[HN Gopher] What if Planet 9 is a Primordial Black Hole? (2019)
___________________________________________________________________
What if Planet 9 is a Primordial Black Hole? (2019)
Author : rbanffy
Score : 143 points
Date : 2021-08-13 09:35 UTC (13 hours ago)
(HTM) web link (arxiv.org)
(TXT) w3m dump (arxiv.org)
| nabla9 wrote:
| That would make physicists happy. Once you locate it, you could
| observe and study it with satellites.
| pixl97 wrote:
| Yep dropping matter in it would allow us to study physics at
| much higher energy than we can generate here on earth.
| Chris2048 wrote:
| plus: a way of generating energy (I think that one depends on
| spin?) and a way of accelerating spacecraft.
| rbanffy wrote:
| Matter tends to glow in agony when falling into a black hole
| while the tidal forces shred its atoms apart. Tidal forces
| should be pretty rough at this size.
|
| The hard part of using a black hole for propulsion is that
| you'll need to drag a planetary mass along. It's an
| interesting engineering problem.
| kadoban wrote:
| There's also the Penrose process which is theoretically
| useful on spinning black holes. I also watched this in the
| past, which has some fun ideas (that are probably a little
| fanciful?) https://m.youtube.com/watch?v=ulCdoCfw-bY tl;dw:
| put a mirror around it and shine light in, get back lots of
| energy and/or blow up your whole solar system.
|
| I'm not sure if any of that would apply to a ~planet mass
| black hole spinning with ~planet sized angular momentum, or
| how solid the physics even is, but it sounds cool anyway.
| mrfusion wrote:
| If these are common would not our exoplanets hunt have found a
| bunch of these? Especially when looking at star wobble.
| pavel_lishin wrote:
| Maybe we have, but without a visual detection, we don't realize
| what we're seeing in the wobble.
| est31 wrote:
| FTR, if you wondered what they meant by "annihilation signals
| from the dark matter microhalo", apparently one of the theories
| for what makes up dark matter is WIMPs which are special
| particles that interact weakly with normal particles but _can_
| interact with each other and result in creation of other, better
| observable particles.
|
| The theory is that in the early universe, WIMPs were created
| spontaneously due to massive temperatures of the primordial
| plasma, but later as the universe expanded and cooled, this
| creation didn't work. However, the WIMPs would still be able to
| react with each other, reducing their numbers, until they'd be so
| rare that annihilations are such a rare event that they don't
| significantly reduce their numbers any more. Then space expanded
| even further.
|
| https://arxiv.org/pdf/1403.4495.pdf
|
| Apparently due to the strong perturbances of the dark matter that
| this black hole creates, it creates potentially detectable
| annihilations, and they discuss which scenarios can be excluded
| or detected with data generated by the FERMI-LAT gamma ray
| telescope.
|
| Not a physicist though, so please correct me if I'm wrong.
| da_chicken wrote:
| Note for the curious: WIMP simply means "weakly interactive
| massive particle". And "massive" here means "has mass," not
| that they're gigantic.
|
| Although they're theorized to have a mass closer to the Higgs
| boson than a proton, which is a lot of mass as far as subatomic
| particles go.
| gmadsen wrote:
| is that synonymous with dark matter as described in galaxy
| structure models?
| binarybanana wrote:
| IANAP, but they're (among others, like MACHOs, primordial
| BHs, etc.) potential candidates for dark matter, yes.
| Sharlin wrote:
| As opposed to MACHOs ("massive compact halo object") where
| the "massive" actually does mean "planetary to stellar mass".
| AtlasBarfed wrote:
| Huh, so the detection of a MACHO candidate would be a WIMP?
|
| That is some delicious astrophysics smorgasborg
| [deleted]
| rich_sasha wrote:
| I think MACHO and WIMP are alternative theories. MACHO came
| first IIRC
| dnautics wrote:
| GP was not well-phrased. I think they meant "the first
| detection of a MACHO candidates could be via a WIMP
| detection" (a black hole planet 9 would likely be in the
| last uneliminated sliver of MACHO candidate space and we'd
| see it via WIMP annihilation)
| binarybanana wrote:
| IIRC, the other way around. The editor who greenlighted the
| WIMP paper for print (and only because it was already an
| established name) regretted this decision once he saw the
| MACHO paper. Apparently he doesn't like cute names.
