Blackholes: Accretion Vs Expulsion

[BDanielMayfield]

When an object falls toward a BH there can be several different outcomes, based on initial conditions. Among these are: (1) If the object's initial velocity is sufficient and it doesn't pass too close to the BH it can pass it by on an open, hyperbolic or parabolic trajectory. (2) The object's initial velocity is such that the object enters a closed elliptical or circular orbit around the BH. (3) the object's initial trajectory and nature is insufficient to avoid destructive capture by the BH.

Case (3) is what this question is regarding, because there are a range of possible outcomes here as well, depending upon what the captured object is and what the initial conditions of the BH are. My question is this: What percent of the captured object's mass will be added to the BH's mass, and how much of it will be ejected out the jets?

Bruce

[Chris Peterson]

When an object falls toward a BH there can be several different outcomes, based on initial conditions. Among these are: (1) If the object's initial velocity is sufficient and it doesn't pass too close to the BH it can pass it by on an open, hyperbolic or parabolic trajectory. (2) The object's initial velocity is such that the object enters a closed elliptical or circular orbit around the BH. (3) the object's initial trajectory and nature is insufficient to avoid destructive capture by the BH.

Case (3) is what this question is regarding, because there are a range of possible outcomes here as well, depending upon what the captured object is and what the initial conditions of the BH are. My question is this: What percent of the captured object's mass will be added to the BH's mass, and how much of it will be ejected out the jets?

You need to be more clear about the scenario. Most black holes don't have jets. If an object falls into one, 100% of its mass is added to the BH. A black hole that does have jets also has an accretion disk. In that case, you have material which is in Keplerian orbit around the BH, but which is subject to drag forces that result in it eventually falling into that BH, except for the small fraction which ends up in any jets that might be present. A large body caught in this way will, I think, just fall in- 100%. The stuff that ends up in the jets is charged particles from the accretion disk- basically, gas and dust.

[neufer]

Most black holes don't have jets. If an object falls into one, 100% of its mass is added to the BH.

• 1) Most black holes don't have jets because nothing is falling into them
  
  2) Even a non rotating black hole swallowing an object with no incoming angular momentum
  is going to emit some gravitational radiation resulting in some mass loss.

[Chris Peterson]

Most black holes don't have jets. If an object falls into one, 100% of its mass is added to the BH.

• 1) Most black holes don't have jets because nothing is falling into them :!:

That's certainly true. But it's more to the point that they don't have accretion disks. Things might occasionally fall into a black hole, as Bruce posits. But the odds are that black hole won't have an accretion disk or jets, and the colliding body isn't going to result in even a transient jet.

2) Even a non rotating black hole swallowing an object with no incoming angular momentum
is going to emit some gravitational radiation resulting in some mass loss.[/list]

Yes. But this is an unmeasurably small percentage of mass, and not at all what I think Bruce is concerned with in this question. 100% is close enough to 99.9999999999999999999999999999999% for our purposes here!

[neufer]

Most black holes don't have jets. If an object falls into one, 100% of its mass is added to the BH.

• 1) Most black holes don't have jets because nothing is falling into them

That's certainly true. But it's more to the point that they don't have accretion disks. Things might occasionally fall into a black hole, as Bruce posits. But the odds are that black hole won't have an accretion disk or jets, and the colliding body isn't going to result in even a transient jet.

My take is that most incoming objects will break apart/spaghettify at the Roche limit
and quickly turn into an accretion disk provided the system has any angular momentum.

It is probably the case, however, that smaller incoming objects allow black holes to feed more fastidiously.

2) Even a non rotating black hole swallowing an object with no incoming angular momentum
is going to emit some gravitational radiation resulting in some mass loss.

Yes. But this is an unmeasurably small percentage of mass, and not at all what I think Bruce is concerned with in this question. 100% is close enough to 99.9999999999999999999999999999999% for our purposes here!

Since gravitational quadrupole radiation scales as the square of the quadrupole moment it is certainly true
that smaller incoming objects radiate a smaller percentage of their rest mass in gravitational waves.

[Chris Peterson]

• 1) Most black holes don't have jets because nothing is falling into them :!:

That's certainly true. But it's more to the point that they don't have accretion disks. Things might occasionally fall into a black hole, as Bruce posits. But the odds are that black hole won't have an accretion disk or jets, and the colliding body isn't going to result in even a transient jet.

