Question about universe

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Question about universe

Well, my question starts off with a question, one from my 5 year old brother - why are stars circles?  Well, I told him a simple answer - he knew the sun was a star, so I said that since the sun is a circle, so was the stars.  But then that got me thinking - why are stars spheres?  I knew that one too - matter tends to clump into spheres because it is the nature of gravity: it pulls equally in all directions from a given point, and an almost of equal ammount of matter tries to converge at this point.  This is how everything works in space, I told myself.  But then I realized it didn't - our solar system, I was led to believe, was flat - everything rotated the same direction, and on the same plane.  The same thing with our galaxy - it isn't spherical either.  So my question is why.  Why does our solar system and galaxy not appear to be spherical?

And on a side note, I went to a childrens museum the other day, and they had this little side exhibet about the history of time - one fact was the discovery of antimatter - "matter that travels backwars in time."  Is that, in fact, true? 

I hope that when the world comes to an end I can breathe a sigh of relief, because there will be so much to look forward to.


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  Roll a lump of clay

  Roll a lump of clay around.

Sounds made up...
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Umm, will play-doh do? 

Umm, will play-doh do? 


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I believe I heard this

I believe I heard this somewhere...

In regards to stars and planets anyway, they become spherical because they are large enough to have a strong enough gravity 'squash' or reshape the matter into a sphere.

That's why smaller bodies are not nearly so close to spherical.

Anybody feel free to correct me if I'm wrong, and I'm not sure about the shapes of galaxies or solar systems.


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First, heavenly bodies

First, heavenly bodies appear to be circular because they are spheres.  A sphere provides the greatest volume with the smallest surface area; thus, gases and molten materials will form them if provided opportunity without other forces acting upon them.

 

Smaller bodies tend to be misshapen because they form from solid materials or if formed while molten, have other forces (ie. gravity) acting upon them.

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interesting point xam.

interesting point xam.

most of us can understand why the planets are round but it is unknown to me why the solar system seems to be "flat" in a sense. the paths of the planets kind of wobble but they don't really stray away from a plane. i guess the same thing can be noticed about "rings" around saturn. they tend to be flat and not a thin layer covering around the planet.

when i was younger and first started to learn about atoms i thought they seemed familar to the solar system. the sun being the neutron and the planets being the protons and electrons that move around it. even a cell has similarities between planets.

it is amazing to think of how enormous everything is and how small we are. we have so much to learn.

i've read a little about antimatter on wikipedia but it would be nice if someone had some good quick description on what it is. what does it look like and can you touch it? can you put it in a box and carry it around? is it airy, fluid or a solid? dark matter and dark energy are also interesting subjects that i am curious about.

 

EDIT: changed nucleus to cell, nucleus is the core, cell is the body

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Well, I'm sure BGH would be

Well, I'm sure BGH would be a much better person to answer this, but I'll give it my best layman's shot.

You've got basically the right idea about gravity forming spheres, and why planetary bodies tend to be essentially spherical.  You should note, though, that gravity works against spheres, too.  The moons of Jupiter, for instance, are constantly being pulled in various ways, so that they're not perfectly spherical.  This accounts for the hot cores that would ordinarily have cooled given their size and age.

So, once you wrap around that, consider that gravity is not the only force at work in the solar system.  First, and most important is motion.  The reason everything doesn't collapse into the sun is that it's at a state near equilibrium, where each body's velocity nearly matches the pull of gravity from the sun.  Each body, however, is a conglomeration of matter that formed as it was grabbed by the sun's gravity.  It was yanked off of its trajectory, which, while it probably wasn't completely straight, was damn close.  The pull of gravity was enough to literally turn the matter around, and get it going in a near-circular orbit.  (Think of a vortex in water...)

Think about it this way.  There are lots of variables in the universe:  gravity, momentum, radiation, etc... For all of them to line up so that things would form perfect spheres or perfect circular orbits would be rather extraordinary.   What we're seeing is an "imperfect" system, where matter and energy are tending toward spheres and circles, but are influenced by many outside forces that throw things slightly off perfection.

Hope that helps.

 

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Ah, I hadn't really

Ah, I hadn't really considered the disc part of the question... maybe I just didn't read the OP correctly.

