How did the sun wind up in the middle of the solar system?
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Since our solar system is already formed, we must try to reconstruct its history by studying current star formation in our local neighborhood, the Milky Way galaxy.
The best model of our solar system's history states that it formed from the collapse of a single interstellar cloud that may have been as large as a light-year across—10 million times larger than the diameter of the sun. The cloud was likely irregular in shape, perturbed by neighboring stars and other clouds. As it compacted and cooled, the cloud's own gravity overpowered any forces acting to stabilize the system. It then proceeded to contract dramatically.
Prior to its collapse, the original cloud probably began with a fixed mass and a slight, random rotation relative to some central axis. This kind of rotational motion is measured by its "angular momentum," which is directly proportional to the system's mass multiplied by the rate at which its material sweeps out area around the rotational axis. A fundamental principle of physics is that angular momentum, like energy, is conserved. As the cloud collapses, both its mass and angular momentum remain constant. Since the rate at which area is swept out is fixed, a smaller cloud has a shorter period of rotation and a contracting cloud "spins faster" with time. A famous example of this phenomenon is the spinning ice skater who pulls in her arms and consequently rotates faster.
As a rotating cloud of interstellar gas collapses, it also tends to flatten. In the case of our solar system, most of the initial interstellar mass helped form the sun. The portion of the mass with the most angular momentum remained in a disk, which then orbited the sun. We believe that the planets formed out of this disk, and therefore the sun is naturally found at the center of this event. Although the sun has about 1,000 times the mass of Jupiter, the orbital motion of Jupiter has a larger angular momentum than the sun, seeing as they both sweep out space around the sun's center.
With modern telescopes we observe disks around young stars, which seems to indicate that these rotating disks that become planets come into being when a star is formed. Current observations show that at least 5 percent of stars that are similar to the sun possess Jupiter-like planets. The fraction of stars surrounded by planets may actually be much larger than that figure.
A large gas cloud condensed and formed the sun; while doing this, it started spinning, and clumps of mass on the periphery formed the planets (while the bulk got in the center and formed the sun itself).
The sun is in the center because the sun is 99.9% of the mass fo the solar system. The matter than formed the planets does not come from the sun itself, it is the left over from the cloud that formed the sun.
By being the biggest thing. So, its gravity keeps the planets circling around it.
The sun was born and its gravity attracted the building blocks for the planets..The sun was there and we jsut started orbiting it (because it is the centr of gravity of our solar system).
Currently, the sun is in the middle because it is very massive and it accelerates the smaller objects around it. One time I was going to build a scale model of our system for my room. I quickly realized that it wouldn't fit. If the sun were a beach ball at one goal-post of a football field, earth would be the size of a marble at the other goal-post. So initially it sounds like earth was nothing more than a piece of space dust.
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