Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: George Voulgaris on 18/05/2010 09:30:02

Title: Do we see the effects of dark matter on a local scale?
Post by: George Voulgaris on 18/05/2010 09:30:02

George Voulgaris  asked the Naked Scientists:
   
Hello,

Enjoying the podcast (http://www.thenakedscientists.com/HTML/podcasts/) and thanks for taking the question, which relates to dark matter.

I understand that the effects of dark matter can be observed in the rotational speeds of galaxies and the orbital velocities of galaxies in clusters, but are there any measurable effects of dark matter at the scale of the solar system such as planetary orbits? Also is it possible for Dark matter to clump together under the effects of gravity?

Thanks again for taking the question.

Regards,

George Voulgaris
Melbourne, Australia.

What do you think?

Title: Do we see the effects of dark matter on a local scale?
Post by: graham.d on 18/05/2010 10:43:06

Dark matter is very hard to detect locally because its effect on ordinary matter, as far as we know, is minimal and just gravitational (and possibly also weak forces). There are researchers looking for neutrino production (in deep mines for example) due to Dark Matter interactions but this is very difficult because the rate is very low.

DM is thought to be distributed more spherically and not as part of the galactic disc, so although there is a large amount of matter its density will be quite low. It would affect planetary orbits but not on a scale we could detect at the present time.

It is also thought that DM will be clumped at the galactic centre. Unfortunately so much is speculation because the nature of the substance is unknown.

Title: Do we see the effects of dark matter on a local scale?
Post by: sithcdw on 19/05/2010 04:45:10

since the DM is classified as matter, then yes, it is possible for it to "clump" together through gravity. In fact i recently watched a tv program on the science channel about dark matter and galaxies. it was theorized that there should be these "clumps" in the universe. and since this dark matter isnt vissible, it should be able to be detected by light diffraction. the light should bend around these "invisible" clumps. and according to the program, this has been observed...
unfortunately i do not remember the name...sorry

Title: Do we see the effects of dark matter on a local scale?
Post by: imatfaal on 19/05/2010 11:51:37

A great use of the distortion of gravitational lensing to investigate dark matter is described here
http://www.spacetelescope.org/news/heic0818/
http://arxiv.org/pdf/0806.2320

In summary and very simplifed hubble spots the cold dark matter through the lensing effect on distant objects and the chandra space telescope spots the non-dark matter which glows in xrays.  the pictures are of a pair of colliding galaxies; the particles of ordinary matter have crashed into each other and are clumped in the middle, whereas the dark matter has passed straight through and out the other side (ie it has not interacted with the opposing real or dark matter except through gravity).