Great Rotating Galaxies!!

Factual Questions
1

Here is a very slow loading picture, called The Hubble Deep Field.

Aside from being a mind boggling example of just how big the universe is, it causes me to wonder about a bit of scientific knowledge I had taken for granted. Galaxies spin, like just about everything else that exists, from electrons, to bosons, to little kids in playgrounds. Planets, stars, moons, and even superclusters spin. There is a whole bunch of arcane mathematics about orbital mechanics to explain why, and how the organization of spinning clouds of condensing matter come to resemble spirals. Fine. I got that. But now for my niggling little question.

The spiral galaxies in the picture are a long way off. Four or five billion light years away, and therefore four or five billion years old. And they seem much like the ones “nearby” like the Nebula in Andromeda or the description of the Milky Way itself. Now, all that organizing is certainly understandable in the mechanics of whirling pools of contracting gasses, and angular momentum exchanges, and such. Except the Milky way, and the Nebula in Andromeda are whirling around at the frantic pace of . . . wait for it. . . keep waiting

. . . no, really keep waiting. . . about four times every billion years. That gives us about forty-eight total revolutions since the big bang. Those galaxies in the Hubble Deep Field can’t have had even that many, more like Twenty-five or Thirty.

Worse yet, four RPB represents the final spin rate for the collapsed aggregate of stars falling into the spiral. The original cloud was much more leisurely, as an inescapable consequence of the same mechanics that are supposed to make the whole thing spin. At least half the revolutions had to come in the last quarter of the galaxy’s life time, after it was already collapsed to its current general size. Those distant spirals had to have become organized into disks in less than fifteen revolutions. My credulity begins to stretch. These whirling clouds of gas have to have some other mechanism acting to create those characteristics in that amount of time.

So, is anyone up to the task? Knowing your ass from a hole in the ground would be a good start, astrophysically speaking. Not that I wouldn’t enjoy hearing your responses on a golly gee basis, if you prefer the karma is karma type of explanation. I am genuinely perplexed by this one.

Tris

Imagine my signature begins five spaces to the right of center.

2

Since you haven’t given an example of such a characteristic, I cannot explain how it could have developed within some given time frame. That being said, I’ll try to tackle your question from the opposite direction — the galaxies are not in the shape we perceive them to be in.

I’m sure you’ve heard of dark matter before, and how the majority of mass within galaxies and the universe are attributed to them. Astronomers actually discovered dark matter by observing the rotation of galaxies. Through various calculations and additional observations, they have also determined that this dark matter must permeate and surround each galaxy in a huge spherical distribution, known as a galactic halo. The size of our Milky Way is often described as spanning 100,000 light years in diameter. If the galactic halo were to be taken into account however, the figure would likely rise by a factor of 5. What I am trying to get at here is that the shiny spirals and disks you often see in photographs are hardly the entirety of a galaxy. A disk at the center of a galaxy can pretty must just pop into existence since that’s where all the star formation activity is. Spirals will quickly appear afterwards because matter that is closer to the center of the galaxy will complete their orbits faster than those farther out. The existing stars and matter will congregate into the spiral, while new starts keep popping into them. I wouldn’t be surprised if it only took a few rotations of the main disk to form a distinguishable spiral. This here, also happens to bring on another issue. Saying that a galaxy completes one revolution for every quarter billion years is quite meaningless. You can only ascribe a period of rotation to some object that is a certain distance away from the center of the galaxy.

3

Last I had heard, even the spiral galaxies are basically disks. The spaces between the “arms” are almost as thick with matter as the arms themselves. The arms just represent (basically) the crest of a compression wave that causes a lot of bright young stars to form. These burn out quickly, but the material stays in place for the next round of compression into bright stars.

You may all now laugh amongst yourselves at my ignorance of stellar mechanics…

Dr. Fidelius, Charlatan
Associate Curator Anomalous Paleontology, Miskatonic University
Projector Emeritus, Grand Academy of Lagado
“You cannot reason a man out of a position he did not reach through reason.”

4

You’re actually quite correct, DrFidelius :slight_smile:

5

That really doesn’t answer my question which is not whether there is a spiral rather than disk shape, but how gravity alone could have imposed either shape in the time since the formation of matter. However, a very good web lecture series on Cosmology I found helped. The portion relevant to this question starts with this page and is fairly easy to understand. Page two is missing, but the series starts with a History of Cosmology and then goes onwith the underlying science in layman’s terms.

Basically my suspicions was correct, gravity alone is insufficient as a causal mechanism. The original material of formation was already separated into sheets, and clumps, and the forces organizing it include the ionization of the gas, acceleration by photonic pressure, and collisions among elements within the cloud. The primordial asymmetric distribution of matter itself is part of the conditions necessary for formation of galaxies.

Of course now I have half a dozen new questions, to replace my original one, but hey, that’s progress.

Response frequency to the topic thus far bodes ill for much more in the way of discussion, but I do thank you gentlemen for your responses. This stuff fascinates me beyond description. Having the Hubble is like peering over God’s shoulder.

He does nice work. (and so much of it!)

Tris

Imagine my signature begins five spaces to the right of center.

6

I do believe that there is a BIG black hole at the center of these spiral galaxies, a resultant of ancient, massive, hydrogen, 1st generation stars (our star is probibly 3rd generation).

If at first you don’t succeed you’re about average.

