What if Planet 9 is a Primordial Black Hole? • Hacker News Board

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

#41

Post by gizmo686 » Thu, Jul 30, 2020, 5:13 AM UTC

Robotbeat wrote: post #25

onlyrealcuzzo wrote: post #23

Earlier quoted context omitted.

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.

Yeah, the event horizon the size of a Planck unit. Again, unless you get super close, it acts identical to a regular planet of the same mass.

Do we actually have a theory that predicts a theoretical minimum size of a Planck length?

Black holes are an artifact of gravity and the theory of relativity. The planck unit comes up as a result of quantum mechanics. Without a working theory of quantum gravity, we do not have a description of what happens in scenerios where both theories are relevent.

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

#42

Post by mhh__ » Thu, Jul 30, 2020, 5:14 AM UTC

wlesieutre wrote: post #5

127 wrote: post #4

Earlier quoted context omitted.

Cool, and absolutely terrifying.

On the flip side, you wouldn't be any less dead if you fell into Jupiter and that's a lot easier to get to

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.

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

#43

Post by scarmig » Thu, Jul 30, 2020, 5:19 AM UTC

hadlock wrote: post #32

onlyrealcuzzo wrote: post #23

Earlier quoted context omitted.

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.

Ted Kazinski was concerned that high energy particle physics would create a blackhole large enough to become self sustaining. If I remember correctly, high energy physics creates tiny black holes during particle collisions, but they "evaporate" faster than they can absorb mass. So to answer your question with my limited understanding, yes, there's a lower limit to stable black holes. Beyond the critical mass, they si…

> Beyond the critical mass, they simply evaporate in a matter of seconds.

For a sense of scale, a black hole with a mass of 2.2 * 10^5 kg will evaporate in roughly 1 second. A 1 kg black hole would evaporate in roughly 100 attoseconds.

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

#44

Post by dreamcompiler » Thu, Jul 30, 2020, 5:20 AM UTC

127 wrote: post #4

wrnr wrote: post #3

A person should be allowed to dream sometimes, how freaking cool would this be. A block hole right in our neighbourhood, even closer than Alpha Centauri. Just imagine what kind of things can be learned from studying it.

Cool, and absolutely terrifying.

Much less terrifying than a 5-Earth-mass planet. Such a planet would be quite easy for a spacecraft to crash into. But if all that mass is the size of a tennis ball, it would be very easy to miss. Unless your aim was perfect you'd just slingshot around it.

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

#45

Post by wrnr » Thu, Jul 30, 2020, 5:24 AM UTC

themodelplumber wrote: post #17

ISL wrote: post #14

One should not miss Figure 1 of the arXiv preprint, which is, alas, absent from the final PRL. https://arxiv.org/pdf/1909.11090.pdf It is among the rarest journal-article figures in physics. If I'd been asked to referee the paper, I'd have campaigned hard to keep it in.

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

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

#46

Post by aaomidi » Thu, Jul 30, 2020, 5:24 AM UTC

mhh__ wrote: post #42

wlesieutre wrote: post #5

Earlier quoted context omitted.

On the flip side, you wouldn't be any less dead if you fell into Jupiter and that's a lot easier to get to

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.

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

#47

Post by FreeFull » Thu, Jul 30, 2020, 5:25 AM UTC

mhh__ wrote: post #42

wlesieutre wrote: post #5

Earlier quoted context omitted.

On the flip side, you wouldn't be any less dead if you fell into Jupiter and that's a lot easier to get to

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.

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

#48

Post by ejolto » Thu, Jul 30, 2020, 5:51 AM UTC

ThatCaio wrote: post #31

onlyrealcuzzo wrote: post #23

Earlier quoted context omitted.

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.

Yes, Tolman–Oppenheimer–Volkoff limit would estimate a star around 1.5-2.5 sun masses could result in a stellar black hole. We don't know much about stars collapsing, and the mass wasted in the process to have a more accurate number at this point.

That's only true for black holes created from the collapse of stars. Primordial black holes would have been created in the early universe and be much much smaller.

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

#49

Post by QuesnayJr » Thu, Jul 30, 2020, 5:52 AM UTC

NamTaf wrote: post #33

ISL wrote: post #14

One should not miss Figure 1 of the arXiv preprint, which is, alas, absent from the final PRL. https://arxiv.org/pdf/1909.11090.pdf It is among the rarest journal-article figures in physics. If I'd been asked to referee the paper, I'd have campaigned hard to keep it in.

I love it. I found it actually useful to get a physical scale understanding of the size of one.

It was the very first thing I wondered when I read the title.

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

#50

Post by QuesnayJr » Thu, Jul 30, 2020, 5:59 AM UTC

gizmo686 wrote: post #41

Robotbeat wrote: post #25

Earlier quoted context omitted.

Yeah, the event horizon the size of a Planck unit. Again, unless you get super close, it acts identical to a regular planet of the same mass.

Do we actually have a theory that predicts a theoretical minimum size of a Planck length? Black holes are an artifact of gravity and the theory of relativity. The planck unit comes up as a result of quantum mechanics. Without a working theory of quantum gravity, we do not have a description of what happens in scenerios where both theories are relevent.

There's an approximation that's expected to hold, semiclassical gravity, where both theories are relevant. This is the background against which calculations of Hawking radiation and black hole evaporation are made.