Black Holes, what we thought 40 years ago

[mielgato]

Greeting Kerbals

Reading stuff about space is kinda a passion for me, be it actual science discoveries, or sci-fi.

A little while ago, I was tidying my house, and stumbled upon a 38 year old book, called "GREAT MYSTERIES: Mysteries of the Universe" By Stemman, Roy, Published by Aldus Books in 1978.

Mind you, the book is 12 years older than me (it was a gift from my grand-ma) and while I strongly suspect it to be mostly "popular science" with some sci-fi toward the end, rather than actual science publication, it is still a great read.

 

In this book, they relate theories about black holes, and one in particular caught my attention, be ready : "Scientist could possibly create tiny black holes within a terrestrial laboratory. However, If they happens to succeed, the result would be catastrophic; According to the British professor, John Taylor : "A black hole with a mass of 1600tonnes, if left alone, would quickly sink toward the center of our planet, eating it rather swiftly, and us with it. And for good measure, Taylor added :" Even if there is a single black hole in our galaxy, then our futur is really dark, as it'll end up devouring us all."  (Please excuse me if it's not the exact same text, as mine is translated in french, so I had to re-translate in english for the forum )

(We of course know this is partly wrong, as we had unknowingly a supermassive black hole in the center of our galaxy for billions of years, and by today's knowledge, it IS a fact, probably he meant on the long run, but we also do know that our sun will die out waaay before the milky way's black hole swallow us, sooo not really a problem, we also know that there is millions of smaller black holes everywhere in the galaxy, remnant of collapsed giant stars if I'm not wrong)

They also suggest that if a spaceship could go through the Schwarzschild radius of a Black Hole without being reduced to space dust from the tidal forces, the spaceship would end up in a different universe. If the spaceship went through the same black hole he came from, it would end up in yet another universe, and another, and another, without being able to ever come back to it's origin.

 

Keep in mind the following : "Our readers will understand that 'Black Holes' are purely the result of mathematical speculation, and is not based on any sort of evidence." which was probably true when the book was published.

Given today's standard and knowledge about these mythical beasts, do you think a black hole weighting less than a Frigate class warship, could survive hawking radiation and eat through the earth ? (hmm, let me rephrase : What if a proton suddenly weighted 1600tonnes, would it become a self sustainable black hole ?)

How about black holes being wormholes toward another universe ?

(no this isn't another OMAGAD LHC IS GONNA DOOM US ALLL!!!1111)

Edited August 1, 2016 by mielgato
typo

[UmbralRaptor]

It sounds rather pop-sci ish. For something that's mostly fun SF but with crunchier science sections, I suggest Black Holes edited by Jerry Pournelle. (Amusingly also published in 1978, with some articles/stories previously published earlier in the 60s/70s). It points to a lot of the theory being in place, though no real simulations, especially related to accretion disks and suggestive but not confirming observations. I'm not sufficiently familiar with the history of radio and x-ray astronomy to judge in more detail.

Scharzchild radius is not a barrier (well, not for entering), and not what destroys incoming objects. Those would be tidal forces, which are mitigated enough with supermassive black holes that objects would not be torn apart until after they had passed the event horizon.

The wormhole solutions are probably mathematically correct, but not accurate descriptions of what actually exist in our universe.

 

I'm not sure with a black hole of that mass, but taking a shot at it:

1600 tons (or more likely given that the source is French tonnes) is a silly amount of energy for a particle accelerator. The newly upgraded LHC hits all of 13 TeV (~2.3e-26 kg). Even the Oh My God Particle (the highest energy cosmic ray ever recorded) was under 50 J (5.6e-16 kg). Going with 1.6e3 kg, I get a lifetime of ~0.41 seconds, and an initial radius of ~1.2e-21 m. Since my GR knowledge is lacking, I'm going to assume a newtonian free-fall and hope it isn't too many orders of magnitude off. The aforementioned mass and time give a distance scale of 2.4e-3 m. That's not a lot of material (a sphere of uranium or tungsten at that radius is ~1 gram), so ¯\_(ツ)_/¯

[Green Baron]

I thought that our understanding of black holes is mainly based on the work of the 70s (Hawking and others).

