Funky dark matter and the rotation curves of galaxies

BoJangles · Jul 9, 2008

This topic arises from the fact (to me) spiral galaxies look a lot like a whirlpool, and as a whirlpool they are easily explained by Newtonian physics. Not some funky density wave induced by some weird dark matter, though I do realise I have 50 years of observational evidence against me.Personally, I don’t like dark matter, and to tell you the truth MOND and their funky friends don’t sit well either. Q1)Is there any evidence from our closest celestial neighbours, to suggest they follow a flat rotation curve? I.e. you would think it would be very easy to tell (observationally, through proper motion) if say… Alpha Centauris’ speed around the Milky Way was indeed proportional to its distance from the centre. Anyone know of any work done on this?Q2)For the dark matter to work in these galactic haloes, wouldn’t it have to be in exact amounts, and in exact densities, and even more to the point wouldn’t it be near impossible to keep this system stable? I.e. when I talk about stability, if the halo wasn’t exactly correct, the galaxy would start to wind its spiral into a blob. Even more question arise, how did it get there, why is it just in a halo and not distributed evenly or clumped in the centre of the galaxy, and how can a spiral galaxy even start to wind with this stuff around it. Q3)If there is a halo of dark matter around our galaxy, and we are indeed close to the edge of the milky way, then it points to reason that dark matter should be running through our solar system, and additionally affecting the planets orbits ( in the tiniest way  ) shouldn’t it?Thank you for your time and i look forward to your abuse

<div class="Discussion_UserSignature"> -------------- Let me start out with the standard disclaimer ... I am an idiot, I know almost nothing, I haven’t taken calculus, I don’t work for NASA, and I am one-quarter Bulgarian sheep dog. With that out of the way, I have several stupid questions... *** A few months blogging can save a few hours in research *** </div>

MeteorWayne · Jul 10, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>This topic arises from the fact (to me) spiral galaxies look a lot like a whirlpool, and as a whirlpool they are easily explained by Newtonian physics. Not some funky density wave induced by some weird dark matter, though I do realise I have 50 years of observational evidence against me.Personally, I don’t like dark matter, and to tell you the truth MOND and their funky friends don’t sit well either. Q1)Is there any evidence from our closest celestial neighbours, to suggest they follow a flat rotation curve? I.e. you would think it would be very easy to tell (observationally, through proper motion) if say… Alpha Centauris’ speed around the Milky Way was indeed proportional to its distance from the centre. Anyone know of any work done on this?</DIV>Yes, that's exactly how "it" was discoveredReplying to: <DIV CLASS='Discussion_PostQuote'>Q2)For the dark matter to work in these galactic haloes, wouldn’t it have to be in exact amounts, and in exact densities, and even more to the point wouldn’t it be near impossible to keep this system stable? I.e. when I talk about stability, if the halo wasn’t exactly correct, the galaxy would start to wind its spiral into a blob. Even more question arise, how did it get there, why is it just in a halo and not distributed evenly or clumped in the centre of the galaxy, and how can a spiral galaxy even start to wind with this stuff around it. </DIV> You are confusing two things. The spiral shape we see is caused by density waves, and does not prepresent the overall rotational motion of a galaxy. The exact amount of dark matter, if it exests, is not crucial. In general, the required distribution to show the effects seen requres it to be a sphere much larger than the visible portion of a galaxy.Replying to: <DIV CLASS='Discussion_PostQuote'>Q3)If there is a halo of dark matter around our galaxy, and we are indeed close to the edge of the milky way, then it points to reason that dark matter should be running through our solar system, and additionally affecting the planets orbits ( in the tiniest way  ) shouldn’t it?Thank you for your time and i look forward to your abuse

Posted by Manwh0re</DIV> Well, we're not particularly close to the edge. And I don't thing halo as you are interpreting it is correct. It's not a ring around the gal;axy, or a halo around it, but a filled sphere in which the galaxy is embedded.So we are indeed surrounded by dark matter, if it exists, whatever it is. <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

BrianSlee · Jul 10, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Yes, that's exactly how "it" was discovered You are confusing two things. The spiral shape we see is caused by density waves, and does not prepresent the overall rotational motion of a galaxy. The exact amount of dark matter, if it exests, is not crucial. In general, the required distribution to show the effects seen requres it to be a sphere much larger than the visible portion of a galaxy.Well, we're not particularly close to the edge. And I don't thing halo as you are interpreting it is correct. It's not a ring around the gal;axy, or a halo around it, but a filled sphere in which the galaxy is embedded.So we are indeed surrounded by dark matter, if it exists, whatever it is. Posted by MeteorWayne</DIV> When the Voyager craft passed through the heliopause and into interstellar space did they have the instruments to detect any of this matter?  i.e. can they measure the densities of the interstellar medium? <div class="Discussion_UserSignature"> "I am therefore I think" "The only thing "I HAVE TO DO!!" is die, in everything else I have freewill" Brian P. Slee </div>

