4 ms·

Could the other branches be our dark matter?

jfengel 4y ago
No. They don't behave at all like dark matter. Among other things, there's no reason for them to be distributed in a halo, nor for some galaxies to lack them.
- plutonorm 4y ago
  Broad statements, do you have the time to elaborate?
  - simonh 4y ago
    Dark matter affects some galaxies, but the rotation of others is completely explained by the observable matter. Why would one galaxy be influenced by its many worlds twins, but not another?
    - jameshart 4y ago
      Sci-fi plot concept answer: because one galaxy is populated by sentient life, and the other isn’t.
      - tremon 4y ago
        Quarantine by Greg Egan explores this concept (the many-worlds theory, without the dark matter).
    - plutonorm 4y ago
      Well because that galaxy in that position might be a low probability event - not many universes have that galaxy at that position. So therefore that galaxy appears to have less dark matter.
  - gus_massa 4y ago
    The Milky Way and other similar galaxies look like spiral drawn in a thick 2D disk. The dark matter halo looks like an invisible 3D ball around the thick 2D disk. Something like https://www.google.com/search?q=dark+matter+halo&tbm=isch https://www.google.com/search?q=dark+matter+halo&tbm=isch
    - tremon 4y ago
      I thought that the main mechanism that produces the 2D disk of matter in galaxies was gravity, and that dark matter is equally affected by gravity as normal matter? What is the prevailing theory as to why dark matter accretion around galaxies is different from normal matter? (edit: to answer my own question, the rabbit hole starts here: https://physics.stackexchange.com/questions/485214/ https://physics.stackexchange.com/questions/485214/ -- basically, accretion happens because light matter can radiate and shed its (kinetic) energy that way. Dark matter does not radiate so it remains in a higher-energy state)
- phkahler 4y ago
  There's no reason for any dark matter to be distributed in a halo. Maybe it makes some math work better for the observations but nobody offers a dynamical explanation of how it would come to be a halo.
  - raattgift 4y ago
    > There's no reason for any dark matter to be distributed in a halo. This was one of the more eye-catching statements in this thread. To be blunt, you're wrong. A straightforward and almost inevitable dynamical explanation has been available (and explored in ever greater detail) since at least the mid-1990s, driven in part by the Saskatoon experiment and subsequently supported by BOOMERanG's observation of the first acoustic peak, and many others lines of evidence since then (see [1] for a less-heavy explanation than what follows). You may wish to check this chapter from a forthcoming graduate-level textbook in galactic dynamics from well-known galactic astrophysicist Jo Bovy <http://astro.utoronto.ca/~bovy/ http://astro.utoronto.ca/~bovy/>, which you can read for free at his site: <https://galaxiesbook.org/chapters/IV-01.-Formation-DM-Halos.html https://galaxiesbook.org/chapters/IV-01.-Formation-DM-Halos....>. There are of course other already-completed textbooks. For example, one can find an excellent pedagogic (if advanced) treatment of primordial Gaussian Random Fields[2] as applied to halo formation in chapter 7 of Mo, van den Bosch & White (2010) <https://www.cambridge.org/core/books/abs/galaxy-formation-and-evolution/formation-and-structure-of-dark-matter-halos/36C7784367F6CC9B5C072F9950B841A6 https://www.cambridge.org/core/books/abs/galaxy-formation-an...> (you can find the chapter on scy hob via its DOI if you don't have institutional or otherwise affordable access). - -- [1] https://lweb.cfa.harvard.edu/~deisenst/acousticpeak/acoustic_physics.html https://lweb.cfa.harvard.edu/~deisenst/acousticpeak/acoustic... from <https://astronomy.fas.harvard.edu/people/daniel-eisenstein https://astronomy.fas.harvard.edu/people/daniel-eisenstein> [2] If you're more visually inclined and can't find the illustrated version of Mo et al., see the diagrams on p.3-5 of this slide deck on GRFs <https://www.astro.rug.nl/~weygaert/tim1publication/lss2016/lss2016.gaussian_fields.handout2.pdf https://www.astro.rug.nl/~weygaert/tim1publication/lss2016/l...> from Rien van de Weijgaert of the Kapteyn Institute at the University of Groningen.

