Are all spiral shaped galaxies spiral because they have a huge blackhole at their centre?

I think that some galaxies spiral because they’re being pulled in towards another galaxy, but for a galaxy to be able to “eat” another galaxy like that they would probably have to have a black hole at the centre too. Wikipedia at least thinks that “Most galaxies are believed to have supermassive black holes at their centers.”

At the very least, this is a beautiful video.

The gravity of the entire star cluster, rather than a sigle gravity point, causes the collisions between galaxies, while at the same time the black hole grows due to the material fed to it by galaxy collisions – a black hole will pretty much clear everything within its sphere of influence (that doesn’t have the velocity to carve an orbit) until there is nothing left within that sphere to fall in.

There are different theories about how spirals form, but in none of them is the presence or absence of a black hole a factor.

Here’s a simple explanation courtesy of NASA:

“Astronomers think that the difference in appearance between elliptical and spiral galaxies is related to how quickly stars were made. Stars form when gas clouds in the protogalaxy collide. If the stars are formed over a long period of time, while some stars are forming, the remaining gas between the stars continues to collapse. Due to the overall motion of matter in the protogalaxy, this gas settles into a disk. Further variations in the density of the gas result in the establishment of “arms” in the disk. The result is a spiral galaxy. If, on the other hand, stars are made all at once, then the stars remain in the initial spherical distribution that the gas had in the protogalaxy. These form an elliptical galaxy.”

I can tell you with absolute authority that nobody knows.

It’s not like a whirlpool. The stars in the galaxy are not infalling towards the black hole. Also, almost all galaxies have supermassive black holes in their centers, not just spiral.

Scientists seem to think that the spiral arms are not permanent features of the galaxy. Rather, they’re “density waves.” What you’re seeing as spiral arms is actually a snapshot of a shifting pattern of stars, sort of like clusters of cars in a traffic jam. The density of cars in a traffic jam shifts over time.

See Density Wave Theory. Same thing explains patterns in Saturn’s rings.

Stars nearer to the center of the gravity and those away from it both move at constant speeds;quite unlike the planets in the solar system, in which the speeds of the planets vary inversely to their distance from the sun.
This anomalous behavior of the stars has been the reason why dark matter is said to exist- occupying 25% of our universe (or some closer value, as far as i have heard. rest 70% or so is dark energy and only about remaining 4% universe is actually known to us right now..)
Or maybe there is nothing like daark matter or dark energy, we just need to redefine gravity-

I should clarify: the spiral arms are like the traffic jam. The stars move through the arms, just like cars move through a traffic jam.

If you looked at the same spiral arm at different times, different stars would inhabit it. But the pattern (like a traffic jam with cars moving through it) remains there.

these density waves and spiral arm traffic jams were totally unknown to me until today!

@krrazypassions, that’s not why stars in a galaxy move differently from planets in the solar system.

The sun contains like 99.8% of the mass of our solar system. It completely dominates the gravity affecting the planets. That’s why planet orbits follow the simple inverse-square law.

In galaxies, there is not nearly as much mass concentrated in the center. So in a galaxy, the stars’ gravities pull each other much, much more than the planets in a solar system pull each other. So, their motions around the galaxy are not nearly so simple.

Again: it’s tempting to think of a galaxy like a whirlpool with a giant black hole in the center sucking everything in, but that’s really not how it works. The black hole is huge, but it’s not that big compared to the mass of the rest of the galaxy (in contrast to the mass of the sun taking up nearly 100% of the mass of the solar system).

Dark matter and energy might end up having something to do with it, but you don’t need to bring them into the equation yet to explain why galaxies work different than solar systems.

thanks for those insights! :)
meanwhile, dark matter was proposed due to the fact that the total mass of the galaxy by brightness method was
much less than
the total mass of the galaxy measured by calculating the radius of galaxy and speed of stars about the edge of the galaxy and using a variation of G= m1m2/r^2 => M= mv^2/r which works well for solar system.

however, as u pointed out, movements in galaxies and distribution of the gravity is might different compared to that in the local frame of reference of a star system and its planets..
therefore, the second method used is faulty and wrong in case of galaxies. since all stars were found to move at equal speeds irrespective of their distance from center of galaxy, we might take speed of star very near to the center and its radius and conclude that mass of galaxy is very low and that value of brightness method is extremely large compared to it, and therefore, there seems to be some kind of Light or Bright matter and Bright Energy

sorry, that last answer from me is quite messy, but I have a strong feeling that Dark Matter and Dark Energy have been proposed due to wrong assumptions. However, I am not an expert so the feeling emerges from whatever little i’ve seen and read about dark matter-energy.

Yah, there is definitely dark matter living in galaxies; I’m just not sure it’s primarily responsible for spiral arms. I mean, dark matter has mass, so it exerts a gravitational force along with the electromagnetically active matter (the stars we can see) in the galaxy… but it’s not THE reason why stars in galaxies move differently than planets in star systems. That reason is simple, and known: because a sun in a star system has almost 100% of the mass.

We know there’s dark matter in galaxies, iirc, because we can measure the bulk gravitic attraction between galaxies. And it’s more than what you’d expect from the matter we can see. But really, it shouldn’t surprise us that there are forms of matter that don’t interact with the electromagnetic force. That’s all dark matter means. Technically, you can say that neutrinos are a form of dark matter, and they’re not mysterious (though scientists have largely ruled out neutrinos as the ID of bulk dark matter in the universe).

I’m afraid I don’t know what you mean by “Light/Bright matter and Bright Energy.” Light matter is matter that interacts with the electromagnetic force (photons mediate this force. Light is energy that is made of photons.) It’s the matter and energy we can observe with a telescope. But there are certainly other forms of matter and energy that we can’t observe through a telescope, beyond their gravitational effects. The name makes it seem more ominous and mysterious than it really is.

