APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

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Expand view Topic review: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by bystander » Wed May 15, 2013 5:20 pm

The Virgo Cluster, as well as the Local Group, are both part of the Virgo Supercluster. Superclusters consist of gravitationally bound clusters of galaxies and are among the largest known structures in the universe.

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by Anthony Barreiro » Wed May 15, 2013 5:15 pm

Psnarf wrote:Thank you for the additional information, of which I was unaware, Ensign NGC3314. Just trying to help keep Dr. Nemiroff within the bounds of scientific certainty. The Sloan Survey site also avoids the deduction that the null hypothesis is false.
"These new discoveries add weight to a picture in which galaxies like the Milky Way are built up from the merging and accretion of smaller galaxies." -From the "Field of Streams" site. Yes, the evidence appears to be growing that the proposition which implies that there is no relationship between the existence of measurable trails and galactic accretion is false, yet there may yet be other explanations for the data. If the jury is still out, we cannot proclaim that galactic accretion is the only explanation for what the data implies.
I think you're clinging too tightly to your logical positivism. If it looks like a duck, waddles like a duck, and quacks, it's probably a duck. When you find yourself getting too wrapped up in the null hypothesis, a sharp application of Occam's razor can cut you free.

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by Anthony Barreiro » Wed May 15, 2013 5:09 pm

Ann wrote:
Chris Peterson wrote:
Anthony Barreiro wrote:The light from a galaxy that is moving toward us will be shifted toward the blue end of the spectrum.
That's true, but outside the Local Group, I don't think there are any galaxies that are moving towards us. All other galaxies are redshifted.
That's not quite true, Chris. There are a few Virgo galaxies which are moving towards us because their internal movement in our directions inside the cluster is greater than the cluster's overall motion away from us. I believe that M90 is an example of such a blue-shifted Virgo galaxy.

Ann
Thanks Ann and Art for reminding me that there are Virgo cluster galaxies moving toward us. Given that the Virgo cluster is "only" 50 million light years distant, this is still close enough for local gravitational effects between nearby galaxies to exceed the overall expansion of the universe. It's pretty cool to have a context in which 50 million light years is a short distance!

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by Psnarf » Wed May 15, 2013 3:04 pm

Thank you for the additional information, of which I was unaware, Ensign NGC3314. Just trying to help keep Dr. Nemiroff within the bounds of scientific certainty. The Sloan Survey site also avoids the deduction that the null hypothesis is false.
"These new discoveries add weight to a picture in which galaxies like the Milky Way are built up from the merging and accretion of smaller galaxies." -From the "Field of Streams" site. Yes, the evidence appears to be growing that the proposition which implies that there is no relationship between the existence of measurable trails and galactic accretion is false, yet there may yet be other explanations for the data. If the jury is still out, we cannot proclaim that galactic accretion is the only explanation for what the data implies.
Aside: the vast distances between identifiable objects in both galaxies makes it unlikely that any stars collide as they pass by, but what about the central black hole? The source of the gravitational attraction between two galaxies doesn't appear to be the stars, but their central cores. Wouldn't the distance between the cores of the Andromeda Galaxy and the Milky Way, for example, vary as a decaying sinusoidal dance until they eventually joined when they got close enough?

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by NGC3314 » Wed May 15, 2013 12:54 pm

Psnarf wrote:The Explanation contains "...Milky Way Galaxy has absorbed several smaller galaxies..." however, the referenced http://apod.nasa.gov/apod/ap080619.html states that the evidence "supports the cosmological scenario...." It is not necessarily a fact that our galaxy has absorbed several smaller galaxies, just that observations of other galaxies support that scenario. It is highly probable, the possibility exist, but we have yet to find any evidence to support that statement with regard to the Milky Way.
There is a subtle difference between a statement of fact and scientific observations that support a scenario.
There is very strong evidence that we see remnants of small galaxies which have suffered a hostile takeover by the Milky Way. The Sagittarius dwarf irregular galaxy is tidally stretched into a very elongated form by the tides of our Galaxy, and the ability to sort stars in distant parts of the Milky Way by distance and chemical makeup has revealed multiple narrow streams of distinct stars such as would result from assimilation of dwarf galaxies into the larger Milky Way (much like we can see in some other galaxies). These are probably best shown in the "Field of Streams" graphic produced from data in the Sloan Digital Sky Survey. It takes many orbits for the stars in a dwarf to completely mingle with the halo of the Milky Way, so these streams can remain identifiable for billions of years.

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by neufer » Wed May 15, 2013 12:18 pm

ta152h0 wrote:
there is no mathematics in economics, you can see that bs mountain from space it is so big.
Click to play embedded YouTube video.
Click to play embedded YouTube video.

