<blockquote>
  <p>As the surface of the earth is solid the crust,</p>
</blockquote>

<p>Correct. </p>

<blockquote>
  <p>underneath the crust the mantle which is liquid,</p>
</blockquote>

<p>No the mantle is also solid, although more plastic than the crust. There is a liquid core below the mantle</p>

<blockquote>
  <p>the liquid density is smaller than the crust. </p>
</blockquote>

<p>No the core is made of iron and considerably denser than the mantle rocks above it.</p>

<blockquote>
  <p>This way the earth can exercise self-rotation. </p>
</blockquote>

<p>I don't know what you mean. Fully solid bodies, liquid bodies, gaseous bodies can all rotate.</p>

<blockquote>
  <p>Therefore, since the sun also self-rotating, the sun's surface is gas; </p>
</blockquote>

<p>Actually plasma, but that is a detail</p>

<blockquote>
  <p>it follows that beneath the gas surface there could only be void which the density smaller than gas, otherwise it wouldn't be possible for the sun to exercise self-rotation. </p>
</blockquote>

<p>No. This doesn't follow. It is not the case that there is a void, for if there were, the plasma would flow into it. In fact density increases with depth.</p>

<blockquote>
  <p>So, is the sun hollow? Or any reason that the sun can only be hollow inside?</p>
</blockquote>

<p>No the sun is not hollow.</p>

CC BY-SA 3.0
2018-04-27T14:45:56.150Z
but self-rotation will result a force that need absorption therefore the underneath has to be less dense, that's my point, no?
Mishu 米殊
CC BY-SA 3.0
2018-04-27T14:47:27.130Z
due to rotation and vigorous activity it will prevent the plasma flow into the void, like a whirlpool the debris will swinging around instead of drop inside immediately, no?
Mishu 米殊
CC BY-SA 3.0
2018-04-27T15:03:15.337Z
@Mishu米殊 What do you mean by "self rotation" ?
StephenG - Help Ukraine
CC BY-SA 3.0
2018-04-27T15:08:45.357Z
+1 for a step-by-step answer brimming with crystal clarity.
John Duffield
CC BY-SA 3.0
2018-04-27T15:09:53.507Z
@StephenG I fear we're being trolled here.  Let's just let it drop.
Carl Witthoft
CC BY-SA 3.0
2018-04-27T15:25:30.017Z
I mean the rotation of earth, say 24 hours one completed rotation, against rotating around the sun once for 365 days; that's not called self-rotation? @StephenG
Mishu 米殊
CC BY-SA 3.0
2018-04-27T17:45:56.857Z
No whirlpool needed, debris atracts one antoher like little magnets, debris don't drop inside because inside is already full of debris, debris inside are hotter and more dense
jean
CC BY-SA 3.0
2018-04-27T18:40:31.313Z
@CarlWitthoft I don't think we have a troll.  We probably just have someone with little science knowledge and possibly a language difficulty - not a native English speaker.  The OP seems to have reasonable reps on other SE sites.
StephenG - Help Ukraine
CC BY-SA 3.0
2018-04-27T14:43:01.807Z
2018-04-27T14:43:01.807Z
James K
<p>With most celestial bodies above a certain size limit, you can safely assume they only become more and more dense the closer you get to the center. This is true for most planets and it's definitely true for the Sun.</p>

<p>But the aggregation state (solid, liquid, gas) does not matter for the spin (I believe that's what you mean by "self-rotation"). If it's spinning, then it's spinning, no matter what it's made of.</p>

<p>What keeps the Sun in one piece is only its gravity, nothing else. The various parts of the Sun are compressed together by the overall gravity of this object. Spin doesn't matter here.</p>

<p>Spin would matter if the Sun was spinning incredibly fast. But that's not the case, it's not even close; it would have to spin by orders of magnitude faster in order to break up because of that. Like, thousands of times faster, I'm not even sure what the number is but it's huge.</p>

<p>Finally, aggregation states are not very important at cosmic scales. Planets like the Earth are technically "solid", but they behave more like fluids, or more like piles of sand, during an impact. Also, the "solid" parts of the Earth actually do flow like liquids over many millions of years. There are no clearly defined rules here.</p>

CC BY-SA 3.0
2018-04-28T16:26:46.910Z
Thanks. But I get that if a large celestial object spins, it will need an inner part that's less solid than the surface to balance off the spinning, or to absorb and re-adjust to keep the status quo, otherwise it may grid, i.e., skipping off from the same spot. What do you think?
Mishu 米殊
CC BY-SA 3.0
2018-04-30T19:38:31.430Z
@Mishu米殊 I honestly don't understand the observation. A solid steel ball can spin just fine, and it's completely solid.
Florin Andrei
CC BY-SA 3.0
2018-04-27T20:11:46.077Z
2018-04-27T20:11:46.077Z
Florin Andrei
<p>[Edited to remove incorrect geological assumptions]</p>

<p>The sun is self-rotating, i.e. it spins on its axis. When something spins, there's an apparent force away from the centre, and matter gets flung out. The sun's surface is gas; it follows that beneath the gas surface there could only be void with the density less than the surface. So, is the sun hollow, and if it isn't, what's the reason that the centrifugal force doesn't spin the matter outwards?    </p>

