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Physics Lesson 22.12.4 - Formation of the solar system
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Welcome to our Physics lesson on Formation of the solar system, this is the fourth lesson of our suite of physics lessons covering the topic of Formation of Galaxies and Solar System. Actual Problems, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.
Formation of the solar system
As we have discussed in tutorial 22.5, the stars experience many changes during their existence, manly resulting from internal explosions. These explosions are more intense in the supernova stage. Hence, despite the primordial Universe has had only hydrogen and helium, it has been enriched with other elements that stars have created at their centre and ejected during internal explosions.
The formation of our Solar System makes no exception from the general rule. Initially it has been just a cosmic cloud (or dust) originating from Milky Way galaxy. After attracting matter from surroundings, it began to collapse about 4.6 billion year ago, where only planets formation era lasted for about 100 million years. However, this dust did not contain only hydrogen and helium; it also contained heavier elements ejected from other stars of the galaxy, which now are found in various celestial bodies of the solar system, especially in the first four, which are earthy planets but also in the core of the gaseous ones.
The following set of figures shows how Solar System has been formed. The first figure shows a cosmic cloud (dust) rotating around itself. In the second figure, gravitational force (which prevails over expanding effect of thermal energy) makes the cloud collapse. As a result, more matter gathers at centre of cloud. It eventually forms the Sun in the third figure (at centre), while smaller amounts of solar dust that were more in periphery and could not get into the centre, form the planets revolving in spiral paths (orbits).
To summarize, the cosmic cloud detached from the rest of Milky Way has collapsed under the effect of its gravity. As a result, the Sun was formed at centre, where most of dust gathered while the other planets were formed by a smaller amount of gas left outside the central part. The Sun has born as a Main Sequence star when thermonucelar reactions of fusion have started to occur at its centre. As for the remaining gas away from this centre, it has condensed due to lower temperatures, resulting therefore in the formation of small celestial objects that were a few hundred meters in dimensions (asteroids). They later attracted each other forming planets and other celestial bodies. There are still today many such small celestial bodies that were not able to form planets, especially between Mars and Jupiter. This set of celestial bodies is known as the Asteroids Belt, we covered this in detail in tutorial 22.1.
The process of asteroids formation in the Solar System has lasted for about 3 millions of years. At a first glance, it looks a long process, but when compared to the age of Milky Way galaxy (13.7 billion years old) the process of the solar system formation was relatively short. In the scientific viewpoint, it helps us describe in detail many phenomena actually occurring in our Solar System. For example, now it is clear why all planets revolve in the same direction around the Sun. This occurs because initially all of them were part of the same cosmic cloud that was revolving as a whole around its centre. In addition, the rotation of the Sun and planets around their own axis is explained well through this model.
Example 1
The actual density of the observable Universe is about 10-27 kg/m3 and its actual radius is 8.8 × 1026 m. At Planck's time, the density of Universe was 1090 kg/m3. What was the radius of Universe at that instant if we assume that actually we are able to observe the entire Universe?
Solution 1
The quantity that has remained constant over time is the mass m of Universe. This helps us compare the other two related quantities: density and volume in the given instants. If we use the index (1) to represent quantities at Planck's time and the index (2) to represent the same quantities now, we have:
ρ1 ∙ V1 = ρ2 ∙ V2
If we consider the Universe as a sphere of radius R, we have
ρ1 ∙ R31 = ρ2 ∙ R32
R31 = ρ2 ∙ R32/ρ1
R1 = ∛ ρ2 ∙ R32/ρ1
= ∛ (10-27 kg/m3 ) ∙ (8.8 × 1026 m)3 )/1090 kg/m3
= 2.06 × 10-13 m
This value is very small; no actual measuring device can detect such a length. Hence, either the Universe is much bigger than we are able to see, or it began from a very small point (or both versions are true).
You have reached the end of Physics lesson 22.12.4 Formation of the solar system. There are 7 lessons in this physics tutorial covering Formation of Galaxies and Solar System. Actual Problems, you can access all the lessons from this tutorial below.
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