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Randy
SFN Regular
USA
1990 Posts |
 Posted - 04/25/2012 : 18:49:07
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"Vast Structure of Satellite Galaxies & Star Clusters Discovered Surrounding Milky Way --Nixes Existence of Dark Matter in Universe
Astronomers from the University of Bonn in Germany have discovered a vast structure of satellite galaxies and clusters of stars surrounding our Galaxy, stretching out across a million light years. The work challenges the existence of dark matter, part of the standard model for the evolution of the universe."
read on at the Daily Galaxy.
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"We are all connected; to each other biologically, to the earth chemically, to the rest of the universe atomically."
"So you're made of detritus [from exploded stars]. Get over it. Or better yet, celebrate it. After all, what nobler thought can one cherish than that the universe lives within us all?"
-Neil DeGrasse Tyson |
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HalfMooner
Dingaling
Philippines
15831 Posts |
Posted - 04/25/2012 : 19:32:40 [Permalink]
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Originally posted by Randy
"Vast Structure of Satellite Galaxies & Star Clusters Discovered Surrounding Milky Way --Nixes Existence of Dark Matter in Universe
Astronomers from the University of Bonn in Germany have discovered a vast structure of satellite galaxies and clusters of stars surrounding our Galaxy, stretching out across a million light years. The work challenges the existence of dark matter, part of the standard model for the evolution of the universe."
read on at the Daily Galaxy.
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If so, that fits nicely with the discovery of NO dark matter near the solar system. It's starting to look to me as though dark matter, as some kind of exotic stuff, may not exist at all. There may only be regular matter, some of which is dark, some of which is in stars, and some stuffed away where the suns don't shine. Dark matter may have turned out to be the modern equivalent of the ancient cartographer's "Here there be monsters" notation on the unexplored parts of their charts.
It's that dark energy stuff that scares the Hell out of me. |
“Biology is just physics that has begun to smell bad.” —HalfMooner
Here's a link to Moonscape News, and one to its Archive. |
| Edited by - HalfMooner on 04/25/2012 19:35:33 |
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On fire for Christ
SFN Regular
Norway
1273 Posts |
Posted - 04/25/2012 : 22:23:39 [Permalink]
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This new discovery doesn't explain away dark matter completely. You still have to buy into Modified Newtonian dynamics.
I suspect it will be picked apart by astronomy bloggers in the coming week.
On a side note, if this structure is so huge and nearby why has no one seen it before? |
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HalfMooner
Dingaling
Philippines
15831 Posts |
Posted - 04/26/2012 : 03:19:26 [Permalink]
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Originally posted by On fire for Christ
This new discovery doesn't explain away dark matter completely. You still have to buy into Modified Newtonian dynamics.
I suspect it will be picked apart by astronomy bloggers in the coming week.
On a side note, if this structure is so huge and nearby why has no one seen it before?
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Yeah, after I posted, I noticed that they were saying something like, "Only 10% of the dark matter expected" was found. So I'm still at least as confused as ever. |
“Biology is just physics that has begun to smell bad.” —HalfMooner
Here's a link to Moonscape News, and one to its Archive. |
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BigPapaSmurf
SFN Die Hard
3192 Posts |
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 04/26/2012 : 06:33:39 [Permalink]
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Nothing annoys me as much as the oft repeated idea that Dark energy is actually energy, there is no evidence that it is energy in any form. I think it is just a property of empty space, perhaps time will tell, but if I hear one more person claim that DE is 90% of the mass/matter in the universe Im gonna scream.
Also not convinced that the universe will expand to the point of particle disintegration. I think it more likely that the areas of mass are not tied to DE expansion, meaning the expansion only takes place where mass is not collected.
I like to use a modified "rubber-sheet" analogy, we have a thin rubber sheet with two galaxies spread apart on top, eventually all of the mass will settle into one place without the comological constant. The cosomological constant is represented as air pressure pushing up on the rubber sheet from beneath. Where there is no mass on top of the sheet(spaces between galaxies) the CC Pressure pushes (ballons) upward which drives the galaxies apart and stretches the space between them. As the mass on top decreases the ability to ballon and stretch increases. If we go back further, the mass is evenly spread across the sheet preventing the CC pressure from spreading the universe until such time as the matter has sufficiently settled into mass clusters.
