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What if Planet 9 is a Primordial Black Hole?

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Re: What if Planet 9 is a Primordial Black Hole?

#111

Post by koheripbal »

FreeFull wrote: post #47
mhh__ wrote: post #42

Earlier quoted context omitted.

Crossing into the event horizon of a black hole has a very profound poetry to it in that you will never be able to communicate back your findings. I find the romance of the destruction of knowledge very intriguing - falling into a black hole is similar to shooting a mathematician in the head in that regard. Great way to go, all things considered.

Except that with a black hole this small, you'll be pulled apart by the tidal forces long before you even reach the event horizon. If you want to make it across the event horizon intact, you need a much larger black hole, like the one in the centre of our galaxy.

Which conversely means that supermassive black holes allow you to pass through the event horizon unharmed.

Re: What if Planet 9 is a Primordial Black Hole?

#112

Post by lmilcin »

Recurecur wrote: post #105
Recurecur wrote: post #100

Earlier quoted context omitted.

It's not that, it's the difference in the gravity field between two points. On Earth, the gravity field is very close to uniform. Near a small black hole, the field changes rapidly and is very strong. It's a "pull" effect, meaning that if you were oriented with your feet towards the object as described by the GP, and 2m tall, your feet would experience 1.6 G more "gravity" than your head. It's a tidal force, literall…

So, I just calculated the orbital speed at 50 km. It came out to 282,378 km/s. The speed of light is 299,792.5 km/s, so we're way into relativistic territory. Good luck having enough energy to build a structure around it! ha

Black hole with radius of 50km (escape velocity of speed of light at radius X is definition of Schwarzshild radius for nonrotating black hole) would have mass of 17 suns.

We are talking about small primordial black holes, in the vicinity of 10-50 times mass of Earth.

At 10 Earths, the radius is 8cm (!!!) and at 50 Earths it is still measly 44cm.

Re: What if Planet 9 is a Primordial Black Hole?

#113

Post by lmilcin »

Recurecur wrote: post #100
pas wrote: post #93

Earlier quoted context omitted.

What does that do? I mean you can walk in 1G just fine, so probably we could go there, take a walk/sit there in 1.6G, and leave, right? That means that if we put a 100km wide structure around it, we can service it easily(?) even without robots.

It's not that, it's the difference in the gravity field between two points. On Earth, the gravity field is very close to uniform. Near a small black hole, the field changes rapidly and is very strong. It's a "pull" effect, meaning that if you were oriented with your feet towards the object as described by the GP, and 2m tall, your feet would experience 1.6 G more "gravity" than your head. It's a tidal force, literall…

The point of using primordial black hole is that it can be very small (in the range of centimiters for its Schwarzshild radius). You can then calculate safe distance from the black hole where the gravitation and gradient generates acceptable forces for your structure. This is of course much more than the centimiters given but still very small compared to astronomical distances you would need to encircle entire Sun.

Another point of using black hole is that you decide its output (by deciding how much matter falls in) which greatly helps building dyson sphere. You can't modify Sun output.

Re: What if Planet 9 is a Primordial Black Hole?

#114

Post by LoSboccacc »

PhantomGremlin wrote: post #39
127 wrote: post #4

Earlier quoted context omitted.

Cool, and absolutely terrifying.

Cool, and absolutely terrifying. Sibling comments are questioning this. But ... what if the black hole's orbit around the sun isn't something approximately circular? What if the orbit resembles a long-period comet? Highly elliptical? What if it puts in an appearance near the sun every 100,000 years? How would we know? What in the historical record could we study?

somehow it never occurred to me that black hole could actually orbit what does it mean for the event horizon to move one side is fairly predictable as space gets swallowed as the black hole advances but the space at the rear side would just sort of pop out of the event horizon or be stretched from the previous position

what would happen to the space behind a black hole moving at relativistic speed?

Bet there some paper I cannot understand about it somewhere

Re: What if Planet 9 is a Primordial Black Hole?

