If the Solar System's 'Planet Nine' is actually a small black hole, here's how we could detect it... wait, what? The suggestion that the Solar System's hypothesized Planet Nine is actually a small black hole could be supported by searching for outbursts of energy using the Vera Rubin Observatory, scientists say. The observatory, previously known as the Large Synoptic Survey Telescope (LSST), has been under construction in Chile since …
Come on, that's glib and you know it. Like most things in life it's not that clear cut. We don't all get sick from other airborne viruses.
It may well be partially airborne. Depends on your interpretation of "airborne". While larger exhaled/expelled droplets fall quickly to the floor, there's some evidence now that smaller droplets can remain in the air for several minutes or more. It also depends on how close you are to the person expelling infected droplets, and for how long.
So while it's believed the primary infection vector is contact, airborne is a viable secondary vector. And even with contact spreading, exposure time and magnitude are factors. It's definitely not exclusively contact or airborne, there's an entire spectrum of possibilities.
Indeed, but El Reg appears to have misread* the paper that speculates that it might be a black hole. That paper discusses Primordal Black Holes which are very different beast to those formed by collapsing stars and the mass is in the same range as that of the speculated Planet 9.
* I know there's a way to report this, but I can't remember what this is
Yes, and as I read TFA right now it says "...estimated to mass something in the order of five to ten earth-sized-planets."
That's not solar masses. The range covers about one-third to one-half of the mass of Neptune.
Source: Planetary Factsheet
Yes, they're hypothetical: you don't get BHs this light by any stellar-collapse mechanism we understand, even slightly, so if they exist we think they must have originated in the very early universe. And the paper is really saying that if this thing is out there, then we should be able to see it, and thus this would be the first (I believe) detection of such a thing, thus showing that they do exist. Or, probably more likely, showing that there are not any in the outer Solar system (which does not show they don't exist of course, just that they don't exist near us).
> if this thing is out there, then we should be able to see it
If a giant fully decorated Christmas tree several earth masses big was out there, we should probably be able to see it too. Does it mean we should start searching for the characteristic flashes of star reflections on Christmas decorations?...
They are trying to prove one hypothetical object by proving another hypothetical object: If "Planet Nine" has (let's say) 15% chances to exist, and primordial black holes (let's say) 1%, the combined chances of a "black hole Planet Nine" are only 0.15%. It's definitely not the best way to find/prove anything, be it purse-sized black holes or that elusive "Planet Nine".
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I think this is a confused argument.
As an example of why this is worth doing consider the question of whether antimatter falls up. I think that it is absurdly unlikely that it does: I also think testing whether it does is completely worthwhile. If it turns out to fall down, well, that's another tiny bit of evidence for GR and we can move on. If it falls up then GR is a dead theory, everything we know about the universe is wrong, Nobel prizes fall from the sky on the people who did the experiment and everything is as cool as fuck.
This is the same thing except not quite as dramatic. I suspect primordial black holes don't exist, and we've already done measurements which show they are at least scarce if they do. Well, here's an experiment which will tell us if any exist in the outer Solar system. In the likely case that it finds none we have another data point which puts an upper bound on how many there are, which is worth having. In the unlikely case that it does find one or more then not only do we know black holes which are either primordial or have some completely unexplained origin exist, we also know of a black hole which we probably could send a probe to without implausible engineering. We could send a probe which does direct measurements of the immediate environs of a black hole. Again, Nobel prizes fall like rain on the people involved and we're suddenly living in a world which is much cooler than fuck.
I'll take 'small chance of discovery which will change physics for ever' any day, thanks.
Finally I suspect we would not be able to see the Christmas tree: it's far away and Christmas trees are not that bright. But I might be wrong about that. Gravitational considerations probably do safely rule it out though (it would collapse and become a planet).
I agree, my point was about searching an exception inside the limits of another exception, thus dramatically lowering the chances of finding either.
I agree with that, but another way of thinking about it is to say that, well, if very light black holes are common, then this is just another approach to looking for them, regardless of the planet 9 thing.
> if very light black holes are common, then this is just another approach to looking for them
While I get your point, it still seems like a long shot. If small black holes were indeed that common, we would most likely already have gotten some hint of their existence, wouldn't we. If they aren't common, the chances of one being right here, sitting quietly in our solar system are vanishingly small. Lottery-winningly small. I know we're special and our system is special, but still... :o)
Well, I'm a skeptic. What can I say.
