Starship Asterisk*

http://antwrp.gsfc.nasa.gov/apod/ap080622.html
<<on close inspection the nucleus of this classic barred spiral itself shows a remarkable region of spiral structure about 3,000 light-years across.>>

A common feature of all barred spirals?

http://antwrp.gsfc.nasa.gov/apod/ap070724.html
http://antwrp.gsfc.nasa.gov/apod/ap070418.html
http://antwrp.gsfc.nasa.gov/apod/ap070328.html
http://antwrp.gsfc.nasa.gov/apod/ap070315.html

Does anyone know if a simulation has been run of the evolution of a galaxy with a black hole at the centre if the black hole suddenly disappeared? Presumably all matter orbiting it's C of G would move off at a tangent, but with some remaining attraction to the galactic C of G? Would it produce a bar?

Hello neufer,

Is that a smaller absorbed galaxy just above the shoulder of the left major arm?

Is it my imagination or do I see may galaxies around the barred galaxy many edge-on? Jeff

Yup. At least a dozen or so. 10 to 1 there's more than that!

I can't shake the feeling that a barred spiral is both barred and spiral because of the interaction of two different laws of physics which run on ever so slightly different math over great distances. Perhaps the speed of gravity waves (if there are such things) changes at a slightly different rate than, say, the speed of the passage of time or the speed of light in the presence of concentrations of matter.

Perhaps these structures we're seeing are something akin to "aliasing" in the laws of physics themselves.

All of what we think we know may need to be rethought on cosmic and relativistic scales.

-Noel

flamencoprof wrote:Presumably all matter orbiting it's C of G would move off at a tangent

I don't think so. I think it would orbit its barycenter:

http://en.wikipedia.org/wiki/Center_of_ ... _astronomy

Also, I know your suddenly disappearing black hole is hypothetical, but the result may be the same in a real case where black holes are expected to "evaporate, shrink, and ultimately vanish" by emitting Hawking radiation:

http://en.wikipedia.org/wiki/Hawking_radiation

Also, the Physics behind barred spirals may be elusive, but they look great.

astrolabe wrote:Hello neufer, Is that a smaller absorbed galaxy just above the shoulder of the left major arm?

Both arms beyond the bar seem to have a curious ribbed (or braided) structure; I assume that you are referring to one or two of the largest ribs.

Frankly, I haven't the foggiest notion of what dynamics are going on here.

Can someone please explain to a non astronomer why the bar of a galaxy such as this is intact? I would've thought the bar would be twisted out of shape by the galaxy's rotation.

From the Astronomy Picture of the Day for Sunday, June 22, 2008:

"Unlike other spiral galaxies, including our own Milky Way, NGC 1300 is not presently known to have a massive central black hole."

I wonder if this is really true. I have found many entries on the Internet claiming that NGC 1300 does have a supermassive black hole at its center:

http://www.ingentaconnect.com/content/b ... .alexandra

Comments?

I will withold comment on the data linked to in the original post due to the fact that it will cost me $54.87 to purchace the article in order to read it.

Do you have a link to the same info that is free to read???

That's the question.

http://hubblesite.org/newscenter/archiv ... 01/image/a

The relevant text from the page I suppose would be:

"Only galaxies with large-scale bars appear to have these grand-design inner disks — a spiral within a spiral. Models suggest that the gas in a bar can be funneled inwards, and then spiral into the center through the grand-design disk, where it can potentially fuel a central black hole. NGC 1300 is not known to have an active nucleus, however, indicating either that there is no black hole, or that it is not accreting matter."

http://antwrp.gsfc.nasa.gov/apod/ap080622.html

I'm looking at the dust trails along the bar. they seem to be drifting toward the center. Maybe something is feeding on them.
Orin