CC BY-SA 3.0
2018-04-27T15:09:21.463Z
Possible world's record for most wrong claims in one paragraph.
Carl Witthoft
CC BY-SA 3.0
2018-04-27T15:21:29.217Z
Welcome. Please edit if you can/may, thanks @CarlWitthoft
Mishu 米殊
CC BY-SA 3.0
2018-04-27T21:00:19.233Z
Density of liquid iron is still near 7gm/cc. Pv = nrT tells  You that gases get denser as pressure increases.
Wayfaring Stranger
CC BY-SA 3.0
2018-04-28T12:06:29.190Z
I've proposed a fairly substantial edit to the question that I hope expresses Mishu's intentions. There's a lot of misunderstanding about centrifugal pseudo-forces, centripetal forces and rotating reference frames, so it might be an opportunity for someone to add a third answer addressing this in layperson's terms.
Chappo Hasn't Forgotten
CC BY-SA 3.0
2018-04-28T22:49:59.400Z
There is *nothing* flat earth-like thing in this question! It is an ordinary astronomics question, and thus it deserves a reopen.
peterh
<the-sun><earth><rotation><density>
Why isn't the Sun hollow?
Mishu 米殊
# Why isn't the Sun hollow?

(Asked by: username_0 on 2018-04-27)

[Edited to remove incorrect geological assumptions]

The sun is self-rotating, i.e. it spins on its axis. When something spins, there's an apparent force away from the centre, and matter gets flung out. The sun's surface is gas; it follows that beneath the gas surface there could only be void with the density less than the surface. So, is the sun hollow, and if it isn't, what's the reason that the centrifugal force doesn't spin the matter outwards?

**Tags:** the-sun, earth, rotation, density
> **Comments:**
> **username_1**: Possible world's record for most wrong claims in one paragraph.  
> **username_0**: Welcome. Please edit if you can/may, thanks @CarlWitthoft  
> **username_2**: Density of liquid iron is still near 7gm/cc. Pv = nrT tells  You that gases get denser as pressure increases.  
> **username_3**: I've proposed a fairly substantial edit to the question that I hope expresses Mishu's intentions. There's a lot of misunderstanding about centrifugal pseudo-forces, centripetal forces and rotating reference frames, so it might be an opportunity for someone to add a third answer addressing this in layperson's terms.  
> **username_4**: There is *nothing* flat earth-like thing in this question! It is an ordinary astronomics question, and thus it deserves a reopen.  

---

## 2 answers

### Answer by username_5 on 2018-04-27. Score: 8

> As the surface of the earth is solid the crust,

Correct.

> underneath the crust the mantle which is liquid,

No the mantle is also solid, although more plastic than the crust. There is a liquid core below the mantle

> the liquid density is smaller than the crust.

No the core is made of iron and considerably denser than the mantle rocks above it.

> This way the earth can exercise self-rotation.

I don't know what you mean. Fully solid bodies, liquid bodies, gaseous bodies can all rotate.

> Therefore, since the sun also self-rotating, the sun's surface is gas;

Actually plasma, but that is a detail

> it follows that beneath the gas surface there could only be void which the density smaller than gas, otherwise it wouldn't be possible for the sun to exercise self-rotation.

No. This doesn't follow. It is not the case that there is a void, for if there were, the plasma would flow into it. In fact density increases with depth.

> So, is the sun hollow? Or any reason that the sun can only be hollow inside?

No the sun is not hollow.

> **Comments:**
> **username_0**: but self-rotation will result a force that need absorption therefore the underneath has to be less dense, that's my point, no?  
> **username_0**: due to rotation and vigorous activity it will prevent the plasma flow into the void, like a whirlpool the debris will swinging around instead of drop inside immediately, no?  
> **username_6**: @Mishu米殊 What do you mean by "self rotation" ?  
> **username_7**: +1 for a step-by-step answer brimming with crystal clarity.  
> **username_1**: @StephenG I fear we're being trolled here.  Let's just let it drop.  
> **username_0**: I mean the rotation of earth, say 24 hours one completed rotation, against rotating around the sun once for 365 days; that's not called self-rotation? @StephenG  
> **username_8**: No whirlpool needed, debris atracts one antoher like little magnets, debris don't drop inside because inside is already full of debris, debris inside are hotter and more dense  
> **username_6**: @CarlWitthoft I don't think we have a troll.  We probably just have someone with little science knowledge and possibly a language difficulty - not a native English speaker.  The OP seems to have reasonable reps on other SE sites.  

---

### Answer by username_9 on 2018-04-27. Score: 2

With most celestial bodies above a certain size limit, you can safely assume they only become more and more dense the closer you get to the center. This is true for most planets and it's definitely true for the Sun.

But the aggregation state (solid, liquid, gas) does not matter for the spin (I believe that's what you mean by "self-rotation"). If it's spinning, then it's spinning, no matter what it's made of.

What keeps the Sun in one piece is only its gravity, nothing else. The various parts of the Sun are compressed together by the overall gravity of this object. Spin doesn't matter here.

Spin would matter if the Sun was spinning incredibly fast. But that's not the case, it's not even close; it would have to spin by orders of magnitude faster in order to break up because of that. Like, thousands of times faster, I'm not even sure what the number is but it's huge.

Finally, aggregation states are not very important at cosmic scales. Planets like the Earth are technically "solid", but they behave more like fluids, or more like piles of sand, during an impact. Also, the "solid" parts of the Earth actually do flow like liquids over many millions of years. There are no clearly defined rules here.

> **Comments:**
> **username_0**: Thanks. But I get that if a large celestial object spins, it will need an inner part that's less solid than the surface to balance off the spinning, or to absorb and re-adjust to keep the status quo, otherwise it may grid, i.e., skipping off from the same spot. What do you think?  
> **username_9**: @Mishu米殊 I honestly don't understand the observation. A solid steel ball can spin just fine, and it's completely solid.  

---

