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Dark matter and black holes
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20 years 9 months ago #8681
by tvanflandern
Reply from Tom Van Flandern was created by tvanflandern
<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Rudolf</i>
<br />What does Tom think of these findings?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">A matter-antimatter "fountain" operating toward the Galactic center has been known for a generation. Attempts to interpret this in terms of "dark matter" are necessarily weak because no one knows what properties dark matter has, including existence. -|Tom|-
<br />What does Tom think of these findings?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">A matter-antimatter "fountain" operating toward the Galactic center has been known for a generation. Attempts to interpret this in terms of "dark matter" are necessarily weak because no one knows what properties dark matter has, including existence. -|Tom|-
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20 years 9 months ago #4128
by Rudolf
Replied by Rudolf on topic Reply from Rudolf Henning
Are there any other indications that 'stuff' like dark matter can exist (outside the galaxy rotation problem)?
Obviously there could be a lot of plain dark normal matter that is not visible as well.
Obviously there could be a lot of plain dark normal matter that is not visible as well.
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20 years 9 months ago #8731
by tvanflandern
Replied by tvanflandern on topic Reply from Tom Van Flandern
<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Rudolf</i>
<br />Are there any other indications that 'stuff' like dark matter can exist (outside the galaxy rotation problem)? Obviously there could be a lot of plain dark normal matter that is not visible as well.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Even before the rotation problem was known, we had problems accounting for all the mass needed to bind galaxy clusters together. The same for superclusters. The larger the scale, the greater the discrepancy between seen and unseen matter (assuming the Newtonian law is still in effect).
Normally, to hide matter, it needs to be as clumped and compact as possible. However, if the mass is big enough to make stars, then thermonuclear fusion creates radiation that makes the mass visible. But if the mass is broken into tiny bits such as gas and dust, that is easily seen as absorption lines in all light passing through it.
So theory has focused on the two mass zones where detection would be hardest: MACHOs and WIMPs. MACHOs (Massive Compact Halo Objects) are planet-sized objects that would be hard to see directly. They have been searched for by looking for gravitational lens effects in the Large and Small Magellanic Clouds. Such objects between here and there would be detected by lensing stars in the two satellite galaxies. But there were not enough of them by far to explain the missing dark matter. WIMPs are Weakly Interacting Massive Particles -- presumably some as-yet-undiscovered quantum particle with mass and enough abundance to make a difference. Again, searches have been mostly fruitless, or at least insufficient to convince astronomers that the dark matter problem is nearing a solution.
The most succssful hypothesis so far is MOND or Modified Newtonian Dynamics, which hypothesizes a minimum acceleration -- a deviation from the Newtonian law of gravity. That explains dynamics without dark matter. It has been robust in its ability to explain phenomena, even ones not known when the hypothesis was formulated. But it has not gained much acceptance because (1) it would undermine the Big Bang; and (2) it is ad hoc, lacking a good physical justification.
MM offers an alternate interpretation and physical justification for a MOND-like mechanism. However, as MM has been further developed lately, it has become increasingly apparent that elysium plays a greater role in galaxy dynamics than I have heretofore appreciated. When I have time, I plan a complete rethink of large scale forces from first principles. -|Tom|-
<br />Are there any other indications that 'stuff' like dark matter can exist (outside the galaxy rotation problem)? Obviously there could be a lot of plain dark normal matter that is not visible as well.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Even before the rotation problem was known, we had problems accounting for all the mass needed to bind galaxy clusters together. The same for superclusters. The larger the scale, the greater the discrepancy between seen and unseen matter (assuming the Newtonian law is still in effect).
Normally, to hide matter, it needs to be as clumped and compact as possible. However, if the mass is big enough to make stars, then thermonuclear fusion creates radiation that makes the mass visible. But if the mass is broken into tiny bits such as gas and dust, that is easily seen as absorption lines in all light passing through it.
So theory has focused on the two mass zones where detection would be hardest: MACHOs and WIMPs. MACHOs (Massive Compact Halo Objects) are planet-sized objects that would be hard to see directly. They have been searched for by looking for gravitational lens effects in the Large and Small Magellanic Clouds. Such objects between here and there would be detected by lensing stars in the two satellite galaxies. But there were not enough of them by far to explain the missing dark matter. WIMPs are Weakly Interacting Massive Particles -- presumably some as-yet-undiscovered quantum particle with mass and enough abundance to make a difference. Again, searches have been mostly fruitless, or at least insufficient to convince astronomers that the dark matter problem is nearing a solution.
The most succssful hypothesis so far is MOND or Modified Newtonian Dynamics, which hypothesizes a minimum acceleration -- a deviation from the Newtonian law of gravity. That explains dynamics without dark matter. It has been robust in its ability to explain phenomena, even ones not known when the hypothesis was formulated. But it has not gained much acceptance because (1) it would undermine the Big Bang; and (2) it is ad hoc, lacking a good physical justification.
MM offers an alternate interpretation and physical justification for a MOND-like mechanism. However, as MM has been further developed lately, it has become increasingly apparent that elysium plays a greater role in galaxy dynamics than I have heretofore appreciated. When I have time, I plan a complete rethink of large scale forces from first principles. -|Tom|-
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20 years 9 months ago #4129
by Jeremy
Replied by Jeremy on topic Reply from
Tom, I was wondering, I know that the galactic rotation curves are correlated with the luminosity of the galaxy. I believe it is the inner bend of the curve that becomes sharper as luminosity increases? Is there any correlation with the shape of the galaxy i.e. do spheroidal shaped galaxies have a more newtonian curve than a flat spiral galaxy?
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20 years 9 months ago #8682
by tvanflandern
Replied by tvanflandern on topic Reply from Tom Van Flandern
<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Jeremy</i>
<br />Is there any correlation with the shape of the galaxy i.e. do spheroidal shaped galaxies have a more newtonian curve than a flat spiral galaxy?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Milgrom recently showed that dwarf spheroidal galaxies also obey the MOND acceleration limit. However, an even newer study of a few elliptical galaxies suggested that these may have little or no "dark matter", meaning that the rotation curves do not bend over and flatten out so sharply.
This is one reason why I think that elysium plays a greater role than I have heretofore appreciated in galaxy dynamics. -|Tom|-
<br />Is there any correlation with the shape of the galaxy i.e. do spheroidal shaped galaxies have a more newtonian curve than a flat spiral galaxy?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Milgrom recently showed that dwarf spheroidal galaxies also obey the MOND acceleration limit. However, an even newer study of a few elliptical galaxies suggested that these may have little or no "dark matter", meaning that the rotation curves do not bend over and flatten out so sharply.
This is one reason why I think that elysium plays a greater role than I have heretofore appreciated in galaxy dynamics. -|Tom|-
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20 years 9 months ago #8684
by Jim
Replied by Jim on topic Reply from
One of the big problems in ever understanding the dymamics of structure in gravity fields is the misplaced gravity center that is common to all the ideas about spheres and disks. There is no center of gravity even though it is very accurate to assume this is a fact when we are outside. When we are inside the mass is all around and so is the gravity so you cannot assume the Center of Gravity is located at any point as, say, the Center of Mass.
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