In this answer they say:

While the conversion of mass matter† to energy in the Sun's core now represents a loss of mass proper matter, it turns out that that energy (trapped in the Sun and slowly diffusing towards the surface) will have the same gravitational attraction as the matter it came from until it actually escapes the Sun!

Now I expect that when mass is converted to energy, it has become an electromagnetic wave that can propagate through matter or empty space.

My question is: How does energy (from fusion reactions still inside the sun) still have gravitational attraction?

  • $\begingroup$ Energy and mass are both equivalent . E=m c**2. $\endgroup$ – planetmaker Feb 29 '20 at 10:15
  • $\begingroup$ Thanks - does that imply that energy has gravitational attraction? $\endgroup$ – hawkeye Feb 29 '20 at 10:19
  • $\begingroup$ yes, exactly that $\endgroup$ – planetmaker Feb 29 '20 at 11:42
  • $\begingroup$ +1 @hawkeye this is definitely a good question and while I am sure the answer is correct I can't explain why, so it deserves a much better answer than I can write! $\endgroup$ – uhoh Feb 29 '20 at 13:47
  • $\begingroup$ "it has become an electromagnetic wave that can propagate through matter or empty space." This isn't really true, as you note in your quote. The electromagnetic wave is very much trapped by all the Sun's matter. It takes a long time for the photons to work their way through all the mass in the sun, bouncing around for a long time before making it into space. $\endgroup$ – userLTK Feb 29 '20 at 14:09

I think it is best not to think of energy having a gravitational attraction, rather that energy, like mass, (since they are equivalent keeping in mind c) will curve spacetime. Electric charges, magnets, and electromagnetic fields will curve spacetime, Scientific American. So whether it is mass or energy, they both will affect the curvature of spacetime, and the sun's total impact on spacetime will not change.


Theoretically you can create a black hole from just energy. Although the amount of energy required to be focused in one spot is impractically huge. And why it’s easier to do it with matter.

So the energy inside the sun should still contribute to its gravitational effect on other bodies until it exits the surface.

  • 1
    $\begingroup$ A photon inside a star does not have mass. By the definition of a photon is a massless particle. The photon doesn't add to the star's mass. $\endgroup$ – Bob516 Mar 2 '20 at 18:54

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