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dark matter hypothesis
aIs it possible that the missing mass, the 'dark matter',
consists of two generations of burned out stars? These would be short lifetimes, hence large masses, according to star formation theory, hence mostly black holes or neutron stars. I don't see that as a problem. What are the counter-arguments? -- Rich [[Mod. note -- Microlensing studies show that at most a small fraction of the dark matter in the Milky Way's halo can be in compact objects of stellar mass. For example, the EROS project https://arxiv.org/abs/astro-ph/0607207 concluded that "machos in the mass range 0.6e-7 M_sun M 15 M_sun are ruled out as the primary occupants of the Milky Way Halo". I don't know offhand what (if any) limits there are for M31 or maybe other galaxies. -- jt]] |
#2
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dark matter hypothesis
In article ,
writes: aIs it possible that the missing mass, the 'dark matter', consists of two generations of burned out stars? No. These would be short lifetimes, hence large masses, according to star formation theory, hence mostly black holes or neutron stars. I don't see that as a problem. What are the counter-arguments? There are several. [[Mod. note -- Microlensing studies show that at most a small fraction of the dark matter in the Milky Way's halo can be in compact objects of stellar mass. For example, the EROS project https://arxiv.org/abs/astro-ph/0607207 concluded that "machos in the mass range 0.6e-7 M_sun M 15 M_sun are ruled out as the primary occupants of the Milky Way Halo". Right. I don't know offhand what (if any) limits there are for M31 or maybe other galaxies. -- jt]] I was co-author on a paper which pointed out that a significant fraction of dark matter can't be on compact objects between us and quasars (i.e. in most of the observable universe), otherwise this would be seen in quasar light curves (which, despite some claims to the contrary, is not the case): http://www.astro.multivax.de:8000/he...sing_qsos.html http://adsabs.harvard.edu/abs/2003A&A...408...17Z [[Mod. note -- URL corrected with author's permission. -- jt]] Also, big-bang nucleosynthesis tells us what fraction of the universe is in baryons; there is no way that stars, being baryonic, could make up a significant fraction of dark matter. |
#4
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dark matter hypothesis
On November 27, Phillip Helbig (undress to reply) wrote:
Is it possible that the missing mass, the 'dark matter', consists of two generations of burned out stars? These would be short lifetimes, hence large masses, according to star formation theory, hence mostly black holes or neutron stars. I don't see that as a problem. What are the counter-arguments? There are several. [[Mod. note -- Microlensing studies show that at most a small fraction of the dark matter in the Milky Way's halo can be in compact objects of stellar mass. For example, the EROS project https://arxiv.org/abs/astro-ph/0607207 concluded that "machos in the mass range 0.6e-7 M_sun M 15 M_sun are ruled out as the primary occupants of the Milky Way Halo". Right. I was co-author on a paper which pointed out that a significant fraction of dark matter can't be on compact objects between us and quasars (i.e. in most of the observable universe), otherwise this would be seen in quasar light curves (which, despite some claims to the contrary, is not the case): http://www.astro.multivax.de:8000/he...sing_qsos.html http://adsabs.harvard.edu/abs/2003A&A...408...17Z I'm unfamiliar with this technique - microlensing refers to the occlusion of distant bright objects, by nearer objects? Thus gravitational lensing effects? I don't understand the primacy of the masses. Wouldn't the statistics depend on the volume of the 'dark' objects? That is, their solid angle arc, how much of the sky they cover? I don't find the reasoning compelling. You looked at quasar variability, and concluded that MACHO doesn't explain it. Isn't it a big leap to say such objects don't exist at all? Also, big-bang nucleosynthesis tells us what fraction of the universe is in baryons; there is no way that stars, being baryonic, could make up a significant fraction of dark matter. Seeing that 80% of the mass of the mass is 'missing', of unknown character, all such origin theories are suspect. -- Rich |
#5
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dark matter hypothesis
In article , jacobnavia
writes: That study assumes a spherical halo around the galaxy. It measures the events when a massive body passes between us and stars in the small and large maghellanic clouds, two satellite galaxies of our own galaxy. IF the halo is spherical THEN the study is right. There is much evidence that galactic halos are spherical. If the halo is NOT spherical but follows the plane of the milky way, i.e. most dead stars are in the galaxy plane and WITHIN the galaxy, that study proves nothing. Note that there are similar studies lucking along the plane of the galaxy towards the bulge. Same result: the bulk of the dark matter cannot be in compact objects of around a solar mass. If we suppose that the galaxy is old, very old, Older than it is normally thought to be? On what grounds? a lot of star corpses should be around within the plane of the galaxy where they spent all their relatively short lives... Star corpses are baryonic, and hence ruled out due to upper limits on the total amount of baryons. To prove/disprove this hypothesis we should look for einstein rings within our own galaxy. One won't see Einstein rings, since a) they are too small and b) occur only when there is (nearly) perfect alignment. Rather, such microlensing surveys look for the brightening then dimming of background objects caused by the gravitational-lensing effect when they pass near the line of sight of a foreground object |
