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Fraser
2007-Jan-08, 08:17 AM
We're finally ready to deal with the topic you've all been waiting for: Schwarzschild swirlers, Chandrasekhar crushers, ol' matter manglers, sucking singularities... ...

Read the full blog entry (http://www.astronomycast.com/black-holes/episode-18-black-holes-big-and-small/)

DannyLiverpool
2007-Jan-08, 10:39 PM
ooooooo im sooo excited, been waitin 18 episodes for this

jwswitzer
2007-Jan-09, 04:08 PM
Frasier and Pamela,

Thanks for another great podcast. My wife and I really enjoy your weekly show. Keep up the good work.

Now for a question about the show. It was mentioned that smaller black holes can vaporize. The analogy was that a glass of water, if left for a time, will vaporize and the water will disappear. However, the water really just changes form from a liquid to a gas. If I understand correctly the laws of physics require the vaporized black hole to not "disappear", but to also change into something else. Just what does it change in to?

John Switzer
Centerpoint, IN

PhilM
2007-Jan-09, 06:45 PM
First let me just say that I love your podcasts and look forward to sync'ing up my IPod every Monday so that I can listen to your podcasts at work.

Now to my questions...

I'm still not clear on the whole black hole evaporation process. If you have these particle pairs that are randomly being generated where one goes into the black hole and the other isn't, how does it evaporate if it is still consuming particles?

Thank you,
Phil M.

DannyLiverpool
2007-Jan-11, 12:23 AM
sooooooo..... if a blackhole 'evaperates' does it push out all the matter is sucked in?????

also is does anyone know any links to the pictures that Pamela and Fasier mentioned???

morlankey
2007-Jan-11, 07:54 AM
So, first off, we know that energy and matter are the same thing (E=mc2). So, when a particle-antiparticle pair gets created, they take some of the energy from local space. When they collide and destroy each other, they give back the energy they took.

At the event horizon of a black hole, energy (and therefore mass) gets taken from the black hole to create a particle-antiparticle pair. One of the particles gets freed into space and, thus, the black hole doesn't get back the energy that got taken from it. This causes it to be less massive. (It gets back half the energy that it gave to create the particle-antipartcle pair in the form of the single particle that it consumes)

So, when matter gets sucked into a black hole, it gets converted into energy. When Hawking radiation occurs, the energy gets transformed into matter again and gets spat out. Make sense?

feraldoc
2007-Jan-11, 12:20 PM
Dr. Pamela suggested googling Plate ways a black hole will hurt you.

Didn't work for me. Did I spell "Plate" incorrectly? Anybody have the link she was talking about?
Thanks.

Mrs B
2007-Jan-11, 01:35 PM
So the black hole is actually eating "negative calories'? It keeps eating but gets lighter by doing so.

Mrs B
2007-Jan-11, 03:15 PM
Hi Feraldoc,
The doctor was talking about dr.Philip Plait. The slideshow she was talking about is called: Seven ways a black hole can kill you!

http://glast.sonoma.edu/presentations/blackhole_1003/index.html

Cheers

Mrs B
2007-Jan-11, 03:22 PM
Hi Feraldoc,
The doctor was talking about Philip Plait, founding father of Bad Astronomy. The slideshow she was talking about is called: Seven ways a black hole can kill you!

http://glast.sonoma.edu/presentations/blackhole_1003/index.html

Cheers

jamesabrown
2007-Jan-11, 05:11 PM
Dr. Pamela suggested googling Plate ways a black hole will hurt you.

Didn't work for me. Did I spell "Plate" incorrectly? Anybody have the link she was talking about?
Thanks.

That would be 'Plait,' as in Dr. Phil Plait, Bad Astronomer Extraordinaire. (http://www.badastronomy.com/bablog/) Here's your link:

Seven Ways Black Holes Can Kill You! (http://glast.sonoma.edu/presentations/blackhole_1003/index.html)

madjack
2007-Jan-11, 10:16 PM
In this episode Pamela described the Earth as a “people hole” I was wondering how big a lump of rock would have to be to have enough gravity to prevent Pamela jumping off it….

morlankey
2007-Jan-12, 05:51 AM
So the black hole is actually eating "negative calories'? It keeps eating but gets lighter by doing so.

Well, if you look at matter and energy as being the same thing (which they are), the black hole isn't realy eating negative calories is it? It's just spewing them out.

Himanshu Raj
2007-Jan-14, 05:52 PM
Hi Fraser! I would like to thank you and Dr. Pamela very much for the great show on “Black Holes Big and Small”. I got to learn a whole lot of new stuff from the show.

Dr. Pamela said that the rate at which materials fall into the black hole is choked by the law of conservation of angular momentum. Materials cannot fall directly straight in until they have a perfectly magical trajectory which never happens to be in the real universe.

Why do not the materials fall straight into the black hole?
Why do they have to go round the massive object before falling into it instead of going straight into it?
How does the law of the conservation of angular momentum apply?

Please explain the physics behind this.

Chas
2007-Jan-17, 07:51 AM
In this episode Pamela described the Earth as a “people hole” I was wondering how big a lump of rock would have to be to have enough gravity to prevent Pamela jumping off it….

I just ran the numbers and, assuming that she can jump up 1 foot on earth and that the asteroid is spherical with a density of 1500 kg/m^3 (making it a C-Type), it would have to have a mass greater than 1.4 x 10^14 kg to prevent her from jumping off it.

Equations look truely terrible in text format. I wrote them out as a MS Word file, but, understandably, the site won't let me attach a doc to a thread post. If anyone is interested in checking my numbers, e-mail me (chassmith1066ATyahoo.com), and I'll be happy to send it to you.

Chas
2007-Jan-18, 05:53 AM
Dr. Pamela said that the rate at which materials fall into the black hole is choked by the law of conservation of angular momentum. Materials cannot fall directly straight in until they have a perfectly magical trajectory which never happens to be in the real universe.

Why do not the materials fall straight into the black hole?
Why do they have to go round the massive object before falling into it instead of going straight into it?
How does the law of the conservation of angular momentum apply?

Please explain the physics behind this.

My $0.02.

