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

Comments and questions about the APOD on the main view screen.
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Beyond
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Re: APOD: Galaxy Collisions: Simulation vs... (2013 May 14)

Post by Beyond » Wed May 15, 2013 3:07 am

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

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

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

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

Post 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.

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

Post 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?

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

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

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

Post 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.
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