| 1 Ignor Ramus |
Dark matter and BH's | maandag 19 november 2001 1:59 |
| 2 Uncle Al |
Re: Dark matter and BH's | maandag 19 november 2001 18:51 |
| 3 Ignor Ramus |
Re: Dark matter and BH's | dinsdag 20 november 2001 14:05 |
| 4 Steve Carlip |
Re: Dark matter and BH's | dinsdag 20 november 2001 19:02 |
| 5 Etherman |
Re: Dark matter and BH's | dinsdag 20 november 2001 23:46 |
| 6 Steve Harris |
Re: Dark matter and BH's | woensdag 21 november 2001 6:01 |
| 7 Ignor Ramus |
Re: Dark matter and BH's | donderdag 22 november 2001 15:56 |
| 8 Bruce Bowen |
Re: Dark matter and BH's | vrijdag 23 november 2001 21:37 |
| 9 Nicolaas Vroom |
Re: Dark matter and BH's | maandag 26 november 2001 17:23 |
If there are supermassive Black holes at the centre of every galaxy, to what extent could they account for the 'missing' mass in the universe (i.e. dark matter) ? Thanks, Ignor
Ignor Ramus wrote:
| > |
If there are supermassive Black holes at the centre of every galaxy, to what extent could they account for the 'missing' mass in the universe (i.e. dark matter) ? |
Negligible contribution. If you fully doubled *all* detectable mass equivalent you would still be short by 80%.
-- Uncle Al http://www.mazepath.com/uncleal (Toxic URL! Unsafe for children and most mammals) "Quis custodiet ipsos custodes?" The Net!
Uncle Al
If there are supermassive Black holes at the centre of every galaxy, to
Negligible contribution. If you fully doubled *all* detectable mass
equivalent you would still be short by 80%.
--
Uncle Al
Doh !! Should have realised that ! Thanks.
Next; if galactic BH's are responsible for the high rotational speeds of
galaxies, offered as objective evidence for dark matter, would I be right in
thinking that that 'only' leaves BB theory/models in support of the
existence of dark matter ? Or is there other experimental or observational
evidence I am not aware of ?
(I am aware of at least some proposals /searches for what comprises d.m.,
such as Wimps, etc.)
Ignor.
Ignor Ramus
They can't be, if they're in the centers of galaxies. The problem with
galactic rotation is not that galaxies are rotating too fast, but that the
rotational speed does not fall off fast enough with distance. If you
put a large mass in the center of a galaxy, stars will rotate faster, but
their velocities will still (at least roughly) follow Kepler's laws, with
speeds varying as r^{-1/2}, where r is the distance from the central
mass---just as the outer planets' velocities are smaller than, say,
Mercury's. What we see instead is speeds that are nearly independent
of r. To explain this, we need mass that's spread out throughout the
galaxy. More precisely, we need the mass M(r) within a sphere of
radius r to be proportional to r, or equivalently, the mass density to
fall off as 1/r^2.
This isn't an unreasonable behavior for dark matter---it is, for
example, the density dependence of an isothermal (that is, constant
temperature) sphere of gas. But adding mass to the *center* of a
galaxy won't help.
[Small mathematical note: in Newtonian gravity, the speed of a
circular orbit at radius r is given by v^2 = GM(r)/r, where M(r)
is the mass inside the orbit. There are small general relativistic
corrections to this, but they're unimportant at galactic scales.]
Steve Carlip
"Steve Carlip"
Next; if galactic BH's are responsible for the high rotational speeds
of galaxies, offered as objective evidence for dark matter
They can't be, if they're in the centers of galaxies. The problem with
galactic rotation is not that galaxies are rotating too fast, but that the
rotational speed does not fall off fast enough with distance. If you
put a large mass in the center of a galaxy, stars will rotate faster, but
their velocities will still (at least roughly) follow Kepler's laws, with
speeds varying as r^{-1/2}, where r is the distance from the central
mass---just as the outer planets' velocities are smaller than, say,
Mercury's. What we see instead is speeds that are nearly independent
of r. To explain this, we need mass that's spread out throughout the
galaxy. More precisely, we need the mass M(r) within a sphere of
radius r to be proportional to r, or equivalently, the mass density to
fall off as 1/r^2.