I don't know the answer with authority, but it seems to me that the slightly imperfect sphere would help answer this question.  Consider a single sphere orbiting another larger sphere.  Each is pulling on the other slightly, such that the larger sphere has a little more mass on the plane of orbit.  Perhaps this tiny difference is enough to continue the trend?

I dunno.  This sounds like a question for a professional.

 

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Here is a nice brief

Here is a nice brief description of planetary formation I found on the web.

http://hyperphysics.phy-astr.gsu.edu/hbase/solar/planetform.html

Quote:
Having only one planetary system that we can carefully observe, we try to generalize from our solar system to model the formation of planets. This involves modeling the gravitational collapse of a large diffuse cloud of gas and dust. Given a non-zero angular momentum of the cloud with respect to some axis, there will be an increase in rotational angular velocity associated with the collapse. The formation of a disk perpendicular to the spin axis results, and in the case of our Sun we would call the growing system with its disk the primitive solar nebula. Modeling from the solar planets, it is judged that the protoplanetary disk must contain a minimum of about 2% of the system mass.

In the protoplanetary disc, cooling leads to the condensation of some of the elements and compounds to dust grains, followed by the formation of larger solid bodies. Gravitational forces including tidal forces are involved. de Pater and Lissauer is a good reference for discussion of some of the stages of planet formation.

I would also add that 'gravity' which hold these bodies together is actually a rather weak force. If a body is struck by another object the energy from such a collision can override the effect of gravity and tidal forces on it. Sometimes this will alter the rotation or location of the object. A good example of this is Uranus, which rotates on it's axis almost parallel to the plane of the elliptic whereas most of the other planets rotate perpendicular to the plane. It is a common theory that Uranus was struck by a fairly large body to knock it out of sync with the of the other planets.

Here is more info on Uranus from wikipedia:

http://en.wikipedia.org/wiki/Uranus_(planet)

Quote:

 

Orbit and rotation

Image showing Uranus, its bands, rings and moons clearly outlining its sideways pose Image showing Uranus, its bands, rings and moons clearly outlining its sideways pose

Uranus's orbit is roughly 84 Earth years long. Its average distance from the Sun is roughly 3 billion km; at that distance, sunlight is barely 1/400 that of Earth.[17] Its orbit was first calculated in 1792, however, almost immediately discrepancies began to appear between the orbit predicted and the actual orbit as observed. In 1841, John Couch Adams, then an undergraduate at Cambridge, first proposed that the discrepancy might be due to the gravitational tug of an unseen planet beyond it. In 1845, Urbain Le Verrier, working at the Paris Observatory, began his own independent research into Uranus's uncertain orbit. On the 23 September, 1846, German astronomer Johann Gottfried Galle, working from information supplied by Le Verrier, located a new planet, later named Neptune, at nearly the position predicted. Le Verrier gained credit for its discovery.[18]

Uranus's rotational period, its "day", lasts roughly 17 hours, 14 minutes. Like all gas giant planets, its core spins more slowly than its upper atmosphere. The fastest region of Uranus's atmosphere, around its south pole, makes one rotation in only 14 hours. Windspeeds in that region reach upwards of 720 kilometers per hour.[19]

Axial tilt

One of the most unusual features of Uranus is its axial tilt of ninety-eight degrees. Effectively, Uranus is lying on its side. Consequently, for part of its orbit one pole faces the Sun continually while the other pole faces away. At the other side of Uranus's orbit the orientation of the poles towards the Sun is reversed. This gives each pole 42 years of continuous sunlight, followed by 42 years of darkness.[20] Between these two extremes of its orbit, particularly at the equinoxes, the Sun rises and sets around the equator normally. Uranus will reach its next equinox around December 2007, and not again until 2049.[21

 

There are bodies in our solar system that orbit the sun outside of the planetary disc and it is also believed this is a result of other objects which knocked them out of the rotational disc.

 

The questions about antimatter are another story.

The fundemental particles that make up atoms are protons, electrons and neutrons, inversely there are complete opposite particles in the universe called antiparticles. When regualr matter and antimatter come in contact they annihilate each other. So, no you would not be able to hold it in your hand.