Their assumption is that the outer Solar system is not particularly special, which I think is plausible in terms of primordial black holes (PBHs) anyway. If that's true then they say that a non-detection of PBHs over the lifetime of the LSST would bound the fraction of dark matter which is in PBHs of ~5 Earth masses by a few times 10^-5. They say that this is orders of magnitude better than current bounds on the DM fraction in such objects.
I'm just paraphrasing the end of the paper here, but assuming they've done their sums then yes, this is potentially significant experiment in that it will either push the bound for the dark matter fraction which is in such objects down (with assumptions that the outer Solar system is not special) or it will find one, which will be cool in other ways but will also tell us that, perhaps, some nontrivial amount of dark matter is in PBHs.
Not solar, so relatively far less impactful gravitationally but according to Hawking's research, shorter lived than large stellar collapse black holes. When they have lost sufficient mass through Hawking radiation, they will rapidly deconstruct with the force of millions of hydrogen bombs.
The fun fact in that scenario is it could happen before our sun pops it's clogs.
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a 5-10 Earth mass black hole will be gaining mass from the CMB, not losing it. The point at which a BH's temperature gets higher than the CMB is somewhere around the mass of the Moon.
Of course the CMB will get colder over time, so at some future point an object this massive will become hotter than it and, if it's not gaining mass by any other mechanism (which it will be) it will start losing mass. Whether that point happens within the life of the Sun is not clear, but probably not.
Wait. If watching from a distance, it seems we should never be able to see a star collapse into a black hole. Rather, we would see a star shrinking slower and slower toward its inevitable collapse, but never quite getting to the Schwarzschild radius due to relativistic time dilation. So how is it that we can see x-ray radiation from matter falling into the black hole when it still looks like a collapsing star that isn't quite yet a black hole from our point of observation?
Yes we see the supernova, but that is also true for stars that become neutron stars. Btw, we have never imaged a neutron star either, just nearby gas clouds glowing from the x-ray emissions it produces. So seeing a supernova is not definitive evidence of the formation of an event horizon. We can only estimate that it will become a black hole based on the star's original mass. Had we a powerful enough telescope, looking into the center of the supernova remnant we should be able to see a neutron star (in x-ray). But for a black hole, we should see the remnant of the star collapsing at a slower and slower rate and getting more and more red shifted. From our observation point, (according to general relativity), time literally stops at the event horizon, meaning we can never see its formation from here.
We see a lot of radiation because things get extremely fierce far outside the horizon. Anything in a close enough orbit around the object ends up in an extremely turbulent environment & gets heated by all of the turbulence to extremely high temperatures: the kinds of temperatures where a lot of the emission is x-rays. It's just this emission of energy which allows the orbits of things in the accretion disk to decay far enough that they ultimately get to the innermost stable orbit from whence they fall in. The innermost stable circular orbit is well outside the horizon: 3 times its radius in fact, although things look different from far away. So almost all the emission comes from relatively far from the horizon.
(Infalling stuff also needs to shed angular momentum, and I'm not sure how this happens.)
The 'distant observer never sees the event horizon form' argument is a bit of a red herring for these purposes. The way to see this is to consider a bunch of observers far from a collapsing star, who are capable of detecting all the light from it which crosses some surface surrounding it (and, obviously, this collapsing star is rather special because it is not surrounded by a supernova: it's just falling cleanly in). So what these observers see is the surface of the star getting redder & redder and dimmer and dimmer as it falls in. But as it gets redder and dimmer, they see fewer photons crossing the surface they are measuring. How long is it (in their frame) before the last photon they will ever see from the collapsing surface has reached them? The answer depends on various factors, but it is not more than a few seconds. Once no more photons reach you from the infalling surface then there is no observation you can do which will distinguish between what you are looking at and a black hole. The same applies for things falling in to the object: yes, in theory they never reach the horizon from the perspective of a distant observer, but in practice it takes no more than a few seconds before no more information will ever reach you from them, at which point nothing matters.
You need to add rather extensive caveats around this for Hawking radiation &c, but none of these matter for distant observers who aren't willing to wait hugely longer than the age of the universe.
