Colliding Conceits (TPOD Nov 26, 2010)

[Nereid]

Colliding Conceits, TPOD Nov 26, 2010, by Mel Acheson

The ESO PR which this is based on does not mention any papers; however, it seems that the observations described in it formed the basis of a paper to be published (in MNRAS) by Li-Hsin Chien, Joshua Edward Barnes: "Dynamically-Driven Star Formation In Models Of NGC 7252" (link is to arXiv preprint abstract).

The abstract:

We present new dynamical models of the merger remnant NGC 7252 which include star formation simulated according to various phenomenological rules. By using interactive software to match our model with the observed morphology and gas velocity field, we obtain a consistent dynamical model for NGC 7252. In our models, this proto-elliptical galaxy formed by the merger of two similar gas-rich disk galaxies which fell together with an initial pericentric separation of ~2 disk scale lengths approximately 620 Myr ago. Results from two different star formation rules--- density-dependent and shock-induced--- show significant differences in star formation during and after the first passage. Shock-induced star formation yields a prompt and wide-spread starburst at the time of first passage, while density-dependent star formation predicts a more slowly rising and centrally concentrated starburst. A comparison of the distributions and ages of observed clusters with results of our simulations favors shock-induced mechanism of star formation in NGC 7252. We also present simulated color images of our model of NGC 7252, constructed by incorporating population synthesis with radiative transfer and dust attenuation. Overall the predicted magnitudes and colors of the models are consistent with observations, although the simulated tails are fainter and redder than observed. We suggest that a lack of star formation in the tails, reflected by the redder colors, is due to an incomplete description of star formation in our models rather than insufficient gas in the tails.

[MrAmsterdam]

By using interactive software to match our model with the observed morphology and gas velocity field, we obtain a consistent dynamical model for NGC 7252. In our models, this proto- elliptical galaxy formed by the merger of two similar gas-rich disk galaxies which fell together with an initial pericentric separation of ~2 disk scale lengths approximately 620 Myr ago.

This piece was written for a scientific audience, right?
As an average reader I would say that a gas state of matter has different properties then a plasma state of matter. Why don't the writers state it as such?

Its always the same reasoning; the cause why an astronomical object has the properties we see nowadays ALWAYS lies in the passed. To say it differently, the input energy of NGC 7252 lies in the passed - and not the present.

A plasma state of matter needs some kind of input energy at the moment we see it (in form of radiation or electric current, etc).

In general I would say using a computer model goes together with having a lot of assumptions which maybe true or not. Did this computer model as stated include the plasma state of matter?

[Nereid]

This piece was written for a scientific audience, right?

Yes; more specifically, those who read Monthly Notices of the Royal Astronomical Society (that's what MNRAS stands for), one of the few (~five?) astronomy/astrophysics journals most astronomers and astrophysicists aim to publish in if they can.

As an average reader I would say that a gas state of matter has different properties then a plasma state of matter.

As a general statement, I'd say the authors (Li-Hsin Chien and Joshua Edward Barnes) would agree with you.

Why don't the writers state it as such?

Probably because their readers (most of them anyway) would know what they meant.

In this case, they are using shorthand ("gas") for what they are representing in their "interactive software", which they describe in Section 2 of the paper; here's a fragment:

The total number of particles in each galaxy is 108544, broken down into 8192 bulge particles, 18432 disk particles, 32768 halo particles, and 49152 gas particles, which are evolved using a smoothed particle hydrodynamics (SPH) code.

Its always the same reasoning; the cause why an astronomical object has the properties we see nowadays ALWAYS lies in the passed. To say it differently, the input energy of NGC 7252 lies in the passed - and not the present.

I think, but am not sure, that the 620 Myr is an output of their simulation, not an input.

In general I would say using a computer model goes together with having a lot of assumptions which maybe true or not. Did this computer model as stated include the plasma state of matter?

A plasma, or even a gas, has many properties. In a computer model you have to choose which ones to include and which to ignore (or approximate with something simple).

Which properties of the plasma state do you think would be appropriate to attempt to model, for this particular astronomical object?

[Sparky]

Which properties of the plasma state do you think would be appropriate to attempt to model, for this particular astronomical object?

Why do you ask?Would you understand if told?..Apparently you do not understand anything about plasma instabilities, and have not picked up any information by just looking at the pictures at TPODS...Try reading them with an open mind to learning.

If you had, there is a short list of plasma state properties that are explained many times in the TPODS, and if you had any comprehension of what is being said you would not need to ask.

<<ad hom deleted - mod>> Conditions ,i suspect , brought on by your ideology.

You are obviously not here to learn, though it is obvious that your education is lacking or hampered by the same ideology that perverts your thinking.

If you really want to understand and acquire an education in plasma instabilities, read the TPODS and direct any questions in a non-deceitful way...

As for me, i have taken all the nonsense propaganda of the consensus cult that i will take, and if members of that cult want to teach me any nonsensical thing, they need to understand their logical weakness and lack of scientific method. If they can not admit the probability of being in error, i will not meet them half way.

I am attempting to unlearn all the nonsense that astronomers and theoretical astrophysicist are espousing.

People here are not in lock step, and this forum allows some hostility from those who's perspective is consensus backed. A generosity that i did not find at consensus forums....

So EXCUUUSE ME if i seem a bit grumpy at times with your deceitful posts...but i do look forward to your post as they are easy targets to play with...