What If Planet 9 Is a Primordial Black Hole?
arxiv.org
arxiv.org
- definitive sink to send all of our nuclear waste (it would be the /dev/null of the Solar System)
- gravitational energy generator (limitless, until we have no more mass to throw in)
Probably the more interesting use is that of an energy source!
The use as an energy source, however, would even outlast the lifetime of the Sun as a star.
When you're in a stable orbit, you are actually spinning around the sun at a huge pace. To gain enough velocity to leave the solar system, you have to increase that pace by an amount that is less than the pace you already have.
As a terrible analogy, it takes less energy to overtake a car that is travelling in front of you at a higher speed than it does to slow yourself to a complete stop.
But to fall to the sun, you need to slow down 75mph. And speeding up and slowing down in space take the same amount of energy.
It is tricky (but possible, with cleverness and a careful schedule) to gain or lose energy this way, but it doesn't matter. If your closest approach is well within the sun's photosphere, it doesn't matter how fast you're going when you get there. So, you can do it with essentially zero delta-v, starting and ending with the same total energy as an object would have co-orbiting with earth, but on an extremely eccentric orbit.
It's not terribly rare (on a geological timeline, at least) for comets to dispose of themselves this way.
Anyway, what is so great about dropping them in the sun? Jupiter swallows comets frequently. Mars is a squalid dump, and so is Venus, at least below the clouds.
The sun is always at one focus of the elliptical orbit. You just can't get the orbit close enough to plasma-brake near perihelion without also pushing your aphelion way out. So you have to aim away from Sol in order to get there at lower energy. Basically, a Voyager probe that stops at the very edge of the gravity well and then plunges straight down. Spiraling down while decelerating is faster, but costs more energy. But as you get closer, you can harvest energy from the solar wind and solar radiation, with solar sails, so the amount of delta-v you have to load onto the launch rocket does not represent your entire delta-v budget.
There are ways to trade off time for delta-v, but at that scale, the ways that really make a difference mean that the person that sets them in motion will be ancient or dead before they finish.
I am only picking at you because you mentioned a rocket. If you said "shoot it to burn in sun" then you would be (mostly) right.
That seems like a lot of effort when you can just send it to nowhere and it will very, very, very likely never hit anything, ever.
Yes I agree that currently a Dyson sphere is the most sensible project humanity could ever think of!!
Quite informative, it seems like the naive approach of going straight into the sun is much more expensive (dv of 24.0 km/s) than escaping the solar system (dv of 8.8 km/s).
But, it seems that there is a trick where you use 8.8km/s to almost escape the solar system, then turn around with very little dv cost and plunge into the sun.
[1] https://en.wikipedia.org/wiki/Delta-v_budget#Interplanetary
At no point on the esacape trajectory can the object's speed fall below √2 times that of a circular orbit at that distance (or else the object would not escape.) At whatever distance you decide to set the controls for the heart of the sun, you must kill its angular velocity with respect to the sun (because, if it has more than a slight angular momentum, it will follow an elliptical orbit that goes around the sun.) Therefore, at every point on the minimal escape trajectory, the delta-v to redirect the payload into the sun is the escape velocity at that distance. With your strategy, the cost of sending the payload into the sun asymptotically decreases towards the cost of sending it on an escape trajectory.
https://en.m.wikipedia.org/wiki/Interplanetary_Transport_Net...
Unfortunately both effects do not seem to offer the kind of multiple-orders-of-magnitude gain required to make interstellar travel practical.
Takes some careful orbits and a long time, but NASA does it all the time.
So what may happen is if you have a low-thrust engine, you will do a burn at the optimal time, then stop and wait an orbit until you reach the optimal time again. But you're not "stockpiling" anything so much as you are just thrusting at the optimal time. And once you reach escape velocity you have to keep thrusting, there is no more opportunity to do another pass.
Seems like a Jupiter gravity assist would always be much more practical.
I think the mass of the body only matters in how much momentum it has. If you fly by an asteroid you will deflect its course. You could convert the entire mass of earth into spaceships and slingshot them past Jupiter and it would barely register.
I thought that just by letting masses getting sucked in while pulling ropes tied to alternators we could generate electricity... is it too naive? The amount of energy given by the fall into the blackhole would be superior than that used to bring the masses there in the first place.
Maybe the "right" way to convert potential energy is via conversion to heat and black-body radiation in the accretion disk? Might be difficult to capture significant percentage of that energy, though. See also [1]
Is it still too unrealistic?
For the radiation energy, it sure makes sense! Moreover isn't it any hard radiations emitted when the hadrons' quarks are torn from each other on reaching the events horizon?
By "ropes" I mean charged particles and by alternators I mean just very powerful electromagnets that can extract the energy of the charged particles falling into the black hole.
My point was that things attached to the outer core of an orbital ring are not in 0 G, but they feel the actual gravity at the particular height the orbital ring is orbiting -- on Earth if you would be sitting on an orbital ring situated at a height of say 300km, you would feel as though you were sitting on a 300km mountain; maybe on a primordial black hole you could build an orbital ring just a few km from the black hole and have spokes going down very close to the black hole (maybe active structures to overcome our current material strength limitations) and let charged particles fall into the black hole and extract their energy as they fall into the black hole.
Or maybe the black hole is small enough that a very crude electromagnets field could just encompass all of the black hole and it could very easily extract all that sweet energy of a charged particle falling into the black hole with an electromagnet an amateur could build in his garage.
https://www.orionsarm.com/eg-article/464790d2497de
The extreme temperatures and pressures in the accretion disk are basically used to fuse the lighter elements together into heavier ones, which are then pulled out by machinery in close orbit.
Because anything in close orbit is by definition plasma.
See also [1].