| Simplicitas wrote:
| "annihilation signals" sounds very troubling
| tejtm wrote:
| matter / antimatter annihilation is the perfectly normal
| state of affairs, we only exist as a fluke because it did not
| happen perfectly.
| Rd6n6 wrote:
| For those who, like me, didn't know what planet 9 was:
|
| > Planet Nine is a hypothetical planet in the outer region of the
| Solar System. Its gravitational effects could explain the
| unlikely clustering of orbits for a group of extreme trans-
| Neptunian objects (ETNOs), bodies beyond Neptune that orbit the
| Sun (Wikipedia)
| tiborsaas wrote:
| "Note that a 10M[?] PBH is roughly the size of a ten pin bowling
| ball"
|
| How to tell something is written by an American :)
| tzs wrote:
| The paper has two authors, one American and one from the UK. If
| I had to guess I'd guess that was from the UK author.
|
| Why? Because in the US ten pin bowling is the only kind of
| bowling most people are aware of, except perhaps in New England
| where candlepin bowling is popular or central Texas where nine
| pin is played. I'd thus expect an American author to simply say
| "bowling ball".
|
| The UK is mostly ten pin, but in the non-English speaking parts
| of Europe nine pin is big. I'd expect a UK author to be aware
| of that and so specify the type of bowling ball.
| mongol wrote:
| Would not a brit compare with a football?
| lamontcg wrote:
| asoccer or ruggers?
| celticninja wrote:
| Sounds right but for the wrong reason possibly.
|
| Lawn bowls is very common. Thus a bowling ball may be taken
| as some to mean one of these[0]. Which is very different in
| size to a ten pin bowling ball.
|
| [0]https://i.ebayimg.com/images/g/tRIAAOSwJddfCxXt/s-l1600.jp
| g
| mattowen_uk wrote:
| As a Brit, my first thought for 'bowling ball' would be
| lawn bowls. But then I'm Gen-X, maybe for British
| younglings it's different?
| teknopaul wrote:
| There is a whole nuther type of bowling in the UK, played on
| grass, no pins, you aim to get your balls closest to a jack.
| isaacimagine wrote:
| Is that Bocci Ball?
| vidarh wrote:
| A variant:
|
| https://en.wikipedia.org/wiki/Bowls
| elevaet wrote:
| In the future our descendents will play galactic boules,
| testing who can place the celestial body in the closest
| orbit to the black hole
| rich_sasha wrote:
| One of the deadliest sports too IIRC, as in, highest chance
| of dying while playing.
|
| Less to do with the dangerous action and more with the 80+
| average player age, but still.
| tejtm wrote:
| A previous thread https://news.ycombinator.com/item?id=23132488
|
| I still like to think if it existed it could be our ticket out of
| the solar system.
|
| (or a braking system for reentering if we ever made it that far)
| ianai wrote:
| "This scenario could be confirmed through annihilation signals
| from the dark matter microhalo around the PBH."
|
| Wouldn't that require locating a mirror behind the PBH and
| bouncing signals back off of it?
| malfist wrote:
| No, just like you can slingshot around planets, blackholes are
| massive enough they can do that to light and other matter. It's
| the primary reason we can "see" them.
| PaulHoule wrote:
| No you might see gamma rays coming from it.
| sabujp wrote:
| there's a 1:1 scale picture of the black hole fig 1:
| https://arxiv.org/pdf/1909.11090.pdf
| ycuser2 wrote:
| I want to touch it.
| klyrs wrote:
| I'd rather hit it with a baseball bat, personally...
| bgandrew wrote:
| and when you close to it it's almost impossible to resist.
| dole wrote:
| "when you stare into the abyss..."
| ISL wrote:
| It is one of my most-favorite figures in a physics paper. I'm
| still bummed that PRL made them remove it in the final version.
| Baeocystin wrote:
| What, really? Why? It's one of my go-to examples of clear,
| impactful data presentation.
| rob74 wrote:
| More precisely, a black hole five times as massive as the
| Earth. And it fits on a page. I think I have to print that out
| and pin it to a wall somewhere...
| tinco wrote:
| At what range would the gravity differential kill you? Would
| you be able to see it before it kills you? If it was close to
| the sun we should be seeing some kind of halo around it due
| to gravitational lensing right?