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"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
| Edited by - BigPapaSmurf on 04/26/2012 06:39:14 |
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 04/26/2012 : 06:38:06 [Permalink]
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Originally posted by HalfMooner
Originally posted by On fire for Christ
This new discovery doesn't explain away dark matter completely. You still have to buy into Modified Newtonian dynamics.
I suspect it will be picked apart by astronomy bloggers in the coming week.
On a side note, if this structure is so huge and nearby why has no one seen it before?
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Yeah, after I posted, I noticed that they were saying something like, "Only 10% of the dark matter expected" was found. So I'm still at least as confused as ever.
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I think what they're saying is that they still can't account for 10% of the mass they expect based on the gravitational lenzing and outer-galactic star velocity data. They'll find it, eventually. |
"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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On fire for Christ
SFN Regular
Norway
1273 Posts |
Posted - 04/26/2012 : 07:00:18 [Permalink]
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| And you know all this because?... |
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 04/26/2012 : 11:46:08 [Permalink]
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| I think about space so much that I dream in scientific notation. |
"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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Tim Thompson
New Member
USA
36 Posts |
 Posted - 04/30/2012 : 17:05:20 [Permalink]
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One should keep in mind that a single paper is not the final word, especially a paper that has not yet been published and has therefore not yet garnered a single citation. One should also keep in mind the rather important difference between fact & interpretation; every paper mixes the two, and it is the reader's job to make sure they can tell which is which. And finally, one must keep in mind the serious difference between blogs, press releases and the actual paper itself.
In this case, see The VPOS: a vast polar structure of satellite galaxies, globular clusters and streams around the Milky Way, by M.S. Pawlowski, J. Pflamm-Altenburg and P. Kroupa, all from the Argelander Institute for Astronomy, University of Bonn, Germany.
Now, read the abstract:
It has been known for a long time that the satellite galaxies of the Milky Way (MW) show a significant amount of phase-space correlation, they are distributed in a highly inclined Disc of Satellites (DoS). We have extended the previous studies on the DoS by analysing for the first time the orientations of streams of stars and gas, and the distributions of globular clusters within the halo of the MW. It is shown that the spatial distribution of MW globular clusters classified as young halo clusters (YH GC) is very similar to the DoS, while 7 of the 14 analysed streams align with the DoS. The probability to find the observed clustering of streams is only 0.3 per cent when assuming isotropy. The MW thus is surrounded by a vast polar structure (VPOS) of subsystems (satellite galaxies, globular clusters and streams), spreading from Galactocentric distances as small as 10 kpc out to 250 kpc. These findings demonstrate that a near-isotropic infall of cosmological sub-structure components onto the MW is essentially ruled out because a large number of infalling objects would have had to be highly correlated, to a degree not natural for dark matter sub-structures. The majority of satellites, streams and YH GCs had to be formed as a correlated population. This is possible in tidal tails consisting of material expelled from interacting galaxies. We discuss the tidal scenario for the formation of the VPOS, including successes and possible challenges. The potential consequences of the MW satellites being tidal dwarf galaxies are severe. If all the satellite galaxies and YH GCs have been formed in an encounter between the young MW and another gas-rich galaxy about 10-11 Gyr ago, then the MW does not have any luminous dark-matter substructures and the missing satellites problem becomes a catastrophic failure of the standard cosmological model.
Note the passages that I have emphasized in red & blue. First, the presence of a correlated ring structure clearly rules out the most simplistic model of galaxy formation, namely spherically symmetrical infall (that's the red part). Second, the presence of a correlated ring structure clearly implies a formation mechanism consistent with the correlated ring geometry (that's the blue part). Those are the real starting points for any serious discussion, subject to the validity of the correlated structure in the first place; their analysis looks good enough to me to accept for the time being that the claimed structure is real, but one must wait for responses and the discussions to see if people with greater expertise than mine are equally satisfied.