[1] https://physics.stackexchange.com/questions/25498/the-sun-as...
Edit: never mind, I just remembered there's a specific distance from a massive object you have to be to hit the focal length sweet spot. I wonder if having a smaller radius makes the focal length shorter?
Basically, gravitational lenses don't have a "focal length" per se. It's not an exact analogy to a classic glass lens. There is a minimum distance you need to be away from an object to use it as a g-lens. But as you get further away than that, it'll work better.
Now, the minimum distance you need to be away from the massive object decreases as the mass of the object increases. So for the sun, you'd have to place a camera about 500AU away to use it. That's too far to be practical at our current technology level. For a smaller object like a planet sized blackhole, you'd have to be orders of magnitude further away. Not very helpful!
Now, it's possible I'm mistaken as I'm thinking about some calculations I did on schwarzchild geometry and I didn't consider what would happen very close to the blackhole where curvature is very high, but my intuition says that it won't be very helpful at all.
That doesn't mean the blackhole won't be helpful though!!! I think there's an ENORMOUS number of useful experiments we could do. And, I think blackholes can be used as very powerful computers, possibly quantum ones, but I don't know the details.
- getting nuclear waste out of Earth's gravity well is risky, if the rocket explodes it scatters nuclear waste throughout the atmosphere. And very energetically, given the amount of rocket fuel needed to achieve this kind of flight
- getting to planet 9 (black hole 1?) will require loads of fuel or lots (>100 years) of time. Lots of time for something to go wrong, lots of time for errors in orbital calculations to accumulate, small target to hit
Extremely small. The paper has a to-scale illustration of the hypothesized black hole.
I wonder what happens to a bus-sized object if you send that black hole through it...
But really it's easier still to manage it on earth itself. Which is why, even at SpaceX prices nobody does that (that and rockets have a nasty habit of suffering rapid unscheduled dissembly.)
Counterintuitively, this is far more expensive than launching it into said black hole, or just out of the Solar System all together.
This is the first order approximation reason.
The earth is orbiting the sun at 30 kilometers per second. So if we launched something into space, since it started on earth, it would have that speed (similar-ish to throwing a ball from a moving car). So that object would now also be orbiting the sun at 30 km/s. We would need to slow it down that much in order to "fall" into the sun.
Once something was in earth orbit, it would only take about 12 km/s of delta v (change in velocity) to escape the solar system.
More info and math here: https://space.stackexchange.com/questions/3612/calculating-s...
At least that's how I see it, but I am far from being an authority on this topic.
Now, the trajectory of an object in solar orbit is exactly at right angles to the direction it needs to go in to hit the sun. No part of this velocity is helpful for getting to the sun - in fact it actively prevents it! The only vector that takes you directly into the sun is one with no sideways component - if you imagine yourself falling right in, any sideways nudge will cause you to miss it by a hair and go flinging off into a highly elliptical orbit. If you just ignore this and just thrust directly at the sun, hoping to overpower everything by brute force, then like a ballerina pulling her arms in, the more you try to get close to the sun with your thrusters, the faster your orbit will go; the closer you manage to get, the further out you'll be flung when you inevitably miss.
All this ignores that the sun is not a point, but quite a large ball - you can get away with some small horizontal velocity. A highly elliptical orbit will still do what you want if its lowest point is below the surface.
You should play Kerbal Space Program. It will very quickly give you an excellent intuition for basic orbital mechanics.
Sad note that also limits your launch window to once every 113 years as I recall from the last time I did the math :-(.
From a technical perspective you push into an elliptical orbit that intersects Venus, you do a slight aerobreak (skim the surface of the atmosphere) to dogleg toward a Mercury intercept, and then as you pass Mercury it tightens your ellipse still further and you head out, and come back and fly through the outer corona of the Sun (which is its hottest point). At which point you're in a degenerate orbit that will go out and come back through the Sun's corona until you've been completely consumed/burned up.
The latter takes a lot less delta v, but it has its drawbacks. Leaving the solar system, you don't have to budget for that rendezvous.
As a counter example, someone mentioned nearly leaving and then cheaply coming back directly into the sun.
While spinning it’s hard to get to the center. Once it stops, it’s easy.
The earth is spinning around the sun. To get to the sun, you need to slow down.
That seems off...googling suggests that the acceleration due to the sun at earth's orbit is a tiny fraction of 1G, and conversely, to have an acceleration of 1G would require going well inside Mercury's orbit.
Load the material into enclosures, bury them hundreds of feet below the sea floor near a subduction zone. Cheaper than rockets, still bloody expensive, and they may be worried about radioactive burps.
Now, black holes probably aren't known to be gateways to other locations, but that comment made me wonder what if they are, and dumping our hazardous waste in them has far reaching consequences somewhere else, then that in turn made me think of what other cosmic-scale consequences of alien technology might be out there.
I mean, if a civilization has planet-spanning tech, their "waste products" could be on the scale of planets too. Somewhere, a species must be burning through solar systems like we're burning the Amazon.
Like was it The Three Body Problem or some other story where an alien species’ faster-than-light travel tech causes the universe to expand faster and faster, making it harder and harder for younger species to produce enough energy for FTL.
That depends on the orientation of this thing. If it is spinning in just the right way, dumping anything into it would be like activating the death star. Even a week astrophysical jet pointed at earth would be a very bad thing. The last place you want to be standing when feeding a black hole is above/below it.
- how is the axis (like finding the head of a fluffy shitzu dog)
- how much is it spinning?
All the fear mongering around nuclear power is beyond hysterical at this point :(
[0] https://en.wikipedia.org/wiki/Radioactive_waste#Low-level_wa...
Waste implies we have no use for it any further. This concept views the world on very limited time scales (wherein we can continue to take from the world and turn things into waste that we have no use for any longer).
