And it's still grasping at straws. The idea of a PBH as planet 9 itself is somewhat sound, but this particular paper assumes not just a significant population of MACHO dark matter, but also an additional WIMP-like particle DM that would produce a detectable signal. Is it theoretically possible? Yes. Would it be amazing to find evidence for it? Of course. Is it likely to happen? No. And we probably won't get a conclusive answer to this either way until we can easily send probes outside the solar system or at least have enormous telescopes on the moon's surface. Until then this topic is mostly an easy path to publishing papers to get tenure.
You can't just make something free floating bigger and bigger without introducing new issues. In particular, as objects get larger in zero gravity, it becomes harder to dampen oscillations. The lighter the object is the more problematic these oscillations become. You also run into issues with thermal expansion.
Objects have a resonant frequency and will jiggle in strange ways. The larger the object, the larger the possible jiggles. The larger the jiggles the larger the destruction.
Are you saying any object in space will naturally be resonating with itself at some frequency or that by proximity and interaction to another object it may cause resonance on another and therefore cause it to jiggle in strange ways.
The latter. Basically [1] but not as exaggerated. Think of things like screws shaking loose over time which leads to structural failure. Plus, no easy means to release that energy like you would when you're attached to a planet.
Look into "Chaos Theory", "Control Theory" and "Damping".
In particular, consider how you would damp an undesired movement by a satellite. A naive approach would be to apply thrust in the opposite direction. However, the control can't be exact, leading to thrust -> thrust <- over and over, eventually to the measurement limit of the thruster's control.
With a large mass, it's replaced with a spring, and converted to heat.
Basically, things that are bolted tightly onto 73 million million million tonnes of rock tend not to flop around very much. It's a near-perfect "momentum sponge".
Things in virtual freefall that can flex (and everything can) do so in response to forces (e.g. thrusting, but also heat stresses, say), and will continue to do so if they start unless you take care to damp them and dump them into heat. There's nowhere for the vibration to "go" unless you design one in. Sometimes the structure of the craft itself has enough damping for practical purposes, especially when you take care to isolate large vibration sources (the ISS has a Sorbothane damper for the treadmill, for example), but when your big floppy (i.e. light) mirror surface has to stay put on a nanometre scale, it's not so simple.
It's a bit like the difference between a tuning fork glued down flat to a table and one hanging from a string.
By any chance do you know the history of these solutions and what what went before understanding this or was it already calculated and known far in advance of needing to account for it?
In the sense of building things that last in space.
I don't know specifically. I imagine that a lot of the concepts came from naval architecture (sloshing of fuel, water and cargo has sunk many ships through the ages, for example, as well as hull resonances called "springing") then aviation (e.g. "flutter", where the wings oscillate, has destroyed planes) and space and missiles (again with the fuel sloshing, and other modes like pogo oscillation where the vibration feeds back into the engines and self-reinforces). Some concept of it also in civil engineering: the Tacoma Narrows bridge is the canonical example.
Fundamentally they're all somewhat similar in that there's a flexible and/or sloshing thing that doesn't have a huge mass that it's rigidly connected to. Spacecraft deployed in space usually have smaller forces on them (no air or water and the hard acceleration is done) but are also much flimsier due to being ultra-light. Telescopes are even worse as even a tiny vibration can ruin the usefulness of the optical paths.
Ok, so basically anything that has any forces on it will end up with oscillations. On Earth it tends to not matter, because those oscillations travel from the object down into the ground, which is really good at damping them because the ground is, uh, pretty big. Even for things not attached to the ground, the atmosphere inherently damps oscillations, because as objects move back and forth in a fluid, a low pressure zone is created behind the object, which pulls it away from the direction it is moving. Also, rigid objects do much better with oscillations, because the entire structure has to move (more mass moving means less movement when the same amount of force is exerted on it). Floppy objects do worse, because one section can start oscillating on its own without transferring that motion to the entire body.
In space, there is nothing to damp the oscillations. They will just continue without active features of the craft to damp them. If they continue unabated a section may reach a resonant frequency, which can quickly cause failure. Even if it doesn't, those vibrations can cause cyclic loading failures, or just affect the stationkeeping of the craft or it's usefulness in gathering scientific data.
To make a spacecraft resistant to oscillations requires devices like gyroscopes or friction dampers, or long weighted booms which decrease the magnitude of oscillations. Making the craft rigid helps, but the larger it is, the less rigid it will be. And to make it more rigid, or to include more anti-oscillation devices, means more weight. That's an important limiting factor when you need to get the object up into orbit.
One misunderstanding some people have is to think that there are no external forces on free-floating structures. This is untrue. Most importantly, they are all affected by the solar wind, which is a generally constant pressure pushing the object away from the sun. Of course they will also be affected by gravity, and if close enough to the earth they will interact with the atmosphere. (There's not really a clean cutoff to where our atmosphere ends and space begins.) As a result, spacecraft have to perform some amount of stationkeeping maneuvers, which involves applying a force on one section of the craft. That itself will cause further oscillations, because the force can never be transferred perfectly to the entire body. (Imagine pushing a piece of paper in the air with a single finger. Yes, you can get the paper to move in a direction, but you cannot get all segments of the paper to move in exactly the same manner when exerting force at only one point.)
So forces on spacecraft are inherently unavoidable, and oscillations happen any time a force is applied. Oscillations are challenging to control in a free-floating vacuum environment, and become more problematic the larger a craft is. This results in fundamental issues with operating very large spacecraft. That's not to say it is impossible. But in space it's not a simple solution to say "just build it bigger."
Thank you very much for that detailed reply. Lots of interesting things to contemplate further based on your descriptions. What incredible complexity to balance things! It makes me wonder if there's systems that are engineered to handle the balancing in a positive-feedback, almost cybernetic way in consideration of all the inputs and outputs that influence each other.
So many things to learn about... thanks!
Also, your description of using the ground to dampen oscillations has very similar implications to electricity and ground... not a coincidence?
Because you have to get the materials into orbit to make something free floating. A telescope on the surface of the moon can be built from locally sourced materials - the moon's surface is largely aluminum oxide, and aluminum is an excellent material for mirrors in an environment where there is no air to form an oxide layer to dull it - so instead of having to send up the entire telescope, you just need to send the equipment to build the telescope (which for big telescopes can be quite a lot smaller and lighter).
Correct. A large hill/small mountain's worth of debris hits the Earth every year. That includes micrometeorites that without an atmosphere, would pepper the Earth's surface.
It's also the reason why any Moon base would be buried under layers of regolith to protect it. Glass domes on the moon are sci-fi fantasy.
Since the moon is tidally locked, the side facing Earth and its far more massive gravity well would experience vastly less debris. It'd be a boring place to build your glass domed moon base, but I don't think it would be completely infeasible. Especially if it was built in a depression in the landscape, the approach angles would be greatly limited.
The ISS gets hit with micrometeorites pretty regularly, without any regolith to protect it. Micrometeorites make correspondingly micro holes, which in said glass dome are patchable.
A 2mm hole in a Soyuz docked to the station was fixed with a bit of Kapton tape and some epoxy, and was detected by a very small pressure drop in the crew spaces.
Larger rocks are more of a problem, but quite rare. Your dome is much more likely to get smashed by someone mixing up the pedals in a rover.
That's not really how gravity works. Gravity is time-symmetric, so it doesn't have the kind of “sucking” behaviour that vacuum cleaners or river valleys on Earth have.
Depends where you put it. You have to consider the trajectories of the material that could pose a threat. Rule of thumb: if the orbital configuration hasn't changed for a few thousand years, look at the craters.
Einstein was able to predict how light was bent around the Sun and Eddington confirmed it right away, it was like Babe Ruth pointing to the stands and hitting a home run.
