Wikipedia:Reference desk/Archives/Science/2023 September 18

= September 18 =

Dark matter attraction and Galaxy size
Let us consider 2 spheres (or disk as for Galaxy) made up of the same large number of n mass elements, therefore of the same overall mass, but of radius r and 2r, a little on the principle of galaxies in space. What is the difference in the forces of gravity applied to an object located at r/2 for the 2 spheres? I suppose that on the same principle as for galaxies and dark matter, the centripetal attraction for such an object is greater for the small sphere. Malypaet (talk) 08:58, 18 September 2023 (UTC)
 * If the mass is spherically symmetric, then the attraction is due to the sphere inside the radius. So what happens will depend on the mass distribution, but likely the smaller galaxy will have higher gravity at a fixed distance. In general relativity you will also have to consider gravitoelectromagnetism which will be much greater for the compact arrangement of spinning mass. Doesn't matter if matter is dark, dim or bright. Graeme Bartlett (talk) 09:57, 18 September 2023 (UTC)
 * See shell theorem. Modocc (talk) 02:42, 20 September 2023 (UTC)

"Normal" basic compounds and extreme of proton affinity
1* What is the most basic chemical compound whose molecules or ionic-molecules are overall e-neutral known? (So obviously this criteria excludes the elusive anionic species such as diethynylbenzene(2-) isomers and lithium monoxide(-)) "Known" means that the candidate chemical species must have been synthesized and detected by some means. I gave a special attention to this problem since these basic chemical species would be reasonably isolated as "normal" substances on certain inert surfaces, not just only exist as diluted gas. 2* What is the most basic inorganic/organic compound whose molecules or ionic-molecules are overall e-neutral known? (If the chemical compound in the first question turns out to be inorganic, then the second question should only be answered for the "organic" part, and vice versa). 3* Can there any inert organic solvent be used to dissolve these compounds (as in the case of liquid alkane solution of organolithium compounds)? 4* What are the values of proton affinity of these superbases, in the case they have been measured (in gas phase, of course)? A reply with a good, reliable and readable source for the mentioned compounds is appreciated. I have searched for the answers in various sites on Internet for this problem, but all cases end up with either the articles about Diethynylbenzene(2-) isomers, or the articles about unrelated aspects of more common superbase compounds */\*. 2402:800:63BC:DB8D:B5B5:F01A:57AA:1D66 (talk) 13:26, 18 September 2023 (UTC)


 * I'm sure you will have read the article superbase. A recent paper that it quotes is 10.1021/acs.jpca.2c00521 which is in a reputable journal. That article mentions some neutral superbases and comments that a reliable solvent is HMPA. Mike Turnbull (talk) 13:56, 18 September 2023 (UTC)