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Just another Hypothetical discussion topic.  But this is one I love asking people and having them realize what it means to be a black hole.

What would happen to Earth and the rest of the solar system, if the Moon suddenly collapsed into a Black Hole?  Ie the moon is replaced with a Lunar (Munar? I'm so confused on that term after playing KSP for so long) mass black hole.   

Ignore the fact that it can't, just that it did....

Late late edit:

Initial assumptions:

1. The initial collapse more or less "swapped out" the Moon with a lunar-mass black hole, and didn't create any additional disturbances normally associated with objects collapsing into black holes 

Other Assumptions get discussed later in the thread and are rendered 'trivial'.  (See expected lifetime due to hawking radiation below)

Edited by Gargamel
Update for recent bump
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The initial blast from the gravitational energy release will be quite significant. I'd have to run the numbers, but I'd guess enough to sterilize Earth and not enough to damage it significantly. From there on, though, the impact on Earth or the rest of the Solar System will be absolutely minimal for the next few billion years. That is, until the Sun grows into red giant stage. At that point, the moon would start accreting matter, eventually merging with the Sun. Radiation from that event might actually be sufficient to scatter what's left of the Solar System, leaving a sub-solar mass black hole as sole remnant.

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Well we'd lose the view of the Moon's surface. Beyond that, some minor changes in tides?

And of course the Hawking radiation... though I'm not sure how much would be released.

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Nothing, really. It might confuse the hell out of some insects (sudden loss of their navigation beacon) and cause the extinction of nocturnal hunters... Otherwise, the difference in gravity to other planets and Earth is zero.
 But in the long run, the moon would lose its mass through Hawking radiation. This would cause the extinction of life on Earth, since our core would cool, the magnetosphere would die out, and we would no longer have a tidal force to keep our rotational axis stable.

Best,
-Slashy

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Earth's sky would become significantly less interesting (no chance of even seeing it through a telescope!). A bunch of people freak out, believing it signals the end of the world. Then nothing else changes. The tides keep coming, and even the satellites orbiting the moon keep right on orbiting*. Space agencies around the world quickly figure out that the moon has suddenly and inexplicably become much smaller, and begin to use what instruments they can on their moon satellites to try to learn about the new object. They move as close as they can, but can't get everything they need without constructing a new, specialized probe. They quickly gain the support needed for this, and some years later it is launched. But before then, KSP players are among the first to bring up the amazing potential - the Oberth effect near the tiny black hole would allow spacecraft to reach distant destinations, fast, as long as they can hold together under the tidal forces. Space probes only need the delta-V to arrive at the Moon to flyby any planet. Space agencies take advantage of this quickly, and we start sending out more space probes than ever, and more cheaply too. Eventually, Mars colonists slingshot past the Moon for a quicker journey in deep space.

*Could someone please verify these two points with math?

Spoiler

Initial assumptions:

1. The initial collapse more or less "swapped out" the Moon with a lunar-mass black hole, and didn't create any additional disturbances normally associated with objects collapsing into black holes

2. The black hole is kept stable by the wizardry of hypothetical scenarios and doesn't evaporate immediately as Stephen Hawking would expect it to

Keep in mind that the gravity of all the worlds in KSP is basically like a tiny black hole in the center of the planet that carries all its mass, and these still act like normal planets gravitationally (for the most part).

Edited by cubinator
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26 minutes ago, K^2 said:

The initial blast from the gravitational energy release will be quite significant. I'd have to run the numbers, but I'd guess enough to sterilize Earth and not enough to damage it significantly.

Ehh, for the sake of the argument, let's skip this step....

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26 minutes ago, K^2 said:

From there on, though, the impact on Earth or the rest of the Solar System will be absolutely minimal for the next few billion years

 

26 minutes ago, Bill Phil said:

Beyond that, some minor changes in tides?

 

18 minutes ago, GoSlash27 said:

Nothing, really

 

11 minutes ago, cubinator said:

Then nothing else changes

That's the point I always have trouble making 'lay people' understand. 

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14 minutes ago, cubinator said:

Initial assumptions:

1. The initial collapse more or less "swapped out" the Moon with a lunar-mass black hole, and didn't create any additional disturbances normally associated with objects collapsing into black holes

2. The black hole is kept stable by the wizardry of hypothetical scenarios and doesn't evaporate immediately as Stephen Hawking would expect it to

Those are the assumptions I'm working under...