Infalling stuff also needs to shed angular momentum, and I'm not sure how this happens.
Isn't that why black holes are not actually supposed to be 0-dimensional point singularities, but actually are hypothesised to end up as essentially 2-dimensional (very rapidly) spinning discs?
Of course, they could be anything inside the Schwarzchild radius. They could be entirely made of bees, and we'd never know, because none of the bees, or the information about their existence, could escape. Not even the increasingly frantic buzzing...
IIRC, the time dilation happens from the perspective of the black hole, not of the observer, so from the perspective of someone at the Schwartzchild radius, ignoring the fact that they would be strung out like spaghetti by the tidal forces and spat out as X-rays, they would never quite see themselves "fall in".
Huh? I thought there would be zero black hole evaporation until close to the heat death of the universe. The background cosmic radiation is currently too hot and will continue to feed black holes of stellar sizes (those we so far only know to form) quicker than they evaporate.
So how would one evaporate before our sun burns out it's hydrogen?
As to the article, I'm also of the persuasion that any black hole big enough or close enough to us to be detectable would probably light up pretty obviously as stuff hit it. But the scientific paper is still good as a concept and test of the limitations and sizes to expect for detection and natural exclusion due to physical constraints.
Well given you estimate mass from gravity pull, obviously not. You don't know the mass inside you only know the gravity outside and it would be the gravity outside that pulls anything around it.
If it was an impossibly small black hole with an apparently small gravitational pull, then they've found something super interesting. It doesn't mean the 'mass' of the stuff in the black hole is small, it means the gravitational constant isn't a constant, and there's a special case here.
Which would then cause a lot of much needed head-scratching as to why these magic constants exist and if indeed they are constants.
https://forums.theregister.com/forum/all/2020/06/04/hubble_early_stars_galaxies/
See the 'we're special' thread in the comments of this article. This is what I want you to find, a weaker 'black hole to universe matter pull' than 'black hole to black hole' pull.
There should be more matter inside black holes than can be accounted for by the gravitational pull.
But then, you don't know what gravity is, or have any proof as to why the magic gravitational constant would be a constant. So you should already be questioning where these magic constants come from and not simply parroting stuff you were taught to parrot at Uni.
Obviously you're a crank, but in case anyone who isn't is reading this: the gravitational constant, G, is rather like the speed of light, c: it's actually a fudge factor because we made a bad choice of units in other places (bad for the purposes of relativity, quite good for practical purposes).
It's easier to understand the problem with c. We measure distance in space in metres. We measure distance in time in seconds. But time is just another dimension in spacetime, so both time and space should have the same units. Let's use seconds for both! Well now we need to express metres in seconds, and ... 1m is 1s/c. In other words a second (often called a light second) is a lot of metres. This problem happens only because, when we chose our system of units, we didn't know time was just another dimension of space, so we made a bad choice of units. Once we switch to good units, then c goes away, completely.
G is the same thing in a different area: when we picked units for mass (and, equivalently, energy: now c has gone the famous Einstein energy relation reads E = m) we didn't understand that mass was intimately related to the geometry of spacetime. So we chose bad units for it: we chose kg. The natural unit for mass is in fact also the second and 1kg is G/c^3 seconds (where G and c have the values they do in SI units). This is a very small number because 1kg makes only a very small difference to the geometry of spacetime: you need really massive objects like planets and stars to make a significant difference.
Once you've changed units to these natural units, G and c just go away: they're both 1.
Note that I chose seconds as my basic thing: you can equivalently choose metres (or furlongs, or microfortnights), and you get different conversion factors by a factor of c (or ...). The mass of the Sun is about 5 microseconds, or equivalently about 1.5km.
These units are often called 'geometrised units' as they represent the underlying geometry of spacetime. There are several variants of them – some people like to absorb an additional factor of 8π to make the field equations of GR even simpler, for instance.
Yeah, it should have been Earth masses, not solar masses. Late-night editing and brain was broken. It's fixed.
Don't forget to email corrections@theregister.com if you spot anything wrong. We check that address all the time whereas we have time to read the comments at the end of the day.
C.