Instead we should always be thinking about reuse of materials. Waste should never be a terminal state so much as the waste products of one process should be converted into a useful input to something else.
Ultimately with limited materials on planet earth, virtually everything needs to exist in a cycle (water cycle, carbon cycle, etc).
The problem with the blackhole idea is that all atoms / baryonic matter could be used for something. When you send them to a blackhole, they literally cease to exist as baryonic matter (or at a minimum are never usable again). Thus, you are literally taking that material out of use (technically they will eventually be converted into energy as hawking radiation).
With enough clean & cheap energy nothing really prevents you from reassembling those particles into something useful.
- That's Sun.
So if there's a 1-20 Earth-mass black hole out there, it hasn't evaporated from anything appreciably larger to get to that point.
How long would we have to wait for it to evaporate before we could use it for energy production?
The earth is quite larger than a black hole with an earth mass. Also the earth has a huge atmosphere to help capture things.
A black hole with the same mass as the earth would be almost impossible to hit in comparison (9mm). No atmosphere to slow things down, very hard to hit, and you have to come within 1.5 * the radius before you can't escape without thrust.
So sure, some dust would be capture, but nothing anywhere close to what the earth captures a day.
Someone told me the other day thought I’d pay it forward!
It's not all that much energy for the timescales involved, you'd be better off just putting say an acre of solar panels in orbit around the sun.
Tiny blackholes are amazing efficient engines for turning mass into energy, once small enough they could be quite a power plant and not picky about what you feed them.
With the gravity of a whole planet it would still attract a lot of stray matter. I don't know how many collisions that would generate though. Mostly just deflected orbits and captured satellites, I assume.
But surely a lot more than a "regular matter" 9mm pellet.
The threshold I could find for surviving since the big bang is around 10^11 kg which is quite a bit smaller than the moon. 10^11 kg is quite a bit compared to human scale, more than the mass of the Three Gorges Dam, but quite small on the astronomical scale (10^11 times smaller than the moon).
So while an earth mass black hole is small (9mm), it will last quite long indeed. The evaporation time is proportional to the mass^3.
Hell we barely notice when a several km comet enters the solar system and I've read about fairly large asteroids getting closer to the earth than the moon before being noticed.
We are going to notice a 9mm black hole? Maybe if it punctured Jupiter first.
Sure if the earth came between Jupiter and it's moons there might be some chaos, but the likelyhood of that is minimal. Even if it did happen we would notice, but the earth massed black hole would be very unlikely to make it into the inner solar system at that point.
The earth is a minor gravitational force in the solar system, most likely the effects would take significant time to notice... well after the nearest approach. Small gravitational tugs take many samples and significant time to notice. For example the outer solar system still doesn't add up... and we have no idea why.
I found these in a quick search. I have a couple 64 core machines available.
https://wwwmpa.mpa-garching.mpg.de/gadget/
We would detect one entering our Solar System.
Now imagine what a strong force an electron could provide :D
Earth by Brin
Hyperion Cantos by Simmons
Ilium by Simmons
Doomsday Effect by Thomas Wren
If I thought for a few more minutes I could probably come up with a half dozen examples (or expanded the definition to include eating the moon or mars, or included ones where it would be a massive spoiler)...
A gravitationally captured/trapped black hole eating earth is relatively common plot device in science fiction.
If the tiny bullet-class black hole makes it through a planet, it could gain significant additional mass, and leave quite an exit wound.
For example, it travels through Earth and then leaves a 9mm hole throughout the planet.
Something in the 10^12 kg range is going to have an atomic scale event horizon so it’s not picking up significant mass as it shoots through the earth.
Also the relative velocities of earth and the black hole is extremely important. Depending on the relative velocities, it's possible that the blackhole simply gets lodged in the earth's core and we're 100% dead, another 100% dead scenario is if it plunges in, out the other side, but then "falls back" for another pass and so on.
Good yarn though.
I've been thinking that it was a misrouted Viking.
Having a tiny radius will reduce the amount of of collisions, but it won't have a significant impact on orbital clearing.
A black hole with 10^11 Kg seems to have a temperature of about 1.2 * 10^12 K. Even though it would be small, it would be emitting crazy amounts of all sorts of photons.
If anything it'd be a lot more valuable then just finding another rock in space.
It's theorized that the existence of Jupiter played a role in clearing out the inner solar system of kinetic kill vehicles, helping create a stable environment for life to evolve on Earth.
They can be created by the collision of topological defects in the early universe, which in turn can be created in phase transitions during the cooling of the universe, like imperfections in quickly frozen ice. Or they can be created by simple collapse following inflation, if inflation is modified to create large inhomogeneities.
Assuming light going into a black hole adds to its mass?
But assuming some light and matter didn't get sucked in and that's what remains, then I can understand why black holes are proposed as a possible answer to the mystery of dark matter.
http://www.wolframalpha.com/input/?i=schwartzchild%20radius%...
Additionally, it's been proposed this universe is a 4d-spatial black hole. In this case, you can re-consider aggregating the entire 3d-spatial universe as a 4d black hole, and the Schwarzschild radius calculation works again.
https://www.nature.com/news/did-a-hyper-black-hole-spawn-the...
Given some of the answers on the Physics StackExchange, I think my error is using a static approximation like the Schwarzschild solution for a dynamic situation — given my grasp of the Einstein field equations is “ooh pretty symbols” this isn’t a huge surprise, though my lack of detailed understanding is a personal frustration.
You're quite right that formation by collapse excludes Schwarzschild.
What you're heading towards is the Vaidya metric -- I don't know of any easy overview of it, but one can think of it in terms of Schwarzschild.