My take is that most incoming objects will break apart/spaghettify at the Roche limit
and quickly turn into an accretion disk provided the system has any angular momentum.

Yes, although unless we're talking about something really unlikely, like a star or large rogue planet, I don't think there would be enough material to form a disk. The body would simply break up, spaghettify, and within a second or less that material would cross the event horizon (barring, perhaps, a near tangential collision).

In fact, I'm not at all sure what would happen in the case of a star colliding with a stellar mass black hole. It's possible that most of the star would simply continue on its path, with a sort of cylinder of material sucked out of it as the black hole passed through. No doubt the final outcome would be strongly influenced by the relative masses of the two objects as well as the speed of the collision. And who knows what the effect of all that internal gravitational attraction would do to the star during the pass-through.

[rstevenson]

... In fact, I'm not at all sure what would happen in the case of a star colliding with a stellar mass black hole. It's possible that most of the star would simply continue on its path, with a sort of cylinder of material sucked out of it as the black hole passed through. No doubt the final outcome would be strongly influenced by the relative masses of the two objects as well as the speed of the collision. And who knows what the effect of all that internal gravitational attraction would do to the star during the pass-through.

Chris, that's the most intriguing idea I've heard in a long time. Of course, now that you say it, a stellar mass black hole would be a lot smaller than a star. My mind boggles at what it might look like as the pass-through occurs. A bit of fireworks, I'm sure. If I was a science fiction writer I'd immediately steal that idea and work it into a book somehow.

Rob

[BDanielMayfield]

Interesting exchange, as I hoped guys. I'll try "to be more clear about the scenario". The target BH can have any typical mass from stellar on up to supermasssive. Let's say it starts out without disk and jets, since that's the more common state. The approaching object could be any naturally occurring body or cloud composed of normal, baryonic matter.

Since what interests me most are cases where such encounters produce jets, let's eliminate encounters that wouldn't produce them, such as BH-BH collisions and trajectories where the infalling object passes though the BH's event horizon.

Bruce

[Chris Peterson]

Interesting exchange, as I hoped guys. I'll try "to be more clear about the scenario". The target BH can have any typical mass from stellar on up to supermasssive. Let's say it starts out without disk and jets, since that's the more common state. The approaching object could be any naturally occurring body or cloud composed of normal, baryonic matter.

Since what interests me most are cases where such encounters produce jets, let's eliminate encounters that wouldn't produce them, such as BH-BH collisions and trajectories where the infalling object passes though the BH's event horizon.

I don't think there are many (or any) realistic scenarios where an infalling object would produce jets. Jets are a product of the interaction between a black hole and an accretion disk, and the latter is substantially made up of gas. Somehow we end up with a sustained large magnetic field which drives the jet production. An object falling into an inactive black hole would probably have all it's material swallowed before any such structure could form.

[BDanielMayfield]

... In fact, I'm not at all sure what would happen in the case of a star colliding with a stellar mass black hole. It's possible that most of the star would simply continue on its path, with a sort of cylinder of material sucked out of it as the black hole passed through. No doubt the final outcome would be strongly influenced by the relative masses of the two objects as well as the speed of the collision. And who knows what the effect of all that internal gravitational attraction would do to the star during the pass-through.

Chris, that's the most intriguing idea I've heard in a long time. Of course, now that you say it, a stellar mass black hole would be a lot smaller than a star. My mind boggles at what it might look like as the pass-through occurs. A bit of fireworks, I'm sure. If I was a science fiction writer I'd immediately steal that idea and work it into a book somehow.

Rob

In the real universe with plausible relative velocities is such a BH punching through a star [with a large portion of the star surviving] even possible? It's not just the BH's event horizon that would bite out a cylinder of the star; everything (all the star's plasma) moving slower than the BH's escape velocity would get captured too.

Bruce

[Chris Peterson]

In the real universe with plausible relative velocities is such a BH punching through a star [with a large portion of the star surviving] even possible? It's not just the BH's event horizon that would bite out a cylinder of the star; everything (all the star's plasma) moving slower than the BH's escape velocity would get captured too.

