Black Hole Ringworld

[Baked Potato]

Is it possible to build a ringworld around a blackhole? I don't seem to be able to.

[annaliseh]

Originally posted by Yang:

Originally posted by annaliseh:

Yeah that all sounds good...but the BH is drawing more substance into its centre which does increase the MASS and so does increase the gravitational pull. This will cause the BH to grow even more. Besides there is more to gravity than just MASS.

There is not more to gravity than just mass (except for the Universal Gravitational Constant, and the distance between the two objects, but since we are only talking about the characteristics of an object which affect the gravitational field it exerts - i.e object specific traits - these are not pertinent to discussion). I have no idea how you would justify such a claim. Newton's Law of Gravitation uses a combination of only these 3 factors to calculate the strength at every point of a field exerted by an object. Whether it's a sun or a black hole, as long as they are of equivalent mass, there is no difference in the gravitational field of the two (except at distances from the black hole which would count as being inside the sun.

Firstly it is a theory! Take the theory of gravitational warp. Many players are complaining about warp drive being removed - as if it really exists currenly. At this point in time it is pure SCI-FI.

Secondly, note the last sentence above. You are speculating that the sun/star and the BH are equivalent in MASS, supposing say SOL suddenly became a BH. On that basis yes I would agree with you but... Question is how big was the star and how many planets did it swallow in the process. We are not talking dust particles here. On the other hand, BH are just theories and pulsars don't prove the existance of BH. They/we are all speculating. No one has actually seen the process.

Originally posted by Yang:

As a consequence, yes you are correct that the BH is drawing in more substance into its centre, which does increase its mass. However, literally all stellar bodies do this, and a sun of equal mass will have an equivalent gravitational force on the matter around it, so it will draw substances towards it and increase in mass at exactly the same rate (basically the same: there's a small time delay since the black hole is smaller so it'll take a bit more time for the matter to travel this extra distance, but this time is obviously negligible to the timescales we are talking about) as the black hole of equivalent mass. So there is still no difference between the star and the black hole of equivalent mass.

Yes all stellar bodies do draw things in - No argument there.


However, Once something enters the accretion disk it would vanish from sight and there is no idea how dense the material is that makes up the core nor the distance of the core surface to edge of the accretion disk. We cannot see it. All those NASA artist concept pictures are simply not fact/true - base on someone's concept. I'm looking at one right now on my tablet.

So with 2 unknowns (ie the MASS and the DISTANCE) how can you determine the these variables except by math.

And who says that the accretion disk edge was the surface of the original star! The gravitational constant may not be under certain conditions/circumstances. Newton's Law may not apply in all situations either.

But keep smiling Yang.

[Yang]

Lord give me strength

Originally posted by annaliseh:

Originally posted by Yang:

There is not more to gravity than just mass (except for the Universal Gravitational Constant, and the distance between the two objects, but since we are only talking about the characteristics of an object which affect the gravitational field it exerts - i.e object specific traits - these are not pertinent to discussion). I have no idea how you would justify such a claim. Newton's Law of Gravitation uses a combination of only these 3 factors to calculate the strength at every point of a field exerted by an object. Whether it's a sun or a black hole, as long as they are of equivalent mass, there is no difference in the gravitational field of the two (except at distances from the black hole which would count as being inside the sun.

Firstly it is a theory! Take the theory of gravitational warp. Many players are complaining about warp drive being removed - as if it really exists currenly. At this point in time it is pure SCI-FI.

There really is not another way to say this: this is a meaningless statement. All of science is made of theories - explanations which have not been proved. This is because statements in science (like energy is conserved, or objects always fall downwards when dropped), unlike mathematics, can never be completely 100% proved or disproved: you can only gather empirical evidence from experiments which either supports or does not support the statement, and you can gather more evidence by repeating experiments or trying different ones which lead to the same conclusions via different methods. If there is a sufficiently large amount of evidence for or against a theory, it is accepted or discarded accordingly by the scientific community. Even obvious ideas (such as 'the Sun orbits the Earth' is a theory - try proving it to the Flat Earthers who subscribe to a geocentric worldview). Sometimes a piece of evidence is so clear that the theory is almost certainly true (for example, if the Earth was flat, we'd see the same stars in Scotland as we would in Argentina. However, observations show this is not the case). Newton's Theory of Universal Gravitation has so much evidence in favour of it that it is universally accepted (except for small groups of Flat Earthers here and there). Tycho Brahe, a 16th century astronomer, took incredibly accurate recordings of the movements of the planets in our system. Newton realised that his equation modelled the movements of the planets such that they mirrored Brahe's readings almost exactly. From there, over 4 centuries, physicists have applied Newton's Law of Gravitation time and time again on other bodies in our solar system (for example predicting the existence of Neptune before it was even observed) and other stars and galaxies, and have shown that predictions by his law have matched actual predictions. Thus there is basically as much evidence for it as any of the other most universally held theories of science. So don't try the 'theory' card on me, because it won't stand.

There is a large difference between Newton's Law of Gravitation and Warp travel in terms of validity as theories. The Alcubierre Drive has thus far been mathematically been proven to not be in contravention of the Laws of General Relativity. The fact that a hypothetical concept has been theoretically proven to not contradict only a few of the laws of physics (it could contradict others which have not been analyzed and linked to it yet) does not make it in any way comparable to Newton's Gravitation, which has, as aforementioned, a very thick wall of evidence showing it not just to be theoretically completely true (i.e not just 'not contradicting some laws of physics'), but also a very precise representation of real world truth.

