A fellow explorer suggested finding a black hole as a planet as a "unicorn" find, and I had a feeling it would not be possible (beyond the fact that no one has found one yet). I was intending to type a short response but it turned out to be quite long-winded so I decided to make it a forum thread.
And for those who aren't familiar, this is what I mean with a star as a planet:
Collection of Wonders, Skaude AA-A h294, is a system with a ringed M star, ringed white dwarf, and ringed neutron star all in planetary orbits around a binary black hole. So why can't a system have a black hole as a planet? Note that I use a lot of technical language so if you have questions feel free to comment.
So why can't a black hole be a planet? There's neutron stars and white dwarfs! The rub is the mass boundaries of procedurally generated stellar remnants. Proc-gen Neutron Stars appear to only have a mass between 0.426 and 2.512 solar mass. Proc-gen black holes appear to only have a mass between 2.516 and ~60 solar masses. These values are derived from EDAstro Records (see their spreadsheets and sort by solar mass, and ignore catalog stars since they defy the laws of physics).
So first, understand how stars can become planets in the first place. Presumably in H mass systems, a main star (and perhaps some secondary stars) are generated from some initial mass function based on the seed of the galaxy. The main star sucks up a lot of the mass of the system, but the rest of the simulated protoplanetary disk is allowed to form planets. The game forward simulates the life of the stars. Also, the game forward simulates orbital time stability and ejects some planets over time.
This process will create normal planets in most solar systems, but if you add a lot of mass to a planet, it becomes a heavy gas giant. And if you keep adding mass, you'll get a brown dwarf. And if you keep adding mass to that, you'll get a late type main sequence star, usually M or K but occasionally G, F, A, even B. These main sequence stars live their lives as though they were stars! They just happen to be in planetary orbits. As a result, you get many familiar phases such as the subgiant phase, giant phase (red giant and even orange giant!), and white dwarf/neutron star stellar remnants. All of these phases can be found in stars as planets.
H mass systems are the only systems with a decent chance of generating early type stars (the ones that could become NS or BH) as planets. This is because the parent star needs to be much heavier than the planet, or else the game will decide that this planet will become a secondary star. I havn't calculated the ratio but it ought to be a bigger difference than 15:1. G mass system will not have heavy enough main stars to support a massive star planet without it turning into a secondary star. So using this conservative 15:1 ratio, if I want a 2 solar mass planetary star I would need a 30 solar mass parent. Otherwise, the planetary star will become a secondary star (star Systemname B, C, etc.). This is conservative I think, and the actual ratio is probably higher.
Another problem is that black holes are only a fraction of their original mass (the rest got blown away in supernova). The upper limit of mass of any proc-gen star is 120 solar mass (it must be a Herbig AEBE) or 106 solar mass (B type supergiant), while black holes have upper limit of 60 solar mass, so lets assume that 50% the mass of the original star gets blown away when it turns into a black hole. In real life I think it's actually closer to 80% of the mass. That means every 30 solar mass black hole, for example, used to be a 60 solar mass star that went supernova. This 50% mass loss is very conservative as well.
Assuming our very conservative limits, in order to create the smallest black hole possible in the game of 2.5 solar mass, we would need a 5 solar mass star to live out its life as a planet...but in order for the 5 solar mass star to even be a planet in the first place, it would need to have a 75 solar mass parent to support it (otherwise it would never have been a planet but start out as a secondary star). This is a conservative estimate, so the actual parent would probably need to be a bit higher than that, but regardless, it demonstrates a point: whatever massive object above 75 solar mass parent that could support our 5 solar mass planet will turn into a black hole sooner than the 5 solar mass planet would, and such a black hole would always be less than 60 solar masses (not able to support the planet anymore, so the planet becomes a secondary).
So for example, naively we might think a 120 solar mass Herbig AEBE could support a 5 solar mass planet (perhaps a bright B class star), and this is absolutely correct, since there exist plenty of B class star planets over 5 solar masses (they are all orbiting Herbigs, not black holes, see edastro records). However, when this herbig AEBE lives out its life and eventually turns into a black hole, the game will make the black hole have less than 60 solar masses, and our 5 solar mass star, which isn't ready to die yet since it is less massive (recall that lower mass stars die slower and have longer lives), will not be bound to the parent and will become a secondary star (e.g. BH + B0Z or something like that). Then, I would reason that the game will eliminate the "impossible" planet configurations such as a circumbinary planet that would now seem way too close to the 2 parent stars.
Now, the astute observer may consider, what if there are multiple parent stars, and our massive planet orbits them all? e.g. ABCD 1. This actually helps a bit. Although a single black hole cannot exceed 60 solar masses, there are some configurations of many black holes whose sum is over 60 solar masses. Since a planet orbiting a barycenter only cares about the sum of the masses of the parents, this would increase our effective limit. I've noticed some multiple black hole systems with over 90 solar masses in total mass. However, it seems this isn't sufficient to generate black holes as planets, not to mention it seems that the more black holes in a system, the less likely there are planets in that system in the first place (perhaps all the mass went to the stars).
Consider the most massive known neutron stars that are planets:
We can see that almost all of the highest (aside from the catalog stars which defy physics) orbit more than one star! And they are all black holes. So if we wanted a black hole as a planet, we would need a similar configuration of many black holes, then have a very massive star planet live out its life and die, and be a whole solar mass higher than the current known most massive neutron star planet. This tells me it would probably be too unlikely to exist.
