Outrider Posted January 30, 2017 Share Posted January 30, 2017 Every time it think it have a decent handle (for a layman) on cosmic expansion I start reading and realize I know nothing. Yehuda Hoffman at the Hebrew University in Jerusalem claims to have discovered a great void that is actually pushing the Milky Way and others towards the Shapley Supercluster. Scientists have known for sometime that Shapley is pulling us and everything is in our neighborhood but it's gravity is not enough to explain the high velocity of our galaxy. The part i don't understand is how it is pushing. The article says because of the dearth of mass in the void expansion is moving at a faster rate. So if guess expansion in that area is moving the surrounding stuff out of the way? Dipole Repeller Astronomers have finally discovered why the Milky Way is barrelling through space faster than the universes rate of expansion. It is being pushed from behind by an enormous void dubbed the dipole repeller. . . . Like everywhere else in the universe, the void is expanding, but without the gravity of any galaxies to keep its expansion in check. This means the expanding void pushes on nearby galaxies (including our own) a bit like bubbles of air expanding inside a rising cake. Link to comment Share on other sites More sharing options...
Lord Antares Posted January 30, 2017 Share Posted January 30, 2017 This is strange. They are saying that the expansion of the universe is affected by gravity because mass is pulling space back so that it expands slower. That would also mean that there is ''resistance'' of a body to the expansion which is proportional to the mass of said body. Also, this would mean that, theoretically, if you had a body with high enough mass, it would overcome the expansion and make space fall inward. kind of like a black hole. Someone correct me if I'm wrong. Also, I don't know what they mean by ''astronomers discovered that the Milky Way, along with all the other galaxies in our neighbourhood, were hurtling towards the same region of space'' Don't all local bodies gravitate in roughly the same direction in the universe? Or are they referring to local movement? As far as I can tell, this has no legitimate proof. It's just a hypothesis. Link to comment Share on other sites More sharing options...
Outrider Posted January 30, 2017 Author Share Posted January 30, 2017 (edited) Hi L.A. As for the second part of your post scientists have known about what they call dark flow for at least 30 years. Not only the Milky Way, the local group, and Andromeda but also all the Superclusters within 2.5 billion light years are heading in the same direction. At first the cosmologists thought it was a large collection of galaxys known as the Great Attractor in fact that's why it was named that. But I think the WMAP survey changed everything and the Shapley Supercluster is now seen as the biggest attractor. https://www.nasa.gov/centers/goddard/news/releases/2010/10-023.html As for the first part of your post I think that expansion only works in the voids between the superclusters so gravity certainly can cancel it out. I just didn't know expanding space could push. Kind of trashes my understanding of expansion. But then that's the fun part. Oh and take everything I say with a very large grain of salt. I am no expert. Edited January 30, 2017 by Outrider Link to comment Share on other sites More sharing options...
Lord Antares Posted January 31, 2017 Share Posted January 31, 2017 I just didn't know expanding space could push. Yes, it's confusing if you think about it. We know space to bend around matter so there would be absolutely no reason for it to push it. On the other hand, how could matter be getting further apart if space wasn't pushing it along with its expansion? The more I think about it, the more questions get raised. all the Superclusters within 2.5 billion light years are heading in the same direction. Yes but what does ''same direction mean''. Does it mean: 1) parallel to one another? That wouldn't make sense to me. The only way that they could be travelling parallel is if they were bound into one body by gravity but that would be the only way they could be moving anyway then 2) inwards from parallel, towards a focal point? Shapley supercluster being the focal point, for example. But that could be easily calculated and verified, no? 3) outward from parallel? But you wouln't be saying this if that were the case and the Shapley supercluster couldn't be the destination then anyway. Link to comment Share on other sites More sharing options...
