Hubble makes 3D dark matter map

BBC has an article:
http://news.bbc.co.uk/2/hi/science/nature/6235751.stm
though no reference to the original article.

--
Hans Aberg

"Hans Aberg" schreef in bericht
...
BBC has an article:
http://news.bbc.co.uk/2/hi/science/nature/6235751.stm
though no reference to the original article.

Maybe this is what you are looking for:

http://www.nasa.gov/hubble
http://hubblesite.org/news/2007/01

De question remains where is this dark matter within our Galaxy.
It can not be in the neighbourhood of our planets because then it
would influence the orbits of our planets.
The orbits resemble point masses.
It can not be in the neighbourhood of the Sun because then there
would be a different explanation (compared with GR) to explain the
perihelion of Mercury.
If there is no darkmatter in the neighbourhood of our Sun then there
should not be any darkmatter in the neighbourhood of any star in the
disc of Our Galaxy.

If that is the case, what worries me, with dark matter maybe only
in the voids between the stars of the disc or completely outside the disc
how can such an arrangement (which constitutes 90% of all matter
of our galaxy) be used to make our Galaxy more stable.

Nicolaas Vroom
http://users.pandora.be/nicvroom/

Hans Aberg wrote:
BBC has an article:
http://news.bbc.co.uk/2/hi/science/nature/6235751.stm
though no reference to the original article.

These seem to be recent and related, but don't have
much depth to them.

http://www.centauri-dreams.org/?p=961
http://www.centauri-dreams.org/?p=535

This is related and has depth, but is from 2004:

http://www.journals.uchicago.edu/AJ/...21/203221.html

The senior author, Richard Massey, of the study in your URL
is apparently a postdoc at CalTech:

http://www.astro.caltech.edu/cgi-bin/postdocs.cgi

With home page he

http://www.astro.caltech.edu/~rjm/

Going to his publications page, we find:

For those with a Nature subscription, the article is here!!!

http://www.nature.com/nature/journal...ture05497.html

FWIW

xanthian, persistent web searcher.

In article , "Nicolaas Vroom"
wrote:

De question remains where is this dark matter within our Galaxy.
It can not be in the neighbourhood of our planets because then it
would influence the orbits of our planets.
The orbits resemble point masses.
It can not be in the neighbourhood of the Sun because then there
would be a different explanation (compared with GR) to explain the
perihelion of Mercury.
If there is no darkmatter in the neighbourhood of our Sun then there
should not be any darkmatter in the neighbourhood of any star in the
disc of Our Galaxy.

Perhaps the solar winds blow it away. Would a dark hole, by observation,
behave any differently?

--
Hans Aberg

"Hans Aberg" schreef in bericht
...
In article , "Nicolaas Vroom"
wrote:

De question remains where is this dark matter within our Galaxy.
It can not be in the neighbourhood of our planets because then it
would influence the orbits of our planets.
The orbits resemble point masses.
It can not be in the neighbourhood of the Sun because then there
would be a different explanation (compared with GR) to explain the
perihelion of Mercury.
If there is no darkmatter in the neighbourhood of our Sun then there
should not be any darkmatter in the neighbourhood of any star in the
disc of Our Galaxy.

Perhaps the solar winds blow it away.

That means you agree that there is no darkmatter in the
neighbourhood of our Sun ?
Nor in the neighbourhood of any star ?

Is that the meaning of the astronomy community
enlarge ?

Would a dark hole, by observation,
behave any differently?

You mean hole or halo ?
If you mean black hole then I do not know the answer
but I expect that the same is true
i.e. no dark matter "at rest"

Nicolaas Vroom
http://users.pandora.be/nicvroom/

Nicolaas Vroom wrote:

"Hans Aberg" schreef in bericht
...

BBC has an article:
http://news.bbc.co.uk/2/hi/science/nature/6235751.stm
though no reference to the original article.


Maybe this is what you are looking for:

http://www.nasa.gov/hubble
http://hubblesite.org/news/2007/01

De question remains where is this dark matter within our Galaxy.
It can not be in the neighbourhood of our planets because then it
would influence the orbits of our planets.

If the density of dark matter
is anywhere close to critical density ~10^-30 g/cc,
its influence on planetary orbits would be negligible

The orbits resemble point masses.
It can not be in the neighbourhood of the Sun because then there
would be a different explanation (compared with GR) to explain the
perihelion of Mercury.
ditto above
If there is no darkmatter in the neighbourhood of our Sun then there
should not be any darkmatter in the neighbourhood of any star in the
disc of Our Galaxy.
ditto above

If that is the case, what worries me, with dark matter maybe only
in the voids between the stars of the disc or completely outside the disc
how can such an arrangement (which constitutes 90% of all matter
of our galaxy) be used to make our Galaxy more stable.

Nicolaas Vroom
http://users.pandora.be/nicvroom/

Dark matter must influence movement of
objects of a certain size range
(such as Pioneer 10 & 11 size or smaller to dust and gases)
which in turn control galactic dynamics.

Richard

In article , "Nicolaas Vroom"
wrote:

De question remains where is this dark matter within our Galaxy.
It can not be in the neighbourhood of our planets because then it
would influence the orbits of our planets.
The orbits resemble point masses.
It can not be in the neighbourhood of the Sun because then there
would be a different explanation (compared with GR) to explain the
perihelion of Mercury.
If there is no darkmatter in the neighbourhood of our Sun then there
should not be any darkmatter in the neighbourhood of any star in the
disc of Our Galaxy.