The lag between a phenomenon being predicted or model sped by theoreticians and actually observed is getting longer and longer in fundamental physics, I mean neutrino oscillations were hypothesized in 1957. The fact that you can’t get a Nobel prize posthumously means a theoretician might never get a Nobel in fundamental physics ever again. So they’ve got to do something speculative like this to have a possibility of a legacy unless you are Ed Witten and can convince people you are a genius without any appeal to experiment whatsoever.
It does point to a programme of observations to try to catch P9 in a gravitational snare and look really hard in that area with all kinds of telescopes and has the double prize of possibly finding non gravitational evidence for DM.
Personally I think interstellar travelers would use FFPs as a resource but the question of how a civilization that lives on an FFP (imagine something like Pluto cut up into small (5000km) ringworlds) finds the next one seems pretty tough to me.
I didn't recognize the name but figured he was the guy who came up with M-theory, and sure enough, that's him. I believe the point here is achieving a legacy within the academy, not being known in pop culture. I think there's a lot of ambivalence about his influence, but it's definitely been large. His papers revealing how the whole superstring thing can be constructed in a way that doesn't blatantly contradict observed reality diverted at least a generation of theorists into the search for the holy grail of a theory of everything, but because we have no means of experiementally probing anything at the scales involved, it has also turned a generation of physicists into algebraic topologists largely divorced from experimental practice.
You can think of him maybe like the Velvet Underground of physicists. They never achieved much popularity themselves, but virtually every rock band of the past 40 years that has gotten popular cites them as an influence, and many artists would rather have that as a legacy than popularity. Similarity, I think a lot of physicists would rather be well known and influential to other physicists rather than becoming the next Michio Kaku or someone else who shows up on television a lot.
In fundamental physics there are few very hard problems that are unambiguously real problems of which I would name: (1) what is dark matter? (2) what is the mass of the neutrino? (3) why is there so much matter in the universe and not so much antimatter? (4) Quite a few strange things about very high energy cosmic rays (Notably 2 is not "physics beyond the standard model", it is "a missing piece of the standard model")
A lot of other questions might not really be "real" in various senses like: it's interesting to speculate that the interior of a quantum black hole is entirely unlike a classical black hole but you're not going to have anyone take a look and come back and tell us and we can just speculate if something kills you at the apparent horizon or not (so many bad ideas including the idea there is an "information paradox" come out believing the classical picture of the black hole interior which is probably just wrong), the "hierarchy problem" and various allergies to fine tuning are really human preferences or things like
where between the experimental errors and the possibility that theorists aren't quite doing the math right and that the answers to 1-4 might account for any difference (I wouldn't be surprised it is if 1-4 have the same answer)
The experiments for (1) and (2) are devilishly hard, there are accelerator observations of CP violations that are a line on (3), but the cosmic scale of (3) and (4) imposes its own difficulties.
Really there are a lot of grad students chasing a moderate number of postdocs who hope to get one of very few permanent positions and out of it all there is a tiny amount of glory to be had.
Condensed matter physics lacks the cosmic difficulties but it isn't dramatically better. How superconductivity works in cuprates
is still quite mysterious after 35 years. I would name check Mark Newman as a standout in the "complex systems" area but the real accomplishment he made in my mind wasn't finding an explanation for "universal" power laws in complex systems but instead proving we didn't know what we were doing when we plotted our statistics on log-log paper and drew a line... And he published about that in a statistics journal not a physics journal but it's OK because the paper is in arXiv anyway.
> the "hierarchy problem" and various allergies to fine tuning are really human preferences or things like
The hierarchy problem is a real problem. The bare Higgs mass, for instance, might be a brute fact (but then again, it might not be), but the effective Higgs mass is some (likely very complicated) consequence of more fundamental physics at energy scales beyond the standard model. We just don't know what it is. But even if those more fundamental constants aren't explicable, they're definitely an explanation.
One of the most significant living physicists, and the only one to have won a Fields Medal (arguably the most prestigious award in mathematics). Known for Chern-Simons theory, contributions to AdS/CFT, and of course M-theory, among many other things. Physicists breaking out into mainstream culture for anything other than popsci is not really a thing that happens anymore, but he's extremely well-known among academics.
Predicting a truly novel observation is rare, and has always been rare. Mostly what physicists do is clarify our understanding of things we've already observed, and extend techniques to handle cases that are more difficult to calculate than the cases that are presently considered tractable. For every one coulomb's law or socks-cling-to-stuff-after-drying effect there are a million papers about figuring out how to calculate the electrostatic fields of various configurations.
The vast majority of what theoretical physicists do is "just math" except that unlike math, it's aimed at a problem posed by nature rather than a problem imagined up on the basis of what seems most interesting.
It's no coincidence that the most important fields of math are well suited to solving physics problems. Looking back through history, so many of the most famous mathematicians were also physicists. Math was invented to solve two kinds of problems: physics and accounting.
> Because in my layperson's eyes that's the difference between math and theoretical physics.
Not really. The distinction, to the extent that there even is one, is mostly a matter of motivation and methodology. Broadly generalizing: mathematical physicists (i.e. mathematicians) are interested in physical theories that seem like they might need interesting new mathematical tools to understand, while theoretical physicists are interested in theories that seem like they might have something to tell us about the true structure of whatever the object of interest is. There are other differences downstream of this, of course:
- mathematical physicists are rigorous while theoretical physicists will let it lapse if that gets them physically correct answers
- physicists care less about inconsistencies in theories they know are wrong anyway
- mathematicians stay long after all the physical content has been mined out (a significant fraction of just-plain-mathematics is the end result of this process)
and so on. But you can find people anywhere between these poles.
Witten can (and sometimes does) produce world-class mathematics when he wants to, but most of his work is on the physics side of the spectrum.
You’re not alone in that. But most scientists that are publicly known are often science popularizers.
Such as Hawkings, Dawkins, Tyson, Cox.. but probably little is known about their actual work. (Exception being Hawkings in that list although he did pass away some years ago so would not count)
Maybe things have changed, but complex systems was my field in the day and my understanding is that progress has been slow there and searches for universality have, at best, shown that physicists universally analyze their data wrong.
Yes, progress might be slow. I just want to point out that fundamental and sub atomic particle physics isn't the only frontier of knowledge. Lots of phenomena in everyday regimes are purely understood, too.
"clever joke" aside: why? Primordial black holes are a rather completely different category from super-massive black holes, with masses theorized as small as a single plank mass. Not a lot of sucking happens when PBH are involved.
Fig1 in the paper shows the exact size of the PBH:
> FIG. 1. Exact scale (1:1) illustration of a 5M⊕ PBH. Note that a 10M⊕ PBH is roughly the size of a ten pin bowling ball.
Things are weird when dealing with Planck quantities, so "almost certainly", but only almost. The main point was that PBH are generally small and look nothing like what people think of if they've only heard of black holes from popular science and sci-fi.
I suppose given the enormous force gradients around even a basketball sized black hole, it could potentially be turned into one of the most efficient ways to convert matter into energy by building an accretion disk around it?
If you get the timing right, you could just shoot those at the enemy near the speed of light, and they would explosively decay right as they arrived. If the mass was low enough, they'd be effectively invisible, wouldn't they? Screw antimatter bombs, these would be pretty horrific. Instead of kilograms' worth of matter-to-energy conversion, you could have hundreds of tons worth. Wonder what that would be in megatonnage?
Other than the whole "you wouldn't be able to move it around" because unless you have a portable gravity projector, that thing isn't going anywhere: it is a gravity sink. Your enemies would have be lured into range, at which point, longbows will do a much, much better job =D
Yes, the amount of gravitational potential energy release is much higher for the same mass than you get from fusion. I’ve seen estimates of 10% - 40% of the mass-energy of the in-falling matter.
You “just” need a way to get the matter there and a way to capture that energy.
Yes it would have. Planck mass black holes aren't even mentioned in this paper, I'm confused as to where this came from. PBH = 'primordial black hole' meaning formed at the beginning of the universe, not Planck Mass Black Hole, which, you're right, would have evaporated instantly.