#6
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dark matter hypothesis
In article ,
writes: I'm unfamiliar with this technique - microlensing refers to the occlusion of distant bright objects, by nearer objects? Thus gravitational lensing effects? Yes. Not necessary occlusion, though; it's enough if a background object is near the line of sight to a foreground object. Due to proper motion, the proximity changes with time, and since the amplification depends on the radial distance, one sees a typical brightening then dimming of the background object. [[Mod. note -- To the original poster (and anyone else unfamiliar with the technique): The Wikipedia article https://en.wikipedia.org/wiki/Gravit...l_microlensing is an excellent introduction. -- jt]] I don't understand the primacy of the masses. Wouldn't the statistics depend on the volume of the 'dark' objects? That is, their solid angle arc, how much of the sky they cover? Not so much their own solid angle, but rather the solid angle within which an appreciable gravitational-lensing effect occurs. I don't find the reasoning compelling. You looked at quasar variability, and concluded that MACHO doesn't explain it. Isn't it a big leap to say such objects don't exist at all? The conclusion is not that they don't exist at all, but rather that they cannot explain most of the long-term variability of quasars. This contradicts a claim that most long-term variability of quasars is due to microlensing, which in turn would imply that they make up at least most of the dark matter in the universe. Executive summary: Yes, at first glance long-term quasar variability is compatible with microlensing, if one looks at individual light curves. However, this hypothesis makes predictions about the distribution of amplifications which are in conflict with observations. Also, big-bang nucleosynthesis tells us what fraction of the universe is in baryons; there is no way that stars, being baryonic, could make up a significant fraction of dark matter. Seeing that 80% of the mass of the mass is 'missing', of unknown character, all such origin theories are suspect. Why? If you have a theory which predicts what all the matter in the universe is composed of, let us know. Otherwise, we discover it, component by component. We know more about some components than about others. For example, we know how many baryons there can be at most. This is not enough to explain most of the dark matter, so there must be some other component. What is surprising or suspect about that? If one thinks that dark matter is somehow strange, one assumes, for no good reason, that all components of the mass of the universe must be detectable via our senses, or by astronomical techniques at the stage they were during the second half of the twentieth century. |
#7
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dark matter hypothesis
On 11/27/18 1:03 PM, Phillip Helbig (undress to reply) wrote:
In article , writes: aIs it possible that the missing mass, the 'dark matter', consists of two generations of burned out stars? No. These would be short lifetimes, hence large masses, according to star formation theory, hence mostly black holes or neutron stars. I don't see that as a problem. What are the counter-arguments? There are several. [[Mod. note -- Microlensing studies show that at most a small fraction of the dark matter in the Milky Way's halo can be in compact objects of stellar mass. For example, the EROS project https://arxiv.org/abs/astro-ph/0607207 concluded that "machos in the mass range 0.6e-7 M_sun M 15 M_sun are ruled out as the primary occupants of the Milky Way Halo". Right. I don't know offhand what (if any) limits there are for M31 or maybe other galaxies. -- jt]] I was co-author on a paper which pointed out that a significant fraction of dark matter can't be on compact objects between us and quasars (i.e. in most of the observable universe), otherwise this would be seen in quasar light curves (which, despite some claims to the contrary, is not the case): http://www.astro.multivax.de:8000/he...sing_qsos.html http://adsabs.harvard.edu/abs/2003A&A...408...17Z [[Mod. note -- URL corrected with author's permission. -- jt]] Also, big-bang nucleosynthesis tells us what fraction of the universe is in baryons; there is no way that stars, being baryonic, could make up a significant fraction of dark matter. The Big-bang nucleosynthesis hypothesis does not warrant such an absolute telling baryon fraction statement in terms of on going BBN mechanistic derivation efforts https://arxiv.org/abs/1810.05976v2 RDS |
#8
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dark matter hypothesis
On Wednesday, 28 November 2018 21:49:18 UTC+1, Richard D. Saam wrote:
