Perhaps a fast spinning star (not spherical) where a black hole forms in the center, but the event horizon is smaller than the equatorial radius but larger than the polar radius?

  • $\begingroup$ Check arXiv:astro-ph/0402191, arXiv:1410.3913 for some ideas related to neutron stars. When "the black hole forms in the center", the previous rebound of collapse has already likely gravitationally unbound the star by that point. As for a normal, fusing star... well, try solving a couple of MHD equations... :-D $\endgroup$ – kkm Apr 10 at 0:02
  • $\begingroup$ You can sort of feel the fusion pressure causing problems, but once you add the magnetic interactions, the toroid starts to look pretty short-lived. $\endgroup$ – Sean Vikoren Apr 12 at 20:32

A ring of particles, e.g., Saturn's rings, can form around a massive center, and can theoretically even exist without a massive center to orbit around; but such a ring is unstable on a time scale that increases with its mass density (that's part of how planets form from dust rings around their parent stars). I strongly suspect that a toroidal star massive enough to generate energy by fusion would be so unstable that it would last days at most -- but doing the calculations is beyond my skill set! Maybe the torus would be stable if it had an enormously strong current running through it. Sounds like a good SciFi gimmick.

  • $\begingroup$ Thank you for the walk through the ring idea. It makes sense that planets form because it is stable and a ring is not. $\endgroup$ – Sean Vikoren Apr 12 at 20:27

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