In the abstract, the authors simply state that "If all the satellite galaxies and YH GCs have been formed in an encounter between the young MW and another gas-rich galaxy about 10-11 Gyr ago, then the MW does not have any luminous dark-matter substructures and the missing satellites problem becomes a catastrophic failure of the standard cosmological model". This statement is justified in the paper by an analysis of the satellite mass/luminosity (M/L) ratio, while the authors point out that the spatial distribution, age distribution and morphology distribution of the Milky Way satellite system are all consistent with tidal origin. This is important: everything except the M/L ratio is consistent with tidal origin. The inconsistency of the M/L ratio depends on the assumption, explicit in the paper, that "TDGs cannot contain large amounts of non-baryonic dark matter" (preprint page 17, section 4.4.6; TDG = tidal dwarf galaxy). But that assumption is itself a dark-matter model-dependent assumption, which means that it depends on the assumed specific physics of dark matter (specifically the thermodynamics of dark matter), and this is in turn not well constrained by observation.
So, the extent to which this result intimidates dark matter cosmology is entirely based on arguably soft assumptions about the specific physics of dark matter. But reading the blog entry, one might think that this pre-print was the definitive death-knell of dark matter. One should avoid jumping to conclusions based on blogs and press releases. |
The point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it. -- Bertrand Russell |
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HalfMooner
Dingaling
Philippines
15831 Posts |
Posted - 05/01/2012 : 05:08:44 [Permalink]
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| Thank you so much for that, Tim! "Too early to draw conclusions" seems to be the wisdom of the day. In science, that's often the case. Great to have an actual expert chime in. |
“Biology is just physics that has begun to smell bad.” —HalfMooner
Here's a link to Moonscape News, and one to its Archive. |
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 05/01/2012 : 10:33:06 [Permalink]
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Originally posted by HalfMooner
Thank you so much for that, Tim! "Too early to draw conclusions" seems to be the wisdom of the day. In science, that's often the case. Great to have an actual expert chime in.
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Yep thats what Im complaining about, the jump to the conclusion that Dark Matter is an exotic/unknown type of matter and that Dark Energy is in fact energy of some kind.
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"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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Tim Thompson
New Member
USA
36 Posts |
Posted - 05/01/2012 : 17:22:51 [Permalink]
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Originally posted by BigPapaSmurf
Yep thats what Im complaining about, the jump to the conclusion that Dark Matter is an exotic/unknown type of matter and that Dark Energy is in fact energy of some kind.
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I disagree that either of these constitutes "jumping to conclusions" (which is quite independent of whether or not either idea turns out in the end to be valid or invalid).
On Dark Matter
It is a fact that the motion of matter in the universe is observed to be significantly inconsistent with the standard physical assumptions. Therefore, the standard physical assumptions need to be either modified, or simply replaced with new assumptions. There are in essence only two real candidates for new or modified assumptions: (1) There is more matter in the universe than we see, providing an unseen source for more gravity than we would have expected, or (2) The standard laws of gravity need to be modified to conform with observation. Of course, both (1) & (2) could be simultaneously true. The first assumption comes in two parts: (1a) There is more ordinary (i.e., baryonic) matter than we see, and (1b) There is additional, as yet undetected nonbaryonic matter. And, of course, Both (1a) & (1b) could be simultaneously true.
In my opinion, and in the consensus opinion of the main stream science community, both (1a) & (1b) are true. It is known that there is more baryonic matter in the universe than previously thought. However, it is also known that all of this previously undetected baryonic dark matter combined falls far short of the mark required to avoid the necessity of more exotic nonbaryonic dark matter (so long as we simultaneously assume that (2) is incorrect and that the law of gravity does not need to be modified). Hence, the bulk of mainstream research is concentrated on figuring out ways to directly or indirectly detect the nonbaryonic dark matter which has thus far remained undetected. However, it should also be noted that there is significant research, exemplified by numerous journal papers, devoted to (2) above, attempting to eliminate the need for any dark matter at all by modifying the laws of gravity. As far as I know, being outside my own area of expertise, these attempts have failed to find a universal solution; e.g., one form of modified gravity might work to solve "this problem" but not "that problem", and so forth, while the assumption of both baryonic, but predominately nonbaryonic dark matter produces universal solutions that simultaneously solve all of the problems (at least in principle), limited of course by observational uncertainty.
