Black Hole Question

[Chef StiX]

Here is a question I don't understand at all. Hopefully all you smart university grads can break it down for me.

Why when falling into a smaller black hole would you get ripped apart by the tidal forces before crossing the event horizon yet in a larger one you wont get torn apart until after you have crossed the event horizon?

[Dr. Skeptic]

Here is a question I don't understand at all. Hopefully all you smart university grads can break it down for me.

Why when falling into a smaller black hole would you get ripped apart by the tidal forces before crossing the event horizon yet in a larger one you wont get torn apart until after you have crossed the event horizon?

There would be no difference, atoms cannot cross an EH. The accretion disk directly outside the EH is composed of high energy particles only. Also, time moves inversely proportional to the proximity of the EH to the point some theories predict that ∆ time is reduced to 0 so it would take "forever" to cross the EH.

[Chef StiX]

Perhaps you can answer this one harry as the source was from one of your links

"For a very large black hole like the one you're falling into, the tidal forces are not really noticeable until you get within about 600,000 kilometers of the center. Note that this is after you've crossed the horizon. If you were falling into a smaller black hole, say one that weighed as much as the Sun, tidal forces would start to make you quite uncomfortable when you were about 6000 kilometers away from the center, and you would have been torn apart by them long before you crossed the horizon. (That's why we decided to let you jump into a big black hole instead of a small one: we wanted you to survive at least until you got inside.)"

http://cosmology.berkeley.edu/Education/BHfaq.html#top

[Pete]

Here is a question I don't understand at all. Hopefully all you smart university grads can break it down for me.

Why when falling into a smaller black hole would you get ripped apart by the tidal forces before crossing the event horizon yet in a larger one you wont get torn apart until after you have crossed the event horizon?

There would be no difference, atoms cannot cross an EH. The accretion disk directly outside the EH is composed of high energy particles only. Also, time moves inversely proportional to the proximity of the EH to the point some theories predict that ∆ time is reduced to 0 so it would take "forever" to cross the EH.

No difference? Most online sources (including Chef StiX's link in his post above) would beg to differ. Also, if what you write were true, how would black holes ever gain mass? Does it accumulate at the event horizon, contributing to the mass that way? Call me ... skeptical.

Also, I'm pretty sure time does not stop at the event horizon at all, by anyone's clock. The passage of time on an infalling test object (e.g. a clock) as measured by a faraway observer will appear to stop at the event horizon because the light emitted by the object takes ever longer and loses ever more energy in climbing away from the black hole, and past the EH, all of the light's possible paths lead to the singularity, so we don't see the clok fall in. The light gets 'infinitely' red-shifted, too, so we would end up seeing a lingering far-infrared image of the object hovering at the event horizon. IANAP, but I'm under the impression that the observed freezing of time is just an optical illusion.

From the infalling object's reference frame, nothing remarkable will happen as it crosses the event horizon. As it falls into the black hole, it will observe outside time to speed up, possibly infinitely only at the singularity...That last bit is speculation on my part, so flame me, don't quote me

To attempt to answer Chef StiX's question: while gravity follows the inverse square law (10x distance = 1/100 of original gravitational pull), tidal force approximates an inverse cube law (10x distance = 1/1000 of original gravitational pull), and drops off much more compared to gravity with increasing distance from the gravitating object.

[Chef StiX]

Ahh ok I thought that probably had something to do with my question. Thanks for clarifying that pete

[Qev]

Pete's pretty much got the right of it, yeah. For a 'traveller' falling into a black hole, and an 'observer' sitting stationary at a relatively safe distance, the whole experience appears quite different. The observer sees the traveller's clock slowing down, and their image redshifting, as they fall towards the horizon, until at the very moment they would reach it, the traveller's clock seems to stop as their image is redshifted beyond observability.

The traveller, of course, sees none of this. To him, his clock just keeps on ticking, and while there are probably some pretty spectacular optical effects (dealing with gravity bending light in amusing ways), he'll never really even know when he passes the event horizon. Long before he reaches the singularity (or whatever they have inside them) he'll get spaghettified.

The disruptive tidal effects of black holes come from the gravitational gradient of the mass of the black hole. For low-mass black holes, you have to get very close to them before you cross the horizon, and the gravity gradient becomes quite steep: across even the small distance from your head to your feet (assuming you're falling feet-first), the force of gravity increases radically... you get stretched, and squished thin at the same time... spaghettified.

