Eli5 Is there any thing stopping a super cool sun from orbiting a elw capable of supporting human life?


Eli5 Is there any thing stopping a super cool sun from orbiting a elw capable of supporting human life?

In: Physics

Did you miss a few words? I’m not sure what you’re asking.

Planets that orbit very small, cold stars can theoretically be close enough to stay warm – but these perilously close orbits have a few major issues.

The planet will inevitably be tidally locked and always present the same face to the star, freezing one side with endless night and boiling the other.

These small stars are also pretty jumpy. Their internal fusion rates are erratic and they spit huge solar flares off into space. That’s a problem when you’re orbiting close enough to actually get hit by the flares. These planets may have their atmospheres ripped away by solar activity.

Are you asking if it’s possible for a star to orbit a planet?

If so, the answer is no. The reason a star gives off light is that it’s so massive that the material in it’s core is under enough pressure to undergo fusion. A planet isn’t massive enough for that, so a planet is necessarily less massive than a star.

Less massive things orbit around more massive things, so a star can’t orbit around a planet.

First of all, the concept of “orbiting something” only works when one thing is *a lot* heavier than the other. Like the Moon and the Earth. Looking at Pluto and its moon Charon (which is 12% of Pluto’s mass), their orbits are more “around each other” than one orbiting the other. They both move around an empty point in space, which is the center of mass of them both. So if you had a sun and a planet roughly the same size, you’d have them move like 2 planets with nothing in the middle.

Second, stars are stars because they have high gravity. The fusion that makes stars hot only works under immense pressure. So in all likelihood, the heaviest object in a system is also the one most likely to be a star.

And third, stars are made up of mostly hydrogen and helium, while the Earth is mostly iron, silicon and oxygen. Those are a lot rarer overall, so it’s less likely that a large body made of heavy elements forms.

TLDR: Geocentric worlds don’t exist because:

* they wouldn’t be “anything-centrtic”
* they would themselves become a star immediately
* they would likely consist of gas, not rock