Good science fiction premise. The presence of the Moon and its stabilizing effect on our planet's climate, the presence of Jupiter with just the right mass to have a stabilizing effect on bombardment while not destabilizing planetary orbits, and then the presence of a primordial black hole allowing the monkeys to study dark matter physics once they reach space. Almost like it was an experimental setup.
There is nothing weird about this paper, the math works, and primordial black holes (which is a astronomical term, not just a plain English descriptor) are not the thing you're clearly thinking of given your rant.
Checking to see if outer planetary motion can be explained in terms of PBH and working out the math as part of that is perfectly normal astrophysics, and good science. Read the paper, it's perfectly fine =)
Given that a huge amount of mass in the universe is unaccounted for with current models, the idea of masses unaccounted for like this surely are still reasonable possibilities.
I like Occam's razor as much as anyone, but it really is starting to seem like there might be more than one cause of the phenomenon called dark matter. My understanding is that WIMPs (weakly-interacting massive particles) are in trouble too, as the LHC has failed to produce them in the expected energy regimes.
No current MOND theories account for the state of our observations of the Cosmic Microwave Background, or the ratios of "things" left from nucleogenesis. The biggest gotcha for MOND is there's no way to reverse the direction of gravity, which would be needed to explain large scale structures without dark matter. (With dark matter, you see things moving toward where the matter is. Absent dark matter, you see things moving away from where matter is, because there is only ordinary matter.)
It wouldn't have to be the main explanation for dark matter though to still be a phenomena. I agree that the evidence is pretty clear that it's not the main driving factor.
"The alternative explanation advanced by the Binary Research Institute is that most of the observable is due to solar system motion, causing a reorientation of the earth relative to the fixed stars as the solar system gradually curves through space (the binary theory or model)."
Glad to know there is a similar theory being proposed.
This is a very "dense" paper. So: if dark matter is something that annihilates itself, that's a two-particle interaction, so its macroscopic rate scales as density squared ρ². If there's a black hole in the solar system, the dark matter halo immediately surrounding it would be compressed far denser than around a normal object, so it'd have a much brighter annihilation signal. Nothing's known about dark matter annihilation. They speculate, if its cross section is large enough, this annihilation could be observable by gamma-ray telescopes like Fermi or the upcoming CTA. And that would distinguish a black hole from something else. That's all I could understand. It'd be a discovery of a solar system black hole, and new dark matter physics, two-for-one.
I'm curious what math led to that funny exponent in eq.(5): ρ(r) ~ r^{-9/4}.
Just a thought, if a black hole that close were discovered there would be another space race to get there. It just sounds so cool to the politicians (who've seen the movies) that any scientist would have no problem convincing them to loosen the purse strings.
For reference, if it exists, it’s closest approach to the sun is more than six times farther than Pluto’s furthest approach and it took New Horizons nearly a decade of travel time to reach Pluto. A probe would be a decades long project. Sending humans would be effectively impossible.
I assume you object to billionaires because they use a disproportionate share of the world's resources? Spending even more resources on them doesn't seem like it would make that better?
Given such a scientifically interesting object so close to us, I can't imagine any other reality than massive world-scale spending to not just "get there first", but first to perform other low-hanging publicity stuns (think first space walk, first moon landing). The fact you _can't_ even land there is a massive accessibility boost. The thought is so exciting. The understanding of physics would be destined to leapfrog, distinctively changing humanity, and nature.
Related; it's instructive to learn that a significant motivation behind the Apollo program was its national defense implications: https://youtu.be/xZFnTBSRKcg?t=137
The moon landings were widely popular at the time, weren't they?
Even the Soviets didn't say they were dumb and wasteful.
(I tend to be a bit milder, and just say that the moon landings should be thought of as spending on entertainment, not on science. Manned space flight in general is very cost-ineffective, if you care about scientific bang for your buck.)
Nope! Majority of Americans thought the Apollo program was a waste of money if you look at polls. This changed after it was successful and now we have retconned our history to say that everybody thought it was a great idea from the start.
I don’t think it’s hypocritical to say that the moon landing was worth it but gearing up to go to a distant black hole is not*
Outside of mining unobtanium, or fossilized unicorns, or HP ink, almost anything else is not commercially viable to mine in space and bring down to Earth. And it will be so even if Starship is ready, and even if that Starship would indeed cost 1-2 mil to launch as advertised. It is always cheaper to mine stuff on Earth, ever rare elements. That's why nobody is seriously doing anything in that direction. Mining asteroid for a local asteroid settlement would be profitable, but there are no asteroids settlements.
Note that, as we cling to geographic borders, some metals might well become unobtainium for some countries.
But yes, agreed, it's way too expensive. And so we're not even going to make that happen. That was the point - it's more attractive than neighboring black holes along several different axes, and it's still not worth it.
What you'd want to do is de-orbit an asteroid made up mostly of precious metals, say, platinum, using something like an Orion drive. Then use the moon as a catcher's mitt (even better if you can use Earth, but K-Ting ourselves is going to be a hard sell at the shareholder meeting).
Refine / cut up your asteroid on the lunar surface, then you need a relatively small amount of dV to put your payloads into a decaying orbit around earth (~1/4 the dV to get into low earth orbit from the surface). Enough heat shielding, and you'll be able to crash your payload into the ocean somewhere for recovery.
Frankly, the biggest issue is that you'd end up flooding the market.
First of all - such asteroid need to exist in the first place. Much more likely that there are asteroids which have higher concentrations of rare ores compared to earth, but nowhere near being "mostly of out them".
Second - humans need to locate this deposit. Remotely. In the asteroid field. We are still finding out deposits in the habitable Earth regions, because that is a hard task, talking about locating deposits in the Belt is an impossible task, and will remain so for a long time.
Third - we need to get there. Excluding flyby's, the best humanity managed is to deliver two 1 ton vehicles to the Mars. And there we had a luxury of aerobraking to save a lot of fuel. Belt is way farther, there is no aerobrake possibility and we will have to deal with other asteroids along the way. We don't have such tech.
Fourth - we will need to strap engines to the asteroid, remotely, with an hour signal lag. Engines which don't exist in any form today. And we need to get fuel to them somehow. Impossible task.
Fifth, we need a Moon colony with robots or humans.
Sixth - high energy tech on the Moon.
Seven - launch facility on the Moon.
And I've probably missed a few other impossible hurdles, writing this. Then IF all of that would exist, you would need it to be at least as cheap as Earth based mining, which is a pipe dream. Any space tech is more expensive by design, sometimes orders of magnitude more expensive. AND finally there need to be an infinitely elastic market on Earth for this new source of materials. Imagine you will sell a billion tons of platinum tomorrow, the price would crash and never ever recover. You see this yourself in your last sentence.
Do we even have a guess where it is right now? The orbit is huge, so the search area is ginormous, even if we would know approximately where in its orbit it would currently be.
Sending humans would be difficult (technically we have the technology already [see Project Orion], it's just illegal), but it's certainly possible to get a probe out there far faster than New Horizons. Travel speed is mainly determined by the delta-v of the upper stage. New Horizons used a Star-48B solid rocket motor to get to its escape trajectory. However, if the probe were smaller, or the launch vehicle bigger, it could have multiple upper stages, significantly increasing the ultimate speed. It might also be feasible to use an ion engine stage with solar panels and a route that dips down below Venus' orbit to get even more speed without increasing the probe mass significantly. In other words, with a large enough budget, we could easily get a probe to those distances in under a decade with no new technology required.
It doesn't have to be political. Discovering a blackhole reachable by humans would be one of the most exciting discoveries possible. It might even unite nations to work together to get there as soon as possible.
If there's really a black hole there, I'd personally donate at least 10% of my year's salary to the program if it means we make it there within my lifetime.
Studying it might allow us to finally unify GR and QM.
