It's pictures like these that leave me speachless.
http://antwrp.gsfc.nasa.gov/apod/image/ ... _f2048.jpg
Dark Matter Proof? Wow! (APOD 24 Aug 2006)
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craterchains
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Norval
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craterchains
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orin stepanek
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Dark Matter Proof? (APOD 24 Aug 2006)
Can someone help explain this to me? I saw the apod last week and thought I was pretty clear on the explanation until the picture made it into my Science News Weekly..
http://www.sciencenews.org/articles/20060826/fob1.asp
Basically I interpret this article as saying:To search for dark matter, Douglas Clowe of the University of Arizona in Tucson and his colleagues used several telescopes and observatories to image an unusually energetic collision between two galaxies that occurred 100 million years ago.
Normally, as galaxies travel through the universe, gravity keeps dark and ordinary matter close together, so the invisible substance can't be distinguished. During a galactic merger, however, hot gases from one galaxy bump into hot gases in the other and both galaxies are slowed by a force similar to wind resistance. But dark matter from one galaxy, in theory, passes right through another galaxy's dark matter (SN: 4/23/05, p. 264: http://www.sciencenews.org/articles/20050423/bob9.asp).
"Dark matter particles don't experience the same type of drag that slows down gas clouds," says Clowe.
His team used a technique called gravitational lensing to locate the main mass in the aftermath of the collision (SN: 5/20/00, p. 332: Available to subscribers at http://www.sciencenews.org/articles/20000520/note10.asp). If dark matter didn't exist, all the mass would have been lumped together with the gases. Instead, the researchers found most of the mass in clumps that appeared to have whizzed past the hot gases.
Only a theory of gravity that includes dark matter can explain the separation, Clowe's team argues in an upcoming Astrophysical Journal Letters.
"This proves in a simple and direct way that dark matter exists," says coauthor Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "It puts to rest the remaining doubt that cosmologists have had until now."
-No problem there-Normally dark matter and ordinary matter are kept close together and the invisible dark matter is indistinguishable
-Sounds good, still no prob-~This is an image of two large galaxy clusters colliding. When they collided their gasses slowed and became super positioned behind their parent cluster.~
-That is understandable, but here are some questions. And for argument sake lets just assume that dark matter is FACT.Dark matter doesn't experience the same type of drag that slows down gas clouds.
1) The mass of the gas is low compared to that of the galaxies with their SMBHs. So why wouldn't one expect to see these results even without dark matter?
2) If the dark matter is close to normal matter, i.e. the gas clouds, why wouldn't its intense gravity hold on to the gas particles, not allowing them to slow.-
-What? Why? Now lets assume there is NO dark matter. We would expect the collision of these two clusters to result in some changes in structure ect. but we know that there is so much space between massive objects, most would pass through unscaved.. Not lumped together with the gasses. Dark matter or not. I don't see how this statement holds any grounds.-If dark matter didn't exist all of the mass would have been lumped together with the gasses.
-Again, why? Can someone explain? Are they referring to the amount of observable gravitational lensing? If so why does that have to be explained by dark matter? Could it not just as easily be that we don't completely understand how much mass could be in those galaxy clusters? Perhaps an extremely large super massive black hole helps keep the clusters together.-Only a theory of gravity that includes dark matter can explain the separation
Hopefully someone can enlighten me on how this is definite evidence.This proves in a simple and direct manner that dark matter exists
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Dr. Skeptic
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I'll try and keep it simple, if you need me to elaborate let me know.
When the galaxies collided the nebulae gasses (red) slowed and generated eminence heat from their colliding.
The speed and position of the departing galaxies can predict their mass.
If the invisible matter were normal dust, dirt and gasses, the "red" area would be much larger.
The estimated mass of the departing galaxies with the nebulae gasses/dust removed (the blue areas) shows that a major % of the matter passed each other with no interactions; 30 to 40 % more mass the visible light would predict.
The 30 to 40 % need to be an invisible mass to does not interact as normal matter would.
The other explanation is that gravity's characteristics do not hold up over large areas.
When the galaxies collided the nebulae gasses (red) slowed and generated eminence heat from their colliding.
The speed and position of the departing galaxies can predict their mass.
If the invisible matter were normal dust, dirt and gasses, the "red" area would be much larger.
The estimated mass of the departing galaxies with the nebulae gasses/dust removed (the blue areas) shows that a major % of the matter passed each other with no interactions; 30 to 40 % more mass the visible light would predict.
The 30 to 40 % need to be an invisible mass to does not interact as normal matter would.
The other explanation is that gravity's characteristics do not hold up over large areas.
Speculation ≠ Science
The real point of this experiment is actually to measure the high temperature gas that fills galaxy clusters and to determine if this gas could be the DM. The point with the observations is that the hot gas is collisional (ie it interacts with other bits of gas) and the galaxies and DM are not, this is because the DM only interacts via gravity and the galaxies are effectively point paricles that just pass through the gaps in each cluster.