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by ta152h0 » Wed May 15, 2013 9:37 am

there is no mathematics in economics, you can see that bs mountain from space it is so big.

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by OzRattler » Wed May 15, 2013 5:14 am

tannaberton wrote:But if everything is flying apart how can they collide?
It is a bit like watching your house burn down as it goes up in smoke...... :wink:

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by neufer » Wed May 15, 2013 2:23 am

Chris Peterson wrote:
Guest wrote:
If we folks are this clever, how is it we can do this for galaxies but not our planet's economy ?
Because the mathematics behind galaxy collisions is much, much simpler than that behind even local economics, let alone the world economy.
http://danbunting.wordpress.com/2012/04/02/sentencing-lies-damned-lies-and-laffer-curves/ wrote:
Sentencing, Lies, Damned Lies and Laffer Curves
by Dan BUnting, April 2, 2012

<<The basic idea of the Laffer Curve is that there is a nice smooth curve of tax rate and revenue return. At the extremes this makes sense. If you are taxed at 1% then increasing it to 2% isn’t going to make any difference to the amount people work, so the tax take by the government goes up. Clearly, if you tax at 100% and then reduce it, the amount of tax the government gets goes up.
ImageImage
So far, so good. The problem is that then people move to say that there is an ‘optimum tax rate’ ie, that there is level of tax where reducing the tax rate can counter-intuitively increases the tax take. So does it work in real life?
Basically, no. It is rubbish. Martin Gardener did an excellent demolition job on it shortly after it was first thought up, coming up with his ‘Neo-Laffer Curve’. The assumption, that the curve is smooth with one only one peak, is clearly wrong and there are many other factors at play. It also assumes that all people are completely economically rational, and the only thing that they care about is money.

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by Chris Peterson » Wed May 15, 2013 12:58 am

Guest wrote:If we folks are this clever, how is it we can do this for galaxies but not our planet's economy ?
Because the mathematics behind galaxy collisions is much, much simpler than that behind even local economics, let alone the world economy.

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by Guest » Wed May 15, 2013 12:50 am

If we folks are this clever, how is it we can do this for galaxies but not our planet's economy ?

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by neufer » Wed May 15, 2013 12:18 am

Chris Peterson wrote:
Anthony Barreiro wrote:
The light from a galaxy that is moving toward us will be shifted toward the blue end of the spectrum.
That's true, but outside the Local Group, I don't think there are any galaxies that are moving towards us. All other galaxies are redshifted.
http://en.wikipedia.org/wiki/Messier_86 wrote: <<Messier 86 (distance: 52 Mly) is an elliptical or lenticular galaxy in the constellation Virgo. It was discovered by Charles Messier in 1781. M86 lies in the heart of the Virgo Cluster of galaxies and forms a most conspicuous group with another giant, Lenticular Galaxy M84. It displays the highest blue shift of all Messier objects, as it is approaching the Milky Way at 244 km/s. This is due to its falling towards the center of the Virgo cluster from the opposite side, which causes it to move in the direction of the Milky Way.

Messier 86 is linked by several filaments of ionized gas to the severely disrupted spiral galaxy NGC 4438 and shows some gas and interstellar dust that may have been stripped, as well as the gas on those filaments, of it. It's also suffering ram-pressure stripping as it moves at high speed through Virgo's intracluster medium, losing its interstellar medium as it moves through it leaving behind a very long trail of hot gas.

Messier 86 has a rich system of globular clusters, with a total number of around 3,800. Its halo also has a number of stellar streams interpreted as remmants of dwarf galaxies that have been disrupted and absorbed by this galaxy.>>

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by Ann » Wed May 15, 2013 12:13 am

Chris Peterson wrote:
Anthony Barreiro wrote:The light from a galaxy that is moving toward us will be shifted toward the blue end of the spectrum.
That's true, but outside the Local Group, I don't think there are any galaxies that are moving towards us. All other galaxies are redshifted.
That's not quite true, Chris. There are a few Virgo galaxies which are moving towards us because their internal movement in our directions inside the cluster is greater than the cluster's overall motion away from us. I believe that M90 is an example of such a blue-shifted Virgo galaxy.

Ann

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by Anthony Barreiro » Tue May 14, 2013 11:41 pm

Chris Peterson wrote:
Anthony Barreiro wrote:The light from a galaxy that is moving toward us will be shifted toward the blue end of the spectrum.
That's true, but outside the Local Group, I don't think there are any galaxies that are moving towards us. All other galaxies are redshifted.
Thanks Chris. This illustrates the general point that distant galaxies are moving apart from one another due to cosmic expansion, while galaxies that are close to one another, like those in our own little local group of 40 galaxies, can move toward one another because of gravitational attraction.