Perhaps the solar winds blow it away.

That means you agree that there is no darkmatter in the
neighbourhood of our Sun ?
Nor in the neighbourhood of any star ?

I do not agree on anything. :-)

Is that the meaning of the astronomy community
enlarge ?

It would be better to get hard facts. Experiecne has it that trying to
find the truth by voting is a poor method in science. :-)

Would a dark hole, by observation,
behave any differently?

You mean hole or halo ?
If you mean black hole...

Sorry, a typo: black hole.

... then I do not know the answer
but* I expect that the same is true
i.e. no dark matter "at rest"

If there is no dark matter around the sun and other stars, the question is
why. If it is due to the solar wind, then black holes should probably not
have any such solar wind, as it is due to start fusion processes, and
would behave differently. If one finds a black hole with objects around,
such a thing could be tested.

--
Hans Aberg

In article ,
Richard Saam wrote:

If the density of dark matter
is anywhere close to critical density ~10^-30 g/cc,
its influence on planetary orbits would be negligible

That's right. In fact, the density of dark matter in the neighborhood
of the solar system is considerably larger than the critical density, but
it's still far too small to have a measurable effect on solar system dynamics.
Working out why is a nice exercise.

The orbital speed of objects in our Galaxy is approximately v=200 km/s
over quite a range of orbital radii, including the Sun's orbital radius.
Assuming the Galaxy's mass distribution can be approximated as a spherical
halo, the mass Mwithin a radius R obeys

GM/R^2 = v^2/R,

so M = v^2 R / G.

Since v is roughly constant as a function of R, the mass in a thin
spherical shell is dM = (v^2/G) dR. The volume of the shell is 4 pi R^2 dR,
so the local density is

rho = v^2 / (4 pi G R^2).

At the Sun's orbital radius, this works out to 7 x 10^{-25} g/cm^3.

If you don't assume a spherical halo, then the numbers change somewhat,
but the order of magnitude doesn't.

Suppose you filled the solar system with material at this density.
The amount of stuff within Pluto's orbit would be equal to this density
times the volume of a sphere of radius equal to Pluto's orbit. That works
out to 6 x 10^{17} kg, or less than a trillionth of a solar mass.

-Ted

--
[E-mail me at , as opposed to .]

In article ,
wrote:

If the density of dark matter
is anywhere close to critical density ~10^-30 g/cc,
its influence on planetary orbits would be negligible
......
Suppose you filled the solar system with material at this density.
The amount of stuff within Pluto's orbit would be equal to this density
times the volume of a sphere of radius equal to Pluto's orbit. That works
out to 6 x 10^{17} kg, or less than a trillionth of a solar mass.

So, if I got it right, the large distance between the stars admits the
dark matter to exist at such a low density that it does no affect the
planetary orbits*within the star systems. And would the planetary friction
be equally*negligible at this low density? Can the dark matter within the
solar system be observed somehow?

--
Hans Aberg

wrote:
In article ,
Richard Saam wrote:


If the density of dark matter
is anywhere close to critical density ~10^-30 g/cc,
its influence on planetary orbits would be negligible


That's right. In fact, the density of dark matter in the neighborhood
of the solar system is considerably larger than the critical density, but
it's still far too small to have a measurable effect on solar system dynamics.
Working out why is a nice exercise.

The orbital speed of objects in our Galaxy is approximately v=200 km/s
over quite a range of orbital radii, including the Sun's orbital radius.
Assuming the Galaxy's mass distribution can be approximated as a spherical
halo, the mass Mwithin a radius R obeys

GM/R^2 = v^2/R,

so M = v^2 R / G.

Since v is roughly constant as a function of R, the mass in a thin
spherical shell is dM = (v^2/G) dR. The volume of the shell is 4 pi R^2 dR,
so the local density is

rho = v^2 / (4 pi G R^2).

At the Sun's orbital radius, this works out to 7 x 10^{-25} g/cm^3.

If you don't assume a spherical halo, then the numbers change somewhat,
but the order of magnitude doesn't.

Suppose you filled the solar system with material at this density.
The amount of stuff within Pluto's orbit would be equal to this density
times the volume of a sphere of radius equal to Pluto's orbit. That works
out to 6 x 10^{17} kg, or less than a trillionth of a solar mass.

-Ted


Ted

An interesting calculation.

Here is another for Pioneer Spacecraft deceleration 'a'

a ~ 2*Area*rho*c2 / M
~ 2*(58,965 cm2)*(6.38E-30 g/cm3)*(3E10 cm/sec)^2 /(241,000 g)
~ 2.8E10-9 cm/sec2 for Pioneer spacecraft

This value of 2.8E10-9 cm/sec^2 is based
on the Universe critical density of 6.38E-30 g/cm^3
and is lower than observed 8.74E-8 cm/sec^2
by a factor of 30.

Your average calculated local density of 7 x 10^{-25} g/cm^3
is quite a bit higher than 30 x 6.38E-30 g/cm^3 or 2E-28 g/cm^3
but there still remains a conceptual mechanism
on how dark matter influences solar objects
according to their area/mass
(Pioneer some and planets negligible).
Perhaps the local dark matter density is on the order of
30 x 6.38E-30 g/cm3 or 2E-28 g/cm^3.

Richard