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Refer to the below minutephysics video, in which they say that in order to reach the Sun from earth, we must first stop revolving around the Sun ie make our tangential velocity zero, and then head straight for the sun, otherwise it is nearly impossible to reach the sun because even a very huge push towards the sun will either send us in an elliptical or hyperbolic orbit:-

https://www.youtube.com/watch?v=LHvR1fRTW8g

If even a little bit of orbital speed tangentially, prevents something from falling into the sun, then I wonder how does the sun formed itself at the beginning? Because, most collapsing material probably would be having at least some tangential velocity with respect to the center.

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  • $\begingroup$ Welcome to Astronomy Stack Exchange! Can you please summarize the contents of the video? Otherwise, link rot can get rid of a lot of useful information. $\endgroup$ – HDE 226868 Jun 26 '17 at 23:01
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Where you're wrong:

even little bit of orbital speed tangentially prevents something from falling into the sun

You need to have huge tangential velocity to escape the sun attraction! The closer you are, the higher the velocity must be for celestial body to avoid falling on the sun.

While Venus is orbiting the Sun at 35.02 Km/s, the Earth is also orbiting the Sun in the same direction at 29.78 Km/s. [Reference]

It's not easy to understand, because there is no clear analogy of how stars form at our level on earth.

Interstellar gas clouds eventually collapse to form stars are very large, very massive, very cold, and very tenuous. The star is at the beginning a little portion of the cloud that is more dense than the rest - it results of local and large scale instabilities (some call it an element of chaos).

Little by little, the density at the center of the cloud increase - at the same time, it has to overcome opposite forces arising from more probable friction. If the gas is cool enough compared to the density, at some point you start having more and more matter, which results in more and more gravitational attraction for surrounding gas.

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  • $\begingroup$ I think you are right. I was thinking about oort cloud and comets - that their velocities are so less, but still they either form a highly eccentric elliptical orbit or hyperbolic orbit, when pushed towards the Sun. But now, I think that I ignored their distance from the Sun. Your first para cleared this. I hope its right. $\endgroup$ – amsquareb Jun 26 '17 at 14:06
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    $\begingroup$ "It's not easy to understand, because there is no clear analogy of this at our level on earth." I think the simplest analogy is trying to throw a stone into orbit. Even with "a little bit" of tangential velocity the stone collides with Earth shortly. $\endgroup$ – Asher Jun 27 '17 at 15:35
  • $\begingroup$ @Asher No, I meant analogy with the sun's formation(title of the question). Edited accordingly. $\endgroup$ – J. Chomel Jun 27 '17 at 16:49

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