Here is a good article describing antimatter:

http://www.lbl.gov/abc/Antimatter.html

Quote:

Antimatter

In 1930, Paul Dirac developed the first description of the electron that was consistent with both quantum mechanics and special relativity. One of the remarkable predictions of this theory was that an anti-particle of the electron should exist. This antielectron would be expected to have the same mass as the electron, but opposite electric charge and magnetic moment. In 1932, Carl Anderson, was examining tracks produced by cosmic rays in a cloud chamber. One particle made a track like an electron, but the curvature of its path in the magnetic field showed that it was positively charged. He named this positive electron a positron. We know that the particle Anderson detected was the anti-electron predicted by Dirac. In the 1950's, physicists at the Lawrence Radiation Laboratory used the Bevatron accelerator to produce the anti-proton, that is a particle with the same mass and spin as the proton, but with negative charge and opposite magnetic moment to that of the proton. In order to create the anti-proton, protons were accelerated to very high energy and then smashed into a target containing other protons. Occasionally, the energy brought into the collision would produce a proton-antiproton pair in addition to the original two protons. This result gave credibility to the idea that for every particle there is a corresponding antiparticle.

A particle and its antimatter particle annihilate when they meet: they disappear and their kinetic plus rest-mass energy is converted into other particles (E = mc2). For example, when an electron and a positron annihilate at rest, two gamma rays, each with energy 511 keV, are produced. These gamma rays go off in opposite directions because both energy and momentum must be conserved. The annihilation of positrons and electrons is the basis of Positron Emission Tomography (PET) discussed in the section on Applications (Chapter 14). When a proton and an antiproton annihilate at rest, other particles are usually produced, but the total kinetic plus rest mass energies of these products adds up to twice the rest mass energy of the proton (2 x 938 MeV).

Antimatter is also produced in some radioactive decays. When 14C decays, a neutron decays to a proton plus an electron and an electron antineutrino, . When 19Ne decays, a proton decays to a neutron plus a positron, e+, and an electron neutrino, .

14C --> 14N + e- +

19Ne --> 19F + e+ +

The neutrino and electron are leptons while the antineutrino and positron are anti-leptons. Leptons are point-like particles that interact with the electromagnetic, weak and gravitational interaction, but not the strong interaction. An antilepton is an antiparticle. In each reaction, one lepton and one antilepton is produced. These processes show a fundamental law of physics - that for each new lepton that is produced there is a corresponding new antilepton.

Although from a distance matter and antimatter would look essentially identical, there appears to be very little antimatter in our universe. This conclusion is partly based on the low observed abundance of antimatter in the cosmic rays, which are particles that constantly rain down on us from outer space. All of the antimatter present in the cosmic rays can be accounted for by radioactive decays or by nuclear reactions involving ordinary matter like those described above. We also do not see the signatures of electron-positron annihilation, or proton-proton annihilation coming from the edges of galaxies, or from places where two galaxies are near each other. As a result, we believe that essentially all of the objects we see in the universe are made of matter not antimatter.

Elementary particle physicists create massive particles by accelerating lower mass particles close to the speed of light, and then smashing them together. The mass/energy of the colliding particles becomes the mass of the created particles. One method includes taking positrons and electrons, accelerating both of them, and smashing them into each other. Out of this energy, very massive particles such as quarks, tau-particles, and the Z0 can be created. Studies of such electron-positron annihilations are carried out at the Stanford Linear Accelerator and at the LEP facility at CERN. A similar technique is used at the Fermi National Accelerator Laboratory except that it involves colliding protons with anti-protons. Collisions of this kind were recently used to produce the sixth type of quark, known as the top. This particle has a rest mass energy of approximately 160,000 MeV, which is nearly the same as the mass of nucleus of a gold atom!

Atoms of anti-hydrogen, which consist of a positron orbiting an antiproton, are believed to have been created in 1995 at the CERN laboratory in Europe. Physicists are now searching for very small differences between the properties of matter atoms and antimatter atoms. This will help confirm or confound our understanding of the symmetry between matter and anti-matter.

 

 

 


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I'm also not a physicist,

I'm also not a physicist, but I've seen a guy make a pizza crust.

If you take a spherical blob of pizza dough and spin it, centrifugal force causes the blob to flatten out and become disk-shaped. The mass of the dough out around the edge of the blob's equator (perpendicular to the axis of spin) hauls on the rest of the dough and stretches it out.  The more and faster you spin it, the flatter it becomes.