Originally posted by annaliseh:

Secondly, note the last sentence above. You are speculating that the sun/star and the BH are equivalent in MASS, supposing say SOL suddenly became a BH. On that basis yes I would agree with you but... Question is how big was the star and how many planets did it swallow in the process. We are not talking dust particles here.

The star did not swallow any planets in the process because it did not go nova. I am not talking about a star, and then the black hole it creates when it goes nova, I am talking about a star and a black hole of the same mass. I have made this clear before.

Originally posted by annaliseh:

On the other hand, BH are just theories and pulsars don't prove the existance of BH. They/we are all speculating. No one has actually seen the process.

Again, 'black holes are theories'. Yes they are, but so is everything in science. We have not directly observed black holes, because they are physically impossible to observe (they absorb all light and EM waves, so how would we see them?). It'd be like a 19th century physicist being asked 'but have you observed these so-called EM waves?'. However, we have very strong evidence by proxy experiments, using gravitational lensing and tracking objects in its vicinity.

No one said anything about pulsars. I don't know where you got that idea from.

Originally posted by annaliseh:

Originally posted by Yang:

As a consequence, yes you are correct that the BH is drawing in more substance into its centre, which does increase its mass. However, literally all stellar bodies do this, and a sun of equal mass will have an equivalent gravitational force on the matter around it, so it will draw substances towards it and increase in mass at exactly the same rate (basically the same: there's a small time delay since the black hole is smaller so it'll take a bit more time for the matter to travel this extra distance, but this time is obviously negligible to the timescales we are talking about) as the black hole of equivalent mass. So there is still no difference between the star and the black hole of equivalent mass.

Yes all stellar bodies do draw things in - No argument there.


However, Once something enters the accretion disk it would vanish from sight and there is no idea how dense the material is that makes up the core nor the distance of the core surface to edge of the accretion disk. We cannot see it. All those NASA artist concept pictures are simply not fact/true - base on someone's concept. I'm looking at one right now on my tablet.

Thank you for pointing out that concept pictures are not factual. How dumb do you think I am?

We don't need to know the density of the black hole, just its mass. We can determine its mass by application of Newton's Law of Universal Gravitation, by seeing the force it exerts on nearby bodies and therefore calculating how much mass it contains.

Once something enters the accretion disk it does not vanish from sight. You are confusing this idea with that of the Schwarzchild Radius, otherwise known as the Event Horizon. The accretion disk a disk of dust and particles which gathers in orbit of the black hole, getting sucked in in a decaying elliptical orbit over millennia. The Schwarzchild Radius is the point at which the acceleration due to gravity is such that even light cannot escape the gravitational attraction and gets sucked in - it is at this point that things vanish, since nothing can travel faster than light and so no information can escape this Radius.

We take the centre of a black hole as its centre of mass and take the distance from this to any object when calculating the gravitational force between the two. This is basic physics. You can prove that the centre of a black hole is its centre of mass (i.e it is homogeneous) by observing the bodies of matter around it and the nature of their orbits, and studies have confirmed this to be true. For example, the position of Neptune (or rather, its centre of mass), and its mass were predicted before it was even observed for the first time by looking at the orbits of Pluto and Uranus.

Originally posted by annaliseh:

So with 2 unknowns (ie the MASS and the DISTANCE) how can you determine the these variables except by math.

You determine these variables by maths, obviously.

Originally posted by annaliseh:

And who says that the accretion disk edge was the surface of the original star!

No one is saying the accretion disk edge was the surface of the original star. Nor am I saying that the Schwarzchild radius was the surface of the star of equivalent mass - I have been saying the exact opposite repeatedly for about half of this discussion thread. The Schwarzchild radius is a lot smaller than the surface of the star and it is within this space that the gravitational strength of a black hole becomes a lot stronger than that of a planet of same mass.

Originally posted by annaliseh:

The gravitational constant may not be under certain conditions/circumstances. Newton's Law may not apply in all situations either.

You are now speaking nonsense. The Universal Gravitational Constant is universal. Also, the fact that Newton's Law is called the Law of Universal Gravitation may suggest that it is also universal. These apply all the time, everywhere, anywhere. There are no instances where the Law of Gravitation appears to be incorrect.

Originally posted by annaliseh:

But keep smiling Yang.

This tends to stop happening when I meet someone of equal arrogance to me on the internet. I will safely claim that I am better than you at physics, in the knowledge that, in the event of this being wrong, I do not really lose anything, since this is all anonymous, unless you try really hard to find me irl (pls dont).

[�[Dire_Venom]�]

Wow, some really good disscusion (plus some not so good), props to Yang for the great explanation.

[Exanthos]

When building a ringworld, all of nearby planets are used to make the structure. Black hole systems seems to have a severe lack of planets, and the ones that have some (supposedly) don't have enough to make a full ringworld, but you can still build a habitat near them (and ironically use the solar stations you can build in them)

[Yang]

Originally posted by Exanthos:

When building a ringworld, all of nearby planets are used to make the structure. Black hole systems seems to have a severe lack of planets, and the ones that have some (supposedly) don't have enough to make a full ringworld, but you can still build a habitat near them (and ironically use the solar stations you can build in them)

We play a game where minerals produced on your home world can be used instantly to build mining stations halfway across the galaxy from the start of the game, and you're saying that it would be impossible to build a ringworld in a system because of a lack of material there?