|
| edit: ok maybe we'd need it to be between us and the sun for
| that to work, the lensing would be that of other stars I
| guess. I suppose the important question is, since it's
| relatively close to us, would it deform space hard enough for
| the gravitational lensing to be noticeable at such close
| proximity.
|
| edit2: more train of thought, just because it's fun, I
| suppose since it's so small and the gravity relatively weak
| (i.e. not as strong as some huge stars or galaxies) any halo
| or distortion would not extend more than a couple meter,
| which wouldn't be noticeable from our distance, right?
| TrainedMonkey wrote:
| As usual the answer is - it depends, but we could estimate
| forces in question. Assuming my math is correct, at 67
| kilometers getting 1 meter closer will results in
| gravitational pull difference of 137kg. At 40 kilometers,
| this number increases to ~623kg. I am assuming bad things
| will happen somewhere between those two ranges.
|
| F = G * (m1 * m2) / r^2 . G = 6.674 / 10^11 (m^3 / (kg *
| s^2)) | m1 = 5 * 5.972 * 10^24 kg | m2 = 100 kg
|
| Only r in the equation above is not a constant, so we can
| compute F(r) - F(r+1) to get a difference in force that
| being 1 meter closer to the black hole would make at a
| distance r. Basically, this is the difference between how
| hard your toes would be pulled down vs your heard if you
| curl into a ball. Distance Force
| Force + 1 Diff in kg 1 1.99286E+17
| 4.98214E+16 1.49464E+16 1000 1.99286E+11
| 1.98888E+11 39797421.92 10000 1992856400
| 1992457888 39851.15023 20000 498214100
| 498164282.3 4981.767364 30000 221428488.9
| 221413727.7 1476.11612 40000 124553525
| 124547297.6 622.744272 50000 79714256
| 79711067.53 318.8474585 60000 55357122.22
| 55355277.03 184.5191277 70000 40670538.78
| 40669376.79 116.1990494
| spfzero wrote:
| Before you got very far into this it would be really hard
| to stay curled up in a ball.
| ebcoajssjofb wrote:
| I believe that the Roche limit would be roughly the same as
| it is on earth. However, the gravity constant would be the
| same. So for something as massive as a person, you should
| not experience any destructive forces until you reached
| extremely close to the object. Probably measured in a
| handful of miles or less.
| pwned1 wrote:
| How far from this black hole would the event horizon be?
| danudey wrote:
| Worth noting: despite the fact that this black hole would
| have an event horizon 4.5 cm in diameter, that doesn't mean
| you could get anywhere near it or put it in a box or
| anything.
| triclops200 wrote:
| That is the event horizon: when discussing a black hole's
| "size", you're discussing the event horizon.
| simiones wrote:
| In the current theory of GR (which predicts the existence of
| black holes), black holes themselves are point singularities
| - so the only meaning for "size" is the event horizon.
|
| Note that physicists don't believe this 0-size point is
| actually correct - the expectation is that a theory of
| quantum gravity would predict some fixed size for the black
| hole, one that also prevents the infinities inherent in the
| GR description of black holes.
| Causality1 wrote:
| Not quite. Point singularities can't spin, and since a
| black hole with no spin as about as possible as real mass
| with a temperature of absolute zero, every black hole we're
| ever likely to observe is actually a ringularity or other
| two-dimensional configuration.
| heavenlyblue wrote:
| What does it mean "to spin" in this case?
| renewiltord wrote:
| It means the black hole has angular momentum, which is
| detectable due to the resultant frame dragging (effect of
| the spinning on the spacetime around it) and presumably
| also due to the flattening of the sphere of the event
| horizon.
| sli wrote:
| Thanks for this comment, it was enlightening. I'd never
| much thought about this because physics is really not my
| forte, but after a few minutes of thinking about it, it's
| really intuitive why a point singularity can't spin. I
| can't _explain_ it in any properly rigorous or technical
| way, but it makes no sense that someone could (by
| convention, of course) designate a "front" and "rear" to
| a mass with zero length in every direction.
| [deleted]
| nkoren wrote:
| As I understand it, the fact that black holes are rotating
| precludes them from actually being a point singularity --
| "rotation" having no meaning for a non-dimensional point.
| So they need to have some kind of disk or ring structure
| (still infinitely thin, however). (Note: I'm not a
| physicist, could be completely wrong).
