<p>No, when we talk of the mass of a star, we mean its Mass-Energy.  That includes the rest mass of particles it is composed of plus the kinetic/heat energy of those particles in our frame of reference, plus the energy in any photons that are part of the sun minus the gravitational potential energy that binds the sun.  These all combine to give the total mass of the star. And it is this mass-energy that results in the star's gravity and inertia.</p>
<p>So when hydrogen nuclei fuse and give out energy (in the form of photons and neutrinos) the total mass-energy is conserved. If a photon has sufficient energy to produce a pair of electron+positron, the total mass energy is conserved. And if that pair annihilate to produce photons, the mass-energy is still conserved.  The total mass is still unchanged.</p>
<p>Note that pair production is not a significant reaction in stars, except in extremely massive stars at the end of their lives. And the loss of radiation pressure caused by pair production destabilises the star and leads almost immediately to supernova.</p>

CC BY-SA 4.0
2021-10-06T05:45:08.527Z
The mass of a star is its gravitational mass. It is less than the rest-mass for a bound object.
ProfRob
CC BY-SA 4.0
2021-10-06T13:41:24.953Z
Regarding @ProfRob's comment, see https://en.wikipedia.org/wiki/Kelvin%E2%80%93Helmholtz_mechanism
PM 2Ring
CC BY-SA 4.0
2021-10-06T05:19:31.457Z
2021-10-06T16:58:08.247Z
2021-10-06T16:58:08.247Z
James K
<p>The mass of a star is determined by its gravitational effects, not by summing up the components that give rise to that gravity.</p>
<p>If we were to do the latter, then we would have to include all the mass <em>and energy</em> in the star. This would comprise of the rest mass of all particles, the kinetic energy of the particles and the energy of massless particles like photons. It also includes the <em>negative</em> gravitational potential energy of the star. (The latter means that a bound star has a gravitational mass that is lower than the sum of its rest mass).</p>
<p>This means that the energy you mention in your question is already included, since it is part of this inventory, whatever form the mass-energy takes.</p>

CC BY-SA 4.0
2021-10-06T05:56:09.083Z
2021-10-06T05:56:09.083Z
ProfRob
<p>I would like to know that, since stars emit a lot of photons where some of them could be producing electrons-positrons pairs, if its mass affects the calculations, and if because of this is different from calculating the mass of a planet (which don't produce high energy photons)...
Are shinning objects more massive than its own particles' masses?</p>

CC BY-SA 4.0
2021-10-05T22:38:59.473Z
All the energy produced by high-energy photons emitted from the stars comes from mass within the star converted to energy in fusion reactions.
notovny
CC BY-SA 4.0
2021-10-06T12:19:01.597Z
You have chosen the wrong answer.
David Hammen
<mass><star-systems><quantum-mechanics>
When calculating the mass of stars, is it considered that additional mass could be added because of pair-production?
Joako
# When calculating the mass of stars, is it considered that additional mass could be added because of pair-production?

(Asked by: username_0 on 2021-10-05)

I would like to know that, since stars emit a lot of photons where some of them could be producing electrons-positrons pairs, if its mass affects the calculations, and if because of this is different from calculating the mass of a planet (which don't produce high energy photons)...
Are shinning objects more massive than its own particles' masses?

**Tags:** mass, star-systems, quantum-mechanics

> **Comments:**
> **username_1**: All the energy produced by high-energy photons emitted from the stars comes from mass within the star converted to energy in fusion reactions.  
> **username_2**: You have chosen the wrong answer.  

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## 2 answers

### Answer by username_3 on 2021-10-06. Score: 2 | Accepted answer

No, when we talk of the mass of a star, we mean its Mass-Energy. That includes the rest mass of particles it is composed of plus the kinetic/heat energy of those particles in our frame of reference, plus the energy in any photons that are part of the sun minus the gravitational potential energy that binds the sun. These all combine to give the total mass of the star. And it is this mass-energy that results in the star's gravity and inertia.

So when hydrogen nuclei fuse and give out energy (in the form of photons and neutrinos) the total mass-energy is conserved. If a photon has sufficient energy to produce a pair of electron+positron, the total mass energy is conserved. And if that pair annihilate to produce photons, the mass-energy is still conserved. The total mass is still unchanged.

Note that pair production is not a significant reaction in stars, except in extremely massive stars at the end of their lives. And the loss of radiation pressure caused by pair production destabilises the star and leads almost immediately to supernova.

> **Comments:**
> **username_4**: The mass of a star is its gravitational mass. It is less than the rest-mass for a bound object.  
> **username_5**: Regarding @username_4's comment, see https://en.wikipedia.org/wiki/Kelvin%E2%80%93Helmholtz_mechanism  

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### Answer by username_4 on 2021-10-06. Score: 5

The mass of a star is determined by its gravitational effects, not by summing up the components that give rise to that gravity.

If we were to do the latter, then we would have to include all the mass *and energy* in the star. This would comprise of the rest mass of all particles, the kinetic energy of the particles and the energy of massless particles like photons. It also includes the *negative* gravitational potential energy of the star. (The latter means that a bound star has a gravitational mass that is lower than the sum of its rest mass).

This means that the energy you mention in your question is already included, since it is part of this inventory, whatever form the mass-energy takes.


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