So when two clusters pass through each other, the DM and galaxies pass straight through, while the hot gas hits each other and tends to slow down. We know that a lot of gas is present as gas between galaxies, in fact probably 90% of the mass of baryons is in this gas, so a lot of people still worried that maybe we had missed some of it and in fact this was the DM.
This experiment proves that that can't be, because when you look at the clusters they have almost the same mass as you would expect of normal clusters that havent been through a collision, so the hot gas does not dominate the total mass of the cluster. As we know the luminous mass (the baryons) doesnt it must mean there is some unseen mass at work there.
Another point is that SMBH really dont make much contribution to the mass of a galaxy (on the order of 1% at most), thats why they are only felt in the very inner regions of galaxies.
So when two clusters pass through each other, the DM and galaxies pass straight through, while the hot gas hits each other and tends to slow down. We know that a lot of gas is present as gas between galaxies, in fact probably 90% of the mass of baryons is in this gas, so a lot of people still worried that maybe we had missed some of it and in fact this was the DM.
This experiment proves that that can't be, because when you look at the clusters they have almost the same mass as you would expect of normal clusters that havent been through a collision, so the hot gas does not dominate the total mass of the cluster. As we know the luminous mass (the baryons) doesnt it must mean there is some unseen mass at work there.
Another point is that SMBH really dont make much contribution to the mass of a galaxy (on the order of 1% at most), thats why they are only felt in the very inner regions of galaxies.
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Indigo_Sunrise
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Wadsworth,
Have you seen this?
http://cosmicvariance.com/2006/08/21/dark-matter-exists
I found it very interesting, informative and pretty easy to understand. It has quite a few links to check out, as well.
Happy reading!
Have you seen this?
http://cosmicvariance.com/2006/08/21/dark-matter-exists
I found it very interesting, informative and pretty easy to understand. It has quite a few links to check out, as well.
Happy reading!
Forget the box, just get outside.
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lankytom
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"Proof" of dark matter
I find myself cringing whenever someone talks about "proof" of dark matter. Dark matter is 18th century astro science and plasma physics is becoming the 21st century astro science. Dark matter is the 21st century version of the "Emperor's New Clothes." For a course in plasma physics 101, I refer folks to: http:public.lanl.gov/alp/plasma/universe.html
(lanl refers to Los Alamos National Laboratory). For a general treatment of the electomagnetic nature of the universe I recommend:
http://www.electric-cosmos.org/index.htm
Or for an interesting cross section view just googleize "gravitational bending+plasma."
The so called pictures of "dark matter" are just pictures conjured up from various frequencies of the light received. Rather than "dark matter" they could easily be merely areas of increased density of plasma clouds. Astronomers that have been paying attention now realize that plasma, not "dark matter" gives much better evidence for the spiral arms on galaxies.
Plasma gives better evidence for galaxy cluster interactions as well.
Note the APOD image from Aug 31, the "Extra Galaxies" picture. The graceful curves of the nearest galaxy can only come from electromagnetic interaction, not from gravitational effects. Gravitational effects would be minimal across 150,000, light years. Witness the lack of dramatic effects on the Magellan clouds. For good gravitational effects look at the accretion disks around "black holes." Note that this is apparently primarilly circular motion. The particle jet emerging from so many galaxy centers is another clear example of electromagnetism and plasma physics.
We probably just need another generation or two of astronomers who have studied electromagnetism and plasma physics in graduate school.
(lanl refers to Los Alamos National Laboratory). For a general treatment of the electomagnetic nature of the universe I recommend:
http://www.electric-cosmos.org/index.htm
Or for an interesting cross section view just googleize "gravitational bending+plasma."
The so called pictures of "dark matter" are just pictures conjured up from various frequencies of the light received. Rather than "dark matter" they could easily be merely areas of increased density of plasma clouds. Astronomers that have been paying attention now realize that plasma, not "dark matter" gives much better evidence for the spiral arms on galaxies.
Plasma gives better evidence for galaxy cluster interactions as well.
Note the APOD image from Aug 31, the "Extra Galaxies" picture. The graceful curves of the nearest galaxy can only come from electromagnetic interaction, not from gravitational effects. Gravitational effects would be minimal across 150,000, light years. Witness the lack of dramatic effects on the Magellan clouds. For good gravitational effects look at the accretion disks around "black holes." Note that this is apparently primarilly circular motion. The particle jet emerging from so many galaxy centers is another clear example of electromagnetism and plasma physics.
We probably just need another generation or two of astronomers who have studied electromagnetism and plasma physics in graduate school.
Lankytom
The problem with modified gravity is that the chance of it being true is like 1 in - millions. Thus, not likely at all! 
I would be willing to debate that dark energy doesn’t exist at all –that, in fact, dark matter is the sole culprit of that which cannot be currently explained.
And I don't think that dark matter is that great of a mystery. I believe that its identity is so unsophisticated that human minds are simply overlooking the basic nature of it.
I would be willing to debate that dark energy doesn’t exist at all –that, in fact, dark matter is the sole culprit of that which cannot be currently explained.
And I don't think that dark matter is that great of a mystery. I believe that its identity is so unsophisticated that human minds are simply overlooking the basic nature of it.