It doesn't need much velocity. Unless it was part of the system to begin with (in which case it wouldn't be on a collision course), it's going to be entering on a hyperbolic orbit. It may speed up hugely under the gravitational influence of the black hole, and it will then slow again moving away from it. By definition, a hyperbolic orbit means that it's moving at a speed greater than the system's escape velocity. The only place it gets difficult (really difficult) to analyze is in considering the tidal effects on the star, and on how much actual stellar material is lost. All standard orbit calculations assume that neither body is changing mass. If there's a significant transfer of mass between the two, however, the problem needs to be approached differently (that's not a very hard problem, but figuring out the mass exchange is).

[rstevenson]

Just taking a quick stab at what might happen if a star like our Sun were to hit, or be hit by, a stellar mass black hole -- a bullseye shot, let's say...

Our Sun has a diameter of about 1.4 million km, while a typical stellar mass black hole will be something like 30 to 50 km in diameter. So assuming a fairly fast pass through, there won't be time for much of the gaseous envelope of the Sun to get vacuumed up by the black hole. No matter the gravity of the BH, the gas just can't move fast enough to get to it before its moved on. Visually, the entry and exit of the black hole may appear similar in scale to a single tornado in the atmosphere of the Earth -- wild and crazy if you're near it, but otherwise unremarkable.

What may be more interesting is what happens when the black hole hits the extremely dense material in the core of the Sun. The core is roughly 300,000 km in diameter, so the black hole is still quite small by comparison. For a rough idea of sizes, imagine a BB pellet fired through a snow ball about 12 m in diameter.

Unless there is a lot of interaction between the electric charge of the black hole (one of its three fundamental properties) and the plasma of the Sun's envelope, I'm thinking there wouldn't be much of a show to look at. Certainly not worth the cost of a round-trip ticket to see it. There may be some extended effects -- I'm thinking the Sun would, in a sense, ring like a bell for some time to come, and I imagine there will be a flurry of ongoing surface effects, sun spots, flares, prominences, that sort of thing.

If the black hole conveniently passes through the Sun from pole to pole, there should be no terrible consequences for our system of planets. Everything should just keep rolling around where it's supposed to roll. If, on the other hand, the black hole came sailing straight across the orbital plane of the planets, we could expect some degree of flinging about to result, depending on which planets were nearest it as it passed by. And if the Oort Cloud and Asteroid Belt are disrupted we may end up with an Even Later Heavy Bombardment, which would definitely spoil your vacation plans for years to come.

Rob

[Chris Peterson]

If the black hole conveniently passes through the Sun from pole to pole, there should be no terrible consequences for our system of planets. Everything should just keep rolling around where it's supposed to roll.

Ever play around with a gravity simulator program? Throw another stellar mass in our system, even passing through from north to south, and it's game over for planetary orbits. Everything will be rolling in a new place. Not good.

[rstevenson]

If the black hole conveniently passes through the Sun from pole to pole, there should be no terrible consequences for our system of planets. Everything should just keep rolling around where it's supposed to roll.

Ever play around with a gravity simulator program? Throw another stellar mass in our system, even passing through from north to south, and it's game over for planetary orbits. Everything will be rolling in a new place. Not good.

I assumed all the planets would get pulled up a bit as the BH approached, then back down a bit as it departed, producing some obliquity in the orbits, but otherwise leaving them pretty much the same. But, now that I've turned on a few more light bulbs (thanks for the wakeup call), I guess all the orbits would also be shrunken -- pulled in closer to the Sun, and none too gently. Time to crunch some numbers... .

Can you suggest a good gravity simulator that will run in the latest Mac OS?

Rob

[Chris Peterson]

If the black hole conveniently passes through the Sun from pole to pole, there should be no terrible consequences for our system of planets. Everything should just keep rolling around where it's supposed to roll.

Ever play around with a gravity simulator program? Throw another stellar mass in our system, even passing through from north to south, and it's game over for planetary orbits. Everything will be rolling in a new place. Not good.

I assumed all the planets would get pulled up a bit as the BH approached, then back down a bit as it departed, producing some obliquity in the orbits, but otherwise leaving them pretty much the same. But, now that I've turned on a few more light bulbs (thanks for the wakeup call), I guess all the orbits would also be shrunken -- pulled in closer to the Sun, and none too gently. Time to crunch some numbers... .

Can you suggest a good gravity simulator that will run in the latest Mac OS?

