I believe it'd be foolish to assume that magic wouldn't affect astronomical phenomena like stellar evolution, But since I'm not smart enough to create the equations for a new fundamental force, I have instead decided on one major effect (for now) existing on stars, and I wish to know how this would effect stellar evolution

  • Stars are much more convective in this universe than in our reality, while remaining just as hot and bright. Stars up to 0.6 solar masses are still fully convective like the smaller red dwarfs present in real life; but still burn just as hot and luminous.

The type of star I'm mostly curious of are fully convective stars capable of helium fusion; which don't exist in real life. I have an idea based on intuition, and I'd like to ask if there's any science backing it up.

Here's the intuition based answer:

They evolve like a red dwarf into a blue dwarf stage (Albeit a lot faster) until helium fusion begins at which point it would turn into a red giant; which would evolve like any other red giant (though slower) until it loses so much mass that helium fusion can't be sustained anymore, at which point it contracts down into a white dwarf.

  • 3
    $\begingroup$ If you are going to invent magic stars why do you need science? Make them how you want! I understand if the magic is just one thing in your universe and you want to keep the rest clean but if you have one magic element it would be good to lay out how exactly it affects the stars. Is it a convection thing? A fusion thing? A helium thing? Then an answer would extrapolate from that to the rest of the star lif cycle. $\endgroup$
    – Willk
    Jul 25, 2021 at 15:22
  • $\begingroup$ I thought the red giant branch was defined by helium fusion beginning. Is this incorrect? At the moment it just makes stars more convective. No affects on fusion or helium. $\endgroup$ Jul 25, 2021 at 23:34
  • $\begingroup$ To be clear (because for some reason you can't edit after 5 minutes), the only reason there are fully convective stars that burn helium is because stars can be more massive while still being fully convective. Up to and past the point where Helium fusion becomes possible late in the stars life normally. $\endgroup$ Jul 25, 2021 at 23:40
  • $\begingroup$ @InfiniteDelta I'm not sure what I was confused about earlier - everything you wrote in the question seems pretty clear; the fault is mine. Sorry about that. $\endgroup$
    – HDE 226868
    Jul 26, 2021 at 0:12
  • $\begingroup$ @Willk I personally find fantasy books more interesting when they include some science, maybe the OP is writing a book for that type of audience? $\endgroup$ Jul 26, 2021 at 1:36

2 Answers 2


Of course, the answer depends on the laws of physics you consider to solve the problem. I’m giving an answer based on really basic laws, but it’s obviously possible to give other answers by taking other theories into account (relativity, nuclear physics, and so on). My answer uses these simple physics models:

  • basic thermodynamic: energy conservation and entropy.
  • classical mecanichs: energy can be "stored" as movements (linear or rotations), and you have centrifugal forces.
  • basic chemistry: nuclear reactions in stars are chemical reactions that produces or consume heat (no radiations are taken into account, this no real nuclear reactions as in modern nuclear models, although I confess this is a shame…).
  • since in your model you have a weight loss due to radiation, we will use this complementary hypothesis: energy can turn into mass, mass into radiations, radiations into energy, or any combination of these (basically more or less "e=mc^2")

These models are valid, even if they are not the most up-to-date ones ^^ Or it’s up-to-date in a late 1920’s world.

In this context, the answer is probably yes, with slight differences, due to these mechanisms:

  • since you have convection, the atoms are getting hotter while getting closer to the heart of the star. The convection movement can also locally increase the pressure, so the temperature (energy exchange between movement and heat).
  • more heat and pressure means more possibilities of nuclear reactions, which brings more light (convection -> energy(heat) -> radiations).
  • more radiations, and more heat, so a higher frenquency of radiation -> red light turns to blue (nuclear physics would be useful here, but I said I would do without it) AND more pressure so more density, so more gravity, so smaller star -> this is your first step (blue dwarf).
  • more accumulated heat but less materials to react, so the energy can just transfer to movement -> the spinning movement increases while nuclear reactions are slower BUT also in convection movement (due to your first hypothesis) -> centrifugal force make the star bigger and at a lower temperature (density decreases), but the nuclear reactions last longer -> this is your second step (red giant), with a little difference: the convection lets more nuclear reactions happen… So it would rather be an "orange giant", not red.
  • at the end of any nuclear reaction (but it will happen sooner than in reality, since the convection lets more reactions happen, so matter reacts faster, so sooner), you have a classic white dwarf. A slight difference will be that convection will not be possible anymore, so the movement will turn into two possible things: rotation speed (you have a spinning white dwarf) or heat (you have a "more-than-white" dwarf, which will looks like a white dwarf in visible range, so no difference).

Convection Prevents Helium Fusion

Red Dwarf Information

Red dwarf stars are fascinating, being both common and low energy. Part of their low energy is the inability to fuse helium produced in the core into other elements. This is because convective forces move the helium outside of the stars center before it is able to fuse. These stars thus collapse into white dwarf stars eventually rather than following the stellar evolution of larger stars.

Magic Would Alter This Process

Certainly magical forces could overcome this limitation, allowing the fusion of helium in the core by providing some forces that keep the helium bound into the core until fusion results. Magic is odd in that it appears to be more "intelligent" than other forces. That is, in most works of fiction containing magic, the magic force tends to anticipate what the magic user intends. Perhaps the stars themselves are intelligent in a similar manner, and simply are building a certain amount of energy while not changing the larger part of their nature, thus remaining convective overall while altering the properties of the convection.

The Stellar Evolution, A Breakdown of What Happens Next

Looking at what this magical change implies we see a few things:

  1. There is more energy generated in the core
  2. Stellar evolution would be altered along with the star's energy level
  3. Size is typically a function of overall energy and the course of stellar evolution

Thus these stars might not be dwarf stars unless affected by other magical processes The energy level affects the color, as you have stated. The normal range would be, going from low to high:

  • Red
  • Orange
  • Yellow
  • Green
  • White
  • Blue

A star with helium fusion would be similar to our own sun, and would likely be yellow in the earliest phases of it's stellar evolution. It would also follow a main-line stellar evolution, but would be slightly smaller than our sun. This implies that a similar level of energy could come from much smaller stars and that life could be in some of the most distant planetary orbits of these small solar systems.

I'm fascinated to learn more about how your interstellar magical fiction evolves. There are certainly people here who can help you in your journey to write interesting and compelling worlds.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .