APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10)

Comments and questions about the APOD on the main view screen.
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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by Psnarf » Wed Sep 10, 2014 6:15 pm

In one of the links, https://public.nrao.edu/news/pressrelea ... luster-gbt, we find the term 'ginormous', perhaps as a contraction of giant and enormous?
Newtonian gravity is accurate to one part in a million, just to give a perspective on when to use relativity formulae for curved space-time. Expansion of curved space-time does not prevent the motion of gravitationally bound galaxies as indicated.
Er, when is that big crunch scheduled? I'll need to get some popcorn to watch it.

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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by Chris Peterson » Wed Sep 10, 2014 6:25 pm

Psnarf wrote:In one of the links, https://public.nrao.edu/news/pressrelea ... luster-gbt, we find the term 'ginormous', perhaps as a contraction of giant and enormous?
The word has been around for more than a half century, and is found in all modern English dictionaries.
Er, when is that big crunch scheduled? I'll need to get some popcorn to watch it.
I don't think there's going to be one. These clusters essentially orbit a common center of mass. Things aren't being pulled together into a single point, anymore than individual clusters, galaxies, or planetary systems. I expect the ultimate evolution will be more akin to colliding galaxies, with everything getting more homogenized.
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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by Guest » Wed Sep 10, 2014 7:10 pm

Chris wrote:
Er, when is that big crunch scheduled? I'll need to get some popcorn to watch it.
I don't think there's going to be one. These clusters essentially orbit a common center of mass. Things aren't being pulled together into a single point, anymore than individual clusters, galaxies, or planetary systems. I expect the ultimate evolution will be more akin to colliding galaxies, with everything getting more homogenized.
Any simulation of more than 2 massive bodies orbiting or similarly attracted to a single center of mass will clearly show that the 'system' of unstable and that massive acceleration forces are imposed on these objects. These objects (galaxies) will be ejected from the system with equally massive velocities (relative to mass) creating a galactic 'pin-wheel' effect of ginormous proportions over galactic time periods. How this can lead to an homogeneous environment when all but two (?) masses are ejected is problematical. Don't you think?

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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by Chris Peterson » Wed Sep 10, 2014 7:17 pm

Guest wrote:Any simulation of more than 2 massive bodies orbiting or similarly attracted to a single center of mass will clearly show that the 'system' of unstable and that massive acceleration forces are imposed on these objects. These objects (galaxies) will be ejected from the system with equally massive velocities (relative to mass) creating a galactic 'pin-wheel' effect of ginormous proportions over galactic time periods. How this can lead to an homogeneous environment when all but two (?) masses are ejected is problematical. Don't you think?
No. That's exactly how I'd describe homogeneous. Over time there is a loss of structure. (It's not a pinwheel; the distribution is essentially spherical, not planar.)
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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by BristolGarry » Wed Sep 10, 2014 8:20 pm

Is there any speculation on what lies at the convergence of the lines in Lanaikea? I would think there would have to be some structure(s) of utterly immense gravitational pull to affect such a huge number of galaxies over such a vast amount of space. I am not an astronomer, and may be wildly misinterpreting this image - if so, please correct me.

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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by FloridaMike » Wed Sep 10, 2014 8:36 pm

I have been trying to figure out why the video below shows a butterfly shaped structure centered on the Milky Way at timestamp 1:25. My conclusion is the galaxies in the 'empty' region between the wings of the butterfly are obscured by our home galaxy.

Correct?
Click to play embedded YouTube video.
Link to video at time stamp 1:25
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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by geckzilla » Wed Sep 10, 2014 8:41 pm

FloridaMike wrote:I have been trying to figure out why the video below shows a butterfly shaped structure centered on the Milky Way at timestamp 1:25. My conclusion is the galaxies in the 'empty' region between the wings of the butterfly are obscured by our home galaxy.

Correct?
Yeah. That's the drawback of living in a nice, big spiral galaxy.
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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by rstevenson » Wed Sep 10, 2014 9:40 pm

epitalon wrote:What strikes me is the fact that many streams of white dots seem to converge to our galaxy and nobody seems to care of that ???
Would our galaxy be at the center of the Universe ?
DMcCartney wrote:Are anyone else's suspicions roused by what appear to be radiants formed of galaxy points, both inside and outside the boundary, that seem to originate from our galaxy? Is this maybe an indication of a perspective error?
I've seen these radiants before in large-scale images showing the universe around us, as mapped by various telescopes and satellites. It seems they are the result of looking out into the universe from our location here in a corner of one galaxy, with lots of intervening gas and dust, stars, clusters, nearby galaxies, and so on in our way. In other words, the radiants are not really lines of galaxies pointing at us; they're just the ones we can see and map. No doubt there are plenty of other galaxies in the areas between the radiants.

