With all the pictures of hurricanes taken from space lately, I can’t help but note the similarity between the shapes of hurricanes and galaxies, right down to the wispy arms and centers (black holes, and eyes). I was going to google for the reason, but was unsure how to word it. Can any dopers answer this for me? Thanks.
By the way, I know that all galaxies don’t have that shape.
Centripetal force at work. Both entities spin which is going to give similar visual effects.
I googled your OP title andgot this
They are both vortices …
The forces at work in Hurricanes are not centripetal, as in a gravitational field. It’s much more complicated, and relates to the Coriolis effect.
This makes sense. Am I correct in understanding that the vortices of hurricanes are caused by temperature variations?
John Mace, there are centripetal forces at work in anything that’s moving in a circle. Gravity is one common source of centripetal force, but it’s not the only one. In a hurricane, the centripetal forces come from the pressure difference between the low-pressure center and the high-pressure outside.
And to the OP, while all or almost all galaxies have a supermassive black hole in the center, it won’t show up in a picture of the whole galaxy, the way a hurricane’s eye would. The central black hole, or even its accretion disk, is far, far smaller than the galaxy as a whole.
Are you sure? I would think it is conservation of angular momentum.
Centripetal force and angular momentum are two concepts which can’t really be disentangled from each other, since they’ll both show up every time you have rotation.
Chronos is correct, the word “centripetal” only defines the direction of the force, towards the center … in a galaxy, this centripetal force is caused by gravity; in a hurricane this centripetal force is caused by the pressure force; so both are correct usages …
We have to be very careful applying the conservation of angular momentum to a hurricane or any cyclone … these particular vortices are under torque, so angular momentum is increasing until they reach their frictional limits … one thing a galaxy doesn’t do is precipitate water vapor so this can’t be relied upon to explain torque there, not sure we can say galaxies are even under torque … but either way, they can both be explained as vortices and all the vortex equations will hold true …
No one knows why an eye forms at the center of a hurricane, so we don’t know why galaxies don’t have eyes … research continues …
Pressure variations, which could be in turn caused by temperature variations, but there are other mechanics that can cause these initiating pressure variations … once the initial vortex is formed and water starts condensing, then it’s just balls out torque that drives the hurricane …
The swirl shape is a constant in nature…i learned that in art school…not science-y…i know…forgive me
Thank you Beckdawrek … sometimes we delve too deep into the science of nature we sometimes forget just how beautiful these things are …
You’re welcome
Apparently, you’re not the only one who’s noticed this, as evidenced by today’s Schlock Mercenary.
worse, “momentum” has no physical manifestation. Its a 4th rule to help apply Newston’s 3… basically momentum is a corollary of Newton’s law “every action has equal and opposite” , its listed as different because its extended to apply over definite time frames… The momentum must be conserved , or the change must be due to external influences.
Beg pardon? Of course momentum (linear and angular) has a physical manifestation. In what sense doesn’t it?
Momentum is the manifestation of the first two of Newton’s Laws.
An object in motion tends to stay in motion. –> Momentum
An object at rest tends to stay at rest. –> Momentum
For every action, there is an equal and opposite reaction. –> Forces apply both directions: on this from that and from this on that.
F= m a is really a simplification for constant mass. With variable mass, mass changes with time, such that
If P(t) = momentum = m(t) v(t), then
F = m(t) dv/dt - u dm/dt
Where u = the velocity of the ejected/accreted mass as seen in the object’s rest frame, also called the ejection velocity.
Kitchen counter science:
Cupboard door of mass m traveling at velocity v has enough momentum p to create bruise diameter d[sub]ouch[/sub] on forehead …