Please provide evidence that we *need* dark matter to explain this
behavior. Surely you meant to say that dark matter is sufficient to
explain this effect.
--
Etherman
AA # pi
EAC Director of Ritual Satanic Abuse Operations
RAFC
AMTCode(v2): [Poster][TĘ][A5][Lx][Sx][Bx][FD][P-][CC]
Etherman wrote in message ...
"Steve Carlip"
Next; if galactic BH's are responsible for the high rotational speeds
of galaxies, offered as objective evidence for dark matter
They can't be, if they're in the centers of galaxies. The problem
with
galactic rotation is not that galaxies are rotating too fast, but
that the
rotational speed does not fall off fast enough with distance. If
you
put a large mass in the center of a galaxy, stars will rotate
faster, but
their velocities will still (at least roughly) follow Kepler's laws,
with
speeds varying as r^{-1/2}, where r is the distance from the central
mass---just as the outer planets' velocities are smaller than, say,
Mercury's. What we see instead is speeds that are nearly
independent
of r. To explain this, we need mass that's spread out throughout
the
galaxy. More precisely, we need the mass M(r) within a sphere of
radius r to be proportional to r, or equivalently, the mass density
to
fall off as 1/r^2.
Please provide evidence that we *need* dark matter to explain this
behavior. Surely you meant to say that dark matter is sufficient to
explain this effect.
It's the simplest explanation that is, consistent with already known
physics. Is it necessary? No, blue fairies could be holding the stars in
tighter orbits, mimicking exactly the gravity of extra matter we don't see.
SBH
--
I welcome email from any being clever enough to fix my address. It's open
book. A prize to the first spambot that passes my Turing test.
Very clear and helpful. Thanks.
Steve Carlip
Next; if galactic BH's are responsible for the high rotational speeds
of galaxies, offered as objective evidence for dark matter
They can't be, if they're in the centers of galaxies. The problem with
galactic rotation is not that galaxies are rotating too fast, but that the
rotational speed does not fall off fast enough with distance. If you
put a large mass in the center of a galaxy, stars will rotate faster, but
their velocities will still (at least roughly) follow Kepler's laws, with
speeds varying as r^{-1/2}, where r is the distance from the central
mass---just as the outer planets' velocities are smaller than, say,
Mercury's. What we see instead is speeds that are nearly independent
of r. To explain this, we need mass that's spread out throughout the
galaxy. More precisely, we need the mass M(r) within a sphere of
radius r to be proportional to r, or equivalently, the mass density to
fall off as 1/r^2.
This isn't an unreasonable behavior for dark matter---it is, for
example, the density dependence of an isothermal (that is, constant
temperature) sphere of gas. But adding mass to the *center* of a
galaxy won't help.
[Small mathematical note: in Newtonian gravity, the speed of a
circular orbit at radius r is given by v^2 = GM(r)/r, where M(r)
is the mass inside the orbit. There are small general relativistic
corrections to this, but they're unimportant at galactic scales.]
Steve Carlip
Steve Carlip
Next; if galactic BH's are responsible for the high rotational speeds
of galaxies, offered as objective evidence for dark matter
They can't be, if they're in the centers of galaxies. The problem with
galactic rotation is not that galaxies are rotating too fast, but that the
rotational speed does not fall off fast enough with distance. If you
put a large mass in the center of a galaxy, stars will rotate faster, but
their velocities will still (at least roughly) follow Kepler's laws, with
speeds varying as r^{-1/2}, where r is the distance from the central
mass---just as the outer planets' velocities are smaller than, say,
Mercury's. What we see instead is speeds that are nearly independent
of r. To explain this, we need mass that's spread out throughout the
galaxy. More precisely, we need the mass M(r) within a sphere of
radius r to be proportional to r, or equivalently, the mass density to
fall off as 1/r^2.
Flash of insight!! Isn't this (radial mass density) what one would
expect from a mass background converging onto and (inviscid) flowing
down a central hole? The mass contained in any thin radial shell is
constant.
Conjecture: Dark matter is falling thru the galaxy radially (very
little angular momentum) and with very little if any interaction with
the light matter, and going down the central black holes!
I wonder if there is any way to measure various galactic central black
holes rate of growth and see if it is consistent with radially
infalling dark matter of a quantity consistent with conjectured radial
densities?
