<p>It's very easy to create a star: you just put an amount of hydrogen gas quite near to each other and gravity will do the rest.</p>

<p>The problem is that the amount of gas you need for that is so large that even replacing the whole earth with hydrogen atoms is far from enough: you need far more hydrogen atoms for that and as such you can't do something on the earth when you need more space than the whole content of the earth :-)</p>

CC BY-SA 3.0
2017-11-15T15:40:30.147Z
2017-11-15T15:40:30.147Z
Dominique
<p>The process by which stars convert hydrogen to helium isn't burning; it is the fusion of the nuclei of atoms. To get nuclei to fuse you need to confine them in a very small space and get them very hot. On Earth we can make things very hot, and we can put things under lots of pressure. The trouble is that we can't do both at the same time. </p>

<p>The usual way we put things under pressure is squeezing them in some sort of vice. But if the thing we are squeezing is many millions of degrees, it will just vapourize our equipment. If we heat up some hydrogen, it expands and we don't get the confinement required for sustained fusion. (But this is how a thermonuclear bomb works)</p>

<p>Now a star is a huge ball of gas. The weight of the gas compresses the inner core of the star to an enormous pressure and traps the heat. A litre of the sun's core would weigh about 150kg at a pressure of about 250 billion atmospheres, and have a temperature of 15million degrees. This combination of temperature and pressure cannot be achieved on Earth. The hydrogen in the sun's core is confined by its own gravity.</p>

<p>Back on Earth we are trying to confine hydrogen with magnetic fields. (See the ITER Tokamak) With this system we will be able to start fusion, but the amount of energy we get out is less than the energy we put in. However solving this problem is merely a technical challenge. If we can work out how to use magnetic fields to confine hydrogen at very high temperatures we will be able to generate power from fusion.</p>

CC BY-SA 3.0
2017-11-14T20:56:49.913Z
2017-11-14T20:56:49.913Z
James K
<p>If we know that the reason a star burns without oxygen and fuel is that it converts hydrogen into helium and we have these two elements on earth then why can’t we make a star on our planet</p>

CC BY-SA 3.0
2017-11-14T01:13:24.353Z
Read this article on [fusion](https://en.wikipedia.org/wiki/Nuclear_fusion) and it should become clearer.
StephenG - Help Ukraine
CC BY-SA 3.0
2017-11-14T09:51:21.353Z
If you are asking about nuclear fusion, it is a thing on earth but still on development. If you talk about a proper star, well, you would need about 100 times the mass of Jupiter of hydrogen (and other stuff) to do that.
Daniel Ibaseta
CC BY-SA 3.0
2017-11-14T15:28:07.313Z
There are many many ways to "burn" without oxygen.  Describing either nuclear fusion or nuclear fission as "burning" is a stretch.
Carl Witthoft
CC BY-SA 3.0
2017-11-14T20:26:37.393Z
Just because we know the physics behind something doesn't mean we have the technology to employ that physics.
zephyr
<fundamental-astronomy>
Why Can’t we make a star
user19651
# Why Can’t we make a star

(Asked by: username_0 on 2017-11-13)

If we know that the reason a star burns without oxygen and fuel is that it converts hydrogen into helium and we have these two elements on earth then why can’t we make a star on our planet

**Tags:** fundamental-astronomy
> **Comments:**
> **username_1**: Read this article on [fusion](https://en.wikipedia.org/wiki/Nuclear_fusion) and it should become clearer.  
> **username_2**: If you are asking about nuclear fusion, it is a thing on earth but still on development. If you talk about a proper star, well, you would need about 100 times the mass of Jupiter of hydrogen (and other stuff) to do that.  
> **username_3**: There are many many ways to "burn" without oxygen.  Describing either nuclear fusion or nuclear fission as "burning" is a stretch.  
> **username_4**: Just because we know the physics behind something doesn't mean we have the technology to employ that physics.  

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## 2 answers

### Answer by username_5 on 2017-11-15. Score: 3

It's very easy to create a star: you just put an amount of hydrogen gas quite near to each other and gravity will do the rest.

The problem is that the amount of gas you need for that is so large that even replacing the whole earth with hydrogen atoms is far from enough: you need far more hydrogen atoms for that and as such you can't do something on the earth when you need more space than the whole content of the earth :-)


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### Answer by username_6 on 2017-11-14. Score: 2

The process by which stars convert hydrogen to helium isn't burning; it is the fusion of the nuclei of atoms. To get nuclei to fuse you need to confine them in a very small space and get them very hot. On Earth we can make things very hot, and we can put things under lots of pressure. The trouble is that we can't do both at the same time.

The usual way we put things under pressure is squeezing them in some sort of vice. But if the thing we are squeezing is many millions of degrees, it will just vapourize our equipment. If we heat up some hydrogen, it expands and we don't get the confinement required for sustained fusion. (But this is how a thermonuclear bomb works)

Now a star is a huge ball of gas. The weight of the gas compresses the inner core of the star to an enormous pressure and traps the heat. A litre of the sun's core would weigh about 150kg at a pressure of about 250 billion atmospheres, and have a temperature of 15million degrees. This combination of temperature and pressure cannot be achieved on Earth. The hydrogen in the sun's core is confined by its own gravity.

Back on Earth we are trying to confine hydrogen with magnetic fields. (See the ITER Tokamak) With this system we will be able to start fusion, but the amount of energy we get out is less than the energy we put in. However solving this problem is merely a technical challenge. If we can work out how to use magnetic fields to confine hydrogen at very high temperatures we will be able to generate power from fusion.


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