Or, I really am the center of the universe.

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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by Ron-Astro Pharmacist » Wed Sep 10, 2014 10:35 pm

In the video describing Laniakea in which the black filaments lead to the Great Attractor and the red into Perseus/Pisces, the structure almost appears toroidal in shape. Personally, all said and done, I would prefer its shape to turn out to be a torus knot because nature seems to like "threes."
600px-TorusKnot.jpg
Me too. It's an odd way to view symmetry though I'm sure nature won't give me a vote. :(

Another video by the same group.
Click to play embedded YouTube video.
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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by Nitpicker » Wed Sep 10, 2014 11:03 pm

On further reading, I've just learned that the Great Attractor -- http://en.wikipedia.org/wiki/Great_Attractor -- is the point to which everything in Laniakea is ultimately "falling" towards, as indicated by the "streamlines" in the APOD. (We are very much on the outskirts of Laniakea). The direction of the Great Attractor in our sky, is near the border of the southern constellations Triangulum Australe (TrA, The Southern Triangle) and Norma (Nor, The Carpenter’s Square).

Using The Pointers, Alpha and Beta Centauri (the two stars we southerners often use to find South on Earth), a line extending from Beta, through Alpha, will point to the Great Attractor, such that The Pointers lie roughly halfway between the Great Attractor and Crux.
The Great Attractor.PNG
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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by Beyond » Wed Sep 10, 2014 11:13 pm

rstevenson wrote:
epitalon wrote:What strikes me is the fact that many streams of white dots seem to converge to our galaxy and nobody seems to care of that ???
Would our galaxy be at the center of the Universe ?
DMcCartney wrote:Are anyone else's suspicions roused by what appear to be radiants formed of galaxy points, both inside and outside the boundary, that seem to originate from our galaxy? Is this maybe an indication of a perspective error?
I've seen these radiants before in large-scale images showing the universe around us, as mapped by various telescopes and satellites. It seems they are the result of looking out into the universe from our location here in a corner of one galaxy, with lots of intervening gas and dust, stars, clusters, nearby galaxies, and so on in our way. In other words, the radiants are not really lines of galaxies pointing at us; they're just the ones we can see and map. No doubt there are plenty of other galaxies in the areas between the radiants.

Or, I really am the center of the universe.

Rob
Rob, i vote for you being the center of the universe, although i donut know why.
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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by Guest » Thu Sep 11, 2014 1:44 am

Chris Peterson wrote:
Guest wrote:Any simulation of more than 2 massive bodies orbiting or similarly attracted to a single center of mass will clearly show that the 'system' of unstable and that massive acceleration forces are imposed on these objects. These objects (galaxies) will be ejected from the system with equally massive velocities (relative to mass) creating a galactic 'pin-wheel' effect of ginormous proportions over galactic time periods. How this can lead to an homogeneous environment when all but two (?) masses are ejected is problematical. Don't you think?
No. That's exactly how I'd describe homogeneous. Over time there is a loss of structure. (It's not a pinwheel; the distribution is essentially spherical, not planar.)
When simulated with thousands of given massive structures, virtually every massive object (galaxies) get ejected from the system at high speed. The remaining (typically) 2 most massive structures have a tendency to orbit around a common center of mass, but also the center of mass ends up with a direction and velocity that is derived from the ejection of other massive objects. Run some simulations and you will see. There is nothing homogeneous or spherical about the resulting model unless you consider a massive vast pinwheel of very fast outward moving objects to be somehow homogeneous or spherical. And yes, pinwheel is accurate. Math is a wonderful tool to model these things. Thankfully computers help in visualizing and understand the outcome.

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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by ianmacara » Thu Sep 11, 2014 2:04 am

Concerning the clear stripes of galaxies that appear to converge on the Milky Way - if this is an artefact caused by iimatedntervening dust, I would estimate that the actual number of galaxies within the volume of space included in this image is at least 100-fold the number shown as white dots. Is this compatible with the estimated total mass in this volume, assuming 5% baryonic matter?