7

Not to sound confrontational, Tris, but I couldn’t find anything on those links you’ve provided that confirm your suspicions. If your question was just how gravity could’ve acted so quickly, the answer is fairly straight forward — it just does :stuck_out_tongue:

The disks and spirals you see are only the visible stars within a galaxy. Stars only form when you have enough matter congregating into one place, and that naturally happens at the center of a galaxy where all the matter is being pulled to. The spiral arms, as **DrFidelius ** has mentioned, are also places where lots of matter congregate and new stars tend to form. I’m not sure, but in a sense, you seem to be making this harder than it really is :wink:

8

Lecture number 24 was the specific part that mentioned the development of structure.

On rereading it, I realize that there were other sources for some of my recent learning, which came from the same set of searches, such as “Three-Dimensional Hydrodynamical Calculations on the Fragmentation of Pancakes and Galaxy Formation” I am currently wading through this, and several other treatises on the subject. It will take me a while to get up to speed, since I have to follow about half the links defining term in most of the stuff I am reading, due to holes in my education.

But, not to sound confrontational, or anything, no, gravity just doesn’t. The answer, or what is known of it turns out to be rather complex. Big surprise. The clumps of matter in the earliest history of the universe did not get that way because of gravity. I am still a bit vague on just what did bring about the sheeting, and fragmenting of the baryon cloud as it expanded, but that feature itself imprinted on the subsequent development very strongly. The influx of kinetic energy from Hawking Radiation might well be a factor, as well, if the primordial mix includes large black holes. Then there is the ionization of gases, and the resulting heating as stellar formation begins, which also has an effect.

A large portion of new information awaits me. I cannot pretend that complete understanding of even that part widely accepted by the scientific community is likely to be mastered by so poor a scholar as myself, but the journey is the destination, in some things.

Tris

Imagine my signature begins five spaces to the right of center.

9

So, according to you, the distance a galaxy is away from us tells us the age of that particular celestial body? Oooops, I think not.

If it worked that way, then, our own galaxy would be subjected to the same treatment, wouldn’t it?

You assume (according to your math [48 spins, at 4 spins per billion years]) that our galaxy is 12 billion years old. Is that because we are 12 billion light years away from… who???

Just because these galaxies are 4 or so BLY away from us doesn’t mean they aren’t older. Am I wrong?

Saludos.

10

Sorry, Eskeptic, that was poorly worded.

The image is what is four billion years old, not the galaxies. The 12 billion year figure for our galaxy is a median figure among the choices for the time since the big bang, generally quoted in my sources as between 9 and 15 billion years as extreme limits, depending on who’s experimental data, and projections you like at the moment. So, I subtracted the four billion years for the age of the image, from the twelve billion years for the age of the universe, and got an estimate of 8 billion years for the age of the galaxies as they appear in the image. Now, all the figures are profoundly approximate, and the point of my inquiry was not that the age of the was precisely any particular amount, but that the similarity over a period believed to be a third of the total duration of the phenomenon of existence was curious.

The mechanics of a gravity only etiology for the formation seemed inadequate, given the images I was seeing. It is not a rigorous analysis, I realize, but a gut level reaction. That reaction sent me on the search and discover mission which currently occupies me. As I mentioned above, in my reply to Zor, the answer is exceedingly complex, but does include many other factors than gravity alone. I am only today beginning to understand how many factors that is.

Sorry for the poorly worded “explanation” which caused your confusion.

Tris

11

Here’s what’s really interesting to me: The stars seem to be rotating about the center at basically the same speed, regarless of their distance.

This is unlike smaller models, where the farther out an object is, the slower the orbit.

12

Yes, that precise factor has come up over and over in my recent searches. The mechanics of galaxy rotation seems to be the root problem behind the search for “dark matter” and other explanations for the “missing mass” of the universe.

This article describes a few of the candidates for the missing mass, (or missing light, as it points out). It is sprinkled with mathematics, but at this level of inspection you have to deal with that. It also mentions cosmic strings, and primordial black holes. I had not realized that Hawking Radiation should have “evaporated” primordial sized black holes in only 12 billion years. I guess they do build ‘em like they used to!

I have spent half my vacation wandering the universe by web proxy. Do I have a life, or what?

Tris

Imagine my signature begins five spaces to the right of center.

13

Yes, that’s a sign that the mass around which the stars are orbiting is distributed rather than localized. If most of the mass were at the center of the galaxy (say, just for example, in a big black hole) then the stars’ orbits would be “Keplerian” and the periods would depend on the distance from the center.

If, however, the mass is distributed roughly evenly through space, then the inner stars would be orbiting around less mass than the outer stars, because the mass outside the inner stars’ orbits would not affect the inner stars. (Inside a uniform spherical shell there is no net gravitational attraction from that shell). The upshot is that, for perfectly homogeneous mass distribution, the orbital period does not depend on the distance from the center of mass.

jrf

14

In addition to the many questions posed here, I’ve also pondered whether the galaxies move “through” space or “with” space.

That is, does a galaxy pass through space like a jellyfish through water or is it embedded in space/time to such a degree that it “drags” space with it akin to an island moving due to continental drift across a techtonically active planet?

Is “galactic drift” even a theory?

Yet to be reconciled with the reality of the dark for a moment, I go on wandering from dream to dream.

15

By the way, to nit-pick, electrons and bosons don’t spin, they have spin, or to be more precise, they have someting called “spin.”

Interesting question though.

Tony

Two things fill my mind with ever-increasing wonder and awe: the starry skies above me and the moral law within me. – Kant