| karmicthreat wrote:
| So small, can I make a ball peen hammer out of it and be the...
| lesser Thor?
| rob74 wrote:
| If you can lift it, er... before it absorbs you, then you
| must already have supernatural powers, so you can join the
| Norse gods.
| karmicthreat wrote:
| And absorbed by black hole would pretty memorable at my
| memorial. Its win-win.
| danudey wrote:
| Probably the only way to die that would also result in
| you outliving everyone you ever knew.
| [deleted]
| api wrote:
| Go lasso that horse and ride it to the stars!
|
| https://en.wikipedia.org/wiki/Black_hole_starship
| lovemenot wrote:
| Halo Drive: Fire a laser around the Halo and get more energy
| reflected back than you put in.
|
| https://www.youtube.com/watch?v=rFqL9CkNxXw&t=2s
| magpi3 wrote:
| Kind of cute. Immediately reminded me of this (for you Beatles
| fans out there).
|
| http://www.westfieldcomics.com/blog/wp-content/uploads/2018/...
| atkailash wrote:
| I want this comic so bad. Hard to find though
| gwbas1c wrote:
| I used to read that to my daughter and make all the voices
| from the movie.
|
| It's a great kids' book.
| munchler wrote:
| And it's oddly terrifying.
| danudey wrote:
| One of these things intersecting with Earth would be an
| interesting way for humanity to end.
|
| The real question is, with the warping of space-time, how
| long would it take for us to perceive the end? Would it seem
| like the black hole started moving incredibly slowly, or
| would our planet start getting torn apart before then?
| lvs wrote:
| A very large black hole would have a hard time sneaking up on
| me, but one the size of a bowling ball on the other hand...
| 50 wrote:
| Einstein: "Time and space are not conditions in which we live,
| but modes by which we think. Physical concepts are free
| creations of the human mind, and are not, however it may seem,
| determined by the external world."
|
| Paul Brunton: "The most valuable metaphysical fruit of the
| quantum theory is its finding that the processes of the
| universe which occur in space and time, emanate from what is
| fundamentally not in space and time."
|
| Nisargadatta Maharaj: "In reality, time and space exist in you.
| You do not exist in them."
| [deleted]
| paulpauper wrote:
| rip my ink cartridge trying to print that out
| cheschire wrote:
| It would be a funny hack to try to trick a printer with
| malformed content to over-print that section of paper a
| multitude of times.
| kragen wrote:
| This is absolutely something you can do with ASCII dot-
| matrix printers, and it's not even malformed! It was common
| to end a line with a CR rather than a CRLF in order to
| overstrike some characters three times for bold, or
| overstrike them with _ for underlining; somewhat less
| common was to overstrike several different characters to
| get a solid block (such as 0, #, and *). (Accented
| characters were likewise achieved by overstriking `, ', and
| ~, but usually using backspace rather than CR.) With a
| normal amount of ink on the ribbon, you would punch through
| the paper after less than ten overstrikes.
|
| I understand that line printers (those that printed a line
| at a time rather than a character at a time) also supported
| overstrike sequences, but I never punched through the paper
| on one. Likewise, presumably the same approach would work
| with a daisy-wheel or typeball printer, but I can't
| testify.
| rwmj wrote:
| Wouldn't there be life-ending amounts of Hawking radiation
| coming from it? In other words, not a black circle :-)
| ninkendo wrote:
| From the PDF:
|
| > On its own, a PBH of mass 5M[?] has a Hawking temperature
| of 0.004 K, making it colder than the CMB, and since it's
| radius is rBH ~ 5 cm, the power radiated by the PBH alone is
| minuscule.
|
| Also wolfram alpha says it would take 7e52 years to evaporate
| from hawking radiation, so it's quite stable: https://www.wol
| framalpha.com/input/?i=%285120*pi*G%5E2*%285+...
| addaon wrote:
| My understanding is that a black hole large enough to be
| colder than the CMB will grow (gain more mass energy by
| absorbing CMB photons, even in "empty" space, than it loses
| by Hawking radiation), continuing to cool.
|
| I assume but am not sure that the cooling of an already-
| sufficiently-cold black hole in this manner is slower than
| the cooling of the CMB itself due to expansion, so that at
| some point as the universe winds down it will begin to
| shrink again and eventually evaporate, but definitely over
| the lifetime of any star we see a black hole this side
| won't radiate significantly, or evaporate.