So, a black hole of five to ten solar masses as planet nine. One has to question the logic here. What is orbiting what? If planet nine is a planet, then it will be in rather "close" orbit to the sun. Otherwise, it cannot be called a planet. But, if it is in the orbital plane with all us other small rocky and gaseous balls, then I'd guess our chances for survival to be zero with a black hole as close as a planet nine.
One has to question, at five to ten solar masses, is a black hole going to orbit this solar system or will this solar system be orbiting that black hole? And then, if we are that close to a black hole, wouldn't any orbital dynamics of this solar system become chaotic? Ah well, we must be close to the event horizon and be in a state of relativistic slowdown. At least we would have plenty of time to ponder the questions of life, the universe and everything(*) when squeezed that close to a black hole.
(*) yes, six times nine and so on...
I'm not sure you understand orbital mechanics correctly. I won't downvote, but you should ask/check/research before posting such an assumption.
Any size of planet or gas giant or star or black hole, can orbit at any distance, providing it's below the Roche limit. Below that the smaller (mass and gravitationally) of the two will be pulled apart by the larger. For example, of the moon got too close to the earth or Mercury to the sun.
However, for bodies closer to the sun their orbits are faster, not their "falling" into the sun. They do fall so extremely slowly, and *large* masses fall at the *same speed* as small ones, so no a black hole does not fall in "quicker" than a grapefruit.
"One has to question, at five to ten solar masses, is a black hole going to orbit this solar system or will this solar system be orbiting that black hole? " All orbits share a centre. Earth-moon, Sun-Jupiter or even Sun-rest of the solar system. You don't ask "which is orbiting which" but "where is the centre of both (or multiple) bodies".
" And then, if we are that close to a black hole, wouldn't any orbital dynamics of this solar system become chaotic?" Only if it's large. As we already know the orbital discrepancy of "Planet X" we already know it's small, so the black hole/planet/error in calculations if Planet X does not exist, is small. Not large.
The calculations are working backwards from the observed discrepancy of a small difference, not forwards from an assumed large black hole.
"Ah well, we must be close to the event horizon and be in a state of relativistic slowdown." No, if anything is that close, spagettification may have already happened, unless talking of intergalactic supermassive black holes, in which case that are often larger than our stellar neighbourhood!
@TechnicalBen. You seem to have arrived here after the Vulture concerned amended a blooper in their article. What now reads "estimated to mass something in the order of five to ten earth-sized-planets" read "ten solar masses" when the article was first posted.
Totally different beast.
IIRC that's about 1/3 the mass of Jupiter.
And yes, on that scale you would need a telescope to find it.
Putting one of the universes most mysterious objects practically in our back yard. Our own baby black hole.
Exciting times. Something to raise a glass to on a Friday at beer o'clock.
> Exciting times. Something to raise a glass to on a Friday at beer o'clock.
Unless it has lost sufficient mass through Hawking radiation that it chooses to go "Boom!" around 17:30 on a Friday afternoon. It'd take a round or too for the wavefront to arrive, but all that local radiation incoming might really ruin my pint.
And, just to make things worse, being only a temporary black hole, it might also have broken global electric charge conservation whilst doing it:
http://dx.doi.org/10.1007/s10701-019-00251-5
Fortunately there is no reason to believe this would also break credit-card charge conservation, so you will avoid getting a nasty shock shortly before being blasted into oblivion. However, you may wish to make sure by paying for the drinks in cash. :-)
Compared to the CMB, it's having food shovelled down it's gob faster than it can burp - by a process we call the solar wind. And that's before we get to all the clutter out there, which will be orders of magnitude more significant. The loss to Hawking radiation can be approximated as zero without any loss of generality; the only question to answer is how quickly has it been putting on weight.
[Wikipedia gives a handy formula which suggests the lifetime of a 5 terrestrial mass black hole in a perfect vacuum would be ~7E52 years. Tthe universe is ~1.4E10 years old. So we are talking about a lifetime which is the_age_of_the_universe5]
It will go boom around Friday at 17:30 (using the astrophysics understanding of "around"). But given the speed of mass loss due to Hawking radiation, that will happen gazillions (to use the technical term) of years from now. However, in the interest of science, I am willing to raise a pint each Friday, and the rest of the days as well (just in case), until it happens.