Oh, I forgot: your equation does not work for galaxies. It only works for solar systems because the sun dominates the solar system’s gravity. It’s not applicable to this question. Dark matter was originally “discovered” because of the motions of galaxies in relation to each other. (Though further evidence did indeed come from the motions of stars within galaxies that imply large amounts of invisible matter. But not based on your equation. At least, I don’t think.)

@krrazypassions If it helps any, think of dark matter as the ice that they put in your soda, or soy in your Taco Bell.

@Nullo I am not sure how i am supposed to correlate these with dark matter… can you elaborate to help me understand?

As others wrote, it’s not that there’s a black hole per se, it’s that there is a center of gravity, and then that the arms have a certain density. All of the mass is attracting all of the other mass, but the shape is about how dense it is, where it is, etc. It is essentially a 3D whirlpool, without the water pressure.

It’s not a whirlpool!

It’s more of a whirlstar.

@krrazypassions It’s filler. It gives a galaxy more mass without being the original product. You can tell that the soda has ice in it (even if there’s a lid on it) because of the way that it affects the drink.

Ok, @Qingu, it is not a whirlpool, but the similarity in shape is not a coincidence, either. It’s just the natural shape pattern of a bunch of matter (water or stars in this case) swirling round a center attracting force of gravity.

@Zaku, (1) it’s not the same shape. Whirpools are not disks with bulging centers. The spiral patterns in a whirlpool are not like those in a spiral galaxy. The most you can say is that they are both round and swirling, which is pretty vague.

(2) The mechanisms are completely, completely different. Whirlpools are turbulent vortexes; they exist in an even, strong gravity field (like Earth’s). Galaxies are not remotely turbulent vortexes and they are certainly not sucked down towards an even field of gravity. As I have been trying to explain, they are not even sucked towards the gravity in the center of the galaxy. The gravity in a galaxy is dispersed throughout.

Now. If you want to talk about rad extraterrestial things that are basically whirlpools, the atmosphere of Jupiter and other gas giants are full of them. But let’s not overstate the case, okay?

@Nullo, the ice actually has slightly less mass than the soda it displaces. Analogy fail. Sorry dude.

@Qingu Analogies don’t have to be a perfect match. In some cases, trying to force a 1:1 match will overstress the analogy, further muddying the issue instead of clarifying it as it was supposed to.

The ice analogy isn’t so bad, but I hate analogies in Physics anyway. If you can’t understand the concept without comparing it to a fucking soft-drink or balloon or whirlpool or something, maybe theoretical physics isn’t for you. It doesn’t have to be equations, you can explain these things qualitatively, without resorting to analogies that merely hint at the nature of things, whilst leaving their implications totally unclear.

The whirlpool is, as @Qingu explains, absolutely nonsensical as an analogy.

Though I’d let the ice-soda one slide, if you were talking to a kid, but I mean come on… it’s dark matter, you can’t simplify it like that in order to convey the implications of it. You’re better off just explaining the implications of it, because that’s all we really know about it anyway….

———

Galaxies do not behave as would be expected from the amount of mass we can observe in them.
They behave as if there is a great deal more mass than we can observe.
The otherwise undetectable dark matter is theorized to account for this mass.

Nothing else is “known” or even theorized about it. We can only guess at its nature, as it is undetectable. It is just a theoretical device, used to account for this ‘extra mass’ that is required to explain why galaxies behave the way they do.

———

Anyway, despite what I just said:

It’s not like ice in soda, it’s more like salt dissolved in a glass of water. You can’t see it, but it is there, and it adds mass to the glass of water.

Right now, the only thing that suggests there is salt dissolved in the water is the fact that it weighs too much for its size, to be just plain water. Much too much, in fact.

So we think ‘maybe there is something we can’t see, dissolved in there’.

And we call it ‘salt’ ‘dark matter’.

The ice analogy is particularly bad because ice does not act remotely like dark matter. You can see ice. The ice interacts with the water. It has less density than the water. And it’s made of water. It’s like everything that dark matter isn’t.

I like the salt analogy. You look at a glass of salt water and at first glance you wouldn’t think it’s any different than fresh water. But when you start doing further experiments (tasting it, or running current through it), it looks like something else besides water is there, something that’s invisible but obviously important.

@The_Idler It serves to convey the point, does it not?
Do keep in mind that most of my Fluthering tends to coincide with sleep deprivation.

@Qingu You are very correct in your details, and make very good, interesting points. I was just responding at a basic level, as @Nullo said. At a basic level, that seemed appropriate to me for the wording of the question, I think it does make sense to relate it to a whirlpool, even though it is not a whirlpool, in many ways. On the other hand, the two-dimensional view from one side does look a bit like a whirlpool, and there are some reasons in common: Stuff is going round and round the center and forming a spiral shape, which is a natural consequence of a central attraction with matter going around it. At that level, it is the same kind of thing, even though it isn’t really the same thing, and there are many fundamental differences as well.

Blackholes existed since very early times and development of galaxies occurred by accretion of cosmic dust…

@krrazypassions nice link, hadnt read about that shit before. Astrophysics is cool sometimes…

@The_Idler lolz…

Nassim Haramein’s picture of the universe is of fractal nature- we live in a blackhole since light and matter from our universe cannot escape it.. similarly, the blackholes that we see have mass of thousands and millions of stars.. thus they themselves contain a universe..

“Astronomers believe that supermassive black holes lie at the center of virtually all large galaxies…”... “Scientist believe that most galaxies, certainly all the spiral ones, have such supermassive black holes in the center….”
wikipedia
space telescope. org
space telescope. org 2
NASA
daily galaxy

Its quite likely now that dark matter is nothing but these Supermassive Blackholes