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deSitter
Still in Old School


Reged: 12/09/04

Galactic evolution
      #5914335 - 06/10/13 11:54 PM

http://en.wikipedia.org/wiki/File:Hubble_sequence_photo.png

Pretty sad eh? Not much advanced from Air Earth Fire Water.

-drl


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Jarad
Postmaster
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Reged: 04/28/03

Loc: Atlanta, GA
Re: Galactic evolution new [Re: deSitter]
      #5914581 - 06/11/13 07:00 AM

That page is just the classifications.

While I agree that we have a lot to learn about galaxy evolution, at least point to a page that has a bit more info:
http://en.wikipedia.org/wiki/Galaxy_evolution

Jarad


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Ira
Carpal Tunnel
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Reged: 08/22/10

Loc: Mitzpe Ramon, Israel
Re: Galactic evolution new [Re: Jarad]
      #5914814 - 06/11/13 10:48 AM

Since we can now look back into space about 11 billion years, why do we not actually see galactic evolution ocurring at different distance/time scales?

/Ira


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Jay_Bird
Carpal Tunnel
*****

Reged: 01/04/06

Loc: USA
Re: Galactic evolution new [Re: Ira]
      #5914939 - 06/11/13 12:06 PM

I think that we DO see signs of galactic 'evolution' Ira, in the non-biological sense that word is used to describe say, landforms changing over time in response to ongong processes.

The wikipedia link Jarad posted is very good

Deepest imaged fields are 13+ Billion LY

That's 25 times the multicellular fossil record duration (and close to 3 times age of earth itself) so the galactic evolution dots to connect are farther apart compared to the record of life that we might think of as an analogue, and the galactic changes superficially seem more subtle in comparison.

Some things galaxies seem to be doing over time:

+ forming rapidly in early universe

+ getting bigger by collision or accretion

+ forming lots of disk or spiral galaxies - is why disks predominate not fully understood?

+ forming more and larger ellipticals over time by collision

+ galaxy clusters are still gravitationaly bound and coalescing, colliding, interacting in our era

+ maybe central black holes, which seem pretty ubiquitous, are changing over time too, active or quiet, or growing by collision as well?


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Ravenous
sage


Reged: 11/14/09

Loc: UK
Re: Galactic evolution new [Re: Jay_Bird]
      #5914973 - 06/11/13 12:27 PM

Quasars are invariably both ancient and distant too, as far as I can remember. A classic example of galaxy evolution.

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davidpitre
Post Laureate
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Reged: 05/10/05

Loc: Central Texas
Re: Galactic evolution new [Re: Ravenous]
      #5915336 - 06/11/13 03:57 PM

Though Edwin Hubble originally seemed to have thought his classification scheme represented a temporal evolution, it has been recognized for around 90 years that his scheme does not relate to galaxy evolution. Though the terms "early" and "late" are still used, they are not in an evolutionary context.

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deSitter
Still in Old School


Reged: 12/09/04

Re: Galactic evolution new [Re: davidpitre]
      #5915402 - 06/11/13 04:35 PM

There is no theory of galactic evolution. There are stupid collision models based on wrong linear computer models. No one has thought seriously about it or published anything serious in decades. Those who would try are hounded out of the clergy.

-drl


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Joad
Wordsmith
*****

Reged: 03/22/05

Re: Galactic evolution new [Re: deSitter]
      #5915425 - 06/11/13 04:51 PM

"There is no theory of galactic evolution."

Here's one.

"There are stupid collision models based on wrong linear computer models."

In other words, there are some theories but you don't like them.

"No one has thought seriously about it or published anything serious in decades."

"Serious" and "seriously" are qualifiers, which simply indicate that you are dismissing all the thinking and publishing about this subject on the basis of your own personal insistence.

"Those who would try are hounded out of the clergy."

This is unsupported. Why not tell us exactly what has happened to you, and others, in specific and verifiable detail so your audience can make an independent judgment of your assertions.






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llanitedave
Humble Megalomaniac
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Reged: 09/26/05

Loc: Amargosa Valley, NV, USA
Re: Galactic evolution new [Re: Joad]
      #5915515 - 06/11/13 05:33 PM

I wouldn't normal agree with asking for personal experiences, but Danny, you have made every single one of your assertions, opinions, and critiques here personal. You've either lionized or demonized every scientist in the business, seemingly making your personal character assessments supercede any data -- or lack of it.

Rarely do we get an objective analysis from you. It's all about the saints and the satans.

And that's just not scientific thinking.


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Ravenous
sage


Reged: 11/14/09

Loc: UK
Re: Galactic evolution new [Re: llanitedave]
      #5916370 - 06/12/13 05:41 AM

First: bear in mind when Mr Hubble proposed this classification, there wasn't even direct evidence what galaxies were. They were thought by many to be "nebulae" not even independent from our our own island galaxy.