It's worth quoting from the abstract of the paper:
[We] find that the upcoming LSST observing program will be able to either rule out or confirm Planet Nine as a black hole within a year.
In other words the sword they're using has two edges: someone has proposed a mad-but-possible idea that there might be a planetary-mass BH in the outer solar System, and they've worked out that if there is, we would be able to know that because of light from accretion flares, and we would also know, if we don't see such events, that it's not there. So what they're doing is not trying to 'prove there's a black hole' there: they're trying to answer the question 'is there or isn't there one there?', with (I assume) the strong supposition that no, there isn't (but it would be absurdly cool if there was).
They go on to say:
We also find that LSST could rule out or confirm the existence of trapped planet-mass black holes out to the edge of the Oort cloud, indirectly probing the dark matter fraction in subsolar mass black holes and potentially improving upon current limits by orders of magnitude.
In other words their proposed observations will rule out or confirm the presence of any such objects in the outer Solar system, thus improving the existing bounds on potential dark matter sitting in small BHs (we already know that there's not much, this, ssuming they don't find any, would improve the bound a lot, at least locally).
First, thank you for the informative posts. More informative than the article, in fact.
Second, after 60 years of following astronomy on and off, I would respectfully suggest that if an idea is possible - as it is in this case - it cannot be mad. It's not that long ago that people would write serious articles about how it would never be possible to detect planets remotely comparable to ours orbiting other star systems. In fact, I can remember when many astronomers dismissed black holes as exceedingly unlikely and probably undetectable. So if this black hole orbiting the Sun is merely extremely unlikely, Pratchett logic suggests there's a 9 out of 10 chance that it's there. (Not really, I am not quite that stupid.)
You are right: I think I was using 'mad' in the 'mad science' sense. And you are certainly right that BHs themselves were originally regarded as, just clearly, not something that could exist but were amusing and odd predictions of general relativity ... until people started finding a few things which could really only be BHs. I vividly remember the moment when I read that you could put limits on the size of quasars because of their variability (if something changes over a timescale t it can be no larger than ct across) and also weigh them, and the only candidate object was a BH: this quite literally sent shivers down my spine (and still does, thinking about it).
A reasonable approach to astronomy seems to be 'if something is possible, no matter how bizarre, it's out there.
That being said, I think this particular thing is unlikely to be true, and that people don't think it is likely to be true: they just want to do the observation so they can know. And it would be as cool as fuck if it was true!
Oh, sorry, I didn't mean to snipe at the article: I thought it was fine (the mass error got fixed and you put in the link to the abstract). In particular I was fine with the title: you're a red-topped newspaper, not an academic journal. Really I was trying to help people who read the article, presumably then did not then bother looking at the paper (this is why I think linking to the abstract page for arXiv papers is better) and then made confused comments. I think el reg's science coverage is great at the moment: keep it up!
"Solar System's mysterious 'Planet Nine' is actually a small black hole"
I am sorry but that is just completely unsubstantiated horsepoo and I would expect to find a lurid claim like that in the Daily Star or National Enquirer.
Despite the searching not even the predicted Planet Nine has been found yet and the only certainty in the far out solar system is that Eris really does exist, that it's more massive than Pluto and that a probe would take decades to get there with current technology.
You missed a crucial bit from the title: 'Here's how boffins can prove ...': yes, the claim is unsubstantiated, but these people have worked out that it is a testable claim, and have proposed a way of testing it which is completely practical to do. That's the whole point of what they want to do: run an experiment which will either say 'yes, there's a BH out there, and we can tell you things about its orbit' or (much more likely) 'no, there's no BH there'.
Things do not 'spiral' in. That implies a continual loss of energy. Perturbation, is simply an exchange of energy, one way or the other. The total amount of energy remains the same. The two participaing objects will simply adopt a new configuration. In effect a differntly shaped ellipse. The only exception would be if one of the objects acquired enough energy to change from an ellliptical orbit to a parabola, and was lost.
Well, yes, they do spiral in, because they lose energy due to gravitational radiation. But the amount of energy lost in such a system would be seriously tiny (I was going to say 'astronomically tiny' but, well... just tiny).
Anyway for all useful purposes you're right, of course.
