If Planet Nine Is a Tiny Black Hole, This Is How to Find It
discovermagazine.com
discovermagazine.com
However, there’s something that niggles me.
If it’s a primordial black hole that has been captured by the sun, why is it (as far as I understand) apparently in the same plane (ecliptic) as all the other major bodies in the solar system? It makes sense for all planets & cetera to be in the same plane because they all originated in the same swirling (flat) planetary nebula... but a captured object could potentially orbit at any inclination (and, considering how massive it is, I doubt it would be coerced into being coplanar by comparatively minor intersections with light bodies such as those present in the Oort Cloud, which are arranged roughly spherically anyway).
Edit: Probably around $100MM: https://www.spacex.com/about/capabilities for the launch, several $100MMs for the (space based?) accelerator and spacecraft, and then a few more for operations and research. Yeah, $1 billion as described in the article seems like a good estimate: https://arxiv.org/pdf/1805.01306.pdf
Since knowledge arising from this experiment will probably only be useful as a common good, there aren't really incentives for this to happen, unless governments decide to go through with it.
NASA's 2020 budget is only $22.6 billion: https://en.wikipedia.org/wiki/Budget_of_NASA
The Apollo program cost $153 billion: https://en.wikipedia.org/wiki/Apollo_program#Costs
Okay, this thing is ten times further away from the sun (400 AU) than Pluto (40 AU), 80 times the distance of Jupiter from the sun (5 AU), very far. Still, it's much closer than our next closest star, Proxima Centauri, which is 265612 AU away, or over 660 times the distance of Planet 9.
Additionally, all black holes constantly emit Hawking radiation https://en.wikipedia.org/wiki/Hawking_radiation Unfortunately for the planet 9 black hole, it only loses mass on balance it's below a certain size, about 0.007 earth mass.
Primordial black holes of that size, if they exist, would be quite useful. However, they would be monumentally hard to find: the black hole above would be 62 micrometres in radius, and have an event horizon temperature of 2.93K. Assuming no changes to the cosmic microwave background, this black hole is unstable: it will eventually radiate away all its mass and disappear. You'll be waiting a while for that to happen, at 20 picowatts, it'll take 1.9e35 gigayears to die.
1. Time dilation dictates that it would take ages for any instrument to get near the black hole, conduct measurements and send its results back to Earth.
2. Time dilation also means you would never see anything fall into the black hole. So studying the inside of the black hole is out of question, too. But arguably this is what would be required to make any breakthroughs in our understanding of black holes.
3. Tidal forces near the event horizon of such a tiny black hole would have catastrophic consequences[1] for anything (human or object) that gets too close to it.
On a related note: It'd be interesting to see in how far such a small BH would actually be capable of "sweeping [its] local neighbourhood clear of objects" like planets are (as was claimed in some comment above). Only then would I expect a significant accretion disk and, possibly, a jet. The reason the answer to this question is not obvious (at least to me) is once again the tiny size of the BH: How would anything manage to fall into the black hole, given that it's so tiny and, thus, very easy to miss?
SpaceX had to test the rocket anyways and have some mass in the nosecone. Elon Musk, on a lark I guess, put his personal car in the nosecone as that mass. You make it sound as if they expensively launched a rocket for publicity. In really, it probably cost a negligible amount in addition to what they already had to spend for testing.
A Sputnik with a radio repeater/reflector aboard or one of these https://en.wikipedia.org/wiki/LAGEOS would have been a gift to future generations in the form of precision gravity tests. No moving parts, can't fail, will orbit the Sun for the remainder of human-time. Only key requirement is a lot of mass and high density.
Yes, launching a car into solar orbit was cool. It was also a waste of a rare opportunity.
Why the hell would they put an actual payload into it. Are you also angry that the Apollo missions didn't put "useful" things into space when they were launching hardware with sensors
Putting an actual payload into the maiden flight of the Ariane 5 made into a very expensive test failure.
Still, I wonder if Elon knew such a satellite was a possibility. I would assume yes, but I'm not sure.
