Nebular hypothesis

[Bilal Hussain]

I have a big confussion about this hypothesis some time I think thak we should make some amendments in this hypothesis....

 

[Phi for All]

No offense, but if you're confused about the Nebular Hypothesis, wouldn't it be more practical to identify your confusion about the model first before amending anything?

[Bilal Hussain]

Dera plz note the statement of hypothesis and aslso about the densties of planets and our star(Sun).

[Phi for All]

Dera plz note the statement of hypothesis and aslso about the densties of planets and our star(Sun).

 

Would you please note the statements you're referring to, and include the parts you find confusing so we know exactly where to start the discussion? Any further information you can give us is greatly appreciated. Thank you.

[Bilal Hussain]

According to the nebular hypothesis, stars form in massive and dense clouds of molecular hydrogen—giant molecular clouds (GMC). They are gravitationally unstable, and matter coalesces to smaller denser clumps within, which then proceed to collapse and form stars. Star formation is a complex process, which always produces a gaseous protoplanetary disk around the young star. This may give birth to planets in certain circumstances, which are not well known. Thus the formation of planetary systems is thought to be a natural result of star formation. A sun-like star usually takes around 100 million years to form.
The protoplanetary disk is an accretion disk which proceeds to feed the central star. Initially very hot, the disk later cools in what is known as the T tauri star stage; here, formation of small dust grains made of rocks and ices is possible. The grains may eventually coagulate into kilometer-sized planetesimals. If the disk is massive enough the runaway accretions begin, resulting in the rapid—100,000 to 300,000 years—formation of Moon- to Mars-sized planetary embryos. Near the star, the planetary embryos go through a stage of violent mergers, producing a few terrestrial planets. The last stage takes around 100 million to a billion years(wikipedia).

 

Plz concentrate on this sentence how it is possible that in a rotating medai the objevt which have very low desity accumulate in the center of media as you all well known sun have very low density as compare to its planets.....

Edited October 18, 2013 by Bilal Hussain

[Ophiolite]

The sun is composed primarily of hyrdogen and helium. Because of its great mass the central portions undergo considerable compression, despite this its gaseous nature accounts for its low density. The Sun has a low density only in comparison with the terrestrial planets. Consider these data of the densities in grams/cc:

 

Sun - 1.41

Mercury 5.43

Venus 5.24

Earth 5.52

Mars 3.94

Jupiter 1.33

Saturn 0.7

Uranus 1.3

Neptune 1.76

 

Note that three of the four giant planets have densities lower than the sun. As noted in your quote solids condense out of the accretion disc and form planetary embryos. The giant planets form cores large enough to attract large volumes of gas. When the proto-sun enters the T-Tauri stage is blasts most of this gas out of the system, leaving the gas and ice giants with rocky cores but a low density, while the terrestrial, rocky planets have a high density because of their silicate and iron composition.

 

Does that help? Reading the full quote I seem to have largely repeated what they said, so I'm not clear what it is you don't understand. The explanation is present in both the quote and what I have said.

Edited October 18, 2013 by Ophiolite

[Bilal Hussain]

Try to understand me I think it is not possible that in a rotationg media the mass of gas accumulate in the the center....

[Strange]

Well, I guess that depends how fast it is rotating. After all, if it isn't rotating then it will collapse, due to its own gravity. So if it is rotating slowly it can collapse, as well. No doubt there is a rotation speed above which it won't collapse. I don't know if any such clouds have been identified.

[Ophiolite]

Try to understand me I think it is not possible that in a rotationg media the mass of gas accumulate in the the center....

Again, the net motions of the GMC following collapse lead to a concentration of material, the bulk of which is gas, at a point determined by those net motions and gravity. That becomes the centre. There is plenty of gas throughout the rest of the accretion disc until the proto-star reaches the T-Tauri stage and 'blasts' any gas that has not accreted to planets, especially gas and ice giants, out of the system.

 

I am at a loss to explain it any more clearly.

[Bilal Hussain]

well thankx bro but I wanna conduct some expariment about this if you have any idea plz tell me.

[Strange]

well thankx bro but I wanna conduct some expariment about this if you have any idea plz tell me.

Experiments would be hard as this depends on the gravitation of the gas cloud, which will be very weak and insiginificant for any experimental set up. You could use a simulation to model what happens (which is, of course, what astrophysicits do).

Edited October 21, 2013 by Strange