Yeah, these things were and are hefty speculated about in the public since sci-fi-authors and movies used them as a "means of transportion". That smell of mystery and doom still lingers above the Schwarzschild sphere .... :-)

That wormhole-thing maybe a valid solution of the formulas of general relativity and they surely have their place in sci-fi, but, well, i haven't yet encountered a serious publication on that subject ....

 

[mielgato]

1 hour ago, UmbralRaptor said:

It sounds rather pop-sci ish. For something that's mostly fun SF but with crunchier science sections, I suggest Black Holes edited by Jerry Pournelle. (Amusingly also published in 1978, with some articles/stories previously published earlier in the 60s/70s). It points to a lot of the theory being in place, though no real simulations, especially related to accretion disks and suggestive but not confirming observations. I'm not sufficiently familiar with the history of radio and x-ray astronomy to judge in more detail.

Scharzchild radius is not a barrier (well, not for entering), and not what destroys incoming objects. Those would be tidal forces, which are mitigated enough with supermassive black holes that objects would not be torn apart until after they had passed the event horizon.

1600 tons (or more likely given that the source is French tonnes) is a silly amount of energy for a particle accelerator.

I will do that, if I happens to find it online

Correct me if i'm wrong, but isn't the schwarzschild radius also called the event horizon ? (i've miss-used the term barrier, it's something i've saw in the book as "Barrière de Schwarzschild, aussi appelée Horizon des évènements" and it landed here, my bad)

Of course it's not what's tearing apart the ship, it was an attempt at translating what was written and I might have been confused, sorry 'bout that !

Yes it's indeed metric tonnes I was talking about, I was unaware that tons and tonnes were different. stupid meh!

About the 1600 tonnes thing, it was more a question about, at which point a black hole can become self-sustainable, what mass does it need to survive hawking radiation long enough so it can "swallow" enough material to grow ? (well that's not technically correct but I can't find a better word)

Still very interesting calculus, but I can't be judge on this, if your GR knowledge is lacking, mine is close to jeb-existent !!

 

Edited August 1, 2016 by mielgato

[YNM]

This is probably a bad approach, but looking at the titles of his other works... Sounds questionable. Still, even Trump bables could be good jokes to read

3 hours ago, UmbralRaptor said:

I'm not sure with a black hole of that mass, but taking a shot at it:

1600 tons (or more likely given that the source is French tonnes) is a silly amount of energy for a particle accelerator. The newly upgraded LHC hits all of 13 TeV (~2.3e-26 kg). Even the Oh My God Particle (the highest energy cosmic ray ever recorded) was under 50 J (5.6e-16 kg). Going with 1.6e3 kg, I get a lifetime of ~0.41 seconds, and an initial radius of ~1.2e-21 m. Since my GR knowledge is lacking, I'm going to assume a newtonian free-fall and hope it isn't too many orders of magnitude off. The aforementioned mass and time give a distance scale of 2.4e-3 m. That's not a lot of material (a sphere of uranium or tungsten at that radius is ~1 gram), so ¯\_(ツ)_/¯

If you have a sphere of water large enough, you can make a black hole. Black hole density kinda goes inverted with its mass.

Edited August 1, 2016 by YNM

[magnemoe]

2 hours ago, mielgato said:

I will do that, if I happens to find it online

Correct me if i'm wrong, but isn't the schwarzschild radius also called the event horizon ? (i've miss-used the term barrier, it's something i've saw in the book as "Barrière de Schwarzschild, aussi appelée Horizon des évènements" and it landed here, my bad)

Of course it's not what's tearing apart the ship, it was an attempt at translating what was written and I might have been confused, sorry 'bout that !

Yes it's indeed metric tonnes I was talking about, I was unaware that tons and tonnes were different. stupid meh!

About the 1600 tonnes thing, it was more a question about, at which point a black hole can become self-sustainable, what mass does it need to survive hawking radiation long enough so it can "swallow" enough material to grow ? (well that's not technically correct but I can't find a better word)

Still very interesting calculus, but I can't be judge on this, if your GR knowledge is lacking, mine is close to jeb-existent !!

 

The event horizon is at the schwarzschild radius and is the point there the escape velocity is higher c so not even light can escape. 
Tides is that destroy you then you get to close, this can happen close to an neutron star too however you can get closer to an black hole and get higher gravity gradient, on the other hand if the black hole is heavy enough the schwarzschild radius get so large you would not get crunching tides before you pass it. 
 

