4 ms·

Let me preface this by saying that I am by NO means an expert in any of this. My thought process was simply along the lines of: 1) If MOND is true, it should

Let me preface this by saying that I am by NO means an expert in any of this. My thought process was simply along the lines of: 1) If MOND is true, it should be evident in the rotational structure of every galaxy observed. 2) Here is a galaxy that doesn't (at first glance, at least -- I need to read the paper you pointed out) show such rotational structure. 3) Hence, this is an "outlier" observation in the panoply of the MOND vs dark matter debate -- one in which MOND seems unsupportable. Nothing deeper than that, and again this is ABSOLUTELY NOT my field!

fghorow 5y ago
FWIW, NGC-1052-DF2 has it's own Wikipedia page, that discusses (and more importantly cites some literature about) the relation between it and MOND. https://en.wikipedia.org/wiki/NGC_1052-DF2 https://en.wikipedia.org/wiki/NGC_1052-DF2
dnautics 5y ago
I think one should run simulations of MOND first; MOND does not directly make a statement about rotational structures; it makes a statement about the gravity law. This galaxy clearly has unique structural considerations that could yield results that you don't expect from a trivial glance at higher order factors. Edit, after digging: someone has, apparently. https://www.researchgate.net/publication/336982682_A_new_formulation_of_the_external_field_effect_in_MOND_and_numerical_simulations_of_ultra-diffuse_dwarf_galaxies_-_application_to_NGC_1052-DF2_and_NGC_1052-DF4 https://www.researchgate.net/publication/336982682_A_new_for... I can't speak to whether or not the paper is any good, but my quick understanding is that: the galaxy is consistent with MOND if the distance to the galaxy has been misestimated; at least one published estimate (that disagrees with most estimations) of how far it is to 1052 falls inside the range where it's explainable by mond. My (limited; I last took astro a very long time ago) understanding is that how we measure distances to foreign galaxies (slam-dunk methods like cepheids don't work if there are no cepheids) could be very sketchy for galaxies of different structures. Here is part of the ongoing debate about distance. Linked is a paper from the perspective that would disfavor MOND (the Trujillo estimate is what needs to be true for 1052 to be consistent with MOND according to the first paper): https://www.pietervandokkum.com/ngc1052-df2 https://www.pietervandokkum.com/ngc1052-df2
- stan_rogers 5y ago
  MOND has very little to say about gravity. It claims that f=ma breaks down at sufficiently low values. That, in turn, implies that the rules should still be consistent with these modifications, and that galaxies with apparently different proportions of dark matter (as it's understood) shouldn't exist - all galaxies with similar visible sizes and structures should be essentially identical in gravitational behaviour, and that simply hasn't been demonstrated to be the case.
  - dnautics 5y ago
    > with similar visible sizes and structures This galaxy is very much not in the normal range of "sizes and structures", and is highly dissimilar to almost all other galaxies observed. the stuff about changing F=ma vs changing Fg is kind of pedantic and immaterial to the topic of simulation, given that the accleration due to gravity is the only thing that is being simulated.
  - dogma1138 5y ago
    I’ve linked above to a paper that attempts to establish what to rotational speed of the clusters should be based on MOND and it’s close enough to the observations that in isolation it still the case that the galaxy either has 1/400th of the dark matter density a normal galaxy would have vs we don’t need dark matter due to MOND.

fghorow 5y ago

FWIW, NGC-1052-DF2 has it's own Wikipedia page, that discusses (and more importantly cites some literature about) the relation between it and MOND. https://en.wikipedia.org/wiki/NGC_1052-DF2 https://en.wikipedia.org/wiki/NGC_1052-DF2

dnautics 5y ago

I think one should run simulations of MOND first; MOND does not directly make a statement about rotational structures; it makes a statement about the gravity law. This galaxy clearly has unique structural considerations that could yield results that you don't expect from a trivial glance at higher order factors. Edit, after digging: someone has, apparently. https://www.researchgate.net/publication/336982682_A_new_formulation_of_the_external_field_effect_in_MOND_and_numerical_simulations_of_ultra-diffuse_dwarf_galaxies_-_application_to_NGC_1052-DF2_and_NGC_1052-DF4 https://www.researchgate.net/publication/336982682_A_new_for... I can't speak to whether or not the paper is any good, but my quick understanding is that: the galaxy is consistent with MOND if the distance to the galaxy has been misestimated; at least one published estimate (that disagrees with most estimations) of how far it is to 1052 falls inside the range where it's explainable by mond. My (limited; I last took astro a very long time ago) understanding is that how we measure distances to foreign galaxies (slam-dunk methods like cepheids don't work if there are no cepheids) could be very sketchy for galaxies of different structures. Here is part of the ongoing debate about distance. Linked is a paper from the perspective that would disfavor MOND (the Trujillo estimate is what needs to be true for 1052 to be consistent with MOND according to the first paper): https://www.pietervandokkum.com/ngc1052-df2 https://www.pietervandokkum.com/ngc1052-df2

stan_rogers 5y ago
MOND has very little to say about gravity. It claims that f=ma breaks down at sufficiently low values. That, in turn, implies that the rules should still be consistent with these modifications, and that galaxies with apparently different proportions of dark matter (as it's understood) shouldn't exist - all galaxies with similar visible sizes and structures should be essentially identical in gravitational behaviour, and that simply hasn't been demonstrated to be the case.
- dnautics 5y ago
  > with similar visible sizes and structures This galaxy is very much not in the normal range of "sizes and structures", and is highly dissimilar to almost all other galaxies observed. the stuff about changing F=ma vs changing Fg is kind of pedantic and immaterial to the topic of simulation, given that the accleration due to gravity is the only thing that is being simulated.
- dogma1138 5y ago
  I’ve linked above to a paper that attempts to establish what to rotational speed of the clusters should be based on MOND and it’s close enough to the observations that in isolation it still the case that the galaxy either has 1/400th of the dark matter density a normal galaxy would have vs we don’t need dark matter due to MOND.