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1 minute ago, 5thHorseman said:

I'm pretty sure cosmic rays from space that are normally blocked by the Moon would then be able to rip American landmarks to shreds.

corebridge480.jpg

 

I really hope that isn't a screencap from an actual movie with that exact scenario as a plot point...but I know deep down that it is... :( 

2 minutes ago, Gargamel said:

 

 

 

That's the point I always have trouble making 'lay people' understand. 

It's actually really good to get them to understand it, though. Kudos to you for explaining it to people! (Also I am going to help out at a star party soon and now I might bring this up for the kids... :D)

3 minutes ago, HebaruSan said:

Solar eclipses would be very different. I assume there would be some kind of lensing effect, but I don't know how to calculate it.

There certainly would, but the whole deal would only be very noticeable for a few meters around the black hole, so you wouldn't even notice it from Earth.

4 minutes ago, Gargamel said:

Those are the assumptions I'm working under...

Good, then we're on the same page. It might be helpful to enumerate those in the OP.

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20 minutes ago, cubinator said:

2. The black hole is kept stable by the wizardry of hypothetical scenarios and doesn't evaporate immediately as Stephen Hawking would expect it to

Here's somebody's black hole calculator:  http://xaonon.dyndns.org/hawking/

https://www.google.com/search?q=mass+of+the+moon => 7.34767309 × 1022 kilograms

Plugging in that value gives a lifetime of 1.056830 × 1045 years. So, not quite "immediately" (assuming the calculator isn't buggy). ;)

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1 minute ago, cubinator said:

I really hope that isn't a screencap from an actual movie with that exact scenario as a plot point...but I know deep down that it is... :(

Close enough. It's from The Core, where the Earth's core stops spinning (!) and because of that the magnetic field starts to (!) falter and because of that solar radiation is coming in through holes in the Van Allen belts (!). To fix this, they build a underground submarine (which is not a correct term but there is no term because the craft cannot exist) to carry several nuclear bombs into the core to detonate them and nuclear bombs fix everything and I can actually feel myself getting dumber explaining it.

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21 minutes ago, 5thHorseman said:

Close enough. It's from The Core, where the Earth's core stops spinning (!) and because of that the magnetic field starts to (!) falter and because of that solar radiation is coming in through holes in the Van Allen belts (!). To fix this, they build a underground submarine (which is not a correct term but there is no term because the craft cannot exist) to carry several nuclear bombs into the core to detonate them and nuclear bombs fix everything and I can actually feel myself getting dumber explaining it.

Yeah, but those bad movies are so much fun to watch...

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Not Much, I'd say.

Tidal forces remains the same, precession etc. remains the same.

The only one I could imagine changing slightly is the tidal braking and the one that changes massively is there'd never be eclipses again. Also people used to lunar calendar will have... problems. (or they'd resort to radio observation or smh.)

Spoiler
56 minutes ago, 5thHorseman said:

solar radiation is coming in through holes in the Van Allen belts

Maybe they stopped singing.

 

Edited by YNM
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No expert here, but…. To anything turn into a black hole, it must be compressed into its Schwarzschild radius

Since the moon weighs about 7.35 x 1022 kg, so  if by some espetacular compression force it turns into a black hole, it's size would be… 0.00010916095764576308 meters.
 

Python 3.6.5 (default, Mar 29 2018, 15:38:43)
[GCC 4.2.1 Compatible Apple LLVM 8.1.0 (clang-802.0.42)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> M = 7.35 * 10**22
>>> G = 6.67408 * 10**-11
>>> c = 299792458
>>> rs = (2*G*M)/(c**2)
>>> print (rs)
0.00010916095764576308
>>>

So, yeah. It would vanish from the skies.

But besides being "black" and sizing less than a millimetre, nothing else would change. The thing would still has mass, the same mass. So the gravitational forces would still be there.

I don't think that any radiation would be emitted at all. It's plain impossible to the Moon to turn into a Black Hole without external mechanical help - the Moon's density is incommensurably smaller than the needed, the known process of a Star becoming a Black Hole doesn't apply.