I can't. It's been a few years since I've used a solar system simulator, and I don't currently have one on this machine (which is Windows, in any case). But it shouldn't be too hard to find one, possibly one that will run in a browser.

BTW, it's just possible that if a stellar mass black hole passed through from north to south - absolutely perfectly- the system might survive. But that's statistically unlikely to the point of being impossible. And other odd things happen, as well- the Sun itself would be pulled out of the ecliptic temporarily by the passage. There are going to be some pretty weird out-of-plane things going on.

[BDanielMayfield]

Just taking a quick stab at what might happen if a star like our Sun were to hit, or be hit by, a stellar mass black hole ...

If the black hole conveniently passes through the Sun from pole to pole, there should be no terrible consequences for our system of planets. Everything should just keep rolling around where it's supposed to roll. If, on the other hand, the black hole came sailing straight across the orbital plane of the planets, we could expect some degree of flinging about to result, depending on which planets were nearest it as it passed by. And if the Oort Cloud and Asteroid Belt are disrupted we may end up with an Even Later Heavy Bombardment, which would definitely spoil your vacation plans for years to come.

Rob

If the black hole conveniently passes through the Sun from pole to pole, there should be no terrible consequences for our system of planets. Everything should just keep rolling around where it's supposed to roll.

Ever play around with a gravity simulator program? Throw another stellar mass in our system, even passing through from north to south, and it's game over for planetary orbits. Everything will be rolling in a new place. Not good.

How massive is this Sun hitting BH Rob? (good example of the type of encounters I'm asking about.) Wikipedia says that stellar massed BHs are typically 5 to several tens of the sun's mass, so, no matter what the angle of approach, Chris is right, "Not good" for the system's survival. Even when such a large mass was a long way from the solar system things would start to go haywire.

Bruce

[rstevenson]

I was thinking of a little 'un, about 5 or so stellar masses. It's boggling to think of something 50 km across being 5 times the mass of our 1.4 million km diameter Sun. Makes it very hard to imagine accurately.

Rob

[BDanielMayfield]

I was thinking of a little 'un, about 5 or so stellar masses. It's boggling to think of something 50 km across being 5 times the mass of our 1.4 million km diameter Sun. Makes it very hard to imagine accurately.

Rob

It could make for the core of a good Sci-fi tale though. A not too advanced intelligent species starts to detect, perhaps decades or even centuries in advance, that their stellar system is on a collision course with some unseen mass. At first, their astronomers haven't learned about Black Holes yet. Science deniers abound as theories are put forward to account for the unprecedented changes that keep happening at an ever more alarming pace. It is proven by astronomers and astrophysicists that BHs are real and that their system is doomed, but the masses see this "the world is ending" talk as foolish. ...

Bruce

[rstevenson]

I was thinking of a little 'un, about 5 or so stellar masses. It's boggling to think of something 50 km across being 5 times the mass of our 1.4 million km diameter Sun. Makes it very hard to imagine accurately.

It could make for the core of a good Sci-fi tale though. A not too advanced intelligent species starts to detect, perhaps decades or even centuries in advance, that their stellar system is on a collision course with some unseen mass. ...

Bruce

There's an odd possibility when binary black holes merge, called a recoil effect. It can impart a velocity of 1000 km/s to as much as 5000 km/s to the resulting body. (Let's assume 1000 km/s for now.) If that resulting larger BH happened to be on a collision course with the Sun, and if it's still in the sub-100 km size, how soon before the collision would we, with all our orbiting and ground-based instruments, detect its approach?

We might first notice a disturbance in our Solar System's Oort Cloud -- if we happened to have pointed something in just the right direction at just the right time, that is. The Oort Cloud stretches from roughly 1000 AUs to about 100,000 AUs from the Sun -- let's just call it 100,000 AUs thick to keep the numbers round. An AU is about 150 million km, so that's 1.5x10¹³ kms of Oort Cloud for the BH to pass through. At 1000 km/s, that means the BH would pass through the Oort Cloud in about [tap,tap,tap] 475 years, if I haven't slipped a cog in working that out. And with the inner edge of the Oort Cloud about 1000 AUs from the Sun, the BH would complete its bullseye hit on the Sun less than 4.75 years after that. (How much less I haven't worked out, but there would definitely be some acceleration going on.)