How much work would it take to create a LAGEOS-like satellite? Presumably they're not just lying around. I couldn't find how much the original LAGEOS satellites cost.
Check out the rocket equation and see what kind of mass fraction you'll need to get hundreds of km/s: https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation
Why would that be true? Individual gas molecules manage to disk-ify and turn in to planets, I don't see why a black hole couldn't. This would presumably happen in the early stages of system formation when there was a lot of stuff flying around separately.
However, more broadly speaking, the angular momentum is conserved, so the result would be more or less the same. However, given the enormous, ridiculous difference of relative masses (and therefore angular momentum) in the case of black holes and some gas particles, I think my initial point stands.
Yes, conservation of momentum is the right way to think about that.
So you’re saying you’d expect a body that were captured at an arbitrary angle to end up orbiting in the same ecliptic as the planets roughly around the sun’s equator?
I don't think this is true. Plenty of (almost everything) things would interact with the black hole's gravitation but not be close enough fall in.
What makes you think that a black hole orbiting the sun is a "planet" by the definition you're using?
More generally, you can't prove things about the physical world just by citing somebody's arbitrary definition of a word.
I would have thought that any model of a black hole in this scenario essentially approximates one of those conditions.
The Sun itself, surely?
A theoretical black hole in our outer solar system would do something similar to low mass objects such as comets and asteroids as well as interstellar gasses.
I dunno, to be honest. I don’t want to appear like I’m a polemicist with an axe to grind and sour grapes, but as I said in my original post... there’s something about this whole thing that just confuses me a bit.
Consider: the reason we think there is anything out there is because we see a lot of bodies that aren't following the expected pattern. For every action, there is an equal and opposite reaction, so perhaps those out-of-order bodies also pulled Planet 9 closer to the standard plane. Repeat a few billion times over a few billion years, each little tug moving it more in-line (and the rest of the solar system out-of-line).
This still depends on it starting relatively close to the same plane, but there may be selection bias involved. Those bodies that met with the solar system and weren't aligned well with the plane may have been more likely to escape again. The one (or ones) remaining are the ones that were well-aligned.
Then the most authoritative string theorist in the world, who hasn't worked on anything relating to experiments in decades, suddenly writes a very short, simple, single-author paper to use this idea to promote Yuri Milner and Mark Zuckerberg's space probes. Now it's the conjunction of two crazy ideas, and it's really taking off. I just don't know why this is happening, or what to make of it.
https://twitter.com/pontifier/status/581538570038460416?s=20
Well worth looking real hard just in case it does exist.
With v_escape = c and delta_v = 10 km/s that's a factor 245, for a final speed of 2450 km/s. That will get you to Alpha Centauri in 535 years.
How ever as a layperson I am at least vaguely aware that there are hyper velocity stars, some observed w/delta-v close to 10% of C if memory serves ...
Which would indicate to me that having a gravity well we can delve arbitrarly deep into has profound implications compared to gravity wells where it you go too deep you run into clouds or dirt.
For example the vessel could be paired, co-orbiting with a sacrificial mass that is dumped into the hole while the vessel leaves at at factor greater than a few hundred.
You can't delve arbitrarily deep into a black hole's gravity well if you want to get something back; you need to stop at the horizon, where the escape velocity equals light speed.
Dumping sacrificial mass into the hole is built into the Oberth effect scenario: the ship's extra speed (relative to the hole) is matched by a lower speed for the ejected reaction mass, which therefore falls toward the hole.
I suppose you could imagine something like a circular accelerator built around the hole and powered by dropping masses into it.
[1] https://newatlas.com/space/fastest-star-hypervelocity-ejecte...
How small can a black hole be and still qualify as a black hole? I guess a better question is what is the least massive black hole observed and what is the smallest current theories allow?
I have no idea what I’m talking about so all of that is probably wrong. I am just not able to wrap my head around it.
Science fiction fodder notwithstanding, from a suitable distance this kind of body would behave exactly like any other gravitationally interacting body, and would perfectly obey the usual laws of motion (Einstein’s General Relativity if you’re insisting on investigating it up close or in minute detail, classical Newtonian dynamics if you’re observing on a broader scale). It has mass, it has inertia, and it would be interacting gravitationally as the textbook “product of masses, reciprocal of square of distance” law. It would be a big, dark, featureless bowling ball with the mass comparable to a gas giant.