1. Humans aren't going to survive in space for 10 years. It's questionable that they'd even survive a trip to Mars without getting riddled with cancer from the cosmic radiation. Sure, if you built a big enough ship to provide some really effective shielding, it's technically possible, but that ship would be enormous and far beyond our current capabilities. I don't think it's feasible at all to launch such a ship from Earth; it would need to be assembled in space.
2. Project Orion is just an idea on paper; it's not within current technology, because no one ever built it. We don't "have the technology" at all. We don't even have the technology to land humans on the Moon. We did decades ago, but we no longer do: all the people who knew how to do that are retired or dead, so we'd have to start over. Of course, we can build powerful rocket motors easier now since we do so regularly now, so building equivalent Moon-landing capability is no longer as difficult as in the 60s, but a lot of things would have to be partially re-invented (e.g., the lander itself, the rover, etc).
3. Does your time estimate include the time needed to decelerate, so the ship doesn't just zip by the black hole with barely any time to collect data? (And if there's people on this ship, they might want to return to Earth...)
You don't just have to get the probe there. (And which probe? You have to design and build it first.) You have to get it there, have it get data, and have the data come back. Otherwise you've just thrown a rock, which, yeah, if we spent a fortune we could certainly throw a rock out vast distances very quickly.
So, you either:
Do a flyby, which requires a slower speed. New Horizon's speed was good for gathering data from Pluto and sending it all back. The hypothesized PBH is small enough to fit in your duffle and probably much darker.
Enter orbit. Easy enough with a 5-10M object. But the orbit has to be a useful orbit. So either you burn a tremendous amount of delta-v to reduce your tremendous speed so you get a compact-enough orbit; which requires even more energy to get out there, or you craft the orbit such that the object itself helps slow you: but that takes time and more speed means more time.
If there is a race to be the first to reach this “black hole” and the racers are careless, is it going to make “the black hole“ alive and getting bigger?
Only if the other planet's orbits take them near enough to the black hole to get sucked in. The main difference between a primordial black hole at about the Earth's mass and a planet at about the Earth's mass is the presumed density of dark matter around it. And I'm guessing there's more hawking radiation coming from the black hole than the planet.
But small black holes with the same mass as the Earth have the same sucking power as the Earth since it's the mass that does the sucking.
If our sun magically turned into a black hole of the same mass tomorrow, nothing would change on earth or in our solar system, except it would get very dark. Nothing would get "sucked in".
We'd all freeze to death in a few days, but the earth would go right on orbiting as if nothing happened.
If our moon turned into a black hole of its same mass tomorrow there would be even less of an effect. We'd notice we could no longer see the moon, but we'd still have tides just like before.
I think it’s hilarious that there could be a space race to get to a golf ball sized invisible object. I see the importance, but at the same time you must admit from a layman’s perspective it’s kinda comical.
These are foundational to the paper at the top's ref [35], which is quoted just before the "funny exponent".
Roughly, let's start with an expanding Friedmann universe, where we treat galaxy clusters as motes of dust, and smear that out into one or more fluids representing nonrelativistic matter and radiation and other relativistic matter, with an identical energy-density at every point in space in an equatorial slicing, with each slice succeeding a spatially-smaller slice and preceeding a spatially-larger slice. At small scales, radiation pressure stabilizes any overdensities or underdensities in the nonrelativistic and relativistic fluids. Eventually expansion causes a transition from radiation-dominance to matter-dominance, allowing overdensities and underdensities to grow.
The papers by Gott and Gunn above consider the evolution of a spherical perturbation, an overdensity, starting at that transition, studying whether shortly after the transition from radiation-dominance, halos can support the evolution of generic galaxies and galaxy clusters. They can; and the "Planet 9" paper at the very top (albeit by way of its ref [34]) takes that further and applies this halo logic to primordial black holes based on that "universality" result (in Gunn 1977, penultimate paragraph).
Essentially what happens is that the nonrelativistic matter in an overdensity self-gravitates and so sticks around as an overdensity from one slice to the next bigger slice. Moreover, neither cold dark matter nor a primordial black hole radiates that early in the universe, so the overdensity can't revert to average through dissipation. Furthermore, the overdensity's gravitation draws in matter from the "shell" outside it (i.e., the rest of the universe); that's the "infall". If the infall is dissipationless, it sticks around in shells well outside the centre of the overdense perturbation.
All of this combines so that the density of an overdense perturbation drops much more slowly than the density in the rest of the universe. The latter drops like cosmic_time^{3/2} while the perturbation's density drops like cosmic_time^{9/4} (in these 1970s papers; in the age of fast computers one would use a profile like NFW <https://en.wikipedia.org/wiki/Navarro%E2%80%93Frenk%E2%80%93...>, and in this "Planet 9 is a PBH" context one might wa...
> I'm curious what math led to that funny exponent in eq.(5): ρ(r) ~ r^{-9/4}.
The actual exponent and its workings-out almost certainly comes from Gott 1975, which I do not remember ever having read <https://adsabs.harvard.edu/full/1975ApJ...201..296G>, so I cannot do it any sort of justice at this time, but see my comment on Gunn 1977 below.
Theres an early history of pre-NFW power-law dark matter density profiles swept up in ref [34] of the Planet 9 preprint, which is cited just before the equation that piqued your curiosity.
[34] is <https://ui.adsabs.harvard.edu/abs/1985ApJS...58...39B/abstra...> which turns out to be part of a 1984 Princeton doctoral thesis, and I am unfamiliar with it although I recognize its author Edmund Bertschinger as well-known from his later 1980s-2000s work in cosmological perturbation theory and cosmological simulations.
[34] also lists Gunn & Gott 1972, Gunn 1977 and Gott 1975 in the references section (bottom of 1st to top of 2nd column). Surprisingly the Planet 9 preprint lists none of these papers.
However, in a way that could be serendipitous: you might enjoy the "funny exponent"s in many the equations of [34], since some involve powers of -8/9, 8/3, -5/2, among others.
I wrote but abandoned an attempt to tease out the detail using the following two seminal papers.
Gott & Gunn 1972, "On the Infall of Matter into Clusters of Galaxies and Some Effects on their Evolution" <https://ui.adsabs.harvard.edu/abs/1972ApJ...176....1G/abstra...> (PDF via top right box), contemplating a Friedmann universe with a spherical homogeneous overdensity that collapses into a galaxy cluster.
Gunn 1977 <https://ui.adsabs.harvard.edu/abs/1977ApJ...218..592G/abstra...> contemplates a spherical but inhomogeneous perturbation, and arrives at a power law of density \propto r^{-9/4}. It relies on Gott 1975 for that, however. This paper is the basis for a "universality" result which indicates that the shape of an overdensity's boundary is essentially preserved over time, even as the matter within the overdensity collapses into various structures. That universality was convenient at the time to avoid having to treat spirals specially, and is in effect claimed as applicable to a PBH equipped with a DM microhalo in the preprint linked at the top.
The "funny exponent" appears in the text just after eqns (8)-(9b) in Gunn 1977.
All of the NASA/ADS abstracts linked in my comment have PDFs available in the top right box on the page.
From the abandoned first attempt (which grew in length and messiness) I'll save two things: the "curious" equation's r_eq and \rho_eq are fixed at the transition from radiation-domination to matter-domination at z ~ 3200 (47 thousand years after the big bang), after which radiation pressure is insufficient to keep perturbations from growing. The transition is also when scale factor a \propto t^{2/3}, and energy density \rho \propto a^{-3(1+w)} where w is close to 0; self-gravitation in the overdensity causes its \rho to drop more slowly, and furthermore draws in matter from the surrounding ~average density shell.
Launch a probe already!
If the anomaly is a planet, ~you've discovered a new planet~
If the anomaly is a black hole, then ~you've discovered a local black hole~
If there is literally nothing there, use the probe for interstellar science.
