Dark matter "halo" is a "flattened disk" ?

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phinds
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I apologize for the fact that this information is 2nd hand but a very intelligent and reliable friend tells me that in “Dark Matter and the Dinosaurs” by Lisa Randall she hypothesizes a disk of dark matter, which she calls “Double-Disk Dark Matter (DDDM)” that is superimposed over the center of the Milky Way galaxy, and which oscillates above/below the plane of the galaxy. The hypothesis is that this oscillation, combined with the orbit of our solar system, and the gravitational pull of the dark matter in the disk, pulls comets out of the Orrt Cloud and sends them towards the earth every 33 million years. She thinks this may be what happened 66 million years ago when the Chicxulub event pushed the dinosaurs to extinction. Her claim is that all of the current data makes this a viable hypothesis.

I thought that current observations were fairly solid that the shape of the halo is that of a somewhat flattened beach ball (like if you put your foot on one and pressed down some) but she seems to believe, unless I'm misunderstanding, both that it is far more flattened and that it shifts up and down relative to the galactic plane.

Can anyone comment knowledgeably on this?

Thanks,

Paul

8/6 5:45pm correction: Friend got back to me after I asked him to see if she cited evidence for the oscillation and turns out he had misunderstood. She was just talking about the oscillation of the solar system relative to the galactic plane. Sorry about this confusion.
 
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  • #2
Orodruin
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If I remember correctly, not all of the dark matter is in the disk. The main bulk of DM would still be in a halo. I may be wrong, but that is the impression I got.
 
  • #3
Chronos
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That would be inconsistent with this recent paper; https://arxiv.org/abs/1805.01408, Mass and shape of the Milky Way's dark matter halo with globular clusters from Gaia and Hubble. As noted in the abstract "Our analysis rules out oblate (q<0.8) and strongly prolate halos (q>1.9) with 99\% probability. Our preferred model reproduces well the observed phase-space distribution of globular clusters and has a disc component that closely resembles that of the Galactic thick disc."
 
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phinds
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That would be inconsistent with this recent paper; https://arxiv.org/abs/1805.01408, Mass and shape of the Milky Way's dark matter halo with globular clusters from Gaia and Hubble. As noted in the abstract "Our analysis rules out oblate (q<0.8) and strongly prolate halos (q>1.9) with 99\% probability. Our preferred model reproduces well the observed phase-space distribution of globular clusters and has a disc component that closely resembles that of the Galactic thick disc."
I'm probably misunderstanding what you are saying but it appears to me that the first part disagrees w/ Randall and the last part agrees with her.

And in either case, what about her concept of the DM mass moving up and down relative to the galactic plane?
 
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kimbyd
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I'm probably misunderstanding what you are saying but it appears to me that the first part disagrees w/ Randall and the last part agrees with her.

And in either case, what about her concept of the DM mass moving up and down relative to the galactic plane?
This paper referenced by the above goes into a bit more detail:
https://arxiv.org/abs/1805.01408

The situation they describe is that dark matter tends to fall into concentrations of normal matter, such that there is indeed more dark matter in the galactic disc. It's difficult for me to parse precisely how much, though. I don't know if it would be enough to explain Randall's model.
 
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phinds
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This paper referenced by the above goes into a bit more detail:
https://arxiv.org/abs/1805.01408

The situation they describe is that dark matter tends to fall into concentrations of normal matter, such that there is indeed more dark matter in the galactic disc. It's difficult for me to parse precisely how much, though. I don't know if it would be enough to explain Randall's model.
OK. Thanks.
 
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I'm curious, phinds. Are you wondering if recent discoveries by Fermi All Sky imaging revealing Xray and Gamma Ray bubbles apparently caused by near relativistic electrons whose source is unknown bears on this, favoring one over the other?
 
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phinds
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I'm curious, phinds. Are you wondering if recent discoveries by Fermi All Sky imaging revealing Xray and Gamma Ray bubbles apparently caused by near relativistic electrons whose source is unknown bears on this, favoring one over the other?
I know nothing of what you speak. I'm just trying to get a read on the reasonableness of Lisa Randall's hypothesis, particularly the part that no one has addressed yet which is that the dark matter halo oscillates up/down relative to the galactic disk.That doesn't seem reasonable to me but I recognize that she knows way more physics than I ever will.
 