Second: based on the above, it was certainly not intended as a proposed evolution.

Third: He was trying to find a good way to classify the structure of these things, whatever they were, for reasons of doing bulk statistics. There was a letter to the RAS I think (sorry I don't have a reference) where he tried to clarify it all, between the lines acknowledging it was all a bit rough and ready. Fascinating reading. Interesting that his first provisional stab at characterising the main features has held for so long.

Fourth: no doubt the current computer simulations/models of galaxy behaviour (evolution and/or collision) will one day be regarded as naive, and there are surely bits missing, but at the moment they're quite useful. Trashing them isn't.


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deSitter
Still in Old School


Reged: 12/09/04

Re: Galactic evolution new [Re: Joad]
      #5916864 - 06/12/13 12:24 PM

Quote:

"There is no theory of galactic evolution."

Here's one.

"There are stupid collision models based on wrong linear computer models."

In other words, there are some theories but you don't like them.

"No one has thought seriously about it or published anything serious in decades."

"Serious" and "seriously" are qualifiers, which simply indicate that you are dismissing all the thinking and publishing about this subject on the basis of your own personal insistence.

"Those who would try are hounded out of the clergy."

This is unsupported. Why not tell us exactly what has happened to you, and others, in specific and verifiable detail so your audience can make an independent judgment of your assertions.









I'm just not going to accept a computer model that is almost surely wrong in principle even from the very naive standpoint of only using gravity as the driving force, as a "theory". A theory of galactic evolution would stretch from gas to arms or gas to elliptical halo or whatever. You would not need to even worry about dark matter because that is already a plain error (Cooperstock). I will also point out that there is not even a theory of globular cluster evolution.

What we have is a naive description based on the assertion that GR is absolutely correct as it stands, that plasmas and magnetic fields and other large-scale electrodynamic phenomena are irrelevant, and even then, that a linear model for GR is right. This isn't a theory, it's fancy taxonomy based on half-baked assertions.

-drl


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Jarad
Postmaster
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Reged: 04/28/03

Loc: Atlanta, GA
Re: Galactic evolution new [Re: deSitter]
      #5917266 - 06/12/13 04:03 PM

Well, I agree that at this point in its development we have more of a set of hypotheses than a cohesive theory.

But I disagree that it is as bad as you seem to think. Yes, the hypotheses so far are based primarily on gravity and ignore electromagnetic effects. But those aren't unreasonable assumptions - the net charge of objects at large scale tends to be close to 0. And while we can see intense local magnetic fields, magnetic field strength drops of with the cube of distance vs. the square for gravity, so again at large scales gravity will dominate.

I think plasma currents and magnetic effects are probably important in terms of stellar collapse in supernovas, and in the behavior of accretion disks and jets, and I think those explosions and jets are probably important to early galaxy development, so I agree they probably have important indirect effects that still need to be explored. But it's not easy to take measurements of those things over great distances, and it's hard to develop good theories on them in the absence of data.

We still have lots to learn, I just think it would be more productive to pick a piece and work on it than to point out that we still have lots to learn. Especially if you point it out in a less than diplomatic fashion - that tends to make people stop listening...

Jarad


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Classic8
professor emeritus


Reged: 04/12/06

Loc: Naperville, IL, USA
Re: Galactic evolution new [Re: Jarad]
      #5917706 - 06/12/13 08:53 PM

This is a somewhat different question, but is there any discrepancy between the level of organization of galaxies and how much time they needed to form, according to current models? Is dark matter required for them to have formed as quickly as they did?

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Joad
Wordsmith
*****

Reged: 03/22/05

Re: Galactic evolution new [Re: Classic8]
      #5917792 - 06/12/13 09:42 PM

Danger, Will Robinson!

Let's put it this way: the reason why astrophysical theory appears to have stalled is not because of some conspiracy on the part of physicists, nor because physicists today are stupid or venal or anything of the sort, but because technological advances in the past couple of decades have triggered an avalanche of data that have never before been available. Those data have presented problems and have left a lot of unanswered questions. Two of those unanswered questions involve apparent (please note the word "apparent") universal expansion beyond what would be expected according to current understanding, and various observed phenomena that appear to require a lot more gravitational mass than can be observed. Not yet knowing for certain what is behind such observations, physicists have coined the terms "dark energy" and "dark matter," in a gesture of humility. I have seen Cal Tech physicists themselves note, with humility, just how little they know.

So my point is that it probably isn't a good idea to base a theory of anything based upon "dark matter" until "dark matter" ceases to be dark and is fully understood or discredited.


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sirchz
super member


Reged: 09/21/09

Re: Galactic evolution new [Re: Jarad]
      #5918793 - 06/13/13 01:28 PM

Quote:

Yes, the hypotheses so far are based primarily on gravity and ignore electromagnetic effects. But those aren't unreasonable assumptions - the net charge of objects at large scale tends to be close to 0. And while we can see intense local magnetic fields, magnetic field strength drops of with the cube of distance vs. the square for gravity, so again at large scales gravity will dominate.