[Green Baron]

17 minutes ago, magnemoe said:

The event horizon is at the schwarzschild radius and is the point there the escape velocity is higher c so not even light can escape. 
Tides is that destroy you then you get to close, this can happen close to an neutron star too however you can get closer to an black hole and get higher gravity gradient, on the other hand if the black hole is heavy enough the schwarzschild radius get so large you would not get crunching tides before you pass it. 
 

Yes, the escape velocity at the Schwarzschild radius is the speed of light (can it be greater ? *doubtful look*). The Roche-limit (Mars moon Phoebus e.g.) is the limit under which a body gets torn apart by tidal forces. Different things.

 

[p1t1o]

48 minutes ago, Green Baron said:

 (can it be greater ? *doubtful look*).

Whilst it may or may not make sense mathematically/physically to say that the escape velocity beneath the event horizon is "greater than c", things that are moving at the speed of light (ie:photons) still cannot escape, so it does make a sort of sense.

[K^2]

40 years ago, paper on Hawking Radiation was just recently published. Concept of black hole evaporation was not known to many people. Today we know that any black hole we can artificially create in a lab will be losing mass faster than it can accumulate it, therefore, presenting absolutely no danger.

Concept of black holes as wormholes to other worlds, likewise, followed from particular mathematical solutions for rotating black holes that have since been proven to be unstable, and therefore, not representing real black holes.

So yeah, our understanding of black holes has changed quite a bit.

[WestAir]

Half expected one of the physicists here to jump in and say "any singularity with a mass greater than x, if created on Earth's surface, will overcome hawking radiation and snowball until it consumes us."

I've been left disappointed.

[mielgato]

11 hours ago, YNM said:

This is probably a bad approach, but looking at the titles of his other works... Sounds questionable. Still, even Trump bables could be good jokes to read

If you have a sphere of water large enough, you can make a black hole. Black hole density kinda goes inverted with its mass.

Ah ! a glimpse of what I was expecting

Well, bear in mind his work is mostly pop-science / sci-fi mixed together, I am not taking it all seriously, but it raised some questions I felt like asking to the community here, as it's the best forum I know for this kind of stuff !

I just kame back from work, and did a quick wikipedia search, here what I found (i'll leave links to sources) :

In 1974, Hawking predicted that black holes are not entirely black but emit small amounts of thermal radiation;^[39] this effect has become known as Hawking radiation. By applying quantum field theory to a static black hole background, he determined that a black hole should emit particles that display a perfect black body spectrum. Since Hawking's publication, many others have verified the result through various approaches.^[96] If Hawking's theory of black hole radiation is correct, then black holes are expected to shrink and evaporate over time as they lose mass by the emission of photons and other particles.^[39] The temperature of this thermal spectrum (Hawking temperature) is proportional to the surface gravity of the black hole, which, for a Schwarzschild black hole, is inversely proportional to the mass. Hence, large black holes emit less radiation than small black holes.^[97]

A stellar black hole of 1 M_☉ has a Hawking temperature of about 100 nanokelvins. This is far less than the 2.7 K temperature of the cosmic microwave background radiation. Stellar-mass or larger black holes receive more mass from the cosmic microwave background than they emit through Hawking radiation and thus will grow instead of shrink.^{[citation needed]} To have a Hawking temperature larger than 2.7 K (and be able to evaporate), a black hole would need a mass less than the Moon. Such a black hole would have a diameter of less than a tenth of a millimeter.^[98]

If a black hole is very small, the radiation effects are expected to become very strong. Even a black hole that is heavy compared to a human would evaporate in an instant. A black hole with the mass of a car would have a diameter of about 10⁻²⁴ m and take a nanosecond to evaporate, during which time it would briefly have a luminosity of more than 200 times that of the Sun. Lower-mass black holes are expected to evaporate even faster; for example, a black hole of mass 1 TeV/c² would take less than 10⁻⁸⁸ seconds to evaporate completely. For such a small black hole, quantum gravitation effects are expected to play an important role and could hypothetically make such a small black hole stable, although current developments in quantum gravity do not indicate so.^[99][100]