| kragen wrote:
| I did the figures a while back on what it would take to build
| a Hawking-radiation-basedv mass-to-energy power plant (in
| orbit, obviously), and I was _astounded_ at how tiny the
| black holes have to be in order to get appreciable power
| output from them.
| gwbas1c wrote:
| > 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.
| phkahler wrote:
| Nibbler would be proud.
| 7373737373 wrote:
| It would be amazing if something like this was a necessary factor
| for the emergence of life in a solar system
| marstall wrote:
| interesting ... in what way?
| bobsterman wrote:
| It would mean the great filter could be behind us.
|
| I'm not sure how a black hole would help create life, an
| inbound Planet 9 would certainly be a hinderince to life's
| existence though.
| 7373737373 wrote:
| Maybe it doesn't help create life, but prevents its
| destruction, like Jupiter protects Earth from asteroids, or
| has another shielding effect.
| thatswrong0 wrote:
| Iirc it's a bit of a myth that Jupiter protects the
| Earth. It does some sometimes capture objects and send
| them away from us, but it also sometimes hurls objects
| straight towards us
| pavlov wrote:
| If there were a black hole in the solar system, is there
| something interesting we could do with it apart from studying?
| DrBazza wrote:
| You could drop matter in there and get 40% of the mass back as
| energy. Not that it's useful energy for us at the moment, but a
| more advanced civilization could probably learn how to ensure
| most comes out as polar jets and harvest that somehow.
|
| https://web.stanford.edu/~wilkinsd/docs/posters/BlackHolesPo...
| mrfusion wrote:
| Easier to build a Dyson sphere around it than the sun.
| dnautics wrote:
| or some sort of roman war bird.
| jsjohnst wrote:
| > roman war bird
|
| Roman? Did you maybe mean Romulan?
| wongarsu wrote:
| A Dyson sphere around a body with 4.5cm radius sounds quite
| manageable. I wonder how small a Dyson sphere could be with
| current materials. I imagine it's mostly limited by
| gravitational forces at that point?
| [deleted]
| [deleted]
| adrusi wrote:
| I think you can also extract energy from it by slingshoting
| an object off the black hole to draw energy from the black
| hole's spin.
| p1mrx wrote:
| Would it be useful to have a large power plant at the edge of
| the solar system? There's not much out there to power.
| darepublic wrote:
| You could use it to execute prisoners perhaps. Death by
| blackhole
| teknopaul wrote:
| The CO2 cost of getting the prisoners from the prison
| outside earth's gravity well and on their way to planet 9
| seems prohibitive.
|
| One more reason for rehabilitation as prison policy.
| Asraelite wrote:
| Maybe more easily study the effects of relativity by sending a
| spacecraft to it?
|
| Sending a spacecraft out hundreds of AU is doable with current
| technology, but it would take many decades.
| Qem wrote:
| It would be a cheap source of additional speed for spacecraft
| in the outer solar system, by means of powered gravity assists.
| See https://en.wikipedia.org/wiki/Oberth_effect
| KineticLensman wrote:
| > additional speed for spacecraft
|
| Extreme rip-your-craft-to-bits tidal effects [0] would make
| life exciting. Also, see 'Neutron Star' by Larry Niven for a
| description of such a manoeuvre, albeit a less dangerous one
| than than sling-shoting a black Hole because of the larger
| size of the neutron star.
|
| [0] https://en.wikipedia.org/wiki/Tidal_force
| piyh wrote:
| If you were really precise, you could tune your assist
| based on distance. You could get a pretty sick change in
| angular momentum relative to the sun since you wouldn't
| have to worry about hitting atmosphere or terrain. If
| you're far away you feel nothing, if you're too close you
| join the singularity, and everything in between is gravy.
|
| Imagine getting a 1970's style planetary alignment, going
| with a Voyager style slingshot and your final assist is a
| couple thousand miles away from a black hole.
| ordu wrote:
| One of aphorisms of Kozma Prutkov[1] was this: "Throwing
| pebbles into the water, look at the ripples they form on the
| surface. Otherwise this activity will be an empty amusement."
|
| I believe, that throwing pebbles into black hole, and watching
| the ripples they form would be very amusing.