If a black hole is spinning, then according to general relativity, space itself near the event horizon will also spin which causes any object approaching the black hole to circle it a bit first before falling in. This would be similar to a piece of styrofoam floating in the bathtub. Once you pull out the stopper, the water starts to spin as goes down the drain, which drags the piece of foam along with it. You would have to flick the foam with a precise amount of force at a precise angle in order to get it to go directly down the drain with no angular velocity. Highly unlikely.

So, do black holes spin?

Short answer, to the best of my knowledge, everything in space rotates around an axis.

-Chas

If I might recommend, Kip Thorn's book Black Holes & Time Warps (http://www.abebooks.com/servlet/SearchResults?sts=t&an=Thorne&y=0&tn=Black+Holes&x=0), is an excellent introduction to the topic.

Mrs B
2007-Jan-18, 07:24 PM
What is quarksoup?
And please let us in on some more details about the bet Hawking and Thorne made!

namcitsym
2007-Jan-19, 03:23 AM
Is there a limit as to how much matter can be consumed by a black hole or will it devour any and all comers across the event horizon? If there is a limit, how is it quantified?

Maddad
2007-Feb-07, 03:39 PM
I was disappointed with Dr. Pamela’s not mentioning several aspects about time transformation with a black hole. She never spoke a word about point of view, but it would radically change what you believe happens. Time slows for a person approaching the event horizon, and stops when he gets there, but only from the point of view of the outside observer. From the point of view of the inbound traveler, his time is completely normal. Instead of stopping, he squirts right on through. If the black hole is massive enough, he might not even be aware that he had passed the event horizon.

On the other hand, his perceives the outside observer’s time as going faster. When the traveler reaches the event horizon, he would see the outside observer experience all the time through the end of infinity.

What I had hoped to see Dr. Pamela explain was the meaning of time from the point of view of the inbound traveler inside the event horizon in explaining the outside observer. This time must be greater than infinity, which I have difficulty understanding.

Fraser
2007-Feb-07, 11:29 PM
I was disappointed with Dr. Pamela’s not mentioning several aspects about time transformation with a black hole. She never spoke a word about point of view, but it would radically change what you believe happens. Time slows for a person approaching the event horizon, and stops when he gets there, but only from the point of view of the outside observer. From the point of view of the inbound traveler, his time is completely normal. Instead of stopping, he squirts right on through. If the black hole is massive enough, he might not even be aware that he had passed the event horizon.


That's covered in our question show.

Maddad
2007-Feb-10, 03:47 PM
Where could I find the question show?

Hamlet
2007-Feb-10, 05:37 PM
Where could I find the question show?

The show is at: Episode 21: Black Hole Questions Answered (http://www.astronomycast.com/questions/episode-21black-hole-questions-answered/). The full archive of shows can be found here (http://www.astronomycast.com/archive/).

bones212
2007-Mar-03, 12:23 AM
I just found your podcast and was listening to the Black Hole questions. I hope I'm not too late to post.

My question refers to the often seen drawings of black holes looking like the swirl in a toilet bowl. It seems to me that the gravity is equal all around it and objects should be drawn from all directions?

EvilEye
2007-Mar-03, 01:28 PM
I just found your podcast and was listening to the Black Hole questions. I hope I'm not too late to post.

My question refers to the often seen drawings of black holes looking like the swirl in a toilet bowl. It seems to me that the gravity is equal all around it and objects should be drawn from all directions?


Black holes are like any other massive body. They spin. There is an equator, and poles.... sort of. Anything that gets close enough begins to follow the rest of the stuff falling in or rotating around it, much like the rings around Saturn. When they finally pass the event horizon they are no longer visible to us. So the only way to show it on a 2d piece of paper is like a toilet bowl swirl. The stuff doesn't get sucked in from every direction although it may have came that way.

Try to imagine merging into traffic. You were going north, and merge into an eastbound lane. You adjust, the eastbound traffic doesn't.

Uranu5
2007-Mar-13, 04:45 PM
So, first off, we know that energy and matter are the same thing (E=mc2). So, when a particle-antiparticle pair gets created, they take some of the energy from local space. When they collide and destroy each other, they give back the energy they took.

At the event horizon of a black hole, energy (and therefore mass) gets taken from the black hole to create a particle-antiparticle pair. One of the particles gets freed into space and, thus, the black hole doesn't get back the energy that got taken from it. This causes it to be less massive. (It gets back half the energy that it gave to create the particle-antipartcle pair in the form of the single particle that it consumes)

So, when matter gets sucked into a black hole, it gets converted into energy. When Hawking radiation occurs, the energy gets transformed into matter again and gets spat out. Make sense?
Soo thats where the jets of particles is both made from and created.....intresting (shup i cant speel :P)

Uranu5
2007-Mar-13, 04:58 PM
Black holes are like any other massive body. They spin. There is an equator, and poles.... sort of. Anything that gets close enough begins to follow the rest of the stuff falling in or rotating around it, much like the rings around Saturn. When they finally pass the event horizon they are no longer visible to us. So the only way to show it on a 2d piece of paper is like a toilet bowl swirl. The stuff doesn't get sucked in from every direction although it may have came that way.

Try to imagine merging into traffic. You were going north, and merge into an eastbound lane. You adjust, the eastbound traffic doesn't.
Think of a black hole not as a hole....but as it truely is... a massive piece of matter (like the sun....jus 200 times more massive and condenced) that has created a gravitational pull = to the speed of light.... since light cant reflect off of its surface we cant see its surface...yet as EvilEye said...its spining so as it PULLS in other matter from different points on the body of the mass creating a black hole which makes the pulled in material move towards the points that are moving across the equater.

publiusr
2007-Mar-16, 06:21 PM
Soo thats where the jets of particles is both made from and created.....intresting (shup i cant speel :P)


I look at it this way. If you throw a rock into a pond what you get back are the ripples. It can't actually leave the black hole--but it will (for lack of a better word) displace its worth in Hawking radiation.

omar
2007-Jun-25, 01:16 PM
well im so happy to have such an awesome show, thanx pamila and frasier.
my question is, how the super massive black hole is formed? and what had feeded it during it's formation????

sheeny
2007-Dec-21, 04:09 AM
Hi Fraser and Pamela!

