Problem 1: The supernova

The first concern I have is one that Zeiss Ikon's answer discusses. To form a black hole, you need some sort of energetic event, likely a supernova. However, a supernova releases three extremely problematic sources of energy:

• High-energy photons, like gamma rays, that have the potential to strip away the atmosphere of any pre-existing planets in the vicinity - or, at the very least, to remove their ozone layers.
• Several solar masses worth of hot, fast-moving ejecta (think something on the order of $\sim$10,000 km/s, heating up any nearby gas as it travels outwards. Again, not super awesome for planets and their atmospheres.
• A flood of neutrinos, carrying away the bulk of the explosion's energy. They're really not phenomenal. That said, I'm unsure of how neutrino heating in an atmosphere would go.

Plus, this supernova's progenitor was probably a massive star, and massive stars have strong stellar winds (on the order of $\sim$1000-2000 km/s), which also have the potential to ablate atmospheres.

We might be able to form a black hole without a supernova, via a situation called a failed supernova. The idea is that a sudden emission of neutrinos prior to core collapse could carry away enough to mass-energy to substantially reduce the luminous energy output of the explosion. The collapse would still create a burst of energy, but it might be much less deadly than a normal supernova, perhaps even preserving the planet's atmosphere, if it already existed.

Now, we haven't gotten rid of the whole neutrino problem; in fact, we've increased it. However, again, perhaps the energy transfer isn't as intense as I think it might be. I'll need to do some reading.

Problem 2: Fun with orbits

You also have to consider that the orbits of the system could get pretty funky. Asymmetry in the explosion could create an effect similar to a pulsar kick, propelling the black hole at several hundred kilometers per second. If it traveled slow enough to remain gravitationally bound to the system, it might be traveling in a fairly elliptical orbit, and if you want to have multiple other stars, you'd have to worry about their orbits being disrupted.

Additionally, plenty of mass is lost during a supernova - most of the progenitor's mass, in many cases. This, too, will disrupt the orbits. It would be interesting to model this to see exactly what would happen, and if the effects would indeed be problematic. Systems with three or more stars are already kinda sensitive to dramatic enough perturbations - and believe me, this mass-loss would be quite the perturbation!

One possible solution would be for the planet-hosting star and the black hole to come together after the supernova occurs - in other words, for one to gravitationally capture the other. This requires a third body to mediate the interaction - so, for instance, if the black hole interacted with a binary star, one of the stars would have to be ejected for the other to become bound to the black hole.

This, of course, presents more orbital difficulties. A three-body encounter would likely disrupt the planet's orbit, if it had already formed. If it formed after the encounter - well, that demands explanation. Perhaps it formed from the debris disk left behind by the progenitor star. But then why would it orbit the secondary star, not the black hole? That, as far as I can see, remains a problem. Capturing the planet, as Cadence suggested, might be a way around it, but the orbital dynamics would be . . . delicate.

posted almost 6 years ago

HDE 226868‭

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