On 11/27/18 1:03 PM, Phillip Helbig (undress to reply) wrote: Also, big-bang nucleosynthesis tells us what fraction of the universe is in baryons; there is no way that stars, being baryonic, could make up a significant fraction of dark matter. The Big-bang nucleosynthesis hypothesis does not warrant such an absolute telling baryon fraction statement in terms of on going BBN mechanistic derivation efforts https://arxiv.org/abs/1810.05976v2 RDS This interesting (up to date) article mentions the word baryonic, however nothing about darkmatter and baryon fraction. [Moderator's note: Since we have a pretty good idea of the total density, the difference between that and the baryonic density is the dark-matter density, more or less by definition. -P.H.] At the beginning of the article we reed: "Nevertheless, it is physics that needs to be considered in any calculation of BBN." I agree if you want to understand the early evolution of the universe it is physics. At the end we read: "The revised abundances exacerbate the deviation of BBN etc perhaps suggesting a crucial greater need for new physics and/or astrophysical explanations." My interpretation is that the birth of non-baryonic matter is not part BBN and started later. [Moderator's note: We don't know what dark matter is, but as far as I know there is no plausible scenario where it forms after BBN. -P.H.] Secondly any explanation requires a definition what darkmatter (i.e. non-baryonic matter) physical is. [Moderator's note: He whatever is not baryonic. -P.H.] The title of the article https://arxiv.org/abs/astro-ph/0501171 is: "Detection of the Baryon Acoustic Peak in the Large-Scale Correlation Function of SDSS Luminous Red Galaxies" Baryon fraction = Omegab/Omagam is dicussed at page 2. Here we read: "A simple way to understand this is to consider that from an initial point perturbation common to the dark matter and the baryons, the dark matter perturbation grows in place while the baryonic perturbation is carried outward in an expanding spherical wave" IMO this is not simple. [Moderator's note: While the process is relatively simple compared to some other things, what is meant is that this is an easy-to-understand rough sketch, not that the entire process is extremely simple. -P.H.] Nicolaas Vroom |
#9
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dark matter hypothesis
On 11/30/18 4:16 PM, Nicolaas Vroom wrote:
On Wednesday, 28 November 2018 21:49:18 UTC+1, Richard D. Saam wrote: On 11/27/18 1:03 PM, Phillip Helbig (undress to reply) wrote: Also, big-bang nucleosynthesis tells us what fraction of the universe is in baryons; there is no way that stars, being baryonic, could make up a significant fraction of dark matter. The Big-bang nucleosynthesis hypothesis does not warrant such an absolute telling baryon fraction statement in terms of on going BBN mechanistic derivation efforts https://arxiv.org/abs/1810.05976v2 RDS This interesting (up to date) article mentions the word baryonic, however nothing about darkmatter and baryon fraction. [Moderator's note: Since we have a pretty good idea of the total density, the difference between that and the baryonic density is the dark-matter density, more or less by definition. -P.H.] [Moderator's note: Quoted text snipped. -P.H.] Ref 1 https://arxiv.org/abs/1810.05976v2 Ref 2 https://arxiv.org/abs/1811.04932 There was a very vigorous response[2] to [1] defending the current BBN calculation "The detailed and correct computation of big-bang nucleosynthesis (BBN) dates back 51 years to the seminal papers of Wagoner, Fowler and Hoyle" (also referenced in 1) but in their conclusions[2]; "We have not been able to identify the source of the discrepancy with [1]" Apparently it comes down to: How do BBN classical Maxwell-Boltzmann plasma baryon relativistic velocity distributions affect nuclear reaction rates? rds |
#10
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dark matter hypothesis
On 01/12/2018 23:00, Richard D. Saam wrote:
On 11/30/18 4:16 PM, Nicolaas Vroom wrote: On Wednesday, 28 November 2018 21:49:18 UTC+1, Richard D. Saam wrote: On 11/27/18 1:03 PM, Phillip Helbig (undress to reply) wrote: Also, big-bang nucleosynthesis tells us what fraction of the universe is in baryons; there is no way that stars, being baryonic, could make up a significant fraction of dark matter. The Big-bang nucleosynthesis hypothesis does not warrant such an absolute telling baryon fraction statement in terms of on going BBN mechanistic derivation efforts https://arxiv.org/abs/1810.05976v2 RDS This interesting (up to date) article mentions the word baryonic, however nothing about darkmatter and baryon fraction. [Moderator's note: Since we have a pretty good idea of the total density, the difference between that and the baryonic density is the dark-matter density, more or less by definition. -P.H.] [snip] At the risk of opening up a new can of worms what do people think of the new paper from Jamie Farnes at Oxford which seeks to unite dark energy and dark matter as a negative mass fluid filling all of empty space (if I have understood his paper correctly). It seems to work... title: A Unifying Theory of Dark Energy and Dark Matter: Negative Masses and Matter Creation within a Modified =CE=9B CDM Framework https://arxiv.org/abs/1712.07962 Arxiv link but now also in A&A'. It makes some testable predictions. -- Regards, Martin Brown |
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