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by Chris Peterson » Tue May 14, 2013 10:50 pm

Anthony Barreiro wrote:The light from a galaxy that is moving toward us will be shifted toward the blue end of the spectrum.
That's true, but outside the Local Group, I don't think there are any galaxies that are moving towards us. All other galaxies are redshifted.

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by Anthony Barreiro » Tue May 14, 2013 7:27 pm

tannaberton wrote:But if everything is flying apart how can they collide?
The entire universe is expanding, so galaxy clusters at great distances from one another are moving apart from one another, as evidenced by the fact that the farther a distant galaxy is from us, the more its light is shifted toward the red end of the spectrum. But within this cosmic expansion, gravity still works over closer distances, so galaxies that are close to one another often become gravitationally attracted to one another and fall into one another's arms, as shown in the video. The light from a galaxy that is moving toward us will be shifted toward the blue end of the spectrum.

As mentioned in the caption, our Milky Way galaxy and the nearby Andromeda galaxy ("only" 2.5 million light years away) are falling toward one another and will merge in about 5 billion years.

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by Anthony Barreiro » Tue May 14, 2013 7:04 pm

This is impressive and beautiful. A couple of thoughts:

The overall shapes of the simulation resemble those of the photographed galaxies, but all the real galaxies seem to have much broader and more diffuse halos of stars and gas than is shown in the simulation. I wonder how many more ones and zeros it would take to simulate the halos.

I'm also curious how much dark matter had to be factored into the simulation to get it to work like the real thing.

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by Borc » Tue May 14, 2013 6:28 pm

One of the things about APOD and astronomy in general that astounds me is that we can make a short video that contains a few galaxies. Contained within the video are trillions of stars and maybe trillions or hundreds of trillions of species. How wondrous and magnificent is our universe?!
Beautiful sim with exceptional accuracy. The individuals involved in this project are amazing.

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by Star Splatter* » Tue May 14, 2013 3:43 pm

Speaking of vast crashes, here's a fun toy --- http://burro.cwru.edu/JavaLab/GalCrashWeb/main.html

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by ta152h0 » Tue May 14, 2013 3:05 pm

the epic battle Godzilla vs Mothra

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by Psnarf » Tue May 14, 2013 3:02 pm

The Explanation contains "...Milky Way Galaxy has absorbed several smaller galaxies..." however, the referenced http://apod.nasa.gov/apod/ap080619.html states that the evidence "supports the cosmological scenario...." It is not necessarily a fact that our galaxy has absorbed several smaller galaxies, just that observations of other galaxies support that scenario. It is highly probable, the possibility exist, but we have yet to find any evidence to support that statement with regard to the Milky Way.
There is a subtle difference between a statement of fact and scientific observations that support a scenario.
--
Obquote: "Dammit Jim, I'm a proofreader, not an editor!" - Dr. McCoy (attrib)

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by metamorphmuses » Tue May 14, 2013 12:28 pm

Great video! I assume the simulation is a result of a highly refined algorithm that, once ready, they simply "turned on" and "let run" without interference. In that case, getting such a close match between the model and the documented observations must be very difficult and is to be commended...

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by Berjerac » Tue May 14, 2013 12:12 pm

the algorithm seems to be sufficiently accurate to enable simulation and study of binary planet systems in which primary and secondary bodies orbit each other sufficient close that both planets are locked in synchronous orbit about each other. on such a planetary system, the same side of both planets would permanently face the same side of the other. pluto and its moon are an example for such a case. however, earth-sized terrestrial planets in the goldilocks zone are to be studied. a geo-mechanical question involving such system: what is the nearest that the two bodies can occur while retaining a perfectly spherical shape (without distortion).
an algorithmic example of such a system:
primary: mass 4.5x10e21 ton ; diameter 11900 km
secondary: mass 5.3x10e20 ton ; diameter 5500 km
distance between primary and secondary: 75000 km
distance of binary planet to parent star: approximately 191 million km
mass of parent star: 0.91 sun ; spectral class of star: G

in fact, binary planetary systems such as this ought to be very common. one aspect of such a system is that both planets should be endowed with a substantial atmosphere. another aspect is that the north-south polar alignment of each planet should be magnetically and geometrically linear ( n-s - - - n-s). this would imply that the region in which each planet faces the other would be characterized by substantial aurora.
artists of fantasy planets have been speculating about binary systems in their work. their portrayal of 'fantasy' alien planets may not be such a fantasy.

Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

by Sadderday » Tue May 14, 2013 11:06 am

Um.... yes, what is a das cloud?

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