If there is no oxygen in the sun, then how is it burning?

My question may be weird but I need a realistic answer for that.

  • 4
    $\begingroup$ You are right, the sun is not burning in chemical meaning. The sun fusions hydrogen to helium and generates energy this way. If the sun would need oxygen to burn, it would have used all oxygen very long ago. $\endgroup$
    – Uwe
    Aug 18, 2017 at 11:39
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    $\begingroup$ The word "burn" is not limited to a fuel-oxygen fire. Pretty much any rapid and steady consumption could be described with the word. Eg. startups burn through their seed capital. Work teams burn through their task queues. Exercise burns calories. "Sun is burning hydrogen" means it's consuming it somehow, not necessarily combusting. It's more linguistic question than physics one : ) $\endgroup$
    – Agent_L
    Aug 18, 2017 at 16:34
  • 1
    $\begingroup$ @Agent_L In the case of exercise, that actually is exothermic oxidation. ;-) $\endgroup$ Aug 18, 2017 at 16:46
  • 1
    $\begingroup$ @chrylis It is. But so is rusting and going rancid - yet those ones are not called burning for some reason. $\endgroup$
    – Agent_L
    Aug 18, 2017 at 16:49
  • $\begingroup$ en.wikipedia.org/wiki/Sun $\endgroup$ Aug 18, 2017 at 17:26

4 Answers 4


The sun is not "burning" in the sense you are used to: there is no chemical reaction going on. Instead, there is a very high pressure in the core of a star (like our sun) due to the high mass that starts/sustains a nuclear fusion process. In our sun, hydrogen is fused to helium and the energy that's released in this process is what makes the sun "glow" and emit energy.


There is oxygen and many other elements on the Sun. The "burning" you refer to is fusion, it does not require oxygen.

Oxygen is created by: 12 C + 4 He ------> 16 O + energy.

In case you are wondering how the carbon for that reaction is created it comes from: 3 (4He) ------> 12C + energy, with the helium derived from: 4 (1H) ------> 4 He + 2 e+ + 2 neutrinos + energy.

Source: https://imagine.gsfc.nasa.gov/educators/lessons/xray_spectra/activity-fusion.html


So, the Sun isn't actually burning, hydrogen is fused to helium (without the need for oxygen). It should be noted that in the presence of carbon, nitrogen and oxygen, stars heavier than the Sun may burn hydrogen to helium by using the C, N and O as catalysts. Even in these stars, however, an absence of oxygen does not prevent nuclear burning.

If you want to read more, try How can a star burn with no oxygen? (Beginner) by Kristine Speakers.

  • $\begingroup$ Just saying that you do not need to do a lot of research in order to find an answer to that... $\endgroup$
    – Matthew
    Aug 18, 2017 at 12:24
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    $\begingroup$ I'm not sure it's helpful to use the word "burn" to explain that the sun isn't actually a fire. $\endgroup$ Aug 18, 2017 at 16:05

The sun is so hot that if any steam were present, it would break down into a "plasma" of parts of hydrogen atoms, parts of oxygen atoms, and electrons. Thus, the sun is not being heated by hydrogen and oxygen chemically burning to form steam. Other answers mention the thermonuclear reactions (between especially fast-moving individual nuclei at the center of the sun) that heat the sun.

According to Andrew M. Davis, Ko Hashizume, Marc Chaussidon, Trevor R. Ireland, Carlos Allende Prieto, and David L. Lambert's 2008 article on "Oxygen in the Sun", the sun has about 468 atoms of oxygen per million atoms of hydrogen.

The article was published in Reviews in Mineralogy and Geochemistry.


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