How was Dark Matter calculated?
Jeffrey H
simulated the milky way on a supercomputer and discovered a
need for additional mass ("dark matter")?
I wonder if they used Newtonian gravity or Einsteinian?
Nathan Urban
Newtonian. You can show that Einsteinian corrections are negligible.
[Followups to sci.astro.]
Louis S Pogoda Jr
first found to be "missing" back in the 30's by Dutch astronomer van Oort.
He looked at stars in the solar neighborhood whose motions were known. He
found that, if you assume these nearby stars are part of the Milky Way and
not just "passing through", they were moving too fast to be gravitationally
bound by the visible mass of the galaxy. Based on the velocities of nearby
stars, there must be about three times more mass in the galaxy than is
visible.
Subsequent studies seem to show that the larger the scale at which you
consider things, the more mass that seems to be missing.
Jeffrey H wrote in message <381a6a83...@news.mindspring.com>...
Aubrey
wondering why a large black hole at the center of our galaxy couldn't
explain this excess speed instead of dark matter. Do you know?
Louis S Pogoda Jr wrote in message ...
Mark Folsom
the galaxy isn't consistent with a large central mass. Rather, it appears
that the excess mass is distributed over a large volume.
Mark Folsom
Aubrey <awi...@email.msn.com> wrote in message
news:#KvGdUwI$GA.307@cpmsnbbsa05...
Louis S Pogoda Jr
apparently more gravitational attraction than that due to *visible* (which
more or less means "luminous") matter - more than can be accounted for by
the stars and gas clouds we see.
Notice that for the solar neighborhood, there apparently needs to be three
times more matter than we can see. Last I heard, large black holes at the
center of galaxies, ours included, where in the millions of solar masses.
That's nowhere near the 100 billion stars in the Milky Way, let alone three
times as great.
My original point was that the existence of some sort of dark matter can be,
and was, inferred before the existence of supercomputers. It isn't
necessary to model the galaxy in anything like realistic detail to come to
that conclusion.
Aubrey wrote in message <#KvGdUwI$GA.307@cpmsnbbsa05>...
z@z
Does anyone know what formula for gravity they used when they
simulated the milky way on a supercomputer and discovered a
need for additional mass ("dark matter")?
> Louis S Pogoda Jr replied:
I think you're assuming the problem is harder to see than it is.
Matter was first found to be "missing" back in the 30's by Dutch
astronomer van Oort. He looked at stars in the solar neighborhood
whose motions were known. He found that, if you assume these nearby
stars are part of the Milky Way and not just "passing through", they
were moving too fast to be gravitationally bound by the visible mass
of the galaxy. Based on the velocities of nearby stars, there must
be about three times more mass in the galaxy than is visible.
Subsequent studies seem to show that the larger the scale at which
you consider things, the more mass that seems to be missing.
> > Aubrey wrote:
That's very interesting. Been wondering about that myself. Now
I'm wondering why a large black hole at the center of our galaxy
couldn't explain this excess speed instead of dark matter. Do you
know?
> > > Mark Folsom replied:
I think that the orbital velocity profile, speed versus radius,
of stars in the galaxy isn't consistent with a large central mass.
Rather, it appears that the excess mass is distributed over a
large volume.
Jeffrey H asked:
I wonder if they used Newtonian gravity or Einsteinian?
> Nathan Urban answered:
Newtonian. You can show that Einsteinian corrections are negligible.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
There is a very simple solution to at least a part of this dark-matter
problem: the inersis hypothesis, i.e. the assumption that inertial
motions do not follow straight lines but depend on the motions of
the surrounding objects. The inersis concept can be considered a
quantitative version of Mach's principle, based on 'weighted averages'
of the velocities of the surrounding material objects (particles).
Inersis can also be considered a relational ether which is dragged
by all particles proportional to their mass and inversely proportional
to their distance (i.e. proportional to lost gravitational potential).
According to this concept, the higher velocities of stars in galaxies
are caused by the same effect as Mercury's non-classical perihelion
shift. Whereas the deviations from classical mechanics are still very
small in planetary systems, they become the higher, the larger the
scale at which one considers things.
The inersis concept as first developed in 1987 is descibed in:
http://members.lol.li/twostone/f31.html (in German)
Assume an isolated group of six identical galaxies forming an
equilateral hexagon. Further assume a little satellite galaxy s
whose distance from galaxy 1 is the same as the distance between
two neighbouring galaxies.
5 6
4 . 1 s
3 2
In the short term the shape of the group can remain stable if
the six galaxies orbit at a given velocity V their common center.
If we assume that inersis of s is affected only by these six
galaxies, we get at the current location of s a tangential inersis
velocity of 27% of the rotation speed of the group. This velocity
is added to the velocity which is needed for s to compensate
gravitational attraction of the group. (See reference above).
In http://members.lol.li/twostone/a4.html (also in German) a
quantitatively more accurate version of the explanation of the
perihelion shifts of the planets can be found. Mercury's shift
results primarily from the sun's rotation. The small shift of
Mars however results primarily from Jupiter.
It should be very easy to introduce the inersis concept into
existing simulations of galaxies. I'm sure that much better
agreement with empirical data will be the result. Maybe also
the problem of the spiral forms of galaxies can be solved in a
simpler and more transparent way.
Wolfgang Gottfried G.