So unless I'm overlooking something that I don't know about physics, it seems analagous that if you take any spherical blob of matter and spin it, it will tend to flatten out along a plane perpendicular to the direction of spin.

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For the shape of solar

For the shape of solar systems and galaxies:

http://en.wikipedia.org/wiki/Kepler%27s_laws

 

Kepler's laws.

 

 

For anti-matter, mathematically anti-particles are travelling backwards in time.  


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Congrats Textom, you've

Congrats Textom, you've earned a place in my sig.


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I understand that all things

I understand that all things don't form to a sphere, mainly because of orbits, but I don't understand why seemingly all orbits go in the same direction.  For example, why isn't there a planet orbiting our sun whose orbit is perpindicular to ours?

I hope that when the world comes to an end I can breathe a sigh of relief, because there will be so much to look forward to.


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xamination wrote:

xamination wrote:
I understand that all things don't form to a sphere, mainly because of orbits, but I don't understand why seemingly all orbits go in the same direction. For example, why isn't there a planet orbiting our sun whose orbit is perpindicular to ours?

There are not any objects I am aware of that have an orbit perpencicular to the normal planetary orbital plane but there are a few objects farther out that are askew from the plane.

http://news.nationalgeographic.com/news/2002/10/1003_021007_quaoar_2.html

 

Mainly the analogy of a pizza crust is a great one, as the nebulous cloud became compressed and began to rotate, it flattened out becoming what is called an accretion disc. The planets were formed in this material that was already in the 'pizza crust' formation. They continued in that same rotational orbital plane and would only be knocked askew if another rather large body struck them from an angle with enough energy to jar them from the plane.


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Here is a good article that

Here is a good article that illustrates why some larger planets like to orbit closer to their stars. It does a good job of describing the gravitational and magnetic pull of the star and it's effect on the nearby planetary bodies.

 

Why some huge planets like to hug starsSpace.com logo

By Ker Than, SPACE.com     Stars form in cloudy nebulas and, shortly after genesis, consume most of the gas of their birthplace and use the surrounding dust and leftover gas to form planets, according to standard theory. 

The gas and dust collapse into a rotating "circumstellar" disk and are drawn toward the star. Planets are thought to sometimes migrate inward after birth, too. But scientists don't yet know what drives the inward spiraling motion.

A new model suggests magnetic instabilities in the disk cause gas to fall onto the star and also helps drag young planets into their final orbits.

"Astronomers observe gas crashing down upon the surfaces of young stars by virtue of the ultraviolet radiation they emit, but a way to transport this gas from the disk to the star has not been convincingly specified," said study team member Eugene Chiang at the University of California, Berkeley.

The new model, detailed online in the June 8 issue of the journal Nature Physics, could also help explain why some planets outside our solar system orbit so close to their parent stars.

The magnetic instability arises from the fact that gas in the circumstellar disk orbits at different speeds depending on its distance from the star. Radiating throughout the disk like spokes on a bicycle wheel are magnetic field lines.

Chiang likens the magnetic field lines to rubber bands binding the inner and outer gas rings together. Because the inner ring rotates faster than the outer one, the magnetic field "rubber bands" stretch in the direction of the rotation.

"What does that do? It pulls back on the inner ring and speeds up the outer one," Chiang told SPACE.com. This acts to slow down the inner ring, causing it to lose momentum and spiral inward to crash onto the star.

Chiang and coauthor Ruth Murray-Clay, also of UC Berkeley, say that recently observed "transitional disks"-gaps in the circumstellar disk that are free of dust-around young stars support their model.

The stellar wind of young stars blows dust out of the transitional disk regions, but has no effect on gas. The magnetic instability the researchers are hypothesizing only works if the spinning gas has sufficient electrical charge. Dust tends to absorb charges and reduce electrical conductivity.

Because the inflowing gas drags embedded objects, including young planets, along with it toward the star, the new model also has implications for planet formation. Hot Jupiters are giant gas planets that orbit closer to their parent stars than Mercury does to our sun and as a result have extremely high surface temperatures.

The new model suggests that planets riding the wave of inflowing gas toward the inner region of their solar systems can be halted by magnetic instabilities in the immediate vicinity of the star.

"Once disrupted, disk gas can no longer drag the planets inward," Chiang said.

Copyright 2007, SPACE.com Inc. ALL RIGHTS RESERVED.