Dark matter, as we now use the term, did not exist in the scientists lexicon until it was brought forth and into the light by the famous astronomer Fritz Zwicky. He was observing clusters of galaxies, back in the early days of our modern understanding of galaxies as stellar systems. By interpreting the redshift of galaxy spectra as a Doppler shift indicating relative motion, he derived the radial velocities of the individual galaxies in the cluster (that's the velocity along the line of sight to the galaxy). At the same time, he derived an estimate of the masses of the individual galaxies by virtue of their luminosity and his knowledge of the mass-luminosity relationship for stars. His conclusion was that the galaxies were moving so fast that the clusters would have flown apart already, unless there were about ten times more mass than he could see. Thus was dark matter born, although he called it by a more appropriate term for the time: "missing mass". It was Edwin Hubble who proved that galaxies are stellar systems, by using the 100-inch Hooker telescope at Mt. Wilson Observatory, which was the largest in the world at the time, and the first large enough to resolve stars that far away (Hubble, 1925, Hubble, 1926, Hubble, 1929). It was only a few years later that Zwicky published his determination of the "missing mass problem", as it came to be called (Zwicky, 1933, Zwicky, 1937).
Of course, Zwicky and his contemporaries and those who followed knew quite well that there could be any number of massive things that they would not expect to see; dim low mass stars, dark clouds of gas & dust in the interstellar medium, planets & etc., in the galaxies, or spread out in the space between them. So naturally, they did not think of looking for any exotic kind of matter. They simply made the natural assumption that there was mass floating around out there that escaped the limited vision of their technology. I fail to see anything spectacularly wrong with that line of reasoning.
In the intervening years, it became evident that a similar problem was visible in the rotation curves of spiral galaxies (e.g., Volders, 1959, Rubin & Ford, 1970; a problem actually anticipated in Oort, 1932).
Until fairly recently, astronomers had continued along the same course as set by Zwicky. They went looking for the missing mass as ordinary matter that has simply escaped their view. But there has been a huge advance in astronomical technology since Zwicky's time, and "simply" has become "not so simply". Infrared astronomers today can see the dust & gas in galaxies that was invisible to Zwicky and we now know that there is not enough to make up the missing mass. Infrared & optical astronomers today can see the low mass stars that Zwicky could not see and we now know that there is not enough to make up the missing mass. X-ray astronomers today can see the gas between galaxies that was invisible to Zwicky and we now know that there is not enough to make up the missing mass. In fact, we now know that all of the mass we can see is still about a factor of 10 too small to make up the missing mass. Our own Milky Way halo has been searched far & wide for low mass red dwarf stars with the Hubble Space Telescope, and searched far & wide for any compact objects, made of either ordinary or exotic matter, and in all cases the missing mass is simply not there (e.g., HST, 1994, Bahcall, et al., 1994, Alcock, et al., 2001, Yoo, Chanamé & Gould, 2004). After decades of exhaustive searches for ordinary matter objects as a source of the missing mass, it is time to face the possibly uncomfortable truth: The missing mass is not missing "simply" because we don't have the technology to see it, but even more "simply" because it simply is not there. What, exactly, do you propose that we should look for, that we have not already looked for exhaustively, without finding?
Meanwhile, parallel to all this, we have finally built the technology required to see the small variations in temperature across the sky in the cosmic microwave background (the COBE & WMAP missions). Those small temperature differences, which we call anisotropies, when interpreted in the context of big bang cosmology, allow a determination of a difference between normal baryonic dark matter and exotic, non baryonic dark matter. The CMB interpretation agrees with the observational results from the conventional astronomers, that the bulk of dark matter must be an exotic, non baryonic form of matter (see Hu, 2001 and Wayne Hu's webpages, particularly the CMB pages).
This is not "jumping to conclusions". Rather, this is "judiciously coming to conclusions based on systematic scientific study".
The same is true for dark energy, but that will have to wait for another post.
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The point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it. -- Bertrand Russell |
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Vast Structure Discovery....Nixes Dark Matter