Great show and I'm really enjoying the series!

I have a question arising from this show relating to Hawking Radiation. I'm struggling to understand how the mechanism described for Hawking Radiation results in the black hole evaporating. I feel there is something that I am missing...

What are the assumptions that underpin Hawking Radiation?

Perhaps I should describe my interpretation/understanding of what happens in Hawking radiation and someone can explain what I've got wrong?...

The premise is that a particle pair (matter / anti-matter I assume) spontaneously appear very near the event horizon. The energy to create this particle pair comes from the quantum fluctuations at the location they were created i.e. just outside the event horizon.

Now before the particle pair can get back together to annihalate each other, one crosses the event horizon, but the other doesn't.

If the particle that crosses the event horizon is always the anti-matter particle, then I see the theory as described working perfectly, but I don't see why the anti-matter particle would always be the one to cross the event horizon:confused:. If there is equal probability of either the matter or antimatter particle crossing the event horizon, then the net statistical result of Hawking Radiation is zero as far as evaporation is concerned. Hawking Radiation may still exist, but have no effect on black hole evaporation.

From the little bit of extra research I've done since listening to the show, I haven't been able to find that any evidence has been collected yet to support the theory of Hawking radiation. Perhaps if there is more out there it would be a good idea for another show? I'm also happy for anyone else to explain to me what I've got wrong in my thinking...:)

Al.

damian1727
2007-Dec-21, 01:08 PM
as i understand it it does not matter which partical goes in and which escapes....the energy for the ''free'' partical has to come from somplace and that place is the black hole ...so it slowly evaporates....

damian1727
2007-Dec-21, 01:14 PM
this guy seems to have it down pat....


There are a number of ways of describing the mechanism responsible for Hawking radiation. Here's one:
The vacuum in quantum field theory is not really empty; it's filled with "virtual pairs" of particles and antiparticles that pop in and out of existence, with lifetimes determined by the Heisenberg uncertainty principle. When such pairs forms near the event horizon of a black hole, though, they are pulled apart by the tidal forces of gravity. Sometimes one member of a pair crosses the horizon, and can no longer recombine with its partner. The partner can then escape to infinity, and since it carries off positive energy, the energy (and thus the mass) of the black hole must decrease.

There is something a bit mysterious about this explanation: it requires that the particle that falls into the black hole have negative energy. Here's one way to understand what's going on. (This argument is based roughly on section 11.4 of Schutz's book, A first course in general relativity.)

To start, since we're talking about quantum field theory, let's understand what "energy" means in this context. The basic answer is that energy is determined by Planck's relation, E=hf, where f is frequency. Of course, a classical configuration of a field typically does not have a single frequency, but it can be Fourier decomposed into modes with fixed frequencies. In quantum field theory, modes with positive frequencies correspond to particles, and those with negative frequencies correspond to antiparticles.

Now, here's the key observation: frequency depends on time, and in particular on the choice of a time coordinate. We know this from special relativity, of course -- two observers in relative motion will see different frequencies for the same source. In special relativity, though, while Lorentz transformations can change the magnitude of frequency, they can't change the sign, so observers moving relative to each other with constant velocities will at least agree on the difference between particles and antiparticles.

For accelerated motion this is no longer true, even in a flat spacetime. A state that looks like a vacuum to an unaccelerated observer will be seen by an accelerated observer as a thermal bath of particle-antiparticle pairs. This predicted effect, the Unruh effect, is unfortunately too small to see with presently achievable accelerations, though some physicists, most notably Schwinger, have speculated that it might have something to do with thermoluminescence. (Most physicists are unconvinced.)

The next ingredient in the mix is the observation that, as it is sometimes put, "space and time change roles inside a black hole horizon." That is, the timelike direction inside the horizon is the radial direction; motion "forward in time" is motion "radially inward" toward the singularity, and has nothing to do with what happens relative to the Schwarzschild time coordinate t.

The final ingredient is a description of vacuum fluctuations. One useful way to look at these is to say that when a virtual particle- antiparticle pair is created in the vacuum, the total energy remains zero, but one of the particles has positive energy while the other has negative energy. (For clarity: either the particle or the antiparticle can have negative energy; there's no preference for one over the other.) Now, negative-energy particles are classically forbidden, but as long as the virtual pair annihilates in a time less than h/E, the uncertainty principle allows such fluctuations.

Now, finally, here's a way to understand Hawking radiation. Picture a virtual pair created outside a black hole event horizon. One of the particles will have a positive energy E, the other a negative energy -E, with energy defined in terms of a time coordinate outside the horizon. As long as both particles stay outside the horizon, they have to recombine in a time less than h/E. Suppose, though, that in this time the negative-energy particle crosses the horizon. The criterion for it to continue to exist as a real particle is now that it must have positive energy relative to the timelike coordinate inside the horizon, i.e., that it must be moving radially inward. This can occur regardless of its energy relative to an external time coordinate.

So the black hole can absorb the negative-energy particle from a vacuum fluctuation without violating the uncertainty principle, leaving its positive-energy partner free to escape to infinity. The effect on the energy of the black hole, as seen from the outside (that is, relative to an external timelike coordinate) is that it decreases by an amount equal to the energy carried off to infinity by the positive-energy particle. Total energy is conserved, because it always was, thoughout the process -- the net energy of the particle-antiparticle pair was zero.

Note that this doesn't work in the other direction -- you can't have the positive-energy particle cross the horizon and leaves the negative- energy particle stranded outside, since a negative-energy particle can't continue to exist outside the horizon for a time longer than h/E. So the black hole can lose energy to vacuum fluctuations, but it can't gain energy.

damian1727
2007-Dec-21, 01:14 PM
glad thats plain :)

sheeny
2007-Dec-21, 10:30 PM
Thanks Damian. There's some more study I need to do I think before I question some of that info:whistle:. The sceptic in me is trying to poke holes in it, but that's not really fair until its understood, and there is some new stuff there I need to digest.:)

Thanks again, I'll chase up those leads and get my head around that first.

Al.