Outrider Posted January 31, 2017 Author Share Posted January 31, 2017 Yes, it's confusing if you think about it. We know space to bend around matter so there would be absolutely no reason for it to push it. On the other hand, how could matter be getting further apart if space wasn't pushing it along with its expansion? The more I think about it, the more questions get raised. Yep I'm confused too. Yes but what does ''same direction mean''. Does it mean: 1) parallel to one another? That wouldn't make sense to me. The only way that they could be travelling parallel is if they were bound into one body by gravity but that would be the only way they could be moving anyway then 2) inwards from parallel, towards a focal point? Shapley supercluster being the focal point, for example. But that could be easily calculated and verified, no? 3) outward from parallel? But you wouln't be saying this if that were the case and the Shapley supercluster couldn't be the destination then anyway. That's a little complicated and I don't think I can choose any of your 3 options.What I do know is that in 1964 Robert Wilson and Arno Penzias discovered the cosmic microwave background and then the 70's scientists measured a slight temperature difference on one side of our galaxy the Milky Way. From this they calculated the direction of travel through the universe and the speed 600 km/second. As I understand it it's sort of like a bunch of rubber ducks in a bathtub and you pull the plug they start out all over the tub but all head for the same place. Just for fun here's another article maybe it will help. https://www.google.com/amp/www.universetoday.com/113150/what-is-the-great-attractor/amp/ But where are we going? Just around in a great big circle? Or an ellipse? Which is going around in another circle… and it’s great big circles all the way up? Not exactly... Our galaxy and other nearby galaxies are being pulled toward a specific region of space. . . . While the Norma Cluster is massive, and local galaxies are moving toward it, it doesn't explain the full motion of local galaxies. The mass of the Great Attractor isn't large enough to account for the pull. When we look at an even larger region of galaxies, we find that the local galaxies and the Great Attractor are moving toward something even larger. It’s known as the Shapley Supercluster. It contains more than 8000 galaxies and has a mass of more than ten million billion Suns. Norma Cluster = Great Attractor Link to comment Share on other sites More sharing options...
Ant Sinclair Posted February 1, 2017 Share Posted February 1, 2017 I read the Forbes article on this and the writer said the scale showing it all was 1.5billion light years across, from looking at the diagrams how far away from the Dipole Repeller would we be? Link to comment Share on other sites More sharing options...
Outrider Posted February 2, 2017 Author Share Posted February 2, 2017 I read the Forbes article on this and the writer said the scale showing it all was 1.5billion light years across, from looking at the diagrams how far away from the Dipole Repeller would we be?Hi Ant Sinclair I read your link with much interest but I'm sorry I can't answer your question. I can only guess (if the diagram is more or less to scale) 800 million light years. Keep in mind that's just a wild guess.The abstract for the article in Nature Astronomy gives the "supergalatic coordinates as [11,000, −6,000, 10,000] km s−1" which is pretty much greek to me. http://www.nature.com/articles/s41550-016-0036 The abstract also gives the size of the diagram as "40,000 km s−1 " so that equals to 1.5 Bly? Link to comment Share on other sites More sharing options...
Ant Sinclair Posted February 2, 2017 Share Posted February 2, 2017 Thanks for replying Outrider, it'll be interesting to find out exactly how far away it is. Link to comment Share on other sites More sharing options...
Mordred Posted February 2, 2017 Share Posted February 2, 2017 (edited) Roughly 220 Mpc from us, https://en.m.wikipedia.org/wiki/Dipole_repeller In regards to the push action this isn't due to gravity. It involves key relations between energy density and pressure. In essence the thermodynamic relations can overcome the localized gravity. Much the same way as to our universe expansion itself. Edited February 2, 2017 by Mordred Link to comment Share on other sites More sharing options...
Ant Sinclair Posted February 2, 2017 Share Posted February 2, 2017 Roughly 220 Mpc from us, https://en.m.wikipedia.org/wiki/Dipole_repeller Thanks for replying Mordred, what in light years would that be? Link to comment Share on other sites More sharing options...
Mordred Posted February 2, 2017 Share Posted February 2, 2017 (edited) [latex]7.176*10^8[/latex] light years Edited February 2, 2017 by Mordred 1 Link to comment Share on other sites More sharing options...