  • #9
PeterDonis
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in “Dark Matter and the Dinosaurs” by Lisa Randall she hypothesizes
I'm just trying to get a read on the reasonableness of Lisa Randall's hypothesis
Since this is a pop science book, the first question would be whether Randall, or anyone else, has made this proposal in peer-reviewed literature. If not, then as far as PF is concerned, the answer to your question is "no". Scientists often try to get away with proposing things in pop science books that they wouldn't dare propose in a peer-reviewed paper.
 
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  • #10
phinds
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Since this is a pop science book, the first question would be whether Randall, or anyone else, has made this proposal in peer-reviewed literature. If not, then as far as PF is concerned, the answer to your question is "no". Scientists often try to get away with proposing things in pop science books that they wouldn't dare propose in a peer-reviewed paper.
Well, here's what I've found so far. Seems very speculative but not outrageously so.

Dark Matter as a Trigger for Periodic Comet Impacts (2014)
https://arxiv.org/abs/1403.0576
In the abstract, there is no mention of the halo oscillation but in a citation on the Harvard University Physics department web page (https://www.physics.harvard.edu/node/283) there IS mention of the oscillaiton.


Other Dark Matter articles she has co-authored:

Point Sources from Dissipative Dark Matter (2017)
https://arxiv.org/abs/1706.04195

Make Dark Matter Charged Again (2017)
https://arxiv.org/abs/1610.04611

and there are others:
http://inspirehep.net/search?p=ea+Randall,+Lisa
 
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  • #11
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I know nothing of what you speak. I'm just trying to get a read on the reasonableness of Lisa Randall's hypothesis, particularly the part that no one has addressed yet which is that the dark matter halo oscillates up/down relative to the galactic disk.That doesn't seem reasonable to me but I recognize that she knows way more physics than I ever will.
Well it was a long shot since so little is known about Dark Matter interactions (especially by me) but I wondered if the new refinement techniques being applied to the Fermi Telescope's All Sky map revealing deep level views of structures previously unseen or even unimagined are already having an impact on dark matter behaviour modeling as I am assuming they will lead to at some point.

You can view this recent study here https://svs.gsfc.nasa.gov/10688
 
  • #12
phinds
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Well it was a long shot since so little is known about Dark Matter interactions (especially by me) but I wondered if the new refinement techniques being applied to the Fermi Telescope's All Sky map revealing deep level views of structures previously unseen or even unimagined are already having an impact on dark matter behaviour modeling as I am assuming they will lead to at some point.
Randall's hypothesis is at least 4 years old so really recent discoveries are clearly not the reason.
 
  • #13
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Hello again phinds.
You have my apology for being at all obtuse but it was only yesterday from digging a bit deeper into the Fermi project that I got confirmation they expect to get data directly pertaining to dark matter. When I posed the first question it had just seemed to me it might and I didn't want to assume without direct confirmation so I was a little tentative.

I wasn't wondering if you thought Randall's hypothesis was based on recent Fermi data. I was wondering if Fermi favored one or the other or added any insight to either, both or generally. I suppose it still might, probably is likely, but it looks like that's coming "down the road" since their recent work is on the software side and is apparently retroactive in that it can be applied to earlier records so they have years of data to play with. They are on Pass 8 now and there's no reason to assume there won't be further refinement as well.

Anyway thank you for your consideration.
 
  • #14
phinds
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I wasn't wondering if you thought Randall's hypothesis was based on recent Fermi data. I was wondering if Fermi favored one or the other or added any insight to either, both or generally.
Good point and I'll be she's keeping up w/ their data to see if it pans out for her. I don't get any sense that she is rabidly doctrinaire about her opinion and if evidence to the contrary turns up she'll revise, or even reject, her current hypothesis.
 
  • #15
phinds
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8/6 5:45pm correction to the OP: Friend got back to me after I asked him to see if she cited evidence for the oscillation and turns out he had misunderstood. She was just talking about the oscillation of the solar system relative to the galactic plane. Sorry about this confusion.

This is a good example of why PF requires direct quotes, not 3rd hand accounts.
 
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