|
| [1] https://en.wikipedia.org/wiki/Kozma_Prutkov
| 95th wrote:
| If it can cause some good amount of time dilation, then send
| people into future by having them orbit around it.
| corty wrote:
| Depending on the size of it, harvest energy from its Hawking
| radiation.
| evanb wrote:
| See also https://en.wikipedia.org/wiki/Penrose_process
| mnw21cam wrote:
| As stated in the paper, the amount of Hawking radiation
| coming off it is absolutely miniscule. The black-body
| temperature of the emissions is much much lower than the
| temperature if you just look into space.
| rbanffy wrote:
| That doesn't look like a lot of energy, but we could enclose
| it in a dishwasher sized box, which is kind of a funny
| concept.
|
| As for the size, the paper has a 1:1 scale drawing of it.
| simonh wrote:
| A box made of any known material that close in would get
| ripped to shreds by tidal forces.
| Thiez wrote:
| It would have to be a pretty sturdy box. Even if such a box
| could be built, it would be tricky to keep the black hole
| in the exact center.
| dantillberg wrote:
| I would like to upvote this 1000 times to underline
| "pretty sturdy box." It can be a particularly amusing
| exercise to do the math for things like this, calculate
| the gravitational forces involved, and compare the
| results to e.g. the strength of steel.
| lanna wrote:
| The net gravitational force is zero:
| https://en.wikipedia.org/wiki/Shell_theorem
| BoiledCabbage wrote:
| I don't see how Shell theory applies here. The box
| wouldn't be inside the blackhole, it'd be outside it.
|
| If the box were a perfect sphere then yes it would have
| zero net gravitational pull on the black hole, but the
| black hole would still have an extremely strong pull on
| it. And that's still assuming it's perfectly centered
| which would be almost impossible to maintain.
| lanna wrote:
| > but the black hole would still have an extremely strong
| pull on it
|
| No, it would not. Newton's third law: if an object has
| zero net pull on the black hole, the black hole also has
| to have a zero net pull on the object. The shell theorem
| is more general than you are assuming: it doesn't matter
| if the heavier object is inside or outside, the
| surrounding object doesn't need to be spherical (it can
| be any shape as long as it fully envelopes the black
| hole) and the black hole doesn't need to be centered. I
| know it is a counter-intuitive result, but it can be
| easily proven with calculus.
|
| See for instance this sentence about Dyson shells: "Such
| a shell would have no net gravitational interaction with
| its englobed star (see shell theorem)"
| https://en.wikipedia.org/wiki/Dyson_sphere#Dyson_shell
|
| Edit: Related, what is bigger? The gravitational force
| the Moon exerts on Earth or the gravitational force the
| Earth exerts on the Moon? Veritasium has a nice video
| explaining the answer:
| https://www.youtube.com/watch?v=8bTdMmNZm2M
| MauranKilom wrote:
| I also exert zero net pull when I tear open a package of
| snacks. Yet the package is destroyed in the process.
| hansvm wrote:
| The net pull on the _center of mass_ of a shell would be
| zero. The pull on any local region would still exist
| though. All that the shell theorem says is that the sum
| of all those local directional forces is zero.
|
| Reading the exact passage you quoted, "the compressive
| strength of the material forming the sphere would have to
| be immense to prevent implosion due to the star's
| gravity."
| aj3 wrote:
| You're wrong despite your confidence. Cage will have zero
| net gravitational effect on the black hole (assuming the
| cage is perfectly symmetrical), but that just means it
| won't by itself exert gravitational force on the black
| hole (and vice versa) causing it to move in any
| direction.
|
| Cage's material will still get attracted to the black
| hole and close to the event horizon structural forces
| exerted by gravity will be hard / impossible to
| counteract with current materials:
| https://en.wikipedia.org/wiki/Strength_of_materials
| kragen wrote:
| You'd probably want to use active control systems to move
| the box around to follow the black hole, with rockets
| when necessary. However, by lanna's reasoning below from
| the shell theorem, if the box were a spherical shell, it
| wouldn't be an unstable equilibrium like a ringworld, so
| your active control system could be pretty sluggish.
|
| Such a box can definitely be built if you make it much
| larger than a dishwasher.
| lvs wrote:
| Finally solves the problem of what to do with cable news
| pundits.
| sgarrity wrote:
| A similar concept is explored in the sci-fi novel Hole, by
| Brandon Q. Morris.
