# Thread: Episode 18: Black Holes Big and Small

1. ## Episode 18: Black Holes Big and Small

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

2. ooooooo im sooo excited, been waitin 18 episodes for this

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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

4. 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.

5. 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???
Last edited by DannyLiverpool; 2007-Jan-11 at 12:48 AM. Reason: Changing question

6. 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?

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## Ways black holes will hurt you.

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.

8. So the black hole is actually eating "negative calories'? It keeps eating but gets lighter by doing so.

9. 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/presentation...003/index.html

Cheers

10. 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/presentation...003/index.html

Cheers

11. Originally Posted by feraldoc
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.

Seven Ways Black Holes Can Kill You!

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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….

13. Originally Posted by Mrs B
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.

14. ## Black Holes Big and Small Just a wonderful show! But a few doubts.

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.

15. ## Escape velocity of an asteroid

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, and I'll be happy to send it to you.

16. ## Spinning Black Holes

Originally Posted by Himanshu Raj
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, is an excellent introduction to the topic.

17. What is quarksoup?

18. ## How much is too much?

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?

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## Black Hole Gravity and Time

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.
Last edited by Maddad; 2007-Feb-07 at 03:46 PM. Reason: Used an incorrect pronoun

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.

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Where could I find the question show?

Where could I find the question show?
The show is at: Episode 21: Black Hole Questions Answered. The full archive of shows can be found here.

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## Black Hole question

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?

24. Originally Posted by bones212
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.

25. Originally Posted by morlankey
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)

26. Originally Posted by 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.
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.

27. Order of Kilopi
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Originally Posted by Uranu5
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.

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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????

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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. 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.

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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....

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