#115

Post by DarmokJalad1701 »

wrnr wrote: post #45
themodelplumber wrote: post #17

Earlier quoted context omitted.

Fascinating. And kind of funny. I wonder, are there any YouTubers who walk through the math in papers like this? Asking because it seems really interesting and sometimes it's fun to learn bits here and there from applied math rather than always working up from the fundamentals.

The channel I find most accessible for laymen, that goes into the maths, is DrAPhysics[1]. It's done by some random English radio jockey with a background in Physics. Nothing on the cutting edge, but I like his simple presentation of manipulating symbols on paper by hand. If you want visuals there is this[2]. [1] https://www.youtube.com/watch?v=foRPKAKZWx8 [2] https://www.youtube.com/watch?v=UfThVvBWZxM

This kind of makes me want to do Youtube videos about stuff that I know. Procrastination is a b*tch though ...

Re: What if Planet 9 is a Primordial Black Hole?

#116

Post by jborichevskiy »

xingyzt wrote: post #91
geoffmunn wrote: post #81

Earlier quoted context omitted.

But given that it's so small, what would the gravitational forces be if you made a shell with a 100km radius? Or pick a number - surely at some point it might be practical to build something.

Size of the object doesn’t matter. Gravitational force depends on its mass and how far away you are from the black hole. Standing on a shell ~6300 km above a black hole with the mass of the Earth is equivalent to standing on the Earth itself.

I have a hard time really accepting this concept given how unintuitive it is to me but I found your comment helpful in that regard.

Re: What if Planet 9 is a Primordial Black Hole?

#117

Post by [deleted] »

wcoenen wrote: post #95
pas wrote: post #93

Earlier quoted context omitted.

What does that do? I mean you can walk in 1G just fine, so probably we could go there, take a walk/sit there in 1.6G, and leave, right? That means that if we put a 100km wide structure around it, we can service it easily(?) even without robots.

You can't "walk" in this 1.6G. You'd experience it while floating freely in space. And the stress on your body would be tension instead of compression. I guess it would feel like hanging upside down, except that your blood rushes to both your feet and your head.

[deleted]

Re: What if Planet 9 is a Primordial Black Hole?

#118

Post by mhh__ »

aaomidi wrote: post #46
mhh__ wrote: post #42

Earlier quoted context omitted.

Crossing into the event horizon of a black hole has a very profound poetry to it in that you will never be able to communicate back your findings. I find the romance of the destruction of knowledge very intriguing - falling into a black hole is similar to shooting a mathematician in the head in that regard. Great way to go, all things considered.

Yes you'd be dead.

I am prepared to put down MTW and dream

Re: What if Planet 9 is a Primordial Black Hole?

#119

Post by meowface »

me_me_me wrote: post #99
canjobear wrote: post #40

Earlier quoted context omitted.

PBS SpaceTime

Half of their stuff goes over my head. And I have to watch videos multiple times, but very interesting channel indeed.

I'm absolutely abysmal at even basic math (arithmetic, algebra), let alone anything involved in theoretical physics, but I've never had any issue understanding that channel because as far as I can remember, they don't actually bring up any equations or other math. Maybe there are some math-y episodes I haven't seen, dunno, but I was under the impression it was targeted at laymen and designed to be as accessible as possible, like many PBS things. I've learned a ton from it and have never felt they went too advanced for regular people.

Now, minutephysics or 3blue1brown? Love their videos, but most of them go way over my head. I find PBS Space Time exponentially easier to follow than minutephysics. Just saying this in case anyone anyone were to otherwise be discouraged from checking it out.

Re: What if Planet 9 is a Primordial Black Hole?

#120

Post by yencabulator »

markonen wrote: post #82
jl6 wrote: post #67

Earlier quoted context omitted.

Was it removed because “exact scale” only makes sense if the article is printed on a specific paper size, which isn’t specified?

Objects in a PDF are specified in points, which is a physical measure (1/72 of an inch, or 0.3528 mm).

And printer drivers often have a "fit on page" feature enabled.

... not that A4 vs US letter would be a huge percentual difference, for this image.

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