I often look at galaxies (with some degree of difficulty and frustration) and find myself striving to understand what creates the multitude of shapes and formations we all see through our respective eyepieces. According to researchers, there are four distinct classes commonly associated with the shapes of the galaxies in our night sky. They are as follows:
(1) spiral – as our very own Milky Way demonstrates with seemingly spiraling arms,
(2) lenticular – considered spiral galaxies without the “arms” or “bands,”
(3) elliptical – which are said to take on a football-like shape and have no apparent rotation,
(4) irregular – galaxies that appear to be in somewhat of a random formation (possibly due to surrounding gravitational forces from neighboring objects).
Both the elliptical and irregular galaxy formations could also be described as having a star cluster like appearance. Young stars within each galaxy are classified as population II by physicists where the older stars make up the bulge form near the center and are classified as population I stars.
So, what causes galaxies to take on such different compositional shapes? One of the now understood causes of galaxy formation is attributed to the fact that many of them have a black hole at their centers (including our Milky Way). Their massive gravitational forces pull in nearby established stellar systems and newly formed stars until they become trapped. But it is said that not all galaxies have a powerful black hole at their centers. If not, then what force has pulled such massive gatherings of cosmic entities into a respectively close proximity and what makes them appear in the shapes that they do?
Let’s think of centripetal forces as they act on Earth. If one were to semi-submerge a textured sphere (for the sake of having some friction) or ball (as a sphere is a more accurate representation of a black hole) into a pool of water and spin it on a fixed 90 degree vertical axis, we might begin to see swirls in the water surface “waking” out from the sphere itself. This could be said to mimic the actions of a spiral galaxy with a black hole at its center that may have a “hightened” rotation and a significant gravitational force based on it’s sheer size and density of mass.
Now take this same semi-submerged ball and create a somewhat severe off-angle oscillating rotational axis while spinning it. Given the “wobble” effect that should present itself when being spun, the patterns on the surface of the water would lose their wave-like wake patterns and become more erratic as it wobbles. Could it be feasible to think that similar behaviors could occur within our galaxies?
Could the variations of a black hole’s massive gravitation pull, angle of axis to it’s rotation and the centripetal forces created by their respectively powerful rotation establish a galaxy’s form? If so, it would indicate that the greater the axial wobble (degrees off 90) from a galaxy’s black hole in its rotation, the greater the possibility that the galaxy’s spiral or disc-like structure will crumble and will develop a more spherical of irregular order. This would render a spread of the combined forces (gravity, centripetal) and the encircling stellar masses across a more spherical pattern rather than an expected organized disc. So the higher the angle off of center of a black hole’s axial rotation, the more it will spread it’s forces from it’s equatorial plane and result in a more random or spherical shape to it’s surrounding galaxy. The “truer” a black hole’s axial rotation is, the more disc-like or spiral-like it it will appear. So what gives one galaxy spiraling arms (spiral galaxy) and another simply a smoother disc-like appearance (lenticular galaxy)? Could the speed of the black hole’s rotation on it’s axis determine this? Does one simply spin faster than the other and thus result in a different disc structure?
I realize this example does not include the galaxies without a central black hole. It would only seem logical that these galaxies begin to form in a random manner and develop and grow based on the multiplication of gravity from the growing number of stars in respective close proximity. As they slowly gather, their gravitational forces begin to work like one. Irregular galaxy’s may be the best representation of a formation without a black hole at it’s center. But this is only a brief assumption considering the fact that it has yet to be proven that there isn’t a black hole hidden within every galaxy.
The tools at our current disposal simply cannot accurately asses this yet. Yet one aspect of galaxy formation I have not covered, the conservation of angular momentum, is simply because it delves into mathematical equations beyond my abilities to follow. If anyone cares to define it in lamens terms for me, I would certainly appreciate it.
SCM
I think your observations make a lot of sense. Now, just looking at the diversity of life on earth, it makes sense that the universe is equally diverse in composition, and maybe more so. Say 2 random stars out there in the mix come close enough to each other for their gravity to start bringing them together. The closer they get, the more gravitation force they produce together would eventually bring in a third, etc. Since stars come in many different sizes, and strengths, I think their coming together would be unlikely to form a symetrical bond. I’m not sure if I’m using the right word there. If one star was larger than the other (likely) one side of the grouping would have a higher gravitational pull than the other. Each stars own centrifugal force produced by it’s own roataion would keep the stars from quickly colliding with each other also. I’m guessing that galaxies without black holes are younger, and haven’t pulled in as many stars to produce that massive gravity. To tell the truth, I’m not sure that black holes are black. I think that they’re simply areas beyond our visual capability, oh, like we can’t see ultraviolet light, or x rays. Our technology can test for many light waves beyond the human capability, but even that is limited to whatever our current state of technology is.
First, I’d like to say thank you for comments as I must admit your points are quite valid. To carry on the discussion, I would agree that stars of relative proximity but of unequal mass will certainly attract via gravitational forces. But my readings have indicated that it is not only possible, but probable that many stellar entities have actually formed as a result of gravity pulling the separate masses into one over extended time frames. If this is true, the same rules could and, I feel, should be applied when referring to galaxy formation and creation of black holes. Even our Moon is said to have been created by cosmic debris pulled together into a sphere under gravitational and centripetal forces over millions of years. I would agree with you that galaxies without black holes must be younger, as they have not had sufficient time to draw in additional combined gravitational and centripetal forces and mass to generate gravitation that exceed measures of an event horizon as seen (or assumed shall I say) in a black hole.
SCM
I agree with your logic but I would go further and say that the size and density of the black hole in the centre of a galaxy is what causes the shape and rotation of the galaxy. Einsteins general relativity is based on the assumption that the size of a mass (density) effects or warps the space around it. Gravity is basically the curvature or warpness of space. In our solar system the sun warps space to create a curvature within which all the planets within that curvature of space rotate around the sun. If you apply general relativity to the massive density of black hole in the centre of the Milky way it is easy to correlate that the rotation of a massive black hole is also rotating and warping space to such a high degree that its effects at the outer reach of the galaxy is what creating its speed and rotation. Now if I could only prove this theory mathematicaly.
Yes, you’re quite right. The fabric of space-time is warped at varying degrees which correlate directly with the size of the mass in its presence. This warping is what we lamens call gravity. But I fail to see how this warping (that in theory should be equally inclusive when referring to how it bends around masses) allows for such drastic variations in galactic structure. Surely there is another force at work here. Logic leads me to believe that the inner cores (or black holes) axis angle of rotations would be a likely candidate to allow for such variations. As I mention in another of my posts, even the Milky Way is a bit of an anomaly in that it is actually shaped more like a baton with elaborate “tassels” stemming from either end. It is far from a perfect spiral. So, if the laws of physics apply equally to large bodies in space and the space-time fabric warps at equal rates to equal masses, how would you explain the drastic variations to the shapes that galaxies appear in?