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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by Nitpicker » Thu Sep 11, 2014 2:58 am

ianmacara wrote:Concerning the clear stripes of galaxies that appear to converge on the Milky Way - if this is an artefact caused by iimatedntervening dust, I would estimate that the actual number of galaxies within the volume of space included in this image is at least 100-fold the number shown as white dots. Is this compatible with the estimated total mass in this volume, assuming 5% baryonic matter?
Where are these clear stripes converging on the Milky Way? I take it you are not discussing the APOD, but some image within the links within the caption?

I watched a couple of the videos within the links. Some included details of the measurements (made from Earth, obviously) forming the basis of this delineation of Laniakea. It showed a 3-D graphic with Earth at the centre and a whole lot of streaks radiating to/from Earth. I interpreted the streaks as uncertainties in the distances of each cosmological object from Earth. But these streaks are not the model of Laniakea developed and shown in the APOD, which shows clearly that the Milky Way is on the outskirts.

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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by alter-ego » Thu Sep 11, 2014 3:40 am

ianmacara wrote:Concerning the clear stripes of galaxies that appear to converge on the Milky Way - if this is an artefact caused by iimatedntervening dust, I would estimate that the actual number of galaxies within the volume of space included in this image is at least 100-fold the number shown as white dots. Is this compatible with the estimated total mass in this volume, assuming 5% baryonic matter?
I'm not sure what you mean by the "clear stripes" either, but regarding the dot density and mass, I think the following is true based on what I've read:
The white dots represent distinct galaxies with distance, peculiar velocity and redshift data. There are about 8000 white dots. However Laniakea is estimated to contain ~100,000 (about 12x more dense then the white dots) with a combined mass of 1017M☉. The Milky Way's apparent mass is about 1012 M☉ so the contained baryonic mass and galaxy count estimates are consistent. I don't know how you estimated a 100-fold galaxy-to-white-dot ratio, but the published estimates are compatible with the 5% baryonic mass ratio.
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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by DougStern » Thu Sep 11, 2014 3:52 am

So if everything is migrating to the centre of the supercluster, what happens at the super cluster centre eventually?

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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by Ann » Thu Sep 11, 2014 4:07 am

Nitpicker wrote:On further reading, I've just learned that the Great Attractor -- http://en.wikipedia.org/wiki/Great_Attractor -- is the point to which everything in Laniakea is ultimately "falling" towards, as indicated by the "streamlines" in the APOD. (We are very much on the outskirts of Laniakea). The direction of the Great Attractor in our sky, is near the border of the southern constellations Triangulum Australe (TrA, The Southern Triangle) and Norma (Nor, The Carpenter’s Square).

Using The Pointers, Alpha and Beta Centauri (the two stars we southerners often use to find South on Earth), a line extending from Beta, through Alpha, will point to the Great Attractor, such that The Pointers lie roughly halfway between the Great Attractor and Crux.
The Great Attractor.PNG
Thanks, Nitpicker! I appreciate your helpful map! :D

I note that the colors of some of the Crux stars have been flipped. It's a problem only for Color Commentators.) :P

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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by alter-ego » Thu Sep 11, 2014 4:27 am

DougStern wrote:So if everything is migrating to the centre of the supercluster, what happens at the super cluster centre eventually?
What is at the "center" is not known. It's not clear that anything different happens if the center is reached. Keep in mind, the Laniakea watershed model displays boundaries as streamlines with cosmic expansion removed. While the animation shows streamline arrowheads all colliding and disappearing, nothing like that is occurring or will occur. Like a globular cluster, stars are orbiting and passing through the center without special events for the most part. On the scale of a supergalactic cluster, the dynamics are probably similar for galaxies (at least the ones that are already in the attractor "valley". Unlike globular clusters, whose spherical size is not affected by cosmic expansion, Laniakea will expand, changing the galactic density and times it takes for a specific member to reach a "center".

I think Laniakea's shape and size will change on the cosmic time scale, galaxies will get further apart on average, and what galaxies do swing through the attractor, things not change much. For static-sized Laniakea 160Mpc, a maximum member velocity ~15000km/sec, the one-way time to reach the center from the edge ~5 billion years, or about 1/3 the age of the universe.

