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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 |
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Hubble makes 3D dark matter map
"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/ |
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Hubble makes 3D dark matter map
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 |
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Hubble makes 3D dark matter map
"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/ |
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Hubble makes 3D dark matter map
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 |
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Hubble makes 3D dark matter map
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 |
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Hubble makes 3D dark matter map
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 .] |
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Hubble makes 3D dark matter map
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Hubble makes 3D dark matter map
In article ,
Hans Aberg wrote: 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. Yes, that's right. And would the planetary friction be equally*negligible at this low density? Yes. Even assuming that the dark matter were made of strongly-interacting particles that bounced off the planets' surfaces whenever they hit them, I think that the time scale for a drag force to change the planets' orbits significantly is much longer than the age of the solar system. I just did that calculation pretty quickly and roughly, so I could have messed it up. If anyone thinks I have, let me know. But if the dark matter were composed of particles that interacted relatively easily with ordinary matter, we'd have detected them by now, by noticing scattering events with particles in the atmosphere or something. That's one of the reasons that the leading hypothesis these days is that the dark matter consists of weakly interacting particles. Such particles would pass right through solid matter most of the time with only a low probability of interacting. In that case, any friction-like force due to planets passing through these clouds of dark matter would be even smaller. Can the dark matter within the solar system be observed somehow? We certainly hope so, but it hasn't been done yet. There are several experiments underway to search for dark matter particles passing through our neighborhood. They're similar in concept to experiments to detect solar neutrinos: they involve looking for the effects of particles bouncing off of atoms in detectors in deep underground labs. There was one controversial claim of a detection a few years ago, but it's generally believed that there was something wrong with that experiment. -Ted -- [E-mail me at , as opposed to .] |
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Hubble makes 3D dark matter map
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