NHR+
2008-Jan-08, 10:54 AM
In the Farmersburg School Questions Show, I just heard Fraser say, that if you go fast enough you'll turn into a black hole. Is that really so? I remember reading somewhere before, that speed does NOT really increase the mass of a moving body. Momentum and kinetic energy, yes, but NOT the mass. And that the whole concept of "relativistic mass" is just confusing and not really needed.

So how about it? What say all yous experts here? :eh:

EDIT: I'm not again sure if this thread is the right place for this kind of post, but I couldn't find the Farmersburg thread, and it's kinda 'bout black holes anyways...

NHR+
2008-Jan-10, 05:01 AM
I remember reading somewhere before, that speed does NOT really increase the mass of a moving body. Momentum and kinetic energy, yes, but NOT the mass. And that the whole concept of "relativistic mass" is just confusing and not really needed.

I happened to find a couple links that say just this:

http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_fast.html
http://math.ucr.edu/home/baez/physics/Relativity/SR/mass.html

Are these just plain old ** then? :confused:

llatpog
2008-Jan-15, 07:47 PM
First, I love this podcast! I found it through I-Tunes and now am caught up in just a few days!

But the ideas behind black holes really have me thinking...so here we go:

1 - In most analogies of a black hole, people think of it as a larger vortex bringing things into it. However, that would mean that gravity is working as a vector...in one area and direction of the entire singularity. However, Gravity should be working in all 720 degrees of the singularity. This is kind of like me standing in American and gravity of earth is affecting a person in China the same way. If this is the case, then woulnd't there be a large sphere of bent light all around a black hole? Thus making it a very bright object rather then a very dim object?

2 - One of the basic laws of physics I was taught was that energy/matter can not be created or destroyed...only changed into something else. If a particle is popped into existance by a black hole...what is it created from? Also part of this...it has been described as a particle and anti-particle are created from the black hole...which causes it to evaporate. However, if gravity of a black hole is strong enough to hold light back...wouldn't the particle that escpaped need to go faster then the speed of light in order to do so? If it does not, wouldn't it feed the Black Hole?

damian1727
2008-Jan-16, 06:14 PM
1/Dont know

2/the virtual partical pair come into existance just outside the event horizon
one falls in one escapes.....virtual particals are popping into existance everywhere its just near the black hole one steals existance...?

llatpog
2008-Jan-16, 06:48 PM
The problem I have with one particle escaping...even at the event horizon...assumes that the particle has some form of velocity in order for it to escape.

I do'nt know if you can create a particle with velocity. First, you would need a lot of energy just to create said particle...then even more energy to move it at the speed of light.

Without moving at the speed of light, the particles would still get sucked into the black hole...meaning one would make it evaporate (the anit-particle) and one would feed it (the particle).

right?

neilzero
2008-Feb-24, 10:31 PM
llatpog may be right that most of the escaped virtual particles would be recaptured by a super massive black hole. This may be one of the reasons these produce very litle Hawkings radiation and micro black holes (if there are any) produce huge amounts of Hawkings radiation. Micro black holes would rarely succeed in capturing anything because they are so tiny. Neil

4tune8chance
2008-Mar-02, 11:24 AM
Yet another black hole question,

If it were possible to divide a black hole in half, and those halves were then below the minimum threshold to create a black hole, would all the matter or energy suddenly be released? (reasoning the gravity no longer being strong enough). If fear I have some error of understanding about the nature of the singularity i.e. once created the mass in no longer critical.

dcl
2008-Apr-26, 02:43 AM
In the following, I provide responses to questions and statements by several conributors to this thread. Each paragraph begins with the name of the contributor to whom that paragraph is applicable. Paragraphs not introduced by a name are continuations of the previous paragraph.

moriankey: The energy consumed in creating a particle pair outside a black hole must necessarily have been borrowed temporarily from the space in which the particles appear because it cannot have passed through the event horizon to arrive there. The process must begin with production of a pair of particles OUTSIDE the black hole, one particle then falling into the black hole and the other remaining outside with enough kinetic energy to prevent it from falling into the black hole. When it first appears, it must already be moving away from the black hole fast enough to escape to infinity.o

Chas: Space will not spin. It will be twisted in the direction of rotation of the black hole by an amount determined by the mass of the black hole and its rotationial velocity. The phenomenon is called "frame dragging".

Mrs. B: "Quark soup" is the name given to the contents of the Universe immediately after quarks, mesons, electrons, and other esoteric particles, comprising a plasma, condense out of the nearly pure radiaton comprising the contents of the Universe during the first moments of the Big Bang.

Hawkinns and Thorne had a bet on whether matter could escape from a black hole. Hawkins later devised the mechanism, involving "Hawkings radiation" that explained how matter COULD escape a black hole, thereby proving himself wrong and losing the bet.

namcitsym: There is no limit to how much matter can fall into a black hole.

Maddad: A person unfortunate enough to fall into a black hole would experience no local slowing of local time, that is how fast his clock ran, as he approached and fell into the black hole. However, he would see time at locations remote from his own location speeding up faster and faster as he approached the event horizon. He'd notice nothing whatever to tell him when he passed through the event horizon. Observers outside the event horizon would never see him pass through the event horizon for it would appear them that time he was going slower and slower as he approached the event horizon. In fact, it would appear to them that he never reached the event horizon, much less passed through it.

bons212: Objects are drawn into black holes from all directions.

Evileye: The way that objects fall into black holes is more like the way comets come into the solar system than the way planets orbit the sun in roughly coplanar orbits. General relativistic frame dragging will tend to pull them into the plane of the black hole's rotation, also collisions between orbiting objects will tend to bring them into the rotational plane of the black hole.