For larger-mass black holes, the horizon can have very large diameters, well beyond the point where the gravitational gradient becomes deadly. So you get to disappear from the universe before you get mangled horribly.

It all comes from the inverse-square behavior of the force of gravity, really.

For the purposes of this example, let's chop the traveller into two halves, and make those halves point-masses separated by one meter (just to keep things simple... and you thought the black hole was dangerous! ). Now, my math isn't terribly precise here, and I'm sure as heck not gonna bother with Relativity (which really would apply at these energies), so I'll keep things in the nice, simple, but not exactly accurate Newtonian realm. But the gist of this should be close enough for jazz.

For a one-solar mass black hole, the event horizon has a radius of:

Rs = 2GM/c^2

= 2950m (almost three kilometers)

So let's say our traveller starts out stationary, with their 'feet' at the horizon, and their 'head' one meter above it.

So for their feet, at radius R (2950m) the acceleration due to gravity is:

a(feet) = GM / R^2

= 1.5252e13 m/s^2

And for their head, at radius R+1 (2951m)

a(head) = GM / (R+1)^2

= 1.5242e13 m/s^2

Those don't look very much different, do they? But let's subtract the second from the first...

delta-a = a(feet) - a(head)

= 1e10 m/s^2

Which is a difference of ten billion meters per second squared, over the distance of one meter. That will kill you dead. Oh yeah.

Now if I do the same for a one million solar mass black hole, with an event horizon radius of:

Rs = 1.475e9 m (nearly one and a half million kilometers)

a(feet) = 6.1009135e7 m/s^2

a(head) = 6.1009135e7 m/s^2

Now, those are pretty much equal down to an error level of one meter per second, so the gravity gradient is pretty gentle out there, despite the fact that the traveller is right at the point of no return.

Weird, huh? That's why big black holes aren't as immediately lethal as their smaller cousins. At least when you're at the event horizon, that is.

Dr. Skeptic: not all black holes are necessarily surrounded by an accretion disk. I'd probably guess that the majority of stellar-mass black holes aren't surrounded by such, at least not for very long, unless they happen to have a companion star upon which to draw matter. But you're definitely right... an accretion disk would be an hideously unpleasant sort of environment.

[BMAONE23]

nice explanation Qev

[harry]

Hello All

Black Holes, are not holes, but supermassive degenerated matter, some call it ultra dense plasma matter and there's other ideas.

If you want answers on Black Holes see the following links: if some are repeated, I'm sorry. But there are some links that maybe of interest to some.

http://imagine.gsfc.nasa.gov/docs/ask_a ... holes.html
http://cosmology.berkeley.edu/Education/BHfaq.html
http://pda.physorg.com/lofi-news-black- ... _3701.html

I do not agree with all the answers, but thats just me.

=========================================
Links on Black Holes
Black holes actually green: official
http://www.theregister.co.uk/2006/04/25 ... les_green/


Black holes influence knowledge of the universe
http://www.physorg.com/news3306.html


How to find a black hole

http://pda.physorg.com/lofi-news-black- ... _7420.html

The Einstein-Rosen Bridge
http://www.krioma.net/articles/Bridge%2 ... Bridge.htm


Visiting a black hole? Allow plenty of time
http://www.theregister.co.uk/2006/01/10 ... ervations/


Star Orbiting Massive Milky Way Centre Approaches to within 17 Light-Hours [1]
http://www.eso.org/outreach/press-rel/p ... 17-02.html



==============================================

Many think that time changes near, at and after the event horison.

Yes the method of recording time will change. That is because electromagnetic radiation is used as a means of communication. If you pull or push light or curve light you will alter the ACTUAL TIME it takes for light to reach its POINT.

ACTUAL TIME NEVER CHANGES
RELATIVE TIME CHANGES


If we travel twice the speed of light from earth, we could look at the past radio signals. The time recorded will be from those signals.

No fantasy no tricks.
============================================

As for small and big black holes the event horison distance, is relative distance to its mass.

[Andy Wade]

Here is a question I don't understand at all. Hopefully all you smart university grads can break it down for me.

Why when falling into a smaller black hole would you get ripped apart by the tidal forces before crossing the event horizon yet in a larger one you wont get torn apart until after you have crossed the event horizon?

There would be no difference, atoms cannot cross an EH. The accretion disk directly outside the EH is composed of high energy particles only. Also, time moves inversely proportional to the proximity of the EH to the point some theories predict that ∆ time is reduced to 0 so it would take "forever" to cross the EH.

No difference? Most online sources (including Chef StiX's link in his post above) would beg