runaway fashion, growing larger endlessly without
stopping and consuming galaxies whole. But they haven't in the last 10
billion years, so dark matter must be spread rather thinly through
space, the study concludes:"
http://content.usatoday.com/communit...tter-density/1

Dear Yousuf Khan:

On Mar 25, 7:26*am, Yousuf Khan wrote:
....
Study: Lack of runaway black holes hints at
dark matter density - Science Fair: Science and
Space News - USATODAY.com
"In calculations, the pair finds that if dark matter
has a critical density (above 250 solar masses
per cubic parsec or about .0003 microgram of
dark matter per cubic mile of space), such black
holes would have grown in runaway fashion,
growing larger endlessly without stopping and
consuming galaxies whole. *But they haven't in
the last 10 billion years, so dark matter must be
spread rather thinly through space, the study
concludes:
snip link now broken by Google Groups

This is not surprising, and DM density is low. We've mapped it. Its
just higher than normal matter is (perhaps).

David A. Smith

dlzc wrote:
This is not surprising, and DM density is low. We've mapped it. Its
just higher than normal matter is (perhaps).

David A. Smith

The study authors are saying that this now makes Dark Matter density too
low to form the structure of the universe, such as those filaments of
Dark Matter with no galaxies. This is otherwise known as the "clumpy"
Dark Matter theory.

Yousuf Khan

Yousuf Khan wrote:

Although the study's authors don't dare to challenge the orthodoxy of
Dark Matter belief, reading between the lines, one can say that this may
actually be the falsification of Dark Matter's existence. A supermassive
black hole of 5 billion Msun is approximately as massive as a whole
dwarf galaxy by itself.

....galactic black holes span a rather large range of masses...

Such a concentrated source of mass should be
swallowing Dark Matter, and swallowing it a rate that makes it a runaway
process.

....this idiocy again? Black holes aren't magic. They don't vacuum up all
matter just 'because'.

By what mechanism other than direct capture would put dark matter into a
black hole?

Unlike Baryonic Matter, Dark Matter can't be kept in check from
falling into a black hole by electromagnetic forces, such as magnetism
or friction, so Dark Matter should be captured endlessly without
resistence. The fact that this isn't happening is very telling.

Uh, electromagnetic forces are what puts matter into black holes. Without
the dissipative effect on angular momentum, the vast majority of matter
would orbit endlessly until kicked out via multibody interactions.


The study author's simply say that DM density must be lower than
expected. Sure that's possible, but that puts an upper limit on Dark
Matter density, making it harder still to fit models around it.

Yousuf Khan

***
Study: Lack of runaway black holes hints at dark matter density -
Science Fair: Science and Space News - USATODAY.com
"In calculations, the pair finds that if dark matter has a critical
density (above 250 solar masses per cubic parsec or about .0003
microgram of dark matter per cubic mile of space), such black holes
would have grown in runaway fashion, growing larger endlessly without
stopping and consuming galaxies whole. But they haven't in the last 10
billion years, so dark matter must be spread rather thinly through
space, the study concludes:"

http://content.usatoday.com/communit.../03/astronomy-
lack-of-runaway-black-holes-hints-at-dark-matter-density/1

eric gisse wrote:
Yousuf Khan wrote:

Although the study's authors don't dare to challenge the orthodoxy of
Dark Matter belief, reading between the lines, one can say that this may
actually be the falsification of Dark Matter's existence. A supermassive
black hole of 5 billion Msun is approximately as massive as a whole
dwarf galaxy by itself.

...galactic black holes span a rather large range of masses...

In this case they're talking about the biggest of the big.

Such a concentrated source of mass should be
swallowing Dark Matter, and swallowing it a rate that makes it a runaway
process.

...this idiocy again? Black holes aren't magic. They don't vacuum up all
matter just 'because'.

By what mechanism other than direct capture would put dark matter into a
black hole?

Mainly by direct capture. A 5 billion Msun blackhole is approximately
100 AU in radius. This should be large enough volume to scoop up a lot
of dark matter without even relying on magnetic effects. Then the
capture of all of this DM will in turn increase the mass and volume of
the blackhole, and it would be able to capture even more DM -- runaway
process. That is, if the density of Dark Matter is high enough.

Unlike Baryonic Matter, Dark Matter can't be kept in check from
falling into a black hole by electromagnetic forces, such as magnetism
or friction, so Dark Matter should be captured endlessly without
resistence. The fact that this isn't happening is very telling.

Uh, electromagnetic forces are what puts matter into black holes. Without
the dissipative effect on angular momentum, the vast majority of matter
would orbit endlessly until kicked out via multibody interactions.

Yes, electromagnetic forces both feed and starve black holes. The
smaller blackholes would need electromagnetic forces to feed them. But a
5 billion Msun blackhole could work even without electromagnetic forces.

Yousuf Khan

i cant help but say how do you know that measuring dark matter isnt
the same thing as Mideival schools measuring epicycles which dont
exist yet they measured them.

Dear Yousuf Khan:

On Mar 25, 7:10*pm, Yousuf Khan wrote:
....
By what mechanism other than direct capture would
put dark matter into a black hole?

Mainly by direct capture. A 5 billion Msun blackhole
is approximately 100 AU in radius.

Meaning the DM would have to pass within say 200 AU to be directly
captured. This leaves a lot of DM *not* captured.

This should be large enough volume to scoop up
a lot of dark matter

Not that much on a galactic scale.

without even relying on magnetic effects.