That's the key, you absolutely need to design a probe where gravity is the guidance system. My take is a primary probe containing hundreds of hyper reflective microprobes, which scatter for billions of miles into space. After a few decades, the primary probe locates where the majority of mircoprobes went, and now you steer the primary probe into Planet 9's gravity well.
I think you're underestimating the area you need to search. See the wiki page[1]. There's so much space to look near, you need a much better guess before you can send any probes. A 9k year orbit, that starts at 340 AU, and has a lot of uncertainty in all the parameters, just leaves too much volume to check naively. And that doesn't even get into the fact that there's not enough light out there to feasibly find probes from their reflections.
Uhhhh, we've got all those "microprobes" which are all of the known objects in the Solar System. A couple of them are a bit macro though (Jupiter in particular).
Combine these four together and you'll quickly realize just how difficult even scoping out the probe's requirements and such would be. Would be cool though.
I think we would be able to detect it. We can navigate spacecraft with high accuracy.
If you can get a spacecraft somewhere in the vicinity of a black hole of decent mass (like a 10km asteroid equivalent) we could probably detect changes in trajectory of the spacecraft from the gravitational attraction.
Or, here's an idea, blow out a tonne of radar chaff in the vicinity of the black hole and watch for how it disperses via radar.
We could also try detecting Hawking radiation that a BH should generate, though that might be pretty faint (I have not done the math).
To quantify this a bit, the search area for Planet X is in the region of many hundreds of AU from the sun. That’s many millions of cubic AU to hunt around in. That’s a lot of chaff, without even considering how we would detect and track the chaff from this far away.
It's sort of the equivalent of trying to find your headphones by walking around with the bluetooth menu open on your phone and waiting to see if they pop up then they must be nearby, except all you know is that they're somewhere on Earth and you don't know where until you come within ten feet or so of them. And in reality it's even harder than that, since the surface of Earth is essentially two-dimensional as far as finding things goes, but a search for a planet would need to cover most of the volume of the greater solar system.
You are correct. At about Luna-mass, then it is hotter than the 3K cosmic background. If it is heavy enough to be a 9P candidate, it would be colder than 3K. You couldn't detect by temp.
You'd have to look for a very precise spike in the EM spectrum at the electron-position annihilation energy equivalent.
Despite being raised on space opera and hard-sf and having a science degree, I am pretty bearish on most space exploration. Having said that, a nearby black hole wouldn't merely be nifty. For reasons we do not understand, the event horizon stops honoring conservation of baryon number (and lepton number, and other numbers). I consider this important because replication of that would allow for direct conversion of uncharged mass to energy, just as any neutral particle crossing the event horizon has its energy (eventually) returned to us. If Hawking radiation is true (we have yet to experimentally verify it), then we know that mechanism exists. Can we do it without a black hole?
Would a small BH have enough of an accretion disc to emit sufficient X-rays to be detectable? While the density of matter in the Oort cloud is low, it is not as low as interstellar space.
"And one would like to launch hundreds of spacecraft (at least) in different directions so that some would come within dozens of AU of Planet 9, rather than hundreds of AU."
Their example of a neat-but-good-luck project could actually achieve the goal is [1]. The spec requires ground lasers that's powered by a 1GW nuclear power plant for propulsion. And, "According to The Economist, at least a dozen off-the-shelf technologies will need to improve by orders of magnitude." [2]
I don't think so. The black holes are, by assumption, tiny and only light passing by very very closely would experience significant lensing. Farther away, the lensing would be the same as near any other planet.
Any singular probe would needed to know where to go searching. Any scanning instruments it could carry we can build and use better at Earth (soon Moon [1], fingers crossed). Your idea would require a swarm, an array, with Earth as a centre piece, effectively forming search beam rotating outwards.
Shouldn't this imply that many star systems also have small blackholes orbiting them, even in between other planets? Just like we found that there are many other earths. If something is possible it will happen again and again in the vast Universe.
I always had a layman pet theory that Planet 9 is a BH, and not just any BH one but the one who's supernova remains seeded the solar system with heavier elements. Sort of like old grandpa blackhole looking after his/her small kid.
relative speed against other stars is very much detectable by red and blue shift of light. We would definitely know if sun revolves around something, meanining changes its direction.
At these distances, the sun's direction if it were orbiting a black hole would have only changed by a fraction of a degree in the hundred or so years we've been able to measure its velocity relative to nearby stars - is that data precise enough that that is not within the margin of error?
It advances scientific knowledge by providing a testable prediction. The prediction can be used to collect data and determine whether there indeed is a black hole orbiting the Sun beyond Neptune.
"here's what we should do" is not advancing science.
do the thing, get the results, and if they're significant, then author a paper.
I think there is a lot of resume oriented science, these days, because publishing lots of papers looks good on your resume. i mean, we can't let actual science get in the way of our science careers, right? we gotta publish papers telling people what we're thinking about, and how to do those things.
Proposing theories and then testing them in data is what the scientific method is.
Many theories were proposed before they were confirmed or refuted in data. Einstein's theory of general relativity is a famous example which was proposed before it could be confirmed by Eddington during a solar eclipse. Black holes themselves were also predicted by Penrose and Hawking before their existence was confirmed.
this type of discourse is very common in physics, where the theoretical physicists propose a testable hypothesis and then the experimentalists verify or disprove it.
Modern physics is too complex and expensive at the cutting edge to do the entire "hypothesis, experiment, result" process in one paper. It's very normal for support for a hypothesis to build up through theoretical physics papers over many years, leading to sufficient funding at a facility capable of testing the hypothesis.
The Higgs Boson is a great example of this, theorized 40 years before it could finally be discovered at the LHC, a machine which wouldn't have been possible at all with the technology of the time when the Higgs boson was proposed as the computing capability to digest the Petabytes of data generated simply did not exist.
Plus, with these things there's a bit of a chicken and egg issue where part of the impetus for building these expensive machines is to test theories which have been gaining support, so if those theories weren't being shared, there's no way to really say if the machines to test them could even exist.
Neutrinos, time crystals and gravitational waves are other notable examples of things where it would not be practical to expect theoreticians to wait the decade(s) for technology to catch up before presenting their theories.
The man produces garbage papers. He characterizes the work as useful stepping stones for other scientists to do the rest of the obvious followup work, which he can't be bothered with. He's too busy churning out thought experiments.
It would be cool, it would also be insanely hard to pin down. It would be about the size of a grapefruit but 5-10x the mass of the Earth. And it's way-way-way out there. Oh, and it's basically invisible. But, if we could find it, pin it down, and send out a probe imagine the science we could do!
If it was found, its amusing to think about how it could actually be studied.
How close could a reinforced probe orbit? Would they just drop test masses in and observe what happens? Maybe drag a kuiper belt object in to make a little accretion disk?
For what it's worth, a primordial black hole Planet 9 is the plot of Stephen Baxter's new book, "Creation Node," which was released about a week ago. (Well, it's the seed of the plot, and then things take a few turns. It's an interesting book!)
As an aside, it takes the first visitors about 30 years to reach it, and they've got better tech than what's available to us today. It's pretty far out.
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[ 2.8 ms ] story [ 517 ms ] threadhttps://news.ycombinator.com/item?id=23993716 - 3 years ago, 119 comments
https://news.ycombinator.com/item?id=28167058 - 2 years ago, 153 comments
Thanks!
[1] https://www.youtube.com/watch?v=XggxeuFDaDU
In particular, consider how you would damp an undesired movement by a satellite. A naive approach would be to apply thrust in the opposite direction. However, the control can't be exact, leading to thrust -> thrust <- over and over, eventually to the measurement limit of the thruster's control.
