by ems57fcva » Sat Aug 21, 2010 3:52 am
bystander wrote:This galaxy looks perturbed. The spiral arms are far from symmetrical and there are shadow arms off to the right. Is there another galaxy close by with which this one is interacting?
Bystander - I think that you have made a very profound observation. I think that this is a case where there are two galaxies that are interacting very strongly. To make matters more interesting, I think that the remnants of the two galaxies are on each side of the central bar of NGC 1365
Here is my take on this galaxy: This is a galactic merger in the later stages of the merger. This is an Antennae galaxies type of situation, but much more evolved, and evolved in a direction that the theorists don't expect and cannot yet model. It appears to me that when the central so-called black holes of two galaxies get close enough, material started boiling off of both of them and into the space between them, forming a bridge. I suspect that what is boiling off is largely dark matter, but it is dragging a fair amount of gas and dust along with it. Indeed, you can see columns of dust and gas being drawn into a whirlpool at the center of the bar.
In any case, if enough material goes into the bridge, if starts forming a new galactic center, with a new "black hole" of its own. This change in the mass distribution of the system keeps the galaxies from just plain sweeping past each other, and also lowers the gravitational gradient for the original central objects (if I may call them "objects" instead of "black holes" now), and so permits even more material to flow out of them. If this process is allowed to proceed long enough, you get something like NGC 1365. If instead the configuration is such that only a limited amount of material is drawn into the bridge before the galaxies move away from each other, that the result will be a narrow bridge connecting the centers of the galaxies for a while. The July 2, 2010 APOD (
http://antwrp.gsfc.nasa.gov/apod/ap100702.html) is an example of this alternate outcome.
So here is what I see in more detail. There is a central bar connecting the remnants of two smaller galaxies, with each galaxy becoming a spiral arm for the unified galaxy. The primary arm of each side was the primary tidal tail for one of the original galaxies. The secondary arm on each side was the secondary tidal tail, now twisted around so that it is parallel to the primary tidal tail as the arms have come to rotate around the new central object. The central bar is a new central bulge, into which gas and dust are still being drawn. The primary source of matter for the new central object is the remnants of the old central objects, located at either end of the bar, where the primary and secondary tidal tails meet.
I admit that this idea raises a lot of questions, but it is what I have been seeing in my mind's eye for some time now.
EMS
[quote="bystander"]This galaxy looks perturbed. The spiral arms are far from symmetrical and there are [i]shadow arms[/i] off to the right. Is there another galaxy close by with which this one is interacting?[/quote]
Bystander - I think that you have made a very profound observation. I think that this is a case where there are two galaxies that are interacting very strongly. To make matters more interesting, I think that the remnants of the two galaxies are on each side of the central bar of NGC 1365
Here is my take on this galaxy: This is a galactic merger in the later stages of the merger. This is an Antennae galaxies type of situation, but much more evolved, and evolved in a direction that the theorists don't expect and cannot yet model. It appears to me that when the central so-called black holes of two galaxies get close enough, material started boiling off of both of them and into the space between them, forming a bridge. I suspect that what is boiling off is largely dark matter, but it is dragging a fair amount of gas and dust along with it. Indeed, you can see columns of dust and gas being drawn into a whirlpool at the center of the bar.
In any case, if enough material goes into the bridge, if starts forming a new galactic center, with a new "black hole" of its own. This change in the mass distribution of the system keeps the galaxies from just plain sweeping past each other, and also lowers the gravitational gradient for the original central objects (if I may call them "objects" instead of "black holes" now), and so permits even more material to flow out of them. If this process is allowed to proceed long enough, you get something like NGC 1365. If instead the configuration is such that only a limited amount of material is drawn into the bridge before the galaxies move away from each other, that the result will be a narrow bridge connecting the centers of the galaxies for a while. The July 2, 2010 APOD ([url]http://antwrp.gsfc.nasa.gov/apod/ap100702.html[/url]) is an example of this alternate outcome.
So here is what I see in more detail. There is a central bar connecting the remnants of two smaller galaxies, with each galaxy becoming a spiral arm for the unified galaxy. The primary arm of each side was the primary tidal tail for one of the original galaxies. The secondary arm on each side was the secondary tidal tail, now twisted around so that it is parallel to the primary tidal tail as the arms have come to rotate around the new central object. The central bar is a new central bulge, into which gas and dust are still being drawn. The primary source of matter for the new central object is the remnants of the old central objects, located at either end of the bar, where the primary and secondary tidal tails meet.
I admit that this idea raises a lot of questions, but it is what I have been seeing in my mind's eye for some time now.
EMS