There's no theoretical lower bound on the mass of a black hole. Once matter has ceased to repel other matter, it will continue to fall inward. A violent impact could generate the forces necessary on a small scale to create micro black holes. Black holes do seem to slowly lose energy though, so small ones would not live very long[0]:
[0]: https://en.wikipedia.org/wiki/Micro_black_hole#Hawking_radia...
Actually, this is completely unknown. While Hawking radiation is a well-established effect in the semiclassical limit (read: when gravity is weak), we don't really know what happens when the Schwarzschild radius reaches scales where tidal effects become noticeable already near the event horizon and, eventually, quantum gravitational effects (supposedly) take over.
In fact, this whole question lies at the heart of the black hole information paradox. Do black holes evaporate completely? Or will evaporation stop at some point, leaving behind a black hole remnant?
If there are extra dimensions that make it especially easy to create a black hole.
Otherwise, you're looking at a Planck mass of 22 micrograms as a lower bound. It's effectively impossible for a violent impact to cram that much matter/energy into a single subatomic point.
Planet Nine has a mass five to ten times that of Earth; that's explicitly mentioned in the article.
Such a black hole can't form from the gravitational collapse of a star, but it possibly could have formed in the early universe. That's what the article means by "primordial black hole".
> How small can a black hole be and still qualify as a black hole?
The theoretical lower limit to the mass of a black hole is the Planck mass, which is tiny (about 10^-5 grams).
We have never observed a black hole smaller than several solar masses, so we've never observed one that wasn't formed from the gravitational collapse of a star. Finding one as small as five to ten times the mass of the Earth, if it exists, would be basically impossible if it weren't hypothesized to be somewhere within our own solar system, and even then, as the article says, it's very difficult. So it's quite possible, from that point of view that there could be primordial black holes of that size out there that we haven't seen. The question is how likely theoretically is it that such black holes could have formed in the early universe, and the range of estimates on that is quite wide, since there's a lot we don't understand about the early universe and about how such holes might have formed.
>However, the .01 c mission sketched in [10] has a spacecraft mass of only 6.6 mg, divided between the sail and the payload. Multiplying this by 100 while keeping the sail mass fixed leaves a payload mass of barely .65 grams.
Oof. That's not a lot.
For some other data points, a thousand ton black hole would explode in 84 seconds. A million ton black hole would last 2600 years as an unimaginably hot point five hundred times smaller than a proton. A billion ton black hole would last 2.6 trillion years as an unimaginably hot point twice as big as a proton.
If it is 5cm across, then it should be rather bright (Hawking radiation). While still tiny, it wouldn't be black.
[1] https://www.vttoth.com/CMS/physics-notes/311-hawking-radiati...
Edit: For those interested, there is an entire article on "Black Hole Thermodynamics" on Wikipedia (https://en.wikipedia.org/wiki/Black_hole_thermodynamics)
Of course eventually the expanding universe will drop the temperature of the cosmic background radiation further and the process will reverse.
Starlink will be a network of very near earth communication satellites. This black hole, if it exists, is far far further out than Pluto.
The probes wouldn’t be even remotely reminiscent of Starlink satellites either.
Also I said "like this".
If you have a mesh of satellites around the earth and used that data along with other astronomy tools, I'm sure there are other things we can learn.
The odds of an alien civilization picking up one of our probes, even if we send out thousands of them, is preposterously small. Imagine trying to such an object if it had been left floating at an unknown point in the ocean; now consider how much bigger interstellar space is than Earth's oceans.
I cannot remember where this quote came from, but I think it was something to do with a missing Russian cargo vessel in the Atlantic.
Not only that, but even if they were picked up, they’d only ever be picked up after coasting through space for millions, possibly tends of millions of years, and in turn it will take hundred of thousands of years for them to make their way here (assuming they have highly relativistic propulsion systems).
So... no.