With a large mass, it's replaced with a spring, and converted to heat.
https://en.wikipedia.org/wiki/Damping
Things in virtual freefall that can flex (and everything can) do so in response to forces (e.g. thrusting, but also heat stresses, say), and will continue to do so if they start unless you take care to damp them and dump them into heat. There's nowhere for the vibration to "go" unless you design one in. Sometimes the structure of the craft itself has enough damping for practical purposes, especially when you take care to isolate large vibration sources (the ISS has a Sorbothane damper for the treadmill, for example), but when your big floppy (i.e. light) mirror surface has to stay put on a nanometre scale, it's not so simple.
It's a bit like the difference between a tuning fork glued down flat to a table and one hanging from a string.
In the sense of building things that last in space.
Fundamentally they're all somewhat similar in that there's a flexible and/or sloshing thing that doesn't have a huge mass that it's rigidly connected to. Spacecraft deployed in space usually have smaller forces on them (no air or water and the hard acceleration is done) but are also much flimsier due to being ultra-light. Telescopes are even worse as even a tiny vibration can ruin the usefulness of the optical paths.
Vibration of telescopes is an issue on Earth as well, e.g.: https://opg.optica.org/ao/abstract.cfm?uri=ao-53-21-4651
In space, there is nothing to damp the oscillations. They will just continue without active features of the craft to damp them. If they continue unabated a section may reach a resonant frequency, which can quickly cause failure. Even if it doesn't, those vibrations can cause cyclic loading failures, or just affect the stationkeeping of the craft or it's usefulness in gathering scientific data.
To make a spacecraft resistant to oscillations requires devices like gyroscopes or friction dampers, or long weighted booms which decrease the magnitude of oscillations. Making the craft rigid helps, but the larger it is, the less rigid it will be. And to make it more rigid, or to include more anti-oscillation devices, means more weight. That's an important limiting factor when you need to get the object up into orbit.
One misunderstanding some people have is to think that there are no external forces on free-floating structures. This is untrue. Most importantly, they are all affected by the solar wind, which is a generally constant pressure pushing the object away from the sun. Of course they will also be affected by gravity, and if close enough to the earth they will interact with the atmosphere. (There's not really a clean cutoff to where our atmosphere ends and space begins.) As a result, spacecraft have to perform some amount of stationkeeping maneuvers, which involves applying a force on one section of the craft. That itself will cause further oscillations, because the force can never be transferred perfectly to the entire body. (Imagine pushing a piece of paper in the air with a single finger. Yes, you can get the paper to move in a direction, but you cannot get all segments of the paper to move in exactly the same manner when exerting force at only one point.)
So forces on spacecraft are inherently unavoidable, and oscillations happen any time a force is applied. Oscillations are challenging to control in a free-floating vacuum environment, and become more problematic the larger a craft is. This results in fundamental issues with operating very large spacecraft. That's not to say it is impossible. But in space it's not a simple solution to say "just build it bigger."
So many things to learn about... thanks!
Also, your description of using the ground to dampen oscillations has very similar implications to electricity and ground... not a coincidence?
It's also the reason why any Moon base would be buried under layers of regolith to protect it. Glass domes on the moon are sci-fi fantasy.
A 2mm hole in a Soyuz docked to the station was fixed with a bit of Kapton tape and some epoxy, and was detected by a very small pressure drop in the crew spaces.
Larger rocks are more of a problem, but quite rare. Your dome is much more likely to get smashed by someone mixing up the pedals in a rover.
https://www.livescience.com/how-many-moon-meteorites
> "if you pick a square kilometer patch of ground, it will be hit by one of those pingpong-sized meteoroids once every thousand years or so"
We've landed in visibly quite smooth areas; for example: https://www.flickr.com/photos/nasa2explore/48299974871
Hence my question.
Einstein was able to predict how light was bent around the Sun and Eddington confirmed it right away, it was like Babe Ruth pointing to the stands and hitting a home run.
The lag between a phenomenon being predicted or model sped by theoreticians and actually observed is getting longer and longer in fundamental physics, I mean neutrino oscillations were hypothesized in 1957. The fact that you can’t get a Nobel prize posthumously means a theoretician might never get a Nobel in fundamental physics ever again. So they’ve got to do something speculative like this to have a possibility of a legacy unless you are Ed Witten and can convince people you are a genius without any appeal to experiment whatsoever.
It does point to a programme of observations to try to catch P9 in a gravitational snare and look really hard in that area with all kinds of telescopes and has the double prize of possibly finding non gravitational evidence for DM.
Personally I think interstellar travelers would use FFPs as a resource but the question of how a civilization that lives on an FFP (imagine something like Pluto cut up into small (5000km) ringworlds) finds the next one seems pretty tough to me.
You can think of him maybe like the Velvet Underground of physicists. They never achieved much popularity themselves, but virtually every rock band of the past 40 years that has gotten popular cites them as an influence, and many artists would rather have that as a legacy than popularity. Similarity, I think a lot of physicists would rather be well known and influential to other physicists rather than becoming the next Michio Kaku or someone else who shows up on television a lot.
A lot of other questions might not really be "real" in various senses like: it's interesting to speculate that the interior of a quantum black hole is entirely unlike a classical black hole but you're not going to have anyone take a look and come back and tell us and we can just speculate if something kills you at the apparent horizon or not (so many bad ideas including the idea there is an "information paradox" come out believing the classical picture of the black hole interior which is probably just wrong), the "hierarchy problem" and various allergies to fine tuning are really human preferences or things like
https://en.wikipedia.org/wiki/Anomalous_magnetic_dipole_mome...
where between the experimental errors and the possibility that theorists aren't quite doing the math right and that the answers to 1-4 might account for any difference (I wouldn't be surprised it is if 1-4 have the same answer)
The experiments for (1) and (2) are devilishly hard, there are accelerator observations of CP violations that are a line on (3), but the cosmic scale of (3) and (4) imposes its own difficulties.
Really there are a lot of grad students chasing a moderate number of postdocs who hope to get one of very few permanent positions and out of it all there is a tiny amount of glory to be had.
Condensed matter physics lacks the cosmic difficulties but it isn't dramatically better. How superconductivity works in cuprates
https://en.wikipedia.org/wiki/High-temperature_superconducti...
is still quite mysterious after 35 years. I would name check Mark Newman as a standout in the "complex systems" area but the real accomplishment he made in my mind wasn't finding an explanation for "universal" power laws in complex systems but instead proving we didn't know what we were doing when we plotted our statistics on log-log paper and drew a line... And he published about that in a statistics journal not a physics journal but it's OK because the paper is in arXiv anyway.
The hierarchy problem is a real problem. The bare Higgs mass, for instance, might be a brute fact (but then again, it might not be), but the effective Higgs mass is some (likely very complicated) consequence of more fundamental physics at energy scales beyond the standard model. We just don't know what it is. But even if those more fundamental constants aren't explicable, they're definitely an explanation.
As it so happens, he's also the guy behind this paper: "Searching for a Black Hole in the Outer Solar System", https://arxiv.org/abs/2004.14192
:-)
The vast majority of what theoretical physicists do is "just math" except that unlike math, it's aimed at a problem posed by nature rather than a problem imagined up on the basis of what seems most interesting.
Not really. The distinction, to the extent that there even is one, is mostly a matter of motivation and methodology. Broadly generalizing: mathematical physicists (i.e. mathematicians) are interested in physical theories that seem like they might need interesting new mathematical tools to understand, while theoretical physicists are interested in theories that seem like they might have something to tell us about the true structure of whatever the object of interest is. There are other differences downstream of this, of course:
- mathematical physicists are rigorous while theoretical physicists will let it lapse if that gets them physically correct answers
- physicists care less about inconsistencies in theories they know are wrong anyway
- mathematicians stay long after all the physical content has been mined out (a significant fraction of just-plain-mathematics is the end result of this process)
and so on. But you can find people anywhere between these poles.
Witten can (and sometimes does) produce world-class mathematics when he wants to, but most of his work is on the physics side of the spectrum.