No. They don't behave at all like dark matter. Among other things, there's no reason for them to be distributed in a halo, nor for some galaxies to lack them.

plutonorm 4y ago
Broad statements, do you have the time to elaborate?
- simonh 4y ago
  Dark matter affects some galaxies, but the rotation of others is completely explained by the observable matter. Why would one galaxy be influenced by its many worlds twins, but not another?
  - jameshart 4y ago
    Sci-fi plot concept answer: because one galaxy is populated by sentient life, and the other isn’t.
    - tremon 4y ago
      Quarantine by Greg Egan explores this concept (the many-worlds theory, without the dark matter).
  - plutonorm 4y ago
    Well because that galaxy in that position might be a low probability event - not many universes have that galaxy at that position. So therefore that galaxy appears to have less dark matter.
- gus_massa 4y ago
  The Milky Way and other similar galaxies look like spiral drawn in a thick 2D disk. The dark matter halo looks like an invisible 3D ball around the thick 2D disk. Something like https://www.google.com/search?q=dark+matter+halo&tbm=isch https://www.google.com/search?q=dark+matter+halo&tbm=isch
  - tremon 4y ago
    I thought that the main mechanism that produces the 2D disk of matter in galaxies was gravity, and that dark matter is equally affected by gravity as normal matter? What is the prevailing theory as to why dark matter accretion around galaxies is different from normal matter? (edit: to answer my own question, the rabbit hole starts here: https://physics.stackexchange.com/questions/485214/ https://physics.stackexchange.com/questions/485214/ -- basically, accretion happens because light matter can radiate and shed its (kinetic) energy that way. Dark matter does not radiate so it remains in a higher-energy state)
phkahler 4y ago
There's no reason for any dark matter to be distributed in a halo. Maybe it makes some math work better for the observations but nobody offers a dynamical explanation of how it would come to be a halo.
- raattgift 4y ago
  > There's no reason for any dark matter to be distributed in a halo. This was one of the more eye-catching statements in this thread. To be blunt, you're wrong. A straightforward and almost inevitable dynamical explanation has been available (and explored in ever greater detail) since at least the mid-1990s, driven in part by the Saskatoon experiment and subsequently supported by BOOMERanG's observation of the first acoustic peak, and many others lines of evidence since then (see [1] for a less-heavy explanation than what follows). You may wish to check this chapter from a forthcoming graduate-level textbook in galactic dynamics from well-known galactic astrophysicist Jo Bovy <http://astro.utoronto.ca/~bovy/ http://astro.utoronto.ca/~bovy/>, which you can read for free at his site: <https://galaxiesbook.org/chapters/IV-01.-Formation-DM-Halos.html https://galaxiesbook.org/chapters/IV-01.-Formation-DM-Halos....>. There are of course other already-completed textbooks. For example, one can find an excellent pedagogic (if advanced) treatment of primordial Gaussian Random Fields[2] as applied to halo formation in chapter 7 of Mo, van den Bosch & White (2010) <https://www.cambridge.org/core/books/abs/galaxy-formation-and-evolution/formation-and-structure-of-dark-matter-halos/36C7784367F6CC9B5C072F9950B841A6 https://www.cambridge.org/core/books/abs/galaxy-formation-an...> (you can find the chapter on scy hob via its DOI if you don't have institutional or otherwise affordable access). - -- [1] https://lweb.cfa.harvard.edu/~deisenst/acousticpeak/acoustic_physics.html https://lweb.cfa.harvard.edu/~deisenst/acousticpeak/acoustic... from <https://astronomy.fas.harvard.edu/people/daniel-eisenstein https://astronomy.fas.harvard.edu/people/daniel-eisenstein> [2] If you're more visually inclined and can't find the illustrated version of Mo et al., see the diagrams on p.3-5 of this slide deck on GRFs <https://www.astro.rug.nl/~weygaert/tim1publication/lss2016/lss2016.gaussian_fields.handout2.pdf https://www.astro.rug.nl/~weygaert/tim1publication/lss2016/l...> from Rien van de Weijgaert of the Kapteyn Institute at the University of Groningen.