Just a comment that charge neutrality doesn't imply electromagnetic effects aren't important. I'm not saying they are important, just that this argument doesn't really justify neglecting them.

If applied to a Hydrogen atom it would say that electromagnetic effects can be ignored, but we know they are very important.

Plasmas are quasi neutral by definition and electromagnetism drives their properties and behavior.


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Jarad
Postmaster
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Reged: 04/28/03

Loc: Atlanta, GA
Re: Galactic evolution new [Re: sirchz]
      #5918899 - 06/13/13 02:21 PM

Quote:

If applied to a Hydrogen atom it would say that electromagnetic effects can be ignored, but we know they are very important.





Depends on what you are calculating about the hydogen atom and what scale they are on. Eletromagnetic effects are very important in determing chemical reactions with the hydrogen atom, but those happen at the atomic scale where separation of charge is significant. In terms of calculating the attraction between one hydrogen atom and a second one a few meters away in a vacuum, we can neglect the electrmagnetic effect and only consider gravity.

On a more macro level, van der waals forces are electromagnetic, and are quite important for how two materials in close contact react with each other (how sticky they are, how much friction, etc.). But again, they have zero impact on how two bodies orbit each other in space.

Quote:

Plasmas are quasi neutral by definition and electromagnetism drives their properties and behavior.




So that brings us to the question of scale again. We know there are plasma currents within stars, for example. And we are pretty confident about them in accretion disks. But do we have any evidence of them on a galactic scale? Not that I am aware of.

So rather than complain about lack of plasma and magnetic effects in the model, perhaps it would be more productive to think about how we would detect such effects if they really exist. Then we can get some useful data to help develop a better theory.

Jarad


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Joel F.
Pooh-Bah
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Reged: 03/19/06

Loc: Overland Park, Kansas
Re: Galactic evolution new [Re: Jarad]
      #5919209 - 06/13/13 05:40 PM

Perhaps the most complee reference to dat on galaxy evolution is the book "Galaxy Formation and Evolution" by Houjun Mo, Frank van den Bosch, and SimonWhite published in 2010 (with 820 pages).

However, it may already be out of date. In the 2012 issue of Annual Reviews of Astronomy and Astrophysics there is an article on hot galactic halos at perhaps one million degrees. Thus therare plasmas and at that temperatue have significant currents. A bit latter an article was published in which there may be some evidence of very significant baryonic mass in these halos.

It is also important torealize that galaxies do have magnetic fields. Also, a hydrogen atom has a magnetic moment, but a hydrogen molecule does not. Thus, the hydrogen atoms ten to be polarized and held in place by these magnetic fields. However, the hydrogen molecule is more easily displace by a disturbance.


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Neutrino?
sage
*****

Reged: 12/14/09

Loc: Wasatch Front
Re: Galactic evolution new [Re: Classic8]
      #5919266 - 06/13/13 06:12 PM

Quote:

This is a somewhat different question, but is there any discrepancy between the level of organization of galaxies and how much time they needed to form, according to current models? Is dark matter required for them to have formed as quickly as they did?




Yes. Without it, the epoch of the formation of galaxies would have started later and thus would not match current observation.


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Joad
Wordsmith
*****

Reged: 03/22/05

Re: Galactic evolution new [Re: deSitter]
      #5919411 - 06/13/13 07:35 PM

"You would not need to even worry about dark matter because that is already a plain error (Cooperstock)."

Sorry, but that cannot be allowed to stand on a science forum. I've done some research on F.I. Cooperstock with regard to his alternative ideas about using GR, rather than Newtonian physics, to calculate galaxy rotation figures.

First, he is a bona fide astrophysicist; his papers have been accepted for publication in peer reviewed publications; and, all in all, he (along with his major co-author) has some very interesting ideas. Because of this he has been taken seriously, and other astrophysicists have assessed his conjecture, and, especially in a paper referring to measurements within the Milky Way galaxy, they have refuted his conjectures in a way that the scientific community has accepted (given the silence on Cooperstock's work since about 2007).

This is not to diminish Cooperstock's intelligence, ability, or sincerity in the least. It sounds like he has been doing good theoretical science, just as it should be done. But he hasn't done away with dark matter.

This is all made clear by a review of papers at Cornell University's arXiv.org.


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sirchz
super member


Reged: 09/21/09

Re: Galactic evolution new [Re: Jarad]
      #5920619 - 06/14/13 01:42 PM

Quote:

So rather than complain about lack of plasma and magnetic effects in the model, perhaps it would be more productive to think about how we would detect such effects if they really exist. Then we can get some useful data to help develop a better theory.




I don't disagree and would be surprised if E&M effects were critically important. They may play some role, but for now ignoring them seems reasonable to me. I was merely being pedantic.


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