Such as Hawkings, Dawkins, Tyson, Cox.. but probably little is known about their actual work. (Exception being Hawkings in that list although he did pass away some years ago so would not count)
The state of fundamental physics. There's still plenty of new and exciting stuff at all the scales from molecules to continents.
For example, there's still lots of exciting work happening in trying to predict the angle of repose that a heap of sand forms.
You “just” need a way to get the matter there and a way to capture that energy.
Checking to see if outer planetary motion can be explained in terms of PBH and working out the math as part of that is perfectly normal astrophysics, and good science. Read the paper, it's perfectly fine =)
But still, every hypothesis for explaining dark matter is close to dead right now. Theoreticians reopening closed cases is a good thing.
It is the gravitational drag of a moving solar system moving around in a spiraling milky way galaxy around a theoretical black hole in the center.
Glad to know there is a similar theory being proposed.
I'm curious what math led to that funny exponent in eq.(5): ρ(r) ~ r^{-9/4}.
I can think of PLENTY of billionaires to send :)
I assume you object to billionaires because they use a disproportionate share of the world's resources? Spending even more resources on them doesn't seem like it would make that better?
Can anyone imagine something concrete?
Even the Soviets didn't say they were dumb and wasteful.
(I tend to be a bit milder, and just say that the moon landings should be thought of as spending on entertainment, not on science. Manned space flight in general is very cost-ineffective, if you care about scientific bang for your buck.)
I don’t think it’s hypocritical to say that the moon landing was worth it but gearing up to go to a distant black hole is not*
* Is also shiny and has movies
* It's cheaper by a good number of orders of magnitude
* It has massive commercial value (bringing home piles of gold. Well, platinum metals)
* It has actual military implications, which is the main motivator for any government progrem
* It gets to call the military research "planetary defense", and there are more cool movies about that.
No government is getting its act together on that. A distant black hole is right out.
But yes, agreed, it's way too expensive. And so we're not even going to make that happen. That was the point - it's more attractive than neighboring black holes along several different axes, and it's still not worth it.
Refine / cut up your asteroid on the lunar surface, then you need a relatively small amount of dV to put your payloads into a decaying orbit around earth (~1/4 the dV to get into low earth orbit from the surface). Enough heat shielding, and you'll be able to crash your payload into the ocean somewhere for recovery.
Frankly, the biggest issue is that you'd end up flooding the market.
Second - humans need to locate this deposit. Remotely. In the asteroid field. We are still finding out deposits in the habitable Earth regions, because that is a hard task, talking about locating deposits in the Belt is an impossible task, and will remain so for a long time.
Third - we need to get there. Excluding flyby's, the best humanity managed is to deliver two 1 ton vehicles to the Mars. And there we had a luxury of aerobraking to save a lot of fuel. Belt is way farther, there is no aerobrake possibility and we will have to deal with other asteroids along the way. We don't have such tech.
Fourth - we will need to strap engines to the asteroid, remotely, with an hour signal lag. Engines which don't exist in any form today. And we need to get fuel to them somehow. Impossible task.
Fifth, we need a Moon colony with robots or humans.
Sixth - high energy tech on the Moon.
Seven - launch facility on the Moon.
And I've probably missed a few other impossible hurdles, writing this. Then IF all of that would exist, you would need it to be at least as cheap as Earth based mining, which is a pipe dream. Any space tech is more expensive by design, sometimes orders of magnitude more expensive. AND finally there need to be an infinitely elastic market on Earth for this new source of materials. Imagine you will sell a billion tons of platinum tomorrow, the price would crash and never ever recover. You see this yourself in your last sentence.
Not if you launch first, and present after ;)
Studying it might allow us to finally unify GR and QM.
1. Humans aren't going to survive in space for 10 years. It's questionable that they'd even survive a trip to Mars without getting riddled with cancer from the cosmic radiation. Sure, if you built a big enough ship to provide some really effective shielding, it's technically possible, but that ship would be enormous and far beyond our current capabilities. I don't think it's feasible at all to launch such a ship from Earth; it would need to be assembled in space.
2. Project Orion is just an idea on paper; it's not within current technology, because no one ever built it. We don't "have the technology" at all. We don't even have the technology to land humans on the Moon. We did decades ago, but we no longer do: all the people who knew how to do that are retired or dead, so we'd have to start over. Of course, we can build powerful rocket motors easier now since we do so regularly now, so building equivalent Moon-landing capability is no longer as difficult as in the 60s, but a lot of things would have to be partially re-invented (e.g., the lander itself, the rover, etc).
3. Does your time estimate include the time needed to decelerate, so the ship doesn't just zip by the black hole with barely any time to collect data? (And if there's people on this ship, they might want to return to Earth...)
You don't just have to get the probe there. (And which probe? You have to design and build it first.) You have to get it there, have it get data, and have the data come back. Otherwise you've just thrown a rock, which, yeah, if we spent a fortune we could certainly throw a rock out vast distances very quickly.
So, you either:
Do a flyby, which requires a slower speed. New Horizon's speed was good for gathering data from Pluto and sending it all back. The hypothesized PBH is small enough to fit in your duffle and probably much darker.
Enter orbit. Easy enough with a 5-10M object. But the orbit has to be a useful orbit. So either you burn a tremendous amount of delta-v to reduce your tremendous speed so you get a compact-enough orbit; which requires even more energy to get out there, or you craft the orbit such that the object itself helps slow you: but that takes time and more speed means more time.
But small black holes with the same mass as the Earth have the same sucking power as the Earth since it's the mass that does the sucking.
We'd all freeze to death in a few days, but the earth would go right on orbiting as if nothing happened.
If our moon turned into a black hole of its same mass tomorrow there would be even less of an effect. We'd notice we could no longer see the moon, but we'd still have tides just like before.
Renormalization.
Huh? Explain. How does that fit?
It's just a power-law distribution for the density of a halo that forms early around the "Planet 9" primordial black hole.
The density ~ r^{{3/2}^2} is a result from 1970s studies of structure formation shortly after Vera Rubin's work indicated that dark matter halos surrounded spiral galaxies. Rubin & Ford 1970 <https://ui.adsabs.harvard.edu/abs/1970ApJ...159..379R/abstra...> emissions regions of M31, begat Gott & Gunn 1972 <https://ui.adsabs.harvard.edu/abs/1972ApJ...176....1G/abstra...> infall of matter onto galaxy clusters begat Gott 1975 <https://adsabs.harvard.edu/full/1975ApJ...201..296G> structure formation and elliptical galaxies begat Gunn 1977 <https://ui.adsabs.harvard.edu/abs/1977ApJ...218..592G/abstra...> formation of massive galactic halos.
These are foundational to the paper at the top's ref [35], which is quoted just before the "funny exponent".
Roughly, let's start with an expanding Friedmann universe, where we treat galaxy clusters as motes of dust, and smear that out into one or more fluids representing nonrelativistic matter and radiation and other relativistic matter, with an identical energy-density at every point in space in an equatorial slicing, with each slice succeeding a spatially-smaller slice and preceeding a spatially-larger slice. At small scales, radiation pressure stabilizes any overdensities or underdensities in the nonrelativistic and relativistic fluids. Eventually expansion causes a transition from radiation-dominance to matter-dominance, allowing overdensities and underdensities to grow.
The papers by Gott and Gunn above consider the evolution of a spherical perturbation, an overdensity, starting at that transition, studying whether shortly after the transition from radiation-dominance, halos can support the evolution of generic galaxies and galaxy clusters. They can; and the "Planet 9" paper at the very top (albeit by way of its ref [34]) takes that further and applies this halo logic to primordial black holes based on that "universality" result (in Gunn 1977, penultimate paragraph).
Essentially what happens is that the nonrelativistic matter in an overdensity self-gravitates and so sticks around as an overdensity from one slice to the next bigger slice. Moreover, neither cold dark matter nor a primordial black hole radiates that early in the universe, so the overdensity can't revert to average through dissipation. Furthermore, the overdensity's gravitation draws in matter from the "shell" outside it (i.e., the rest of the universe); that's the "infall". If the infall is dissipationless, it sticks around in shells well outside the centre of the overdense perturbation.