Ant Sinclair Posted February 2, 2017 Share Posted February 2, 2017 [latex]7.176*10^8[/latex] light years Thanks again Mordred, most useful, I'll be able to adjust some constants now for a few things Iam looking at. Link to comment Share on other sites More sharing options...
louis wu Posted February 3, 2017 Share Posted February 3, 2017 (edited) The actual paper can be found here https://arxiv.org/ftp/arxiv/papers/1409/1409.0880.pdf A video is an important component of the paper and is found http://irfu.cea.fr/laniakea or http://vimeo.com/pomarede/laniakea I found the video mind blowing and beautiful. The method is the Cosmicflows-2 catalog of galaxy positions and velocities together with standard cosmology are used as prior distribution for variational Bayesian analysis. Wiener noisy signal processing is heavily used, in deriving the velocity and density flow data. The analysis used H0 = 75.2 km s−1 Mpc−1 : The Planck team found H0 = 67.3 km s−1 Mpc−1, I find the difference a little disturbing, but I am not really competent to criticise the paper. The paper claims that the difference should not affect the derived velocities. Edited February 3, 2017 by louis wu Link to comment Share on other sites More sharing options...
Mordred Posted February 3, 2017 Share Posted February 3, 2017 (edited) Thanks for the links helps the discussion alot. The difference between the Planck value and the one the paper uses shouldn't have too much influence on the findings. The value is most likely more reflective of the late time Hubble flow value. Hubbles constant is only constant everywhere at a particular time slice. Over time it does vary. The calculator on my signature in the H/H_0 column reflects this detail. Edited February 3, 2017 by Mordred Link to comment Share on other sites More sharing options...
Outrider Posted February 3, 2017 Author Share Posted February 3, 2017 [latex]7.176*10^8[/latex] light years Yay my wild guess (800mly) was off by less than 100. Lol Hi Mordred and Luis thank you both for your comments and links. Am I correct in assuming that the distance calculated depends on which theoretical model is used? Link to comment Share on other sites More sharing options...
Mordred Posted February 3, 2017 Share Posted February 3, 2017 The only model being used in this case is LCDM the differences in Hubble constant is the localized Hubble value for the time correlating to the past value. Roughly 7 million years ago. Whereas the Planck value is Hubble constant today Link to comment Share on other sites More sharing options...
Outrider Posted February 3, 2017 Author Share Posted February 3, 2017 Roughly 220 Mpc from us, https://en.m.wikipedia.org/wiki/Dipole_repeller In regards to the push action this isn't due to gravity. It involves key relations between energy density and pressure. In essence the thermodynamic relations can overcome the localized gravity. Much the same way as to our universe expansion itself. I wasn't thinking of push gravity but because I have seen a number of threads on the board in the past pushing that idea I can see why you made that clear.I have read quite a few articles on the Repeller in the last couple of days and there seems to be two schools of thought here. 1. The dipole repeller actually does push because the space in that region (due to less gravity) is expanding faster than the space around it. I think this is Yehuda Hoffman's stance. He is the author of the paper that started all this. 2.The dipole repeller just seems to push because there is more mass ahead than there is behind. IOW Shapley Supercluster is pulling and the void, dipole repeller, is not so we go faster. Link to comment Share on other sites More sharing options...
Mordred Posted February 3, 2017 Share Posted February 3, 2017 (edited) Correct but it includes the relations you quoted. On the paper though he specifies the density of matter and the cosmological constant density. Though radiation density is still involved. Edited February 3, 2017 by Mordred Link to comment Share on other sites More sharing options...
Outrider Posted February 3, 2017 Author Share Posted February 3, 2017 So both 1 and 2 are correct? The faster rate of expansion in that area and the lack of mass (gravity) to hold us back are both factors in our rate of velocity towards Shapley Supercluster? Link to comment Share on other sites More sharing options...
Mordred Posted February 3, 2017 Share Posted February 3, 2017 (edited) Yes both are involved. On a related scenario matter collapsing into LSS aids expansion in the same manner when you include the thermodynamic influences. Edited February 3, 2017 by Mordred 1 Link to comment Share on other sites More sharing options...
Outrider Posted February 3, 2017 Author Share Posted February 3, 2017 Thanks Mordred I probably have a few more questions later when I have more time. You are a lot of help! Link to comment Share on other sites More sharing options...
Mordred Posted February 3, 2017 Share Posted February 3, 2017 your welcome and feel free to ask more questions when needed 1 Link to comment Share on other sites More sharing options...
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