Uranu5: "a gravitational pull = to the speed of light" is like comparing monkeys and trees. Gravitational pull is force. The speed of light is a speed, There is no way to compare force with speed. The rotation of a black hole has nothing to do with its gravitational effects although its rotation can affect its gravitational effect through general relativistic frame dragging. A black hole does not "pull in other matter from different parts of the body of the mass creating the black hole which makes the pulled in material move towards the points that are moving across the equater."

sheeny: The mechanism of evaporation from a black hole involves quantum-mechanical "tunneling". In classical mechanics, nothing can escape from a black hole. The contents of a black hole can be seen as a collection of particles in thermodynamic equilibrium, the most energetic particles falling just short of having enough energy to escape from the black hole. In quantum mechanics, particles can "borrow" energy from the vacuum but must return it after a brief time, but that time is long enough so that the borrowed energy enables them to pass throuugh the event horizon. Through this mechanism, a few photons, neutrinos, electrons,and a few more massive particles can occasionally escape from the black hole. The photons appear outside the event horizon as blackbody radiation at a temperatuure only a degree or so above absolute zero. There's also the model that you described. But the model involving tunneling seems closer to what actually happens. As you stated, evidence for the existence of Hawking radiation has yet to be found.

Vanamonde
2008-May-02, 09:14 AM
I think, as I understand it, the energy for Hawking's radiation ultimately comes from the mass of the black hole. That is why it is thought that a smaller black hole would shrink and finally explode as it no longer has enough mass to accelerate stuff to C. The paradox is one particle of the pair escapes and one enters the event horizon, yet the black hole loses mass (equal to the mass times velocity of the escaped particle. I don't understand why).

Hawking's radiation may have been observed in collisions between gold nuclei at the Relativistic Heavy Ion Collider (RHIC) . I do not understand this article by Dr. Horatiu Nastase (http://arxiv.org/abs/hep-th/0501068) enough to determine this. Work from the Large Hadron Collider (LHC) should shed more light on this subject, in the next year or so, maybe.

It is a great time for astrophysics!

dcl
2008-May-02, 05:34 PM
I'll offer answers and responses to some of the questions and comments raised by contributors to this thread. Each begins with the pseudonym of the contributor of the question or comment followed by the question or comment, followed by ":--", and, starting on the next line, my answer or comment.

jwswitzer: It was mentioned that smaller black holes can vaporize. The analogy was that a glass of water, if left for a time, will vaporize and the water will disappear. However, the water really just changes form from a liquid to a gas. If I understand correctly the laws of physics require the vaporized black hole to not "disappear", but to also change into something else. Just what does it change in to?:--

All black holes evaporate, not just small ones. But only small ones evaporate fast enough for the evaporation rate to be appreciable. Black holes are believed to evaporate through a quantum mechanical procress that involving pairs of conjugate particles such as electrons and positrons. There is no good description in terms of classical physics. It involves "borrowing" energy from the vacuum, that is, from space itself, just outside the event horizon of a black hole subject to the requirement that the energy be returned to the vacuum within a time prescribed by the uncertainty principle of quantum mechanics. The process has been pictured as spontaneous creation a pair of conjugate particles such as electrons and positrons from vacuum energy just outside the event horizon, one of the particles then falling through the event horizon while the other acquires enough energy through its fall into the black hole to repay the borrowed energy, The substance of the vaporized black hole is passed into the escaping particles. The actual process is much more complicated, involving quantum field theory.

PhilM: If you have these particle pairs that are randomly being generated where one goes into the black hole and the other isn't, how does it evaporate if it is still consuming particles?:--

See my answer to jwswitzer's question.

morlanky: When matter gets sucked into a black hole, it gets converted into energy. When Hawking radiation occurs, the energy gets transformed into matter again and gets spat out. Make sense?:--

Matter falling into a black hole is not converted into energy: It contributs to the mass of the black hole. The matter falling into the black hole is not converted into energy via black-hole evaporation. See my answer to jwswitzer's question.

The black hole is, in a sense, consuming negative calories. In return, it's spitting out positive, not negative, calories.

Himanshu Raj: Why do they (massive particles) have to go round the massive object before falling into it instead of going straight into it? How does the law of the conservation of angular momentum apply?:--

Strictly speaking, particles do NOT need to go around the massive object before falling into it. Infalling objects are extremly unlikely to be headed directly toward the massive object. No matter how small the anglke it's heading if off center, its inbound path will be put it on a heading that would take around the center of the massive body. If this path intercepts the massive object's surface, in the case of a black hole its accrettion disk or its event horizon, it will fall in. The law of conservation of angulart momentum is what insures that the above will happen.

Chas: I wrote them out as a MS Word file, but, understandably, the site won't let me attach a doc to a thread post. If anyone is interested in checking my numbers, e-mail me, and I'll be happy to send it to you:--

Perhaps you cannot attach a Word file, but you can copy it into your response, although you'll find that you'll have a limited character set: no bolds, italics, or underscores, superscripts, or subscripts, and limited if any special characters such as integral signs. My comments are copied from Word files.

Black holes, like everytthing else, almost certainly spit, although there is no requirement that they MUST spin. It would be extremely unusual to find one that was NOT spinning. General relativitistic frame dragging would deflect the path of an infalling object if it was headed directly toward the center of the black hole. An appropriate deviation of its path would still allow it to fall directly into the black hole.

Mrs B: What is quarksoup?:--

Quark soup is the name given to the contents of the Big Bang universe immediately after quarks, electrons, and a few antiparticles condensed out of the primordial pure electromagnetic radiation constituing the the Universe during the Planck era preceding 10 exp -43 seconds, the brief interval of the Big Bang history not accessible to model particle physics.

namcitsym: Is there a limit as to how much matter can be consumed by a black hole or will it devour any and all comers across the event horizon? If there is a limit, how is it quantified?

Theory knows of no limit on how large and massive a black hole can become.

Maddad: Time slows for a person approaching the event horizon, and stops when he gets there, but only from the point of view of the outside observer. From the point of view of the inbound traveler, his time is completely normal. Instead of stopping, he squirts right on through. If the black hole is massive enough, he might not even be aware that he had passed the event horizon.

On the other hand, his perceives the outside observer’s time as going faster. When the traveler reaches the event horizon, he would see the outside observer experience all the time through the end of infinity.