Which would have zero effect on DM. That which is inherently
chargeless isn't going to care about the apparent motion of charges
somewhere. If it had charge, some light could interact with it, and
it wouldn't be Dark.

Then the capture of all of this DM will in turn
increase the mass and volume of the
blackhole, and it would be able to capture
even more DM -- runaway process. That is,
if the density of Dark Matter is high enough.

It is *by definition* zero near the center of a spiral galaxy. The
densities, if DM were "stuff", would be extremely low, and the
velocities extremely high. Piece of cake to exit from very close
approaches, if not in the same direction...

David A. Smith

dlzc wrote:
Dear Yousuf Khan:

On Mar 25, 7:10 pm, Yousuf Khan wrote:
...
By what mechanism other than direct capture would
put dark matter into a black hole?
Mainly by direct capture. A 5 billion Msun blackhole
is approximately 100 AU in radius.

Meaning the DM would have to pass within say 200 AU to be directly
captured. This leaves a lot of DM *not* captured.

Not really, the escape velocity of Dark Matter would be much lower than
light speed. If the speed of DM was 1/10 of light speed, then given a
square root relationship between distance and gravitational strength,
then the blackhole's influence would be 100 times farther away than its
event horizon, which would be a radius of 10,000 AU. Of course if the
speed of DM was even lower, then the blaokhole's zone of influence would
be even larger.

The most popular DM model is the Cold Dark Matter model, which would
require non-relativistic DM particles, with speeds quite a bit less than
1% light speed.

without even relying on magnetic effects.

Which would have zero effect on DM. That which is inherently
chargeless isn't going to care about the apparent motion of charges
somewhere. If it had charge, some light could interact with it, and
it wouldn't be Dark.

Which was of course the point I was making.

Then the capture of all of this DM will in turn
increase the mass and volume of the
blackhole, and it would be able to capture
even more DM -- runaway process. That is,
if the density of Dark Matter is high enough.

It is *by definition* zero near the center of a spiral galaxy. The
densities, if DM were "stuff", would be extremely low, and the
velocities extremely high. Piece of cake to exit from very close
approaches, if not in the same direction...


But that's an entirely arbitrary definition. There must be a reason why
it's zero near a galactic centre. Something must be clearing it out.

Yousuf Khan

Yousuf Khan wrote:
dlzc wrote:
Dear Yousuf Khan:

On Mar 25, 7:10 pm, Yousuf Khan wrote:
...
By what mechanism other than direct capture would
put dark matter into a black hole?
Mainly by direct capture. A 5 billion Msun blackhole
is approximately 100 AU in radius.

Meaning the DM would have to pass within say 200 AU to be directly
captured. This leaves a lot of DM *not* captured.

Not really, the escape velocity of Dark Matter would be much lower than
light speed. If the speed of DM was 1/10 of light speed, then given a
square root relationship between distance and gravitational strength,
then the blackhole's influence would be 100 times farther away than its
event horizon, which would be a radius of 10,000 AU. Of course if the
speed of DM was even lower, then the blaokhole's zone of influence would
be even larger.

Escape velocity is irrelevant for objects approaching
from outside the system, since conservation of energy
dictates a symmetrical energy profile: they gain
kinetic energy (speed) as they fall in and shed it as
they rise back out of the gravitational well. Any body
that has enough speed to approach the well from a long-
way-off has enough energy to leave to the same long-way-
off distance, barring direct impact.

Only if the obects can shed energy by another mechanism
(friction, impact, etc.) can they be captured.

Dear Yousuf Khan:

On Mar 28, 8:09*pm, Yousuf Khan wrote:
dlzc wrote:
Dear Yousuf Khan:

On Mar 25, 7:10 pm, Yousuf Khan wrote:
...
By what mechanism other than direct capture would
put dark matter into a black hole?
Mainly by direct capture. A 5 billion Msun blackhole
is approximately 100 AU in radius.

Meaning the DM would have to pass within say
200 AU to be directly captured. *This leaves a lot of
DM *not* captured.

Not really, the escape velocity of Dark Matter would
be much lower than light speed. If the speed of DM
was 1/10 of light speed, then given a square root
relationship between distance and gravitational
strength, then the blackhole's influence would be
100 times farther away than its event horizon,

"influence" is *not* direct capture.

which would be a radius of 10,000 AU. Of course
if the speed of DM was even lower, then the
blaokhole's zone of influence would be even larger.

The most popular DM model is the Cold Dark
Matter model, which would require non-relativistic
DM particles, with speeds quite a bit less than
1% light speed.

Falling from a large distance towards a black hole, turns "Cold Dark
Matter" relativistic.

without even relying on magnetic effects.

Which would have zero effect on DM. *That which
is inherently chargeless isn't going to care about
the apparent motion of charges somewhere. *If it
had charge, some light could interact with it, and
it wouldn't be Dark.

Which was of course the point I was making.

Then the capture of all of this DM will in turn
increase the mass and volume of the
blackhole, and it would be able to capture
even more DM -- runaway process. That is,
if the density of Dark Matter is high enough.

It is *by definition* zero near the center of a
spiral galaxy. *The densities, if DM were
"stuff", would be extremely low, and the
velocities extremely high. *Piece of cake to
exit from very close approaches, if not in the
same direction...

But that's an entirely arbitrary definition.

It is the definition that creates the need for Dark Matter. If you
start at the rim, and work your way in, it seems to me that no Dark
Matter is required.

There must be a reason why it's zero near a
galactic centre. Something must be clearing it out.

If there is no friction, then the only matter near the center is
moving *very* fast. High speed = low density (since pressure is non-
existent either way).

David A. Smith