All of this combines so that the density of an overdense perturbation drops much more slowly than the density in the rest of the universe. The latter drops like cosmic_time^{3/2} while the perturbation's density drops like cosmic_time^{9/4} (in these 1970s papers; in the age of fast computers one would use a profile like NFW <https://en.wikipedia.org/wiki/Navarro%E2%80%93Frenk%E2%80%93...>, and in this "Planet 9 is a PBH" context one might wa...
I'm guessing this refers to https://en.wikipedia.org/wiki/Cherenkov_Telescope_Array ?
The actual exponent and its workings-out almost certainly comes from Gott 1975, which I do not remember ever having read <https://adsabs.harvard.edu/full/1975ApJ...201..296G>, so I cannot do it any sort of justice at this time, but see my comment on Gunn 1977 below.
Theres an early history of pre-NFW power-law dark matter density profiles swept up in ref [34] of the Planet 9 preprint, which is cited just before the equation that piqued your curiosity.
[34] is <https://ui.adsabs.harvard.edu/abs/1985ApJS...58...39B/abstra...> which turns out to be part of a 1984 Princeton doctoral thesis, and I am unfamiliar with it although I recognize its author Edmund Bertschinger as well-known from his later 1980s-2000s work in cosmological perturbation theory and cosmological simulations.
[34] also lists Gunn & Gott 1972, Gunn 1977 and Gott 1975 in the references section (bottom of 1st to top of 2nd column). Surprisingly the Planet 9 preprint lists none of these papers.
However, in a way that could be serendipitous: you might enjoy the "funny exponent"s in many the equations of [34], since some involve powers of -8/9, 8/3, -5/2, among others.
I wrote but abandoned an attempt to tease out the detail using the following two seminal papers.
Gott & Gunn 1972, "On the Infall of Matter into Clusters of Galaxies and Some Effects on their Evolution" <https://ui.adsabs.harvard.edu/abs/1972ApJ...176....1G/abstra...> (PDF via top right box), contemplating a Friedmann universe with a spherical homogeneous overdensity that collapses into a galaxy cluster.
Gunn 1977 <https://ui.adsabs.harvard.edu/abs/1977ApJ...218..592G/abstra...> contemplates a spherical but inhomogeneous perturbation, and arrives at a power law of density \propto r^{-9/4}. It relies on Gott 1975 for that, however. This paper is the basis for a "universality" result which indicates that the shape of an overdensity's boundary is essentially preserved over time, even as the matter within the overdensity collapses into various structures. That universality was convenient at the time to avoid having to treat spirals specially, and is in effect claimed as applicable to a PBH equipped with a DM microhalo in the preprint linked at the top.
The "funny exponent" appears in the text just after eqns (8)-(9b) in Gunn 1977.
All of the NASA/ADS abstracts linked in my comment have PDFs available in the top right box on the page.
From the abandoned first attempt (which grew in length and messiness) I'll save two things: the "curious" equation's r_eq and \rho_eq are fixed at the transition from radiation-domination to matter-domination at z ~ 3200 (47 thousand years after the big bang), after which radiation pressure is insufficient to keep perturbations from growing. The transition is also when scale factor a \propto t^{2/3}, and energy density \rho \propto a^{-3(1+w)} where w is close to 0; self-gravitation in the overdensity causes its \rho to drop more slowly, and furthermore draws in matter from the surrounding ~average density shell.
1: https://en.wikipedia.org/wiki/Planet_Nine
1. Space is big.
2. Space is REALLY big!
3. This thing would be tiny.
4. This thing would be invisible.
Combine these four together and you'll quickly realize just how difficult even scoping out the probe's requirements and such would be. Would be cool though.
If you can get a spacecraft somewhere in the vicinity of a black hole of decent mass (like a 10km asteroid equivalent) we could probably detect changes in trajectory of the spacecraft from the gravitational attraction.
Or, here's an idea, blow out a tonne of radar chaff in the vicinity of the black hole and watch for how it disperses via radar.
We could also try detecting Hawking radiation that a BH should generate, though that might be pretty faint (I have not done the math).
You'd have to look for a very precise spike in the EM spectrum at the electron-position annihilation energy equivalent.
Despite being raised on space opera and hard-sf and having a science degree, I am pretty bearish on most space exploration. Having said that, a nearby black hole wouldn't merely be nifty. For reasons we do not understand, the event horizon stops honoring conservation of baryon number (and lepton number, and other numbers). I consider this important because replication of that would allow for direct conversion of uncharged mass to energy, just as any neutral particle crossing the event horizon has its energy (eventually) returned to us. If Hawking radiation is true (we have yet to experimentally verify it), then we know that mechanism exists. Can we do it without a black hole?
"Searching for a Black Hole in the Outer Solar System", https://arxiv.org/abs/2004.14192
"And one would like to launch hundreds of spacecraft (at least) in different directions so that some would come within dozens of AU of Planet 9, rather than hundreds of AU."
Their example of a neat-but-good-luck project could actually achieve the goal is [1]. The spec requires ground lasers that's powered by a 1GW nuclear power plant for propulsion. And, "According to The Economist, at least a dozen off-the-shelf technologies will need to improve by orders of magnitude." [2]
[1] https://breakthroughinitiatives.org/initiative/3 [2] https://en.wikipedia.org/wiki/Breakthrough_Starshot#Technica...
I agree tho, #LaunchTheProbe #NASA
[1] - https://en.wikipedia.org/wiki/Lunar_Crater_Radio_Telescope
A supernova-born black hole ( https://en.wikipedia.org/wiki/Stellar_mass_black_hole ) would be far more massive than the sun - so the entire solar system would obviously revolve around it, not the sun.
Also, the birth of such a black hole is a supernova explosion - which would not leave any solar-system-forming remains kicking around nearby.
https://en.wikipedia.org/wiki/Stellar_parallax_method#Histor...
https://en.wikipedia.org/wiki/Redshift#History
this seems to be a paper describing something that could be true, probably isn't, and doesn't advance science as a whole at all.
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.12...
It advances scientific knowledge by providing a testable prediction. The prediction can be used to collect data and determine whether there indeed is a black hole orbiting the Sun beyond Neptune.
do the thing, get the results, and if they're significant, then author a paper.
I think there is a lot of resume oriented science, these days, because publishing lots of papers looks good on your resume. i mean, we can't let actual science get in the way of our science careers, right? we gotta publish papers telling people what we're thinking about, and how to do those things.
Many theories were proposed before they were confirmed or refuted in data. Einstein's theory of general relativity is a famous example which was proposed before it could be confirmed by Eddington during a solar eclipse. Black holes themselves were also predicted by Penrose and Hawking before their existence was confirmed.
The Higgs Boson is a great example of this, theorized 40 years before it could finally be discovered at the LHC, a machine which wouldn't have been possible at all with the technology of the time when the Higgs boson was proposed as the computing capability to digest the Petabytes of data generated simply did not exist.
Plus, with these things there's a bit of a chicken and egg issue where part of the impetus for building these expensive machines is to test theories which have been gaining support, so if those theories weren't being shared, there's no way to really say if the machines to test them could even exist.
Neutrinos, time crystals and gravitational waves are other notable examples of things where it would not be practical to expect theoreticians to wait the decade(s) for technology to catch up before presenting their theories.
https://www.youtube.com/watch?v=aY985qzn7oI
His skype rant to SETI leadership about how nobody is taking the idea of contact or evidence of alien civilizations seriously, is really sad.
How close could a reinforced probe orbit? Would they just drop test masses in and observe what happens? Maybe drag a kuiper belt object in to make a little accretion disk?
As an aside, it takes the first visitors about 30 years to reach it, and they've got better tech than what's available to us today. It's pretty far out.