Hi lankytom nice links, I have a couple of points about them though.
The first is the link to the lanl website, Its a pretty good website, but with very little detail, none of it controversial to astronomers at all. I've looked all over it as as far as I can tell there is nothing in there at all about plasma physics discounting DM. If I have missed the page in there can you link to it please? Its important as that page is handled by proffessional physicists so I would tend to take it seriously.
The other link however is pretty much trash (sorry if it happens to be yours), it uses the same tired arguments of Arp to try and connect quasars and galaxies that have been thoroughly discounted by large Quasar surveys.
I think the problem most physicists have with electromagnetic fields having much to do with galaxy formation over cosmological scales is simply that on those scales the Universe is neutral electrically. I seriously doubt that electromagnetics is so poorly understood that it could allow forces appreciable to gravity over large scales.
I did the google for "gravitational bending+plasma" and found http://www.plasmaphysics.org.uk/research/lensing.htm is that what I should be looking at. If after a quick glance I have it right this site says general relativity is wrong, because
) and why all other general relativistic phenomena fit the theory so well.
I'm not sure what your point is about the magellanic clouds is, could you explain it please? I guess you mean that you don't see them greating gravitional arcs or something like that, but then you wouldnt expect them to as they are very small dwarf galaxies, with masses ~1/20 of the MW which itself isnt actually that big, and certainly wouldnt be chosen as a prime target to search for arcs. Gravitational arcs are generally only found aroun very large clusters of galaxies with masses 1000x the MW. Although a few have been found around very large galaxies.
In terms of BH accretion you are quite right, but electromagnetics has always been an integral part of dealing with the plasma accretion disc, its clearly not true that astronomers ignore this, it would be impossible to model accretion discs without it.
The first is the link to the lanl website, Its a pretty good website, but with very little detail, none of it controversial to astronomers at all. I've looked all over it as as far as I can tell there is nothing in there at all about plasma physics discounting DM. If I have missed the page in there can you link to it please? Its important as that page is handled by proffessional physicists so I would tend to take it seriously.
The other link however is pretty much trash (sorry if it happens to be yours), it uses the same tired arguments of Arp to try and connect quasars and galaxies that have been thoroughly discounted by large Quasar surveys.
I think the problem most physicists have with electromagnetic fields having much to do with galaxy formation over cosmological scales is simply that on those scales the Universe is neutral electrically. I seriously doubt that electromagnetics is so poorly understood that it could allow forces appreciable to gravity over large scales.
I did the google for "gravitational bending+plasma" and found http://www.plasmaphysics.org.uk/research/lensing.htm is that what I should be looking at. If after a quick glance I have it right this site says general relativity is wrong, because
this of course is quite a claim and flies in the face of many observations. If this is indeed the case then plasma physics also needs to explain how gravity works (hey you broke, you fix itit is unreasonable to assume that immaterial and massless objects like light can be in any way subject to a gravitational interaction.
) and why all other general relativistic phenomena fit the theory so well.I'm not sure what your point is about the magellanic clouds is, could you explain it please? I guess you mean that you don't see them greating gravitional arcs or something like that, but then you wouldnt expect them to as they are very small dwarf galaxies, with masses ~1/20 of the MW which itself isnt actually that big, and certainly wouldnt be chosen as a prime target to search for arcs. Gravitational arcs are generally only found aroun very large clusters of galaxies with masses 1000x the MW. Although a few have been found around very large galaxies.
In terms of BH accretion you are quite right, but electromagnetics has always been an integral part of dealing with the plasma accretion disc, its clearly not true that astronomers ignore this, it would be impossible to model accretion discs without it.
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craterchains
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craterchains
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It would obviously be "foolishness" to ones like you astro.astro_uk wrote:Norval you are a fool.
Where is you evidence Norval?
Are you the same Pete of this posting?
http://www.sciforums.com/showthread.php ... ge=2&pp=20
I can see why YOU have to take meds. We have no need of them.
Norval
"It's not what you know, or don't know, but what you know that isn't so that will hurt you." Will Rodgers 1938
I may just join Sciforums as well now.
The only medication I take is the odd paracetamol for a hangover.
So I repeat, lets have some evidence. Maybe we can all chant it together?
Lets have some evidence!
Not necessarily Norval, If you could provide me with some evidence that is compelling I could become your strongest advocate. I work in astronomy and we frequently have to revise our thinking, I'm not yet so old that I'm stuck in my ways.It would obviously be "foolishness" to ones like you astro.
The only medication I take is the odd paracetamol for a hangover.
So I repeat, lets have some evidence. Maybe we can all chant it together?
Lets have some evidence!
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Pete
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Oh, my quote was supposed to convey the tone I detected in your post in a mildly humourous manner. I wasn't saying I take medication (which I don't)craterchains wrote:Nope, I haven't seen those forums before. But I love how he totally owned the "longest crater chain in the solar system"astro_uk wrote:Are you the same Pete of this posting?
http://www.sciforums.com/showthread.php ... ge=2&pp=20
craterchains wrote:I can see why YOU have to take meds. We have no need of them.
Norval
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craterchains
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