BoJangles · Jul 11, 2008

Thanks for your previous response. But Let me try to understand this a little further.So… dark matter is uniformly distributed in a huge sphere encasing the entre galaxy and more. And this spherical encasement, basically, gravitationally affects the stars (especially in the outer regions of the galaxy) more than the gravitational affects by the centre of the galaxy (stoping them from flying off). So this stuff acts like a giant fudge number to keep the stars orbiting (excuse my creative terminology). And obviously the gravitational affects of this stuff must outweigh the galaxy itself. I'm just wondering why our planets spin the way they do if this stuff is such a great force and uniformly distributed. Is it because although it has a great affect on galactic structures its only small compared to the affects of planet sized objects running around a solar system? <div class="Discussion_UserSignature"> -------------- Let me start out with the standard disclaimer ... I am an idiot, I know almost nothing, I haven’t taken calculus, I don’t work for NASA, and I am one-quarter Bulgarian sheep dog. With that out of the way, I have several stupid questions... *** A few months blogging can save a few hours in research *** </div>

BoJangles · Jul 11, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>When the Voyager craft passed through the heliopause and into interstellar space did they have the instruments to detect any of this matter?  i.e. can they measure the densities of the interstellar medium? Posted by BrianSlee</DIV>The current understanding is (someone correct me if I'm wrong), if dark matter does exist it must be made of non baryonic matter (i.e. stuff we know little about). Additionally back in the days of voyager, and even today we have no real instruments that can prove or disprove dark matter, only computer models. I believe they can measure the density of space, but that relates more to baryonic matterWiki has more on baryonic matterhttp://en.wikipedia.org/wiki/Baryon   <div class="Discussion_UserSignature"> -------------- Let me start out with the standard disclaimer ... I am an idiot, I know almost nothing, I haven’t taken calculus, I don’t work for NASA, and I am one-quarter Bulgarian sheep dog. With that out of the way, I have several stupid questions... *** A few months blogging can save a few hours in research *** </div>

BrianSlee · Jul 11, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>The current understanding is (someone correct me if I'm wrong), if dark matter does exist it must be made of non baryonic matter (i.e. stuff we know little about). Additionally back in the days of voyager, and even today we have no real instruments that can prove or disprove dark matter, only computer models. I believe they can measure the density of space, but that relates more to baryonic matterWiki has more on baryonic matterhttp://en.wikipedia.org/wiki/Baryon   Posted by Manwh0re</DIV> My understanding was that dark matter was ordinary baryonic matter that could not be detected easily due to the fact that it does not emit large amounts of energy in the electromagnetic spectrum. <div class="Discussion_UserSignature"> "I am therefore I think" "The only thing "I HAVE TO DO!!" is die, in everything else I have freewill" Brian P. Slee </div>

aphh · Jul 11, 2008

Dark matter can be verified using a gravitational lens. The lens enlarges the view behind the lens more than the mass calculated based on the luminosity of the stars would otherwise suggest.Besides detectable matter, the effect of gravitational lens suggests undetectable matter exists. Also, without the dark energy supposedly emitted by dark matter, the universe would shrink, not enlarge at ever-increasing velocity.

DrRocket · Jul 11, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>The current understanding is (someone correct me if I'm wrong), if dark matter does exist it must be made of non baryonic matter (i.e. stuff we know little about). Additionally back in the days of voyager, and even today we have no real instruments that can prove or disprove dark matter, only computer models. I believe they can measure the density of space, but that relates more to baryonic matterWiki has more on baryonic matterhttp://en.wikipedia.org/wiki/Baryon   Posted by Manwh0re</DIV>Here is a tutorial on dark matter.http://web.mit.edu/~redingtn/www/netadv/specr/012/012.html <div class="Discussion_UserSignature"> </div>

MeteorWayne · Jul 11, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>When the Voyager craft passed through the heliopause and into interstellar space did they have the instruments to detect any of this matter?  i.e. can they measure the densities of the interstellar medium? Posted by BrianSlee</DIV> Well the Voyagers are not yet in interstellar space.And the fact is, that if we haven't been able to detect it here on earth, the Voyagers have less capable instruments than those at our disposal now, since they were designed 35 years ago.We are bathed in dark matter here, if it exists, whatever it is. So we first need to detect it here before there's any chance to design insturments to detect it in space.The "dark matter" missions that are in the design stage now will only detect the gravitational effects, which so far is the only way we know that it might exist. <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

MeteorWayne · Jul 11, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Thanks for your previous response. But Let me try to understand this a little further.So… dark matter is uniformly distributed in a huge sphere encasing the entre galaxy and more. And this spherical encasement, basically, gravitationally affects the stars (especially in the outer regions of the galaxy) more than the gravitational affects by the centre of the galaxy (stoping them from flying off). So this stuff acts like a giant fudge number to keep the stars orbiting (excuse my creative terminology). And obviously the gravitational affects of this stuff must outweigh the galaxy itself. I'm just wondering why our planets spin the way they do if this stuff is such a great force and uniformly distributed. Is it because although it has a great affect on galactic structures its only small compared to the affects of planet sized objects running around a solar system? Posted by Manwh0re</DIV> It is not a great force, it is a very weak force. The only reason it could affect galaxies is because there's so much of it.On a local scale, the gravity of normal matter overwhelms it, making it impossible, or very very very very very very difficult to detect above the noise level. <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

MeteorWayne · Jul 11, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>My understanding was that dark matter was ordinary baryonic matter that could not be detected easily due to the fact that it does not emit large amounts of energy in the electromagnetic spectrum. Posted by BrianSlee</DIV> More correctly, it does not emit or absorb EM radiation. <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

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Funky dark matter and the rotation curves of galaxies

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