|
| I'd give it a 3/5 - fun read, not a classic.
|
| https://www.goodreads.com/book/show/43566986-the-hole
| smoyer wrote:
| Wouldn't the capture of a PBH by Sol be more like forming a
| binary system with a large distance between the two bodies?
| Intuitively it feels like capturing something with that much mass
| would result in our sun "wobbling" with respect to its expected
| path through the Milky Way.
| corty wrote:
| The Sun also wobbles because of the planets. Primordial black
| holes are (depending on theory of creation and path in later
| life) smaller than stellar black holes, maybe far smaller, in
| the order of lunar mass or even particle magnitude mass. So the
| wobble from a PBH will be overshadowed by that of Jupiter and
| the other planets. The sun doing a wobble of more than 30AU
| (what you would expect for a 1 solar mass PBH somewhere past
| neptune) with respect to the galaxy would have been detected
| ages ago, even the parallax measurements of yore are precise
| enough for that. From that fact, the magnitude of disturbance
| in other planets' and TNOs' orbits and the absence of
| gravitational lensing observations, our PBH should be in the
| order of planetary masses.
| ben_w wrote:
| > particle magnitude mass
|
| IIRC, that small would evaporate almost instantly[0]. I think
| you're thinking of particle _radius_ , which would be
| mountain mass[1].
|
| [0] this formula says less than a plank time and is therefore
| wrong: https://www.wolframalpha.com/input/?i=5120p%28G%29%5E2
| %28mas...
|
| [1] https://www.wolframalpha.com/input/?i=0.1nm*c%5E2%2F2G
| corty wrote:
| Yes, if it would have particle mass at the time of the big
| bang it would have evaporated long ago. But all small black
| holes do evaporate (the smaller, the faster), so if PBHs
| were e.g. car-mass at the big bang, they could just be the
| right size for particle-masses right now (and gone in a few
| years).
| ben_w wrote:
| 1.7e11 kg is a pretty big car: https://www.wolframalpha.c
| om/input/?i=%28%28%28h-bar%29%28c%...
|
| And again, the predicted lifespan of a proton-mass black
| hole is _significantly less than a plank time_ , which in
| turn is therefore a sign that -- one way another -- the
| maths doesn't actually apply to that situation in the
| first place.
| scatters wrote:
| The minimum mass for a black hole is the Planck mass,
| approximately 21 micrograms. Such a black hole is a
| Planck length in radius, has a Hawking temperature of the
| Planck temperature, and will decay in Planck time,
| releasing Planck energy of 1.9 GJ (about the same as a
| tank of gasoline).
| 0xTJ wrote:
| It's not any different (at large distance) than any other
| object of the same mass.
| sneak wrote:
| I think it depends on the mass of the object so captured? AIUI
| the mass of planet 9/PBH is estimated at 5-10 earth masses,
| which at that distance would not wobble sol (330,000 earth
| masses) very much.
|
| Not all black holes have to be big; a 10 earth mass black hole
| would be quite tiny.
| Thiez wrote:
| The paper actually depicts a 5 earth mass black hole at 1:1
| scale, if you are curious.
| wayoutthere wrote:
| Black holes in general are much smaller than people think.
| The event horizon of a 10 solar mass black hole is only
| something like 12 km across. That's basically the head of a
| pin at space scale.
|
| Supermassive black holes are on a whole different level
| however.
| lrem wrote:
| The most mind-boggling bit is the inverse relation between
| mass and density. Quoting[1]:
|
| > A black hole of 387 million solar masses would have the
| average density of water and would be comparable to a giant
| water balloon extending from the sun almost to Jupiter.
|
| [1]: https://arxiv.org/abs/1312.0340
| piyh wrote:
| A sphere of water extending to the orbit of Jupiter is a
| LOT of water.
| shadowgovt wrote:
| I sort of love this train of thought because it's simultaneously
| not impossible and hilariously hands-up shruggy about the problem
| of why we can't find planet 9.
|
| "What if the reason the only evidence of planet 9 we have is
| gravity is that gravity is the most observable aspect of planet
| 9" would be expert-level trolling if it weren't actual science.
| :)
| vardump wrote:
| Should have (2019) in the title.
|
| Previous discussion:
| https://news.ycombinator.com/item?id=21078068
| verytrivial wrote:
| A [2019] on the title is justified I think.
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