Schwarzschild is a static solution: an eternal, time-independent, everywhere-vacuum, pointlike mass. There is no radiation in Schwarzschild.
Vaidya has the same spherical symmetry, but the central mass is time-dependent. The central mass can radiate away or absorb incoming radiation, but with the condition that the radiation is spherically symmetrical.
Radiation in Vaidya is technical: it is a "null dust" -- it follows null geodesics and does not self-interact, so it shares properties with light ((classical) light rays have no charge, and don't clump; breaking down light rays into particle-like elements leaves each element having no rest mass in its own Local Inertial Frame).
As long as it is sufficiently close to a null dust, Vaidya can model practically any collapse of radiation to a black hole. Unfortunately the spherical symmetry is a hard constraint for the exact solution, and is easily broken by matter self-interactions. However one can certainly play around with numerical approximations to the Vaidya solution, and if one does that enough for a particular family of perturbations of the exact solution, an intuition is likely to develop.
However, a kugelblitz from a collapsing null dust is within the gift of the exact Vaidya solution.
You can take a "swiss cheese" approach to a very early expanding universe filled with radiation (of the technical type above) peppered with Vaidya regions which evolve. Vaidya is time-dependent and can deal with a tapering off of incoming radiation as long as it's always spherically symmetrical, with the result that eventually you have a "cheese" that is an expanding radiation-filled spacetime and "holes" which are vacuoles which asymptote towards Schwarzschild, and around each "hole" a thin-shell Israel junction. The asymptotic behaviour is because the dust crossing the junction into the Vaidya vacuole is (a) cosmologically redshifted within the "cheese" and (b) diluted by the metric expansion of the "cheese". The radiation already inside the junction at early times collapses onto the central mass. The two combine to effectively shut off the incoming radiation, leaving behind a very close approximation of the Schwarzschild vacuole.
(Aside: for massive dusts, one would use a Lemaître-Tolman-Bondi metric instead of Vaidya, and one still runs into problems when breaking the conditions of spherical symmetry and no-self-interactions in the dust. LTB has a couple neat properties which are suitable for physical cosmology "swiss cheese" models if one assumes that the radiation exiting the galaxy-cluster "holes" is negligible -- starlight arriving in our galaxy cluster from distant galaxies likely adds basically nothing to the mass of our cluster as a whole, and our galaxy-cluster isn't losing much weight through its starshine out to infinity; ditto for neutrinos and heavier particles).
In summary, primordial black holes are pretty easy if the very early universe is filled with a homogeneous, isotropic dust -- radiation as a null dust, or some massive dust, or even some combination. In the initial dust one expects Jeans instability, and a power-law distribution for the total masses of the resulting vacuoles. Plenty of small primordial black holes, fewer big ones. What would cut off really small black holes originating along these lines? Unknown. If nothing is found, this type of model loses its attractiveness.
There are several other models for primordial black holes, but they look a lot less like the kugelblitzes you talked about a few comments above.
One other note, although I don't have space to develop it here: we can form black holes from gravitational radiation alone, even in a spacetime with zero matter. Gravitational radiation is not the same as matter radiation in the technical sense above: apart from the mathematical details of which tensors encode it (Riemann vs stress-energy) more physically gravitational radiation strongly self-interacts, so we generally can't treat it as a null dust.
> personal frustration
GR doesn't really come easily to anyone, even (and sometimes especially) with people who are mathematically gifted. Even Einstein and Hilbert struggled with it, and in the last century only a small number of exact solutions -- none of them better than a fair-enough-to-be-useful approximation to astrophysical observations -- have been found. There have been many many many false starts. Consequently one has to develop an understanding of where exact theory starts to diverge from exact observation (and what one can do about it with arcane tricks), and I don't think that's really possible without understanding the exact theory first.
Lastly, I don't know what you're thinking about here:
> the Schwarzschild radius for the mass of the visible universe is bigger than the visible universe
The visible universe is not even slightly approximated by the interior part of Schwarzschild metric. In particular, galaxy clusters are flying apart rather than collapsing to a point. Additionally, there are no apparent tidal stresses on galaxy clusters, even the ones at highest redshift: the Weyl tensor, which essentially encodes tidal stresses, is nothing like a black hole solution (not even under time-reversal wherein we get a "white hole", because we would then see spaghettification in reverse: galaxies evidencing ellipsoidal early galaxy-clusters with later galaxy-clusters becoming markedly rounder).
Event horizons can appear all over the place, including in perfectly flat spacetime (for Rindler observers, for example). There are lots of very-not-like-black-hole-spacetime settings in which there are global event horizons. The salience is in what trajectories radiation and other types of matter take, rather than that the matter-in-the-bulk can be partitioned by horizons that produce Lorentz-contraction observables.
Going back to our swiss-cheese model above: in the far far far future the cheese part is essentially empty of radiation because it has all diluted away with expansion, while the holes are also empty of radiation because it has all fallen onto the central mass. Both empty, highly curved spacetimes, but with very different trajectories for the null dust: flying to infinity versus flying into a point.
Edit: so, how do we locate it exactly?
More recent solar sails and plasma based propulsion systems have achieves significant improvements since then. If it was a priority I don't see why would couldn't go 10x as far within in the next decade.
To learn that the conditions of the early universe could have create sub-stellar mass black holes means there could be tons of small black holes out there lurking in interstellar space.
What would happen if one of them got close enough to our Sun to begin accreting gas from the Sun?
- Could it eat the entire Sun and cause our solar system to go dark?
- As it gained sufficient mass from the Sun, it would switch from orbiting the Sun to them being a binary system. Would that destabilize the orbits of planets?
- Or disturb a ton of Oort cloud bodies and potentially cause tons of comets and raise the risk of impact events?
- At what point would the Sun's fusion stop?
