What are Non-Spherical Structures in Astronomy?

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In summary, astronomy is full of spherically symmetrical things, with a few exceptions. Most merging systems are no longer spherically symmetric. The most common shape in astronomy is the disk. Galaxy clusters are aspherical. Asteroids are aspherical, but if they are big enough they will eventually become spherical. Our own galaxy may have a triaxial component.
  • #1
ohwilleke
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Most of the stuff in astronomy is spherically symmetrical, or very nearly so. Stars, galactic cores, and planets all seem to be.

I can think of exceptions of such the arrangement of matter in disk like solar systems or the outer portions of spiral galaxies, small irregular asteroids, nebula, and "superstrands" that impact large scale structure.

Can anyone think of other exceptions?
 
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  • #2
most merging systems are no longer spherically symmetric. Not many galaxies are spherically symmetric.

I think you should rephrase your first line to read "A lot of the stuff in astronomy is assumed to be spherically symmetric for ease of calculation"
 
  • #3
Asphericity is more common in astronomy than one might think. matt.o is absolutely right that it's often just assumed for simplicity and that the visible part of galaxies generally doesn't take a spherical form (though the dark matter halo is assumed to be spherical in most cases).

Next to the sphere, probably the most common shape in astronomy is the disk. Not only do some galaxies show this form, but we see disks around compact objects (like neutron stars), young stars, and even a planetary disk around our own star. Disks are common because gravity has a tendency to cause clouds of matter to collapse, and with conservation of angular momentum, small initial rotation rates will be amplified. When the rotation rate is large, there is a new symmetry along the axis of rotation that cannot be neglected in the dynamics. In the absence of this rotation, there is no reason the system should prefer any direction and a sphere is the natural shape to take on.

A shape that's often considered when talking about galaxies is the triaxial ellipsoid. The stars of elliptical galaxies are often modeled this way. We're still trying to determine whether or not our own galaxy has a triaxial component.

Although often modeled as spheres, galaxy clusters are actually highly aspherical. Here's the weak lensing map of one such cluster:

http://astro.uchicago.edu/home/web/joffre/comb3266.gif

The reason the mass distribution isn't as spherical as, say, stars, is that it hasn't had nearly enough time to relax into a lowest energy configuration. Larger objects take longer to do so and the universe is still young relative to the relaxation time of a galaxy cluster.

Finally, as you mentioned, there are filamentary structures in the large-scale distribution of matter. One expects this from the Zeldovich approximation of an object collapsing under gravity with negligible rotation. Basically, an object with some random shape initially will tend to collapse along its smallest principal axis first, forming a pancake. Then, it will collapse along its second shortest axis, forming a filament. Part of my thesis project is actually to determine whether the large-scale mass distribution is dominated by filamentary structures or "pancake" structures (also called "walls").
 
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  • #4
asteroids...
 
  • #5
I guess asteriods are aspherical but if it is big enough then it's gravity will pull it into a sphere. That's why planets and stars are spheres. A galaxy can be disk shaped just because that is the way the planets and stars aligned themselves...
 
  • #6
Really cool ST! And will there also be a collapse along the 'third axis' (to form roughly spherical blobs)? (BTW, what cluster is this? and where can we read more?)

Welcome to Physics Forums, Mike Centore!

To an OOM or three, you're right; however, we must not forget rotation (Jupiter is certainly NOT a sphere!), nor material strength (e.g. Vesta, also certainly NOT a sphere).

To add to what Space Tiger wrote, when the detailed studies of galaxy clusters are finally done, we find that they are not (generally) spherical; and the (very few) detailed studies of the DM distribution in rich clusters also shows an 'as-yet-not-relaxed' picture; for example.
 
  • #7
Nereid said:
Really cool ST! And will there also be a collapse along the 'third axis' (to form roughly spherical blobs)?

Yup. That's basically what we expect, the infall of matter into clusters and along filaments.


(BTW, what cluster is this? and where can we read more?)

Abell 3266. Can you be a bit more specific about what you'd like references for? I don't know of anything that specifically addresses this question, but I could give references on many of the details covered above.
 
  • #8
Abell 3266. Can you be a bit more specific about what you'd like references for? I don't know of anything that specifically addresses this question, but I could give references on many of the details covered above.
Thanks ST.

Now I know the cluster, I can (most likely) use Google Scholar to find any relevant papers.

I was asking mainly about where one could read up on the weak lensing analysis of this cluster, and see if there were more (e.g. SZE, analysis of X-rays from the IGM, estimates of cluster mass from the Virial Theorem, ...), and also to see where - in the spectrum of richness and compactness - this particular cluster fit.

Will you be doing analyses related to rich clusters? quasar clusters??
 
  • #9
Nereid said:
I was asking mainly about where one could read up on the weak lensing analysis of this cluster, and see if there were more (e.g. SZE, analysis of X-rays from the IGM, estimates of cluster mass from the Virial Theorem, ...), and also to see where - in the spectrum of richness and compactness - this particular cluster fit.

Try here


Will you be doing analyses related to rich clusters? quasar clusters??

I'll be focusing on filamentary structures, though I have a colleague doing cluster-finding in SDSS.
 

Related to What are Non-Spherical Structures in Astronomy?

What are non-spherical structures?

Non-spherical structures refer to any object or system that does not have a spherical shape or symmetry. This can include irregularly shaped molecules, crystals, or even larger structures like planets or galaxies.

Why do non-spherical structures form?

Non-spherical structures form due to a variety of factors, such as the arrangement of atoms or molecules in a system, external forces acting on the structure, or the presence of impurities within the structure. These factors can cause the structure to deviate from a spherical shape and form a more complex and irregular shape.

What are some examples of non-spherical structures in nature?

There are countless examples of non-spherical structures in nature, including snowflakes, crystals, viruses, and even the shape of our planet Earth. In the microscopic world, cells and bacteria also have non-spherical shapes.

How do scientists study non-spherical structures?

Scientists use a variety of techniques to study non-spherical structures, such as X-ray crystallography, electron microscopy, and computer simulations. These methods allow scientists to visualize the structure and understand its properties and behavior.

What applications do non-spherical structures have?

Non-spherical structures have a wide range of applications in various fields, including materials science, biology, and engineering. For example, understanding the structure of viruses can help in the development of vaccines, while studying the shape of nanoparticles can lead to new materials with unique properties.

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