[math-fun] H Baker on gravitation funnyness in galaxies
HB: Some of the evidence for "dark matter" ... We know that there is a supermassive black hole consisting of 4.1-4.5 million solar masses at the center of the Milky Way: https://en.wikipedia.org/wiki/Milky_Way
--supermassive BHs in galaxies are only, like, 0.5% of the galaxy mass, or less. So they don't really matter for this, but they do matter in the sense that they seem to stabilize galaxies, and may even be crucial for that.
Our Sun is roughly in the plane of the Milky Way, and "sees" forces from every bit of mass in the Milky Way. I claim that our Sun "sees" larger-than-expected forces from masses approx 180 degrees around the Milky Way due to *gravitational lensing*.
--this effect should be negligibly small. The optical lensing should be of the same order, and it clearly is negligibly small.
I'd love to know if this gravitational lensing effect is very strong compared with the usual centripetal forces on the Sun. In particular, what % addition speed does this lensing effect add to the speed of the Sun around the center of the Milky Way?
--It'll be a tiny amount. Well below 1%. -- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)
Beware of applying the lensing principle to the static gravitational field. I'm not saying there is lensing, and I'm not saying there's not; just be careful. The basis of this caution is the fact from electromagnetic theory that the electric field of a charge moving at constant velocity is directed towards (or away from) the instantaneous position of the charge. It does not point to where the charge was at an earlier time as if the field propagated at the speed of light. -- Gene From: Warren D Smith <warren.wds@gmail.com> To: math-fun@mailman.xmission.com Sent: Saturday, July 18, 2015 2:26 PM Subject: [math-fun] H Baker on gravitation funnyness in galaxies
HB: Some of the evidence for "dark matter" ... We know that there is a supermassive black hole consisting of 4.1-4.5 million solar masses at the center of the Milky Way: https://en.wikipedia.org/wiki/Milky_Way
--supermassive BHs in galaxies are only, like, 0.5% of the galaxy mass, or less. So they don't really matter for this, but they do matter in the sense that they seem to stabilize galaxies, and may even be crucial for that.
Our Sun is roughly in the plane of the Milky Way, and "sees" forces from every bit of mass in the Milky Way. I claim that our Sun "sees" larger-than-expected forces from masses approx 180 degrees around the Milky Way due to *gravitational lensing*.
--this effect should be negligibly small. The optical lensing should be of the same order, and it clearly is negligibly small.
I'd love to know if this gravitational lensing effect is very strong compared with the usual centripetal forces on the Sun. In particular, what % addition speed does this lensing effect add to the speed of the Sun around the center of the Milky Way?
--It'll be a tiny amount. Well below 1%. -- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)
On 7/18/2015 4:23 PM, Eugene Salamin via math-fun wrote:
Beware of applying the lensing principle to the static gravitational field. I'm not saying there is lensing, and I'm not saying there's not; just be careful. The basis of this caution is the fact from electromagnetic theory that the electric field of a charge moving at constant velocity is directed towards (or away from) the instantaneous position of the charge. It does not point to where the charge was at an earlier time as if the field propagated at the speed of light.
-- Gene
It's the same for GR. If you try to make Newtonian gravity "relativistic" by having the force point toward the retarded position of the source it doesn't work at all. Brent
participants (3)
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Eugene Salamin -
meekerdb -
Warren D Smith