> perturb its orbit just enough to send it spiralling into the inner solar system
Don't worry, IIRC it is supposed to take about a dozen thousand years to make an orbit, so for all intents and purposes it's stationary, hanging there in the sky. Even if it starts "spiraling", it won't arrive anywhere near us for the best part of a million years... (And also only if it manages to not get ejected by Jupiter.)
"Because black holes are intrinsically dark, the radiation that matter emits on its way to the mouth of the black hole is our only way to illuminate this dark environment,"
In other words:
"The thing about a black hole - its main distinguishing feature - is it's black. And the thing about space, the colour of space, your basic space colour, is black. So how are you supposed to see them?"
Because they accrete stuff, and that process is anything but black.
This we all know, but it's also worth pointing out that there is nothing particularly special about a black hole, in terms of its potential to accrete things, beyond its mass. For something planet sized, it's not going to accrete things any faster, or energetically, than anything else of the same mass, so it won't have any more of an accretion disk than, say, Neptune. Neptune, of course, was discovered because its gravitational effects suggested there was something there, and it could be seen, unlike something that is black...
Well hum. Space doesn't absorb incident light, it just does not reflect it. And that's kind of the same a BH, which after all really is just a deformed bit of space(time). Indeed there's a nice idea that I haven't quite got sorted out which is that the reason the event-horizon of a black hole is black is because its a surface which is in your future, and you don't get light back from surfaces which are in the future. (This is slightly wrong: the event horizon is actually a null surface.)
But surely you do get light back from a surface which was in your future when you sent it out? In exactly the same way that if you aim a laser at one of those reflectors on the Moon, and if your dispersion could be low enough, you would actually have to aim at a point about 240m on from where the reflector was when the laser pulsed. (My number may be inaccurate but I think the principle is sound.)
Everything that goes into a black hole (ie through its event horizon) never gets out; indeed even if the something has "only just" passed through and the black hole then suddenly and implausibly evaporates almost infinitely fast[2]. The event horizon is not just a surface in the future, it's a surface in the infinitely far future for anybody with the good sense to avoid falling in[1], isn't at all reflective, and is only a "surface" in a mathematical sense.
[1] But then, if you happen to be falling into the black hole, it -- neither the event horizon nor the singularity are infinitely far in your future at all, they're a finite time away. Have fun!
[2] This sentence is at best probably only "sort of true", and would very likely enrage any passing general relativists.
So a candidate now is a black hole that weighs about 5 or 10 Earth equivalents? Even if such a thing could exist, it would have a very tiny accretion disk, cruising around in near-interstellar space, and probably having long ago cleared out much of the Oort cloud objects in its orbit.
And I am skeptical that such a thing could actually exist. Would a 5 or 10 earth equivalent black hole actually be able to trap light, even if you collapsed that 5 or 10 Earth equivalents of mass to an infinitely dense singularity? Would it form an actual accretion disk, versus just a set of planetary rings, because there is an insufficient gravity well to force a collapse of the accretion disk material into the singularity?
So maybe Planet Nine doesn't exist, and the problem is that our understanding of how gravity functions is flawed. Given the mysteries around dark matter and dark energy, that is certainly a possibility. Or maybe Planet Nine is a traveling fragment of a neutron star or a black hole from some past unknown calamity that was trapped by our solar system's gravity. Or perhaps Planet Nine is out there and is a planet, but it has a uniquely unreflective surface because it is essentially a large iron-rich asteroid, or the metallic core of an old gas giant where the gas atmosphere has long been stripped away by some force..
Classically there is no lower bound to the mass of a black hole: the mass is just a parameter. And a 5-10 Earth-mass object is far, far above any quantum limit. And yes, such a thing could very definitely accrete matter: in fact it would be a lot nastier in relative terns than a very massive object as the tidal effects are worse. The total power you would get from it would be much less but anything getting near it is definitely going to get disrupted.
The problem for small black holes is that there is no mechanism that we understand that starts with a star (or anything) and ends up with a black hole this light. There are mechanisms which could possibly have formed them in the very early universe, which is one reason people are interested in finding, or not finding, them. We already have upper bounds on how many there can be from microlensing observations, and I think the general opinion is that they may well not exist at all.
But none of this says anything about gravity: I think the evidence for any planet nine is a but weak in the first place: this is just one more thing people want to rule out.
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