- Obviously this depends on the binary dance of the 2 bodies, but rapidly the sun would be pulled apart.
- Would there be X-rays and particle jets like a micro-version of a quasar?
I really hope someone is modeling this!
HOWEVER. Getting a black hole into a tight orbit - I don't know how that might happen. A black hole from outside the solar system would be coming in on a parabolic path past the sun. It would shoot right back out of the solar system.
If the BH managed to absorb enough mass from the sun, I would imagine that would throw off it's trajectory enough it could become captured into an orbit. On each subsequent fly by / through the sun, it would capture additional mass. This would reduce the period of the orbit.
In a situation like this, you have an increasingly massive object passing through the solar system in an irregular pattern. That can't be good.
But for it to destabilize the orbit of planets through the orbit of a binary system, it is quite plausible once the blac hole has gained sufficient mass for it to count as a binary system and not simply a planetary mass black hole orbiting a stellar mass sun[1].
[1] https://arstechnica.com/science/2013/01/binary-star-systems-...
First the outer layers of the sun are not very dense, but as a larger fraction of the matter for the black hole comes from the sun the slower (relative to the sun) the black hole would get. The slower the black hole is that closer it would come to the center of the sun. The closer to the center of the sun the denser the sun is.
The pressure of the sun is at least 10,000 times greater than the center of the earth which is 3,500 kilobar. Wouldn't the amazing gravity gradient and the 3,500 kilobar pressure result in a very well fed black hole that would double in mass within say a few days? Sure a accretion disk would form and start pushing back the matter at the north and south poles to reduce the feeding rate.
Sure black holes generally increase is size slowly, but they aren't usually inside a gas cloud of 1.4grams/cm^3 at a pressure of 3,500 kilobar and having an entire suns worth of mass to provide resistance to the accretion disk allowing for matter to fall in quicker.
I've heard numbers like you mentioned for atom sized size black holes that fell within the earth, but the main problem is that the likelyhood of swallowing an atom is so small that it grows incredibly slowly.
Do you have to send a probe close and throw something in it?
However a lensing event seems possible, it greatly increases the effective radius of detection and is much more distinctive. Not sure what the smallest lensing event witnessed is, all the ones I'm aware of were a solar mass or more.
I don't know the physics enough to know if a small (earth to neptune mass) blackhole could redirect enough star lights to detectable by an earth (or earth orbit) telescope.
With a huge database containing the time series of the sky you can start searching for unknown objects that stick out because they are a change from the previous exposures for that part of the sky.
With enough data mining of those previous exposures you could find likely candidates and get telescope time to check out where you expect it to be next.
This is similar to how things like Oumuamua and 2I/Borisov were found.
> This scenario could be confirmed through annihilation signals from the dark matter microhalo around the PBH
One possibility is gravitational lensing. The abstract also mentions detecting "annihilation signals from the dark matter microhalo around the PBH". Not that I understand that completely, and I don't believe (corrections welcome) that dark matter annihilation by black holes has been confirmed experimentally.
I believe high energy particles are released by black holes as they consume matter, so that might be another way to detect a small black hole instead of a similar mass rock.
However if it's big enough to be messing with orbits around neptune it's likely pretty large. If it's large then the hawkings radiation isn't going to be visible.
So if it's moon mass it's going to be 0.1mm and at 2.7 kelvin or so. Earth mass is 9mm, but even colder. Generally for the orbital changes they are seeing in a wide variety of objects it seems like the mass is even larger still.
Even seeing pluto is hard, even a jupyter mass black hole is only 3 meters or so. So no I don't think we could detect it via hawking radiation.
We might however see high energy particles resulting from the somewhat messy feeding that black holes are known for. If we sent a probe it could plausibly get close enough to directly observe hawkings radiation. Pretty amazing thought, maybe we will get that lucky.
Surely a "large nuclear bomb" isn't very strong when you're talking about things on black hole scale?
Ah, looks like I was "a bit" low. Wiki claims 5×10^6 megatons of TNT when it finally evaporates. Apparently about the energy the shoemaker level struck Jupiter.
From a distance there is no difference in lensing between a black hole and an regular object of the same mass.
From close there would be a difference, but if you could resolve something that small you would be able to directly image the object.
An earth mass blackhole is going to have 10, 1000s, or even millions of Gs depending on how close the light gets.
Seems like you'd get stars periodically blinking from places they shouldn't be, as light trajectory should have missed earth, but gets bent by the black hole. So while the black hole itself would be invisible at that distance, and occultations would be invisible, seeing stars in the wrong place would still be visible.
You are only bending a minute faction of the light from the star traveling toward you. It's not enough light to see, and it's too small to resolve (unless you could resolve the black hole in the first place).
Think about it: The redirected light only has the "size" of the gravitation field in question. For an earth sized mass thats 9mm. Even if you did 9km (which wouldn't bend much) you couldn't see it, never mind 9mm.
We'd basically see extremely energetic particles coming from a nearby source. Since no other known physical process can generate such high energy particles (not even fusion in main sequence stars), we'd have to conclude that there is probably some extremely dense object there.
https://arche-arc.blogspot.com/2018/11/mythcomics-lucifer-ri...
Were such theories about a hypothetical planet beyond Pluto already existent when this series was created, back in the mid-'80s?
The combined system of that singularity plus a hard spherical shell at radius 261 km (anchored by some sci-fi means that does not contribute significant mass) has a density of 134 g/mL, 6 times as dense as pure osmium, but being mostly empty space inside. And having a surface area of 856000 km^2, 0.6% the land area of Earth. Such a body could retain an atmosphere and sustain ecological cycles.
I don't have a physics degree, but how close would Earth have to get to such an object before the Earth is within that object's Roche limit?