But who knows? The ED galaxy still holds a lot of mysteries and maybe everything I said is complete nonsense, or maybe there is just enough leeway that our "unicorn" does exist. Curious on your thoughts.
And for those who aren't familiar, this is what I mean with a star as a planet:
Collection of Wonders, Skaude AA-A h294, is a system with a ringed M star, ringed white dwarf, and ringed neutron star all in planetary orbits around a binary black hole. So why can't a system have a black hole as a planet? Note that I use a lot of technical language so if you have questions feel free to comment.
So why can't a black hole be a planet? There's neutron stars and white dwarfs! The rub is the mass boundaries of procedurally generated stellar remnants. Proc-gen Neutron Stars appear to only have a mass between 0.426 and 2.512 solar mass. Proc-gen black holes appear to only have a mass between 2.516 and ~60 solar masses. These values are derived from EDAstro Records (see their spreadsheets and sort by solar mass, and ignore catalog stars since they defy the laws of physics).
So first, understand how stars can become planets in the first place. Presumably in H mass systems, a main star (and perhaps some secondary stars) are generated from some initial mass function based on the seed of the galaxy. The main star sucks up a lot of the mass of the system, but the rest of the simulated protoplanetary disk is allowed to form planets. The game forward simulates the life of the stars. Also, the game forward simulates orbital time stability and ejects some planets over time.
This process will create normal planets in most solar systems, but if you add a lot of mass to a planet, it becomes a heavy gas giant. And if you keep adding mass, you'll get a brown dwarf. And if you keep adding mass to that, you'll get a late type main sequence star, usually M or K but occasionally G, F, A, even B. These main sequence stars live their lives as though they were stars! They just happen to be in planetary orbits. As a result, you get many familiar phases such as the subgiant phase, giant phase (red giant and even orange giant!), and white dwarf/neutron star stellar remnants. All of these phases can be found in stars as planets.
H mass systems are the only systems with a decent chance of generating early type stars (the ones that could become NS or BH) as planets. This is because the parent star needs to be much heavier than the planet, or else the game will decide that this planet will become a secondary star. I havn't calculated the ratio but it ought to be a bigger difference than 15:1. G mass system will not have heavy enough main stars to support a massive star planet without it turning into a secondary star. So using this conservative 15:1 ratio, if I want a 2 solar mass planetary star I would need a 30 solar mass parent. Otherwise, the planetary star will become a secondary star (star Systemname B, C, etc.). This is conservative I think, and the actual ratio is probably higher.
Another problem is that black holes are only a fraction of their original mass (the rest got blown away in supernova). The upper limit of mass of any proc-gen star is 120 solar mass (it must be a Herbig AEBE) or 106 solar mass (B type supergiant), while black holes have upper limit of 60 solar mass, so lets assume that 50% the mass of the original star gets blown away when it turns into a black hole. In real life I think it's actually closer to 80% of the mass. That means every 30 solar mass black hole, for example, used to be a 60 solar mass star that went supernova. This 50% mass loss is very conservative as well.
Assuming our very conservative limits, in order to create the smallest black hole possible in the game of 2.5 solar mass, we would need a 5 solar mass star to live out its life as a planet...but in order for the 5 solar mass star to even be a planet in the first place, it would need to have a 75 solar mass parent to support it (otherwise it would never have been a planet but start out as a secondary star). This is a conservative estimate, so the actual parent would probably need to be a bit higher than that, but regardless, it demonstrates a point: whatever massive object above 75 solar mass parent that could support our 5 solar mass planet will turn into a black hole sooner than the 5 solar mass planet would, and such a black hole would always be less than 60 solar masses (not able to support the planet anymore, so the planet becomes a secondary).
So for example, naively we might think a 120 solar mass Herbig AEBE could support a 5 solar mass planet (perhaps a bright B class star), and this is absolutely correct, since there exist plenty of B class star planets over 5 solar masses (they are all orbiting Herbigs, not black holes, see edastro records). However, when this herbig AEBE lives out its life and eventually turns into a black hole, the game will make the black hole have less than 60 solar masses, and our 5 solar mass star, which isn't ready to die yet since it is less massive (recall that lower mass stars die slower and have longer lives), will not be bound to the parent and will become a secondary star (e.g. BH + B0Z or something like that). Then, I would reason that the game will eliminate the "impossible" planet configurations such as a circumbinary planet that would now seem way too close to the 2 parent stars.
Now, the astute observer may consider, what if there are multiple parent stars, and our massive planet orbits them all? e.g. ABCD 1. This actually helps a bit. Although a single black hole cannot exceed 60 solar masses, there are some configurations of many black holes whose sum is over 60 solar masses. Since a planet orbiting a barycenter only cares about the sum of the masses of the parents, this would increase our effective limit. I've noticed some multiple black hole systems with over 90 solar masses in total mass. However, it seems this isn't sufficient to generate black holes as planets, not to mention it seems that the more black holes in a system, the less likely there are planets in that system in the first place (perhaps all the mass went to the stars).
Consider the most massive known neutron stars that are planets:
We can see that almost all of the highest (aside from the catalog stars which defy physics) orbit more than one star! And they are all black holes. So if we wanted a black hole as a planet, we would need a similar configuration of many black holes, then have a very massive star planet live out its life and die, and be a whole solar mass higher than the current known most massive neutron star planet. This tells me it would probably be too unlikely to exist.
But who knows? The ED galaxy still holds a lot of mysteries and maybe everything I said is complete nonsense, or maybe there is just enough leeway that our "unicorn" does exist. Curious on your thoughts.