What I had hoped to see Dr. Pamela explain was the meaning of time from the point of view of the inbound traveler inside the event horizon in explaining the outside observer. This time must be greater than infinity, which I have difficulty understanding.:--

Your understanding of temporal phenomena associated with black holes is correct. Because the radial and temporal components of the Schwarzschild metric switch roles inside the event horizon, I wouldn't want to predict what the unfortunate traveller would experience before he, she, or it was torn apart by tidal forces, as would certainly happen no matter whatever the size of the black hole.

bones212: It seems to me that the gravity is equal all around it and objects should be drawn from all directions?:--

Correct except for the effect of general relatavistic frame dragging, that would deflect paths toward orbits around the rotational axis of the black hole.

Evileye: Black holes are like any other massive body. They spin. There is an equator, and poles.... sort of. Anything that gets close enough begins to follow the rest of the stuff falling in or rotating around it, much like the rings around Saturn. When they finally pass the event horizon they are no longer visible to us. So the only way to show it on a 2d piece of paper is like a toilet bowl swirl. The stuff doesn't get sucked in from every direction although it may have came that way.

Try to imagine merging into traffic. You were going north, and merge into an eastbound lane. You adjust, the eastbound traffic doesn't.:--

Your description is correct for movement outside the event horizon. Because of the exchanged roles of time and radial distance inside the event horizon, the picture is much more complicated and is not readily described.

publiusr: If you throw a rock into a pond what you get back are the ripples. It can't actually leave the black hole--but it will (for lack of a better word) displace its worth in Hawking radiation.:--

A black hole emits radiation steadily even nothing if falling into it.

omar: My question is, how the super massive black hole is formed? and what had feeded it during it's formation?:--

It forms by accretion of matter from its surroundings, the galaxy in whose center it is embedded. It's fed mostly by stars but also by gas, mostly hydrogen, and dust.

omar: What are the assumptions that underpin Hawking Radiation?:--

See my response to jwswitzer's question near the beginning of this thread.

damian1727
2008-May-02, 08:15 PM
glad someone knows it all ;)

dcl
2008-May-03, 03:11 AM
This is my second batch of answers to questions asked by contributors to this thread. Each answer starts with the contributor's pseudonym, followed by his question, followed by ":--", then my response starting on a new line following a blank line. Responses start following the last entry in my previous list.

sheeny: I'm struggling to understand how the mechanism described for Hawking Radiation results in the black hole evaporating. What are the assumptions that underpin Hawking Radiation?

Your understanding is of the mechanism of Hawking radiation is essentially correct aside from the reservation concerning quantum field theory stated in my response to jwswitzer's question in my previous contribution to this thread. Hawking radiation should appear outside the black hole whether annihilation occured inside or outside the event horizon. If it occurred inside the event horizon, collision of the escaping particle with other particles would constitute the Hawking radiation. If it occurred outside the event horizon, the annihilateion energy itself would constitute the Hawking radiation To date, Hawking radiation has not been observed.

damian1727: As I understand it it does not matter which partical goes in and which escapes....the energy for the ''free'' partical has to come from somplace and that place is the black hole ...so it slowly evaporates. [Answering llatpog] the virtual partical pair come into existance just outside the event horizon one falls in one escapes.....virtual particals are popping into existance everywhere its just near the black hole one steals existance...?... glad someone knows it all:--

Correct, He complimented me by saying, "This guy seems to have it down pat." I can say the same for him.and then some! I doubt that anyone knows it all,

NHR+: I just heard Fraser say that if you go fast enough you'll turn into a black hole. Is that really so? I remember reading somewhere before, that speed does NOT really increase the mass of a moving body. Momentum and kinetic energy, yes, but NOT the mass. And that the whole concept of "relativistic mass" is just confusing and not really needed.:--

Everything Fraser is quoted as having said is totally untrue. The following statements are true:
No matter how fast you go, you will NOT turn into a black hole. Your mass WILL become infinite as seen by stationary observers as your speed approaches the speed of light. As seen by them, you will be moving very close to the speed of light, and your speed as seen by them will change negligibly whether you use energy trying to accelerate or to slow down. The concept of mass in special relativity is indeed confusing, bugt that does not eliminate need for it.

If the links you cited support the above quoted statements, their contents, too, are nonsense. There are lot's of people whose favorite pasttimes seem to be trying to debunk Einstein. So far, Einstein's relativities, both special and general, have stood up under the most rigorous testing. Your response to llatpog regarding appearance of particles outside the event horizon is correct.

llatpog: In most analogies of a black hole, people think of it as a larger vortex bringing things into it. However, that would mean that gravity is working as a vector. If a particle is popped into existance by a black hole...what is it created from? if gravity of a black hole is strong enough to hold light back...wouldn't the particle that escpaped need to go faster then the speed of light in order to do so? If it does not, wouldn't it feed the Black Hole?

The cited analogs are nonsense. Black holes are spherical, not circular, the fact that a nonrotating black hole would be a rarity notwithstanding. Black holes are black because they do not emit any sort of radiation whatever other than Hawking radiation, which has yet to be observed. Particles do not "pop" into existence from black holes. Only Hawking radiation is thought to be able to appear to come out of a black hole. Particles never emerge from black holes. The only way for a particle to appear emerging from a black hole is for the observer to see a particle appear just outside the event horizon and not notice that an antipartice appeared there at the same time.

neilzero: llatpog may be right that most of the escaped virtual particles would be recaptured by a super massive black hole. This may be one of the reasons these produce very litle Hawkings radiation and micro black holes (if there are any) produce huge amounts of Hawkings radiation. Micro black holes would rarely succeed in capturing anything because they are so tiny.:--

llatpog IS right on all counts,

4tune8chance: If it were possible to divide a black hole in half,...:--

It's hard to say what would happen. Theory does not cover that possibility.

Vanamonde: as I understand it, the energy for Hawking's radiation ultimately comes from the mass of the black hole. That is why it is thought that a smaller black hole would shrink and finally explode as it no longer has enough mass to accelerate stuff to C.:--

A small black hole does not accelerate anything to the speed of light., It is only via Hawking radiation that a smaller black hole is expected to finally explode.

Vanamonde
2008-May-03, 05:27 AM
A small black hole does not accelerate anything to the speed of light., It is only via Hawking radiation that a smaller black hole is expected to finally explode.