Edit: According to https://en.wikipedia.org/wiki/Roche_limit the Roche limit d = Rm * (2 * MM/Mm)^(1/3) for Rm = radius of the satellite, MM = mass of the primary, and Mm = mass of the secondary. So in this case d = 6380 * (2 * 5/1)^(1/3) = 13,745km. In astronomical terms, very nearly a bulls-eye.
The radius of the event horizon for a black hole even the size of Jupiter is only 2.5 meters.
Wikipedia gives the formula d=R_m*(2m_M/m_m)^{1/3} which matches that intuition.
So plugging in numbers you get 2.15 times the radius of Earth, which becomes 13 750 km.
For comparison, Earth-Moon distance is approx. 400 000 km.
It doesn't have any special ability to slingshot things to crazy speeds.
Remember - the slingshot doesn't add speed from the gravity of the object, it ads speed from the rotation of the object around the sun.
Slingshot uses the motion of the planet around the sun, and pulls the probe along with it in the same direction that the planet is orbiting the sun.
The probe comes in perpendicular to the solar orbit, and leaves parallel to the solar orbit, and faster (relative to the sun). Relative to the planet there is no change in speed.
Kind of like bouncing a ball against a moving car. Relative to the car nothing happened, but relative to the ground the ball is faster.
Gravity burn is more complicated. (Oberth effect)
Imagine a stationary rocket (bolted to the ground). All the energy of the fuel is in the exhaust, and none in the rocket.
Now imagine the reverse - a really fast rocket, now way more of the energy is in the rocket (and less in the exhaust).
So what do you do? You fall toward a planet, and at the point where you are moving fastest, you fire your rocket. Now not only does your fuel have the energy inherent in it, it also has all the energy from falling toward the planet.
And this is the big idea here: You leave that fuel behind as exhaust! So when you climb back out of the planet you don't carry the fuel with you.
Normally falling toward a planet, and leaving the planet exactly cancel out. But you used the oberth effect to leave the fuel behind at the point where the fuel has the most kinetic energy.
https://phys.org/news/2017-08-theory-heavy-elements-primordi...
This paper is :
215.9 × 279.4 mm (Letter, portrait)
You'll get a Nobel prize or two if you could prove that..
Besides wouldn't the 'ground' gravitate towards the black hole than the other way around?
1 minute (at 50km/sec) later it would be 3000 km the acceleration 4.5G or so.
1.5 minutes later it would 1500 km away the acceleration would be 17G or higher.
2 minutes later it would be on the surface, and everything ripped up (including buildings, soil, bedrock, crust, and the magma below would go from being accelerated up at incredible velocities to an even more intense acceleration down.
Over that 2 minutes the black hole is going to chew the hell out of the earth for 1000s of km in all directions and that's just the start of the fun.
As it hits the surface everything within 1000km will be experiencing 40G. The pressure waves will go from negative (as the black hole pulls the atmosphere away from the earth) to a HUGE over pressure as magma, bedrock, and water get slammed back down into the earth at 40G. Said over pressure wave of intense heat and pressure will expand outward from the point of impact and create problems world wide.
Worse on the opposite side it will just take a large chunk with it (approximately the volume of which the black hole has significantly more than 1G of gravity) which could easily take a continent with it, or say most of the pacific ocean.
I could see ocean levels and air pressure lowering significantly. After all why would the air stick around a 1G planet instead of a more than 1G black hole?
The area from which the air is removed is likely to be somewhere around 12,000 km wide (the area of which the black hole applies more than 1G).
So I'm not sure I believe the "barely enough time to move" thing when for minutes the accelerations will be crazy.
We treat it that way because, despite it showing that our model of physics is breaking down at that point, it works really well for most real purposes. But look at string theory, loop quantum gravity, etc., and you will find plenty of the variants within those umbrellas do not have a singularity at the heart of black holes.
Radius = (2 * Gravitational Constant * Mass)/(Speed of Light^2)
The gravitational attraction from a given distance from the center would be the same as for Earth. For example, if you're 4,000 miles from the center, you'll experience a 1-g acceleration. The difference is that, because of the black hole's smaller size, you can get a lot closer to it.
The good news is it would pass effortlessly through the earth and not go to the earth's core and stay there. After all where is the resistance going to come from?
Now if the blackhole was brought to rest at the earth surface it wouldn't reach escape velocity (11.2 km/sec), but anything coming from way past pluto would likely have a much larger velocity.
The bad news is that having an earth skewer the earth at high speed is going to cause some pretty crazy gravitational interactions.
Also some of the matter falling into the black hole from earth would be consumed, but some of it would radiated out, no idea if that would be worse than the physical disruptions or not.
Thats putting it very mildly. Its actually quite an interesting thought exercise - As this black hole approached earth its gravity would counteract earth's gravity, meaning everything near where it "touched down" would experience near zero-g as it approached. The opposite side of the earth would experience greatly increased gravitational pull...
Then while the black hole was inside the earth, everything would be experiencing close to 2G, then zero G for a bit for the poor souls on the side of the earth where it exited.
Because of the fantastic amount of momentum it would have, and it would certainly be travelling at well over earth escape velocity I would expect it would travel straight through earth and keep going, not even coming close to stopping inside earth.
The affects on earth would be very... bad.
I'd imagine it would trigger devastating global earthquakes, as well as epic rock slides from the changing gravitational forces. Not to mention the tsunamis from the oceans sloshing around like water in a giant bath, as well as all the rockslides both above and below water. It would be a mess.
Assuming this object would be travelling at 100km/sec, and the gravity would maybe begin to badly affect us when it was 50,000 km out from the surface of the earth (?) then it would take about 16 hours to travel from this distance, impact the earth and then reach this distance out the other side.