So yes, we might well have a chance to detect it on its way in. But then what? What could we possibly do? There's no known technology that could get a large part of the human race off the Earth. Nor do we know of any likely way, even assuming great technological advancements, to move so many people very far. So we'd end up with one of those scenarios involving the choosing of a small number of people to form a safe gene pool, getting them into space in a long-term livable habitat, and launching them on a multi-generational trip (using a sling-shot around the BH to gain speed, of course!) to a possibly livable planet around another star. Such a trip might be the beginning of our species spreading throughout this end of the Milky Way -- or more likely, it would be the last miserable gasp of our unlucky selves.

Either way, it'd make a great story -- which I've already started to write.

Rob

[BDanielMayfield]

Still on the BH-star collision tract, how fast would the pass through have to be to leave some of the star unswallowed? The BHs size is defined by the limit surrounding it where the escape velocity (ev) equals c, 300,000 km per second. But, for example, what would the ev be out at 0.7 million km (the Sun's radius) from a 5Sun BH center? If the whole star passes through a region where the ev is greater that the max v at closest approach then the whole star is destroyed, no question about it, imo. So what if the BH can't swallow fast enough: that's what the accretion disk is for.

Bruce

[Chris Peterson]

Still on the BH-star collision tract, how fast would the pass through have to be to leave some of the star unswallowed? The BHs size is defined by the limit surrounding it where the escape velocity (ev) equals c, 300,000 km per second. But, for example, what would the ev be out at 0.7 million km (the Sun's radius) from a 5Sun BH center? If the whole star passes through a region where the ev is greater that the max v at closest approach then the whole star is destroyed, no question about it, imo. So what if the BH can't swallow fast enough: that's what the accretion disk is for.

Keep in mind that in a two-body interaction, the center of mass of the system doesn't change.

[rstevenson]

Nice coincidence seeing this article on a binary pair of stars featuring a likely BH and what's left of a larger star, now a white dwarf, in a very close orbital pairing.

Sifting through the paper and the article, I find these helpful gleanings...

... A UCXB with an orbital period of 28.2 min indicates a donor white dwarf mass of ∼ 0.02M⊙ ... and thus suggests an accretor mass of ∼ 1M⊙.

In order to make such a close pairing, one possibility is that the black hole smashed into a red giant star, and then gas from the outer regions of the star was ejected from the binary. The remaining core of the red giant would form into a white dwarf, which becomes a binary companion to the black hole. The orbit of the binary would then have shrunk as gravitational waves were emitted, until the black hole started pulling material from the white dwarf.

That gives me a little more meat to put on the bones of the idea.

Rob

[Doum]

rstevenson wrote:

So we'd end up with one of those scenarios involving the choosing of a small number of people to form a safe gene pool, getting them into space in a long-term livable habitat, and launching them on a multi-generational trip (using a sling-shot around the BH to gain speed, of course!) to a possibly livable planet around another star. Such a trip might be the beginning of our species spreading throughout this end of the Milky Way -- or more likely, it would be the last miserable gasp of our unlucky selves.

question: is it essential to leave the solar system? The space long-term habitat can be lauch around neptune. So if the sun survive and have giant solar storm, the distance from the sun that neptune is should reduce the ammount of radiation or whatever danger.(if the black hole is coming from north of the sun and go sought the effect on neptune should be minimal). After a few dozen years, it will be possible to determine if earth or mars are going back to have a more stable orbit. Then go back there.

Oups.
( Just thought of it. The back hole will bring many comets from the Oort cloud. So the space habitat around neptune might be an hazardous environnement.)

im still not sure that leaving the solar system is essential. May be go a 1000 Au and then come back later when everything is more stabilise. At least it will not take 20000 years to go to another solar system.

Just a tought.

[rstevenson]

Yeah, they'd probably try that. Not just one ship, I'm sure, so lots of different survival scenarios might be possible, or at least attempted.

Rob

[Chris Peterson]

We might first notice a disturbance in our Solar System's Oort Cloud -- if we happened to have pointed something in just the right direction at just the right time, that is.

We've never observed anything in the Oort cloud. It is, in fact, a hypothesized structure, inferred from the presence of comets, from some theory, and from some observations of other stellar systems. While few doubt it exists, we largely lack the ability to examine it directly. So we're not going to see any disturbance there. The closest region where we're going to see disturbances in is the scattered disc, probably something closer than 100 AU. No time to take any real action.