The mechanical power used to compress the Moon, on the other side, could inflict some colateral effects on us. Since the 3rd Newton's Law would still apply, such energy would irradiate towards us. I don't know how to measure and don't have the slightest clue about how to research the needed data for this. But I think it's reasonable to assume the at least the part of Earth facing the event would be scorched.

Edited by Lisias
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1 hour ago, HebaruSan said:

Solar eclipses would be very different. I assume there would be some kind of lensing effect, but I don't know how to calculate it.

The optical cross-section of such a small black hole would be tiny. Nothing we'd be able to spot from Earth, even through a telescope, and even if we knew were to look. You'd have to send probes, which would have to get pretty darn close to the singularity, before you could actually image it.

1 hour ago, Bill Phil said:

And of course the Hawking radiation... though I'm not sure how much would be released.

Almost shocking little. See my signature. Moon is a bit heavier than Rhea, so the output will have effective temperature of a brown dwarf star coming from an absolutely tiny object. It would be entirely undetectable. If it forms a tiny little accretion disk, you'd be able to pick it up on IR cameras of a space probe orbiting nearby.

 

All in all, Moon-mass black hole will be almost entirely undetectable, except for its gravity. It's fun to picture what a civilization living on a world orbiting or being orbited by a tiny little black hole would think of it. There would be absolutely no indication of any object, but rocks flying through that region of space would curve as if there was a moon/planet there. How long would it take astronomers to guess that there is a super-dense massive object there?

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45 minutes ago, Lisias said:

it's size would be… 0.00010916095764576308 meters.

About the size of a gnat's head, for perspective. A gnat's head orbiting Earth with the moon's mass at the moon's SMA. But in reality, it wouldn't actually *be* that size. The gnat's head would be just the event horizon. The actual moon would continue to compress beyond that point into a singularity; beyond our ability to image, even with an electron microscope.

 Best,
-Slashy

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This would make Earth much more astronomer-friendly.
No Moon, but a pretty accuratel point in the sky, useful when passing/crossing different stars and planets.

Probably, a weak source of X-rays and high energy particles which pass close to its surface. But unlikely significant for anything but astronomic observations.

A useful catapult for interplanetary crafts, which can now perform Oberth maneuver close to it.

Of course, a natural relativistic laboratory. Physics would go much faster.

A pack of crafts would be orbiting it. If not a whole micro-dyson-sphere.

A bottomless sink for any orbital wastes.
Just gather your old sats, attach an old nuke engine and send this to the hole.

Unsure what about mentally challenged persons. Is their fullmoonophilia caused by light or by tide.
Probably by light, so they would be more calm. (Or redistribute their feats more uniformly).

Probably, long-range birds and some insects would fail the navigation. So, some ecosystems would change.

Wolves get absolutely unhappy.

As well as lovers.

Let alone druids. This would be a real tragedy.

Muslim and probably Hebrew chronology would be in trouble, as afaik they require observed (not calculated) Moon to record a new month beginning.
So, they would do something with this.

LOP-G (former DSG) would sink in a waterfall of money.

While LHC would go bankrupt.

We would never check if there are alien structures on the Moon, and if Apollos have really landed, lol.

Attilan would fall with all its citizens.

Edited by kerbiloid
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10 minutes ago, kerbiloid said:

Muslim and probably Hebrew chronology would be in trouble, as afaik they require observed (not calculated) Moon to record a new month beginning.

Not just them, but if we're talking about an alternate evolution, I wonder what impact this would have on everyone's perception of time. If the rising and falling of the sun was the minute hand, then surely the moon was the hour hand.

And how much longer would it have taken to conceive the idea of a heliocentric system comprised of orbiting spheres?

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Hmm. Energy released as Hawking radiation would be tiny. But an obiect falling into event horizon (even that minuscule) should still release significant amount of energy. If we could feed the Moonhole trash and harness this energy bursts, we would have a handy power plant in the Earth's orbit :)

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3 hours ago, Reactordrone said:

Think of the gravity assists you could get from it.

I don't think there'd be much advantage there, since you leave with the same relative velocity you came with. 

Gravity assists harness the body's orbital velocity, which wouldn't change.

Best,

-Slashy

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