I'm not sure how much energy would be released by the matter being consumed by the black hole - It might not be very much, after all its total gravitational pull wouldn't be very high, but would be travelling at probably at least 50+ km/second - certainly more than 11km/sec (earth escape velocity) The matter in front of the black hole might simply be swallowed up without much fuss, or if there is any "resistance" to this matter falling down past the event horizon I'd imagine it would be like a continuous series of nuclear bombs going off as matter was flash heated to the point of spontaneous nuclear fusion before it passed the event horizon.
The one good point to note in all of this is it would be extraordinarily difficult to disturb this object from its object so it fell into the inner solar system. After all, it has the same mass as earth, and we don't have to be worried about random stuff disturbing earth's orbit.
I did do a super simple simulation trying to explore if you could escape from beyond the event horizon where time dilation becomes so extreme that even very rare events become common. One of those extremely rare events could be when a galaxy collides with a second galaxy and the black holes at the center end up merging.
Turns out you could escape from falling into a particular black hole if you had a second black hole to counteract the gravity. Unfortunately even while you are at zero acceleration, you end up inside an even larger event horizon formed by the two black holes. Your choices would be to fall into the first black hole, fall into the second, or wait for them to collide. Even the waiting isn't a particularly good option. While being outside the event horizon of a very large black hole minimizes the spagetification problem, there's no such protection inside the event horizon.
In any case if interested in reading sci-fi based on black holes check out https://en.wikipedia.org/wiki/Black_holes_in_fiction
One number I saw was for Comet Kyakutake which now has a 70,000 year period, was 58 km/sec. At that speed it would take about 4 minutes to skewer earth. But things would be pretty crazy for something like 3 times that.
Imagine the object is 10,000km away, the nearest edge of the earth is starting to notice less gravity, around 1/2 a G. Walking becomes difficult, homes, bridges, trees, etc would equalize to 0.5G loads, likely making all kinds of interesting noises. Driving would feel like it's on snow/ice (with half the traction, but the same mass).
About a minute later there would be zero gravity over a decent fraction of the near side of the planet. Rivers overflow their banks, cars float into the air with the slighted bump, and any step taken is your last.
Likely volcanos and fault lines would experience significant pressure changes and might well go off. The atmospheric pressure of 15 pounds per square inch (22,500 pounds per square meter) disappears.
Any cars on suspended structures like bridges would be flung into the air as the weight of the entire bridge is suddenly removed. Every car would launch as soon as it hit the smallest bump. Even just the 3000 pounds of car compressing the tires would be enough to launch the car with gravity is removed.
Most humans are still alive. People within a few 1000km in pain, getting bends, and exposed to very low pressures. The atmosphere has going from 15 psi to close to zero.
One minute later the object is 3000 km away, and now acceleration towards it is on the order of 47 M/sec^2, earth is only pulling people back with 9.7M/sec^2 so everything within 1000km is accelerating away from the earth at 4G or so.
First it's all water, most buildings, and all cars that leave the earth's surface and accelerate towards the black hole. Then it's plants, soil, and everything but the bedrock. Then the bedrock, mountains, and the entire earths crust that leaves.
Vertical (or towards the black hole if you prefer) acceleration keeps increasing. Enough to throw significant debris all over the planet, into orbit, and even above escape velocity. The significantly impacted part of the planet has gone from a few % to 25%. Air on the closest half of the planet is rushing towards the impact point at 1000s of miles per hour (accelerated at 15 psi).
Distant locals half way between where the black hole enters and exists are going to start noticing crazy winds and air pressure changes as a decent chunk of the earth atmosphere is leaving the planet.
Seconds later the acceleration is up to 40G or so, it's still 1000 km away, but nothing can resist the acceleration. The deep internal pressures of the earth make things worse as a nearest 1000km of the earth gets pulled on by 40G forces. Think of super volcano the side of a continent, but worse. On the near side of the planet there's really no surface to speak of. Just a giant cloud tormented by the ever increasing gravitation gradients. Spagatification reduces the cloud to small hot particles.
A minute later the object hits where... the surface was. The acceleration of 25% of the earth or so has just reversed direction, with even higher because it's now the earth + black hole. A minimal amount of matter was consumed by the black hole, adding a nice light show at as a few % of the mass consumed is turned into energy.
Now a fraction of the planet has gone from zero PSI sucking the rest of the earths atmosphere in (15 PSI of negative pressure), to a huge over pressure (1000s of PSI of positive pressure) as a everything that left is slammed back into earth. Everything within a 1000km radius of the impact zone saw a negative acceleration of at least 40G followed by a positive acceleration of 41G. The circulate shock wave will be easily heard round the world and will cause a world wide maelstrom just from the energy involved, even ignoring the world wide rain of white hot debris.
I don't think the earth would quite be at the level of a planetary object called synestia, but it's on it's way (look it up).
After another minute the black hole is near the center of the earth, and the entire earth sees 2G of gravity. The energy already imparted into the earth is substantially more than if you ran the moon into the earth at 130,000 mph.
The next minute isn't too bad, oceans, earthquakes, winds, and storms are all off charts in intensive compared to anything besides maybe the center of a nuclear bomb. But nothing worse than what has happened... yet.
Then there's a huge gravitation spike on the opposite side of the planet, north of 40G over a 2000 km diameter circle, but more damaging. As bad as the approach was, the exit wound is worse. It ends up taking a 1000 km deep (earth crust is only 30km or so) chunk of the earth with it. This makes the previous super volcano eruptions look like childs play. The hole left behind could easily drain all the worlds oceans, or if filled with magma would cause the earth to deflate and cause elevation changes world wide. Air pressure would drop world wide, and what was left would be heavily polluted with embers, smoke, and be way too hot to breath. In fact I'm not sure the earth would have a crust at this point.