Are you sure? Even if it very small, if a particle enters it's gravity well, it will be accelerated. After all the very definition of a black hole is a gravity well that has an escape velocity greater than the speed of light. Typically, a body will accelerate a smaller falling body to or near it's escape velocity unless it has a vector in a different direction. The return of the Apollo spacecraft is an example in the macroworld as they were close to the Earth's escape velocity when they re-entered the atmosphere.

Is this not true, even on the very small scale? Now, I imagine that a capture virtual particle of the pair that leds to Hawking radiation will not be so accelerated as musch it "cheats" by coming into existence so close to the Schwarzschild radius.

Even the effect of the Earth's gravity has been measured on neutrons -
this (http://www.iop.org/EJ/abstract/0264-9381/3/4/024/) is not the article I read on it in Scientific American but is yet another example, one that is online.

damian1727
2008-May-03, 08:04 AM
dcl where did copy your original pat post from i cant remember?

thanks 4 the input

:)

dcl
2008-May-03, 08:59 PM
Responses to Vanamonde and damian 1727: For each, I'll enter your pseudonym, followed by the comment to which I'm labout to respond, then, on a new line, "dcl:" followed by my response. To clarify your remark, I'll occasionally enter explanatory words into your text inside square brackets.

Vanamonde: Are you sure (that a small black hole does not accelerate anything to the speed of light)?

dcl: One of the things that the special theory of relativity is famous for is that it tells us is that it would require an infinite amount of energy to accelerate anything to the speed of light and, once there, the accelerated object would have infinite mass. That is, it would require an infinite amount of energy to change its speed, no matter by how little. When you think about it, that's a rather amazing statement. Needless to say, that cannot be proved experimentally because it would require expenditure of an infinite amount 0f energy to prove it, and that just isn't possible..

Vanamonde: Even if it very small, if a particle enters it's [the black hole's] gravity well, it will be accelerated.

dcl: True.

Vanamonde: After all the very definition of a black hole is a gravity well that has an escape velocity greater than the speed of light.

dcl: Almost true. The escape velocity of a black hole IS the velocity of light, not greater than it. Since the velocity of light cannot be achieved by matter, matter cannot escape from a black hole.

Valamonde: Typically, a body will accelerate a smaller falling body to or near it's escape velocity unless it has a vector in a different direction.

dcl: There may be some special situations in which this may be true, but they would need to be contrived. It's not true in general.

Vanamonde: The return of the Apollo spacecraft is an example in the macroworld as they were close to the Earth's escape velocity when they re-entered the atmosphere.

dcl: I don't see return of the Apolla spacecraft as an example of a body accelerating a smaller falling body to ore near its escape velocity.

Vanamonde: Is this not true, even on the very small scale?

dcl; No.

Vanamonde: Now, I imagine that a capture virtual particle of the pair that leds to Hawking radiation will not be so accelerated as musch it "cheats" by coming into existence so close to the Schwarzschild radius.

damian1727: dcl where did copy your original pat post from i cant remember?

dcl: I didn't copy it from anywhere. I wrote it myself on my computer with myown two hands, all ten of them! In case you're wondering whether I know how to write such scientific-sounding stuff, try Googling either "Donald C. Livingston" or "The Physics of Microwave Propagation"!

damian1727
2008-May-03, 10:02 PM
yeah sorry typo was asking where i copied it from.....

damian1727
2008-May-03, 10:06 PM
anamonde: After all the very definition of a black hole is a gravity well that has an escape velocity greater than the speed of light.

dcl: Almost true. The escape velocity of a black hole IS the velocity of light, not greater than it. Since the velocity of light cannot be achieved by matter, matter cannot escape from a black hole..



?


but nutrinos and photons...light DO go light speed so surely shirley the escape velocity must be greater altho i grant there is no greater ...mmm

never thought of that,,,

Vanamonde
2008-May-04, 05:27 AM
dcl: I don't see return of the Apolla spacecraft as an example of a body accelerating a smaller falling body to ore near its escape velocity.

Apollo 10 spacecraft fires it's engine and leaves it's orbit from the moon and returns to the Earth. At the time the Command module hits the atmosphere, it reaches 39,895 km/h (about 24,900 mph), the highest speed any human being has ever moved (relative to the Earth). Escape velocity is 40,320 km/h. This speed was mostly the result of the fall, not from the rocket - the rocket just push the craft to where the Earth's gravity takes over.

And truth, the vector was carefully chosen, so I understand your statement about this example being contrived. But no matter what the size of a black hole's gravity well (meaning that part where is substantial), unless a particle has a significant vector against, I fail to see why it would not be overwhelmed and accelerated to at least close to C before reaching the event horizon. But I also know that Things in the Quantum World are very different. I don't pretend to understand the quantum effects of a tiny black hole other than what I have read about Hawking radiation.

Mmm, I wonder if a particle can enter a stable orbit about a quantum black hole? Talk about a superatom!!!

Sorry, if I am dense. This has been a good workout for my brain and I do appreciate your time!

dcl
2008-May-04, 04:21 PM
damian1727: but nutrinos and photons...light DO go light speed so surely shirley the escape velocity must be greater altho i grant there is no greater

dcl: Neutrinos were recently found to have mass, so they cannot escape from black holes either. As for photons, they can just barely reach the event horizon from the black hole at its center; they cannot penetrate it.

damian1727
2008-May-04, 09:32 PM
but they do move at the speed of light....

dcl
2008-May-05, 01:27 AM
damian1727: but they do move at the speed of light.

dcl: Not so. If a particle has any mass at all, it cannot move at the speed of light. It would require an infinite amount of energy to accelerate it to that speed, and it would have infinite mass when it reached that speed. Neutrinos move very close to the speed of light, but their tiny masses are still sufficient to prevent them from gaining that last little bit of additonal speed.

damian1727
2008-May-05, 07:26 AM
but light moves the speed of light right? and it cannot escape...

it would be great if in our lifetime the lhc or somthing gave us a clue as to wtf is going on in there

another thing that has always puzzled me is the entropy of black holes

they are supposed to carry no information...all information destroyed upon entry as it where.... but it retains the MASS information.... it knows how massive it is ..how much it holds and how long it will take to radiate away....is that not information? and how is this information kept intact in a singularity!!!!