You can see that the convergent streamlines that come to a sudden end in the animations don't correctly give you insight into the galactic dynamics of the cosmic future.
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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by Chris Peterson » Thu Sep 11, 2014 4:36 am

Guest wrote:When simulated with thousands of given massive structures, virtually every massive object (galaxies) get ejected from the system at high speed. The remaining (typically) 2 most massive structures have a tendency to orbit around a common center of mass, but also the center of mass ends up with a direction and velocity that is derived from the ejection of other massive objects. Run some simulations and you will see. There is nothing homogeneous or spherical about the resulting model unless you consider a massive vast pinwheel of very fast outward moving objects to be somehow homogeneous or spherical. And yes, pinwheel is accurate. Math is a wonderful tool to model these things. Thankfully computers help in visualizing and understand the outcome.
I'm not sure of your point. I agree, most of the mass gets ejected. Homogenized. But in the case of a supercluster, the end result isn't going to be just two galaxies. And there will be no pinwheel.
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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by Chris Peterson » Thu Sep 11, 2014 4:37 am

DougStern wrote:So if everything is migrating to the centre of the supercluster, what happens at the super cluster centre eventually?
I don't think everything is migrating to the center. This model identifies a center of attraction. That's a concept important to orbits.
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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by Nitpicker » Thu Sep 11, 2014 4:38 am

Ann wrote:
I note that the colors of some of the Crux stars have been flipped. It's a problem only for Color Commentators.) :P
Have they? I can't see which ones based on my own raw, RGB images of Crux. (The map was created with Stellarium.)

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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by Nitpicker » Thu Sep 11, 2014 4:47 am

alter-ego wrote:
DougStern wrote:So if everything is migrating to the centre of the supercluster, what happens at the super cluster centre eventually?
What is at the "center" is not known. It's not clear that anything different happens if the center is reached. Keep in mind, the Laniakea watershed model displays boundaries as streamlines with cosmic expansion removed. While the animation shows streamline arrowheads all colliding and disappearing, nothing like that is occurring or will occur. Like a globular cluster, stars are orbiting and passing through the center without special events for the most part. On the scale of a supergalactic cluster, the dynamics are probably similar for galaxies (at least the ones that are already in the attractor "valley". Unlike globular clusters, whose spherical size is not affected by cosmic expansion, Laniakea will expand, changing the galactic density and times it takes for a specific member to reach a "center".

I think Laniakea's shape and size will change on the cosmic time scale, galaxies will get further apart on average, and what galaxies do swing through the attractor, things not change much. For static-sized Laniakea 160Mpc, a maximum member velocity ~15000km/sec, the one-way time to reach the center from the edge ~5 billion years, or about 1/3 the age of the universe.

You can see that the convergent streamlines that come to a sudden end in the animations don't correctly give you insight into the galactic dynamics of the cosmic future.
Good comment. I found it very helpful. I suppose we could think of the model Laniakea as a snapshot in spacetime, of this portion of the universe, as it appears to us now. I imagine that over time, the centre of attraction may shift, as well as the streamlines and the boundary, and some bits may even be flung across the border, incoming and outgoing.

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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by Ann » Thu Sep 11, 2014 2:48 pm

Nitpicker wrote:
Ann wrote:
I note that the colors of some of the Crux stars have been flipped. It's a problem only for Color Commentators.) :P
Have they? I can't see which ones based on my own raw, RGB images of Crux. (The map was created with Stellarium.)
My semi-bad. :wink: All the colors are correct except that of Acrux, Alpha Crucis, an early B-type star which is quite blue in color.

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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by DavidLeodis » Thu Sep 11, 2014 7:43 pm

I get a distinct feeling that I may be the only person that does not understand what is going on in regard to this APOD :!: . My brain hurts :wink:. :cowboy: (I just like that latter smilie).

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Re: APOD: Laniakea: Our Home Supercluster of... (2014 Sep 10

Post by chuckster » Thu Sep 11, 2014 8:00 pm

What makes the galaxies move toward a "center" ? Doesn't gravity become a minor player over these distances, due to dark energy, dark matter and space expansion ? Intuitively, you'd think gravity is acting to bring things together, but hasn't that been proven to not be the case, over large distances ? Can the momentum from space expanding behind a cluster, as well as that left over from the Big Bang close the distance between it and another cluster faster than space expansion can increase the distance between them, or am I lost in circles, here ? Wouldn't be the first time. Dimbulb minds want to know !