Depending on the exit I could see all land ending up below the ocean (the average land elevation being much more even than today) or ocean levels being dramatically lower (if the black hole left through the center of the pacific ocean).
Any water within 6000 km or so of exit would be gone, land would be less.
Seems unlikely at this point that the earth rotation would be the same speed, or even the same direction. The orbit around the sun might change some, but not a big deal compared to everything else.
Seems plausible there might still be single cell bacteria alive, but not much more.
What would be the optimal speed for a collision?
All of these numbers are off by many orders of magnitude. You're fundamentally misunderstanding how gravity works.
If you were standing on the surface of the Earth and an Earth-mass black hole were magically stationary 1 km underneath your feet you wouldn't experience something close to 2G, you'd experience something closer to 40 million G.
Check out [1] for more details, and [2] for a calculator where you can play with the gravitational formula.
1. http://www.physbot.co.uk/gravity-fields-and-potentials.html
2. https://www.wolframalpha.com/input/?i=surface+gravity+calcul...
An interesting part about it would likely be what would be left of earth, since I guess earth's core material would be rather eager to be swallowed by the PBH, and we rely on a couple of properties of the core for the electromagnetic field. I'd imagine this would never be the same planet afterwards, at least not with the same gravitational attraction... or even comparable properties within the next geologic timescale.
If you drop a black hole into the sun, the sun dies.
Seems a wee bit more dangerous to me.
It's possible there are one or more black holes orbiting inside the Sun right now. They might be the reason sunspots exist.
Practicing your impression of Calvin’s dad, I see…
If higher than it's going to keep going, if lower, then yes eventually it's going to consume the sun.
A black hole the mass of the earth is 9mm. The weight of a cubic cm of sun is around 1.41 grams. The black hole isn't really going to notice.
The pass through the sun is around 1.39102e+11 cm * 1.41 grams per cm^3 = 139 million KG. So the earth weighs around 4.2* 10^16 more than what a black hole sized hole in the sun weighs.
However, that 4 billion g acceleration is a problem even if it is only for a very short time. If the black hole is going at .999999999c, which is far more than we can hope for, something withing about 100m it's path would be accelerated due to the gravity of the black hole so much that it ends up moving at hundreds of thousands of miles per hour, and stuff within a few dozen meters becomes relativistic. Even ignoring the stuff very close to the path of the black hole, the stuff at hundreds of meters from the path would release an epic amount of kinetic energy. My envelope isn't large enough to see just how large, but certainly enough to leave a melted/vaporized tube at least a few hundred meters across all the way through the earth, and this is a gross underestimate.
Would make for a pretty impressive anti-podal volcano if nothing else.
I did hear one theory that the Tunguska event was an evaporating black hole, I don't think there's much scientific evidence to back that up though.
I forget the story, but some scary advanced weapon technology gets abandoned, sold on the black market, and ends up in India. Random folks there figured out you could chip the containment vessel, feed it sewage, and bounce a laser off it to capture energy and power the village. Complications ensue.
Yeah, but you're not accounting for all the kinetic energy the black hole is going to impart on the Earth, which is the main factor in this hypothetical disaster.
Let's assume for simplicity that the radius of the Earth is 5000 km, and the black hole is moving at 1000 km/s.
That means that as soon as it's approximately 5000 km out we'll have around 5 seconds where around half of the Earth isn't the Earth's surface in any meaningful sense anymore, rather it's a bunch of rocks that have just crossed the zero G barrier between the Earth and the black hole, and are now in freefall "upwards" from the Earth.
I'm too lazy now to calculate how far a rock on the surface will travel "upwards" given the approaching black hole, but let's just assume a constant 9.8 m/s^2 for the whole 5 seconds to understate this disaster (it's going to be a lot more than that). You'll fall ~120 meters in 5 seconds in freefall in Earth gravity.
So by the time the black hole passes the "crust" that crust is already hovering some hundreds of meters in the air, and will rapidly fall down and re-compress as the black hole passes.
I wouldn't be surprised if the energy transfer is enough to turn the entire surface into liquid magma, but I haven't done that back-of-the-envelope calculation.
You are assuming the stuff near the surface is being pulled up, but the stuff under that isn't being pulled up, so rocks are 'flying away from the earth and towards the black hole'. In reality the only net force you can 'feel' from gravity is due to tidal forces, so this would have an effect more like 'squeezing' the earth and the energy would be spread throughout the entire interior. For an earth-mass black hole, however, the difference in acceleration between something 1000km away and something 2000km away is still stupidly high (about 30g), so your assumption is correct!
But generally, this is my point. A slow moving black hole is going to rip the earth apart, a fast moving black hole is 'less dangerous' because it just punches a hole and keeps going, with almost no interaction with the earth, even though that is counter-intuitive. Yes, things would get pulled away from the surface of the earth, but they would only feel that pull upward for a very, very short amount of time, not long enough to be substantial. A small black hole, say the mass of a meteor or something, might go through the earth and not even be noticed, it's far less dangerous than a meteor of the same mass would have been.
A fast moving black hole isn't 'nearby' very long, it would go from far away to far away in microseconds.
However, as the mass gets large enough, the dynamical friction on the black hole is so large that it leaves behind significant kinetic energy by melting a hole through the earth, no matter how fast it is going. https://en.wikipedia.org/wiki/Dynamical_friction
If you neglect dynamical friction, as far as I know an earth mass black hole could potentially go right through the earth and we wouldn't have to worry so much, but it depends on the specific path it takes since it could still disrupt the Earth's orbit.
Just whatever the predominant gravitational influence is
Maybe this semantical exercise doesnt matter here if the mass of the black hole is so small