dcl
2008-May-05, 08:53 PM
amian1727: but light moves the speed of light right? and it cannot escape...

dcl: By definition!

damian1727: it would be great if in our lifetime the lhc or somthing gave us a clue as to wtf is going on in there

dcl: I'll be surprised if the LHC tells us anything about black holes. Hoperully, it'll find Higgs particles and tell us all about what causes matter to respond to forces, that is, why matter has mass. That's the big hope.

damian1727: another thing that has always puzzled me is the entropy of black holes

dcl: Entropy increases any time anything loses any part of whatever structure it possesses. When something falls into a black hole, it becomes compressed into a dimensionless point containing no properties whatever. Such an object contains no information.

damian1727: they are supposed to carry no information...all information destroyed upon entry as it where.... but it retains the MASS information.... it knows how massive it is ..how much it holds and how long it will take to radiate away....is that not information? and how is this information kept intact in a singularity!!!!

dcl: Once inside the event horizon, information on its mass is lost to the outside world because its mass increases to infinity as it falls into the interior of the black hole.

damian1727
2008-May-05, 11:22 PM
i like the entropy answer..ta

but we know how much mass is in a black hole..? if i throw the sun into a black hole the holes mass goes up by one solar mass ... so the information is in there someplace ?

?

dcl
2008-May-06, 02:14 AM
damian1727: but we know how much mass is in a black hole..? if i throw the sun into a black hole the holes mass goes up by one solar mass ... so the information is in there someplace ?

dcl: No, it isn't. When the sun was compressed into a dimensionless point with no properties at all, not even color or mass, angular momentum or velocity, its information content was totally gone, gone, gone. It's a dimensionless, colorless, odorless, nonrotating, shapeless, thoughtless, emotionless, nonthinking, nonopinionated, nonpulsating, point. It's nothing, nothing, nothing. It has no information, none at all, not even a teeny weeny bit. (!)

damian1727
2008-May-06, 07:16 AM
so how come the black holes mass increases by 1 solar mass?
im sure your correct i just am not understanding... its not nothing tho is it ... its still there in our universe having an effect on things and it knows how much matter is in it innit?

lol

gotta love a black hole

dcl
2008-May-06, 08:08 PM
damian1727: so how come the black holes mass increases by 1 solar mass?
im sure your correct i just am not understanding... its not nothing tho is it ... its still there in our universe having an effect on things and it knows how much matter is in it innit?

dcl: Once a mass ihas fallen past the event horizon of a black hole, it falls all the way into the singularity, where it is compressed into a dimensionless point. Any information that it may have contained is destroyed by that final process.

damian1727
2008-May-06, 09:30 PM
then how do we on the outside know accurately
how much mass fell in??.... what you are saying does not explain how the black holes mass is kept... if all information was lost as you say then we could not measure how much had fallen in..which we can so even tho we are told everything you have been saying i stand by the fact that information about the mass must be retained in the singularity.... or a black holes mass would not relate to what the hole has inside it...

dcl: Once a mass ihas fallen past the event horizon of a black hole, it falls all the way into the singularity, where it is compressed into a dimensionless point. Any information that it may have contained is destroyed by that final process.

if this was the case you would not be able to measure the mass that has fallen in as that information would have been lost...which it is not is it?

?

:):):):)

damian1727
2008-May-06, 09:33 PM
ie if you throw ten million tons into a black hole you can after measure the fact its mass has increased by ten million tons...

is that not information?

dcl
2008-May-07, 01:37 AM
Information theory is not one of my strong points, hut it's my understanding that mere AMOUNT of mass does not constitute "information" in the informationi theory sense, especially when that mass is indistinguishable from other any other mass that may constitute part of the contents of the single dimensionless point at the center of a black hole.

damian1727
2008-May-07, 07:49 AM
i guess you could not store any bits in it but it is interesting that there must be some accounting system in there so it knows how massive it is...
:eek::eek::eek:

NHR+
2008-May-07, 11:33 AM
Everything Fraser is quoted as having said is totally untrue. The following statements are true:
No matter how fast you go, you will NOT turn into a black hole. Your mass WILL become infinite as seen by stationary observers as your speed approaches the speed of light. As seen by them, you will be moving very close to the speed of light, and your speed as seen by them will change negligibly whether you use energy trying to accelerate or to slow down. The concept of mass in special relativity is indeed confusing, bugt that does not eliminate need for it.

It seems to me, that there might still be some sort of on-going debate about this relativistic mass thingy among the real physicists. I'm not a real physicist, but you certainly seem to be, so I'm very likely just to take it easy and just believe whatever you're saying... ;)

But moving too fast just won't turn you into a black hole, in any frame of reference ('cause if it did happen in one, it'd had to happen in all the others, too, right?), that was the key point I was making, I guess...


If the links you cited support the above quoted statements, their contents, too, are nonsense. There are lot's of people whose favorite pasttimes seem to be trying to debunk Einstein. So far, Einstein's relativities, both special and general, have stood up under the most rigorous testing. Your response to llatpog regarding appearance of particles outside the event horizon is correct.

I don't think debunking Einstein was the point in those links at all, more like on the contrary, I would say. I don't remember exactly what it used to say there, when I first linked the page, but currently it seems to be much more "pro-relativistic mass" than it was back then, in January of this year, I guess. Here's the same link again, though the contents of the page have now changed a bit:

http://math.ucr.edu/home/baez/physics/Relativity/SR/mass.html

Says there, that the concept of relativistic mass is still very "useful". OK by me then, I guess; let those who calculate these things for work, on a daily basis, use it if they want to... :)

dcl
2008-May-07, 01:33 PM
Don't believe everything even physicists say either. Even physicists, as godlike as they are, are known to make mistakes. The great Newton said light consisted of particles, not waves. Then it was found that they're waves. Then to really confuse the issue, it was found that they're particles on even days and waves on odd days (huh?). He said gravitational forces hold planets in orbit. Then Einstein said, "Not so. It's warping of space". There are many other examples throughout the history of science. Maybe 100 years from now we'll marvel at how naive Einstein's theories were.