Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

What if Planet 9 is a Primordial Black Hole?

link.aps.org

Post reply on HN
Print view View original

71–80 of 127 posts

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

#71

Post by sidcool »

317070 wrote: post #53
sidcool wrote: post #51

Since it's a black hole, it's gravitational effect would be at least as much as the Sun. Is there evidence to support this tug of war?

Black holes do not have more gravity per mass than any other object. Put the other way, if the sun would suddenly change into a black hole without losing a lot of mass, the earth would still follow the exact same orbit.

That's true. My point was that if there were a solar mass object beyond Pluto, it would have significant effect on orbits of all planets. But apparently PBHs can be lighter

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

#72

Post by infogulch »

bouncycastle wrote: post #69
manigandham wrote: post #60

Earlier quoted context omitted.

Not sure if you meant it that way but information actually can't be created or destroyed in quantum mechanics. This is known as the no-hiding theorem [1] which has been experimentally proven and which leads to the black hole information paradox. [2] 1. https://en.wikipedia.org/wiki/No-hiding_theorem 2. ttps://en.wikipedia.org/wiki/Black_hole_information_paradox

So, is it kind of like a cryptographic hash function?

Somewhat. Like a hash function, it projects some large state space (the hash input/you) onto a different state space (hash digest/2d-surface of a BH). But a hash digest actually has lost information, i.e. it's guaranteed by pigeonhole principle that some two inputs have the same digest, which means you lose the information about which one it was. Whereas a black hole scrambles you, but none of the "bits" are actually erased, just smeared out and projected onto the surface.

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

#74

Post by sidcool »

p1mrx wrote: post #54
sidcool wrote: post #51

Since it's a black hole, it's gravitational effect would be at least as much as the Sun. Is there evidence to support this tug of war?

This paper postulates a black hole with 5-15 times Earth's mass, which is considerably less than the sun.

I see. That's lighter that Jupiter. Do PBHs have singularity like regular black holes?

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

#76

Post by holler »

p1mrx wrote: post #54
sidcool wrote: post #51

Since it's a black hole, it's gravitational effect would be at least as much as the Sun. Is there evidence to support this tug of war?

This paper postulates a black hole with 5-15 times Earth's mass, which is considerably less than the sun.

incredibly hard to conceive 15 Earths shrunk down to the size of a grapefruit! fascinating

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

#77

Post by lovehashbrowns »

onlyrealcuzzo wrote: post #23
Konohamaru wrote: post #7

Earlier quoted context omitted.

This is not scary. Yes the event horizon will expand the more matter falls into its gravity well, but otherwise a black hole acts like a normal planet orbiting the Sun.

Is there a theoretical limit on the minimum mass of a black hole? It's counter-intuitive to me that something could get dense enough to form a black hole and not have more mass than the Sun, or at least enough mass to steal Pluto.

Schwarzschild radius and the Compton wavelength both combine to say that in theory, the minimum mass required for a quantum black hole is the Planck mass(ish). They might not be possible or they might require more energy than what we can produce today.

https://link.springer.com/article/10.1140/epjc/s10052-017-54...

This article looks interesting and will probably go into more detail if you are wanting to know more. I will read it tomorrow. Great question!

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

#78

Post by Sharlin »

geoffmunn wrote: post #73

I've been wondering - if the black hole was very small (I've read elsewhere that it would be grapefruit sized), would it be possible to build some kind of box around it so you couldn't accidentally go into the event horizon?

There's no material that you could make the box or shell out of that could withstand the gravitational forces near the black hole. Even the gravity differential (tidal forces) is strong enough to rip anything apart (the so-called spaghettification). And if you made the shell large enough (planet-diameter), it would collapse into a spherical body just from its self-gravity, never mind the additional gravity of the PBH.

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

#79

Post by lmilcin »

If this was true, this would be extremely fortunate for our civilization if we can figure out not to kill ourselves in next couple hundred years.

Black holes offer about the most effective process to extract energy from matter, orders of magnitude more efficient than fusion and it is not picky about what kind of matter you put in.

You can put a Dyson sphere/swarm around small black hole and extract something on the order of up to 40% of mass-energy equivalent of the falling matter. With BH of the mass of Earth the sphere would be pretty small and easy to make.

Post reply on HN