 

From what I read I understand the following : For a black hole to evaporate through hawking radiation, it need to be hotter than the cosmic microwave background (2.7 Kelvin ?), and If a black hole has the mass of the moon, it'll have a diameter of (less than) 1/10mm (becuz BH are supa dense), and is expected to evaporate (in fact, it seem that Moon black hole is the biggest BH that can evaporate, anything bigger would be colder, thus getting more material than their evaporation rate. The smaller the black hole is, the faster it evaporate. (kind of been answered by multiples peeps, but it was almost chinese to me I need simplicity, I just spent a day servicing a catamaran, and where I live, temp tend to skyrocket in boats, above the 40°c, maybe my brain has melted )

 

Now i'm pondering about another question, can we, humans, make a stellar black hole hotter in the future ? Would it be useful for anything ? (right now I can't think of something)

 

ps : If i'm not wrong, D=m/v

[MeticulousMitch]

I was curious to see how much power a black hole of 1600 tons would output through Hawking radiation, and according to this site the figure is 33 gigatons per second. I immediately thought of the What If? scenario where an indestructible hair dryer of absurd (although still around 10 000 times less than the black hole) power is accelerated past escape velocity simply by the reaction force of the superheated plasma around it. But would this happen to a black hole? I get the feeling that with so much energy being emitted nearby, the black hole would be explosively ejected into space, but then again I am not sure whether basic action/reaction momentum transfer is valid at an event horizon...

[YNM]

@ OP : Density is equal to mass divided by volume, but for black holes, the biggest player is the mass - a certain mass have a certain schwarzild radius (event horizon distance from center, to say), and this affect the volume of the thing, hence it should also affect the density. If you work it out it'll be in inverse, not sure of the power.

[lugge]

On 2.8.2016 at 0:53 AM, mielgato said:

A stellar black hole of 1 M_☉ has a Hawking temperature of about 100 nanokelvins. This is far less than the 2.7 K temperature of the cosmic microwave background radiation. Stellar-mass or larger black holes receive more mass from the cosmic microwave background than they emit through Hawking radiation and thus will grow instead of shrink.^{[citation needed]} To have a Hawking temperature larger than 2.7 K (and be able to evaporate), a black hole would need a mass less than the Moon. Such a black hole would have a diameter of less than a tenth of a millimeter.^[98]

This is interesting. Can anyone confirm this assumption?

I always thought every black hole will, some day, be completely evaporated.

[WinkAllKerb'']

Spoiler

 

^^ not 40 but 20/30 vuglaris, anyway anyway a classics

[Laie]

On 8/1/2016 at 1:01 PM, Green Baron said:

escape velocity at the Schwarzschild radius is the speed of light (can it be greater ? *doubtful look*)

It makes for a useful figure of speech. Just as we can talk about negative Kelvin, or division by zero. Another way of saying just how weird and outlandish it is.

Hey. It's not called a singularity for nothing.

[WestAir]

On 08/03/2016 at 4:43 AM, lugge said:

This is interesting. Can anyone confirm this assumption?

I always thought every black hole will, some day, be completely evaporated.

Eventually. It is my understanding that the background will cool to nothing, eventually, and then so will smbh's. I could be wrong, and in which case one of our smarter members will correct me.

[kBob]

Boy I remember a lot of speculation about that time of micro-singularities eating the Earth from the inside (and this was long before the LHC worries).  I think this mostly came from some sci-fi books of the time.  Someone should have cashed in on this by selling do it yourself micro singularity kits with manuals for the care and feeding of your pet singularity sort of like the pet rock craze.  No doubt the same people afraid of that were the same ones who panicked when there was going to be a "grand alignment" of all the planets.

On ‎7‎/‎31‎/‎2016 at 9:56 PM, mielgato said:

"Our readers will understand that 'Black Holes' are purely the result of mathematical speculation, and is not based on any sort of evidence." which was probably true when the book was published.

Ummm the first black hole was discovered in 1971, so seems the author was a bit off.

From Space.com:

The first object considered to be a black hole is Cygnus X-1. Rockets carrying Geiger counters discovered eight new X-ray sources. In 1971, scientists detected radio emissions coming from Cygnus X-1, and a massive hidden companion was found and identified as a black hole.