Gravitationally bound isothermal gas sounds good too. Again, is the
rate of growth of the central black holes consistent with the
conjectured dark matter density?
-Bruce
Steve Carlip
Next; if galactic BH's are responsible for the high rotational speeds
of galaxies, offered as objective evidence for dark matter
They can't be, if they're in the centers of galaxies. The problem with
galactic rotation is not that galaxies are rotating too fast, but that the
rotational speed does not fall off fast enough with distance. If you
put a large mass in the center of a galaxy, stars will rotate faster, but
their velocities will still (at least roughly) follow Kepler's laws, with
speeds varying as r^{-1/2}, where r is the distance from the central
mass---just as the outer planets' velocities are smaller than, say,
Mercury's. What we see instead is speeds that are nearly independent
of r. To explain this, we need mass that's spread out throughout the
galaxy. More precisely, we need the mass M(r) within a sphere of
radius r to be proportional to r, or equivalently, the mass density to
fall off as 1/r^2.
This isn't an unreasonable behavior for dark matter---it is, for
example, the density dependence of an isothermal (that is, constant
temperature) sphere of gas. But adding mass to the *center* of a
galaxy won't help.
I do not understand why you need dark matter in order to explain
the rotational curve of a galaxy.
My point is that if you have calculated the mass for r = 40000ly
with an almost flat rotation curve
you need very little mass to make the r 10000ly larger
with the same rotation curve.
As I started before first do a simulation with vissible matter
and see if it matches the rotation curve.
A possible BH in the center will only marginal
change the total mass of a galaxy
(and the shape of the rotation curve)
Created: 28 November 2001
Back to my home page Contents of This Document
3 Dark matter and BH's
Van: Ignor Ramus
Onderwerp: Re: Dark matter and BH's
Datum: dinsdag 20 november 2001 14:05
>
Ignor Ramus wrote:
what
> >
dark
> >
extent could they account for the 'missing' mass in the universe (i.e.
> >
matter) ?
>
4 Dark matter and BH's
Van: Steve Carlip
Onderwerp: Re: Dark matter and BH's
Datum: dinsdag 20 november 2001 19:02
>
Next; if galactic BH's are responsible for the high rotational speeds
of galaxies, offered as objective evidence for dark matter
5 Dark matter and BH's
Van: Etherman
Onderwerp: Re: Dark matter and BH's
Datum: dinsdag 20 november 2001 23:46
>
Ignor Ramus
> >
>
6 Dark matter and BH's
Van: Steve Harris
Onderwerp: Re: Dark matter and BH's
Datum: woensdag 21 november 2001 6:01
>
>>
Ignor Ramus
>> >
>>
>
7 Dark matter and BH's
Van: Ignor Ramus
Onderwerp: Re: Dark matter and BH's
Datum: donderdag 22 november 2001 15:56
>
Ignor Ramus
> >
>
8 Dark matter and BH's
Van: Bruce Bowen
Onderwerp: Re: Dark matter and BH's
Datum: vrijdag 23 november 2001 21:37
>
Ignor Ramus
> >
>
>
This isn't an unreasonable behavior for dark matter---it is, for
example, the density dependence of an isothermal (that is, constant
temperature) sphere of gas. But adding mass to the *center* of a
galaxy won't help.
9 Dark matter and BH's
Van: Nicolaas Vroom
Onderwerp: Re: Dark matter and BH's
Datum: maandag 26 november 2001 17:23
>
Ignor Ramus
> >
>
What you need is a 3D model of a galaxy, with a bulge of roughly
r = 10000 ly , a disk of r = roughly 40000 ly in the xy plane
and consisting of only vissible matter.
I have done the same
See my home page https://www.nicvroom.be
and check the information behind: 12 Darkmatter.
If you want to understand why the speed of the sun is the way
it is by assuming that all the mass is in one point is very
misleading. You must start from a 3D picture.
Excluding a possible BH the gravitational force in the center
of a galaxy is zero, because (excluding z direction) there
is even as much mass in the +x as in the -x direction.
implying that v=0.
(For the y direction the same logic applies)
If it does not you can add invissible matter, but I'am very
doubtfull if you need.