Humbly I suggest I already considered that:- "but with some remaining attraction to the galactic C of G?", I have Googled "barycentre" & think we are talking about the same thing?. As for Hawking radiation, that is not on the time-scale we are discussing. I am being run-it-up-the-flagpole-&- see-if-it-flaps speculative, in that out there I see few straight lines, most appear to be electromagnetic jet squirts, & this looks like a gravity phenomenon. Lobbed to you, catch if want. And yeah, I saved the image to my desktop in the hope that someone might admire it, but no takers so far.
p.s Note also the question posted by Cherax, which I only saw when I previewed this post.

apodman wrote:

flamencoprof wrote:Presumably all matter orbiting it's C of G would move off at a tangent

I don't think so. I think it would orbit its barycenter:

http://en.wikipedia.org/wiki/Center_of_ ... _astronomy

Also, I know your suddenly disappearing black hole is hypothetical, but the result may be the same in a real case where black holes are expected to "evaporate, shrink, and ultimately vanish" by emitting Hawking radiation:

http://en.wikipedia.org/wiki/Hawking_radiation

Also, the Physics behind barred spirals may be elusive, but they look great.

As I've mentioned elsewhere, we tend to think of galactic structure in terms we are familiar with - i.e. water circling a drain or a cyclonic weather system. What we are seeing on a galactic scale may appear similar, but it seems to me it must be at least somewhat a coincidence.

Matter clumps together because the presence of a concentration of the stuff in space-time causes time to slow and thus an acceleration is generated toward the center of mass. This effect, called gravity, by the best measurements of man so far propagates at the speed of light.

So consider this: Any bit (e.g., star, nebula, etc.) of matter flying through space in a given galaxy is influenced gravitationally by the other matter in the places in which it appears from the vantage point of that bit of matter at a given moment. According to the theory of relativity, what's happening at the same time (as viewed by a 5-dimensional being) on one edge of a galaxy can't begin to affect the "stuff" on the other edge for 100,000 years or so. The way I envision it, over a very long time the subtle variation in the forces of gravity because of the dynamics of the system, as that force propagates across the system, yields the structure we see.

In visualizing (and analyzing) the familiar spiral structures in our own frames of reference, these relativistic effects do not apply; things on our planet are just on too small a scale. However, in the case of cyclones we may be seeing the spiral structure because of the relatively slow propagation of forces and effects on a grand scale that move relatively slowly through the mediums in which they form (e.g., atmosphere), and so there could well be some analogies there well worth studying. In short, the bands of clouds on the north edge of a hurricane don't have a clue what the clouds on the south edge are doing right now, yet the things are eerily symmetrical as seen from space.

These structures form on vast, grand scales not because of something the matter within can sense throughout the entire system "in real-time", but because of the physics and properties of the medium (space-time, atmosphere, etc.) they form in, and the dynamic effects in all 4 dimensions.

It seems to me that we have this wonderful vantage point, courtesy electromagnetic waves that travel over great distances (e.g., light), to view a "snapshot" of what's happening in distant face-on galaxies "all at once", almost as a 5-dimensional being might. Truly a view of the Gods!

If we can come up with math/theories/models that describe the dynamics of what's being observed on galactic scales then we may well reach a truer understanding of the laws of physics and the universe than we have ever had.

-Noel

astrolabe wrote:Is that a smaller absorbed galaxy just above the shoulder of the left major arm?

I think I see what your reference is. At 10 o'clock there is a beige knot surrounded by a blue swirl, just above where the left major spiral arm begins. Certainly looks like it could be a dwarf galaxy to me.

Cherax wrote:Can someone please explain to a non astronomer why the bar of a galaxy such as this is intact? I would've thought the bar would be twisted out of shape by the galaxy's rotation.

The (longitudinal) gravitational force of a cylinder of diameter 'd' and length '2L' is something like:

F(z) = | arctan [(z-L)/d] | - | arctan [(z+L)/d] |

For moderately wide diameters 'd'
this force law could approximate a linear spring:

For d < |z| < L : F(z) ~ - K * z

especially if one includes extra mass concentrations for |z| < d
such as a central (black hole?) concentration
with it's own independent spiral motion.

For moderately wide diameters 'd' this (longitudinal) force law:

F(z) = | arctan [(z-L)/d] | - | arctan [(z+L)/d] | - A/(z*z)

"could" allow for orbits which
(when extended into the region d < |z| < L )
stay, more or less, within the cylinder.

neufer wrote: For d < |z| < L : F(z) ~ - K * z

G'day Art,

The z direction, is that perpendicular to the disk of the galaxy? Or is the z direction along the bar of the galaxy? Judging the choise of a cylinder it is more likely to model the bar itself.

Cherax wrote:Can someone please explain to a non astronomer why the bar of a galaxy such as this is intact? I would've thought the bar would be twisted out of shape by the galaxy's rotation.

THAT's the question. I originally posted "That's the question" immediately after the quoted question above, but the time stamps in this forum sometimes act in mysterious ways, and that reply now appears after another post and makes no sense at all. So sense is restored at great length.

henk21cm wrote:

neufer wrote: For d < |z| < L : F(z) ~ - K * z

G'day Art,

The z direction, is that perpendicular to the disk of the galaxy? Or is the z direction along the bar of the galaxy? Judging the choice of a cylinder it is more likely to model the bar itself.

Yes.
The cylinder (and z axis) can be thought of as rotating around the x axis with centrifugal force equal to K * z approximately balanced by the cylinder's gravitational force.

A fine example of a spiral trailing its arms, the mass of the galaxy descending into the centre .. yet viewed edge on, the centre will bulge out on both sides .. clearly an example of the 'distortion' of time.

neufer wrote: The cylinder (and z axis) can be thought of as rotating around the x axis with centrifugal force equal to K * z approximately balanced by the cylinder's gravitational force.

The force (proportional to the distance from the center of the galaxy, attractive towards the center) explains why stars don't shoot out of the 'barrel' of the cylinder. They are in a state of 'z-equilibrium'. But equally intriguing is why these stars don't diffuse through the 'walls' of the cylinder, and spread out. The 'z-equilibrium' has no influence on any lateral motion, i.e. the 'φ-equilibrium'.

Art, do you happen to know an explanation for the absense of lateral motion?

henk21cm wrote:

neufer wrote: The cylinder (and z axis) can be thought of as rotating around the x axis with centrifugal force equal to K * z approximately balanced by the cylinder's gravitational force.

The force (proportional to the distance from the center of the galaxy, attractive towards the center) explains why stars don't shoot out of the 'barrel' of the cylinder. They are in a state of 'z-equilibrium'. But equally intriguing is why these stars don't diffuse through the 'walls' of the cylinder, and spread out. The 'z-equilibrium' has no influence on any lateral motion, i.e. the 'φ-equilibrium'.

Art, do you happen to know an explanation for the absence of lateral motion?

A gravitational force of EXACTLY : - K * z defines an harmonic oscillator
such that all the objects will have the same periodicity. (Note also that stars on the back & front sides of the bar will get a gravitational pull back to the center.)

What I have given is just a hand waving argument that suggests how a bar galaxy might maintain itself (to first order) if the bar stars are distributed so as to emulate a simple harmonic oscillator gravitational field along the bar. (By contrast, I couldn't begin to suggest a simple model of how the spiral arms of a spiral galaxy maintain themselves. The bar galaxy is a much simpler case IMO.)

neufer wrote: . . . I couldn't begin to suggest a simple model of how the spiral arms of a spiral galaxy maintain themselves. . .

Is it well-established fact that a spiral galaxy will maintain its spiral arms in a stable "end-state"?

Is it not possible that the time-constants are such that the time necessary for attainment of a stable end-state has not yet elapsed for any galaxies visible to us?

(EDIT: After all, many galaxies appear to have undergone far fewer than 100 total rotations given the accepted age of the universe.)