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Fraser
2006-Nov-21, 01:55 AM
NASA's most powerful supercomputer has helped researchers simulate the halo of dark matter that surrounds the Milky Way. This dark matter is invisible to our telescopes; however, it does interact with regular matter through its gravity. This new computer simulation shows how the dark matter clumps together into "subhalos" within the larger halo surrounding the Milky Way. This is a bit of a puzzle, since the dark matter doesn't match the clumping of the satellite galaxies that surround us.

Read the full blog entry (http://www.universetoday.com/2006/11/20/dark-matter-halo-around-the-milky-way/)

antoniseb
2006-Nov-21, 01:36 PM
This sub-halo idea is pretty interesting. One thing that concerns me about it is that we are doing a number of Earth-bound experiments looking for dark-matter particles via collisions with very cold matter. The image associated with the story suggests that we can't really count on a uniform density of dark matter in our place in the galaxy. I don't know what the density ratio of clumps to non clumps out here 10 KPc from the center is, but the image makes it look bigger than 10:1. If true, this will make detection even more difficult.

GOURDHEAD
2006-Nov-21, 02:49 PM
This new computer simulation shows how the dark matter clumps together into "subhalos" within the larger halo surrounding the Milky Way. This is a bit of a puzzle, since the dark matter doesn't match the clumping of the satellite galaxies that surround us. My! how the witch doctors have extended their domain. By cleverly replacing chicken bones with supercomputers they may escape falsification for many more days. They didn't seem to state what they quantatively "knew" about dark matter that may have given their simulation a cubic planck length of credibility. If I develop a strong opinion, I'll share it.

John Mendenhall
2006-Nov-21, 03:42 PM
My! how the witch doctors have extended their domain. By cleverly replacing chicken bones with supercomputers they may escape falsification for many more days. They didn't seem to state what they quantatively "knew" about dark matter that may have given their simulation a cubic planck length of credibility. If I develop a strong opinion, I'll share it.

Thank you. I promised the moderator and others some time ago that I would not go berserk about dark matter / dark energy for at least one month, and I'm now up six weeks and counting. As long as you keep up the good work, I can avoid stepping on the toes of the 99% of the astronomical community that are worshiping at the altars of the invisible gods.

JustThisGuy
2006-Nov-21, 04:15 PM
Sometime ago I recall you mentioning of the orbit of our sun around the galaxies center and reading your description of calculations which show an oscillation thru the galactic plane. Do you think that this map would allow more precise calculations and would they significantly alter the predicted path and periodicity of the oscillations?

antoniseb
2006-Nov-21, 04:22 PM
Do you think that this map would allow more precise calculations and would they significantly alter the predicted path and periodicity of the oscillations?

Hi JustThisGuy, welcome to the BAUT forum.

No this map can't help, because it is not a map of our galaxy, it is a map of a simulation of our galaxy.

JustThisGuy
2006-Nov-21, 07:01 PM
Thanks for answering the question. Looking at the drawing, I thought a radial distribution of mass could be calculated. Is the mass ratio for the galaxy's mass to the mass of it's halo of dark matter known?

antoniseb
2006-Nov-21, 08:43 PM
Is the mass ratio for the galaxy's mass to the mass of it's halo of dark matter known?

Yes, and the overall distribution density of the dark matter at each radius is known... though in both cases, it is known within some relatively broad limits.

GOURDHEAD
2006-Nov-22, 02:00 PM
Is "known" the same as "predicted by the simulation"?

antoniseb
2006-Nov-22, 02:47 PM
Is "known" the same as "predicted by the simulation"?
No. There are many measurements that tell us the amount of dark matter at various distances from the center of the galaxy, and likewise the amount of visible matter. Both measurements are somewhat imprecise, but they do provide the order of magnitude.

folkhemmet
2006-Nov-24, 05:23 AM
The article describing this simulation mentioned the missing dwarf galaxy problem, but the scientists involved in the study admitted that there may be reasonable astrophysical explanations for the problem.

"There are other explanations. It may be that most of the subhaloes were sterilised by ultraviolet light from the earliest stars. That heated up intergalactic gas, making it more difficult to capture. And perhaps supernova explosions blasted gas out of many of the nascent dwarf galaxies, ending their brief lives," he said.

Hopefully by 2010 or so GLAST will detect some of the sub-halos predicted by the simulation, as the telescope will be a factor of 10-100 better than its predecessor.

antoniseb
2006-Nov-24, 01:39 PM
Thanks Folkhemmet for the note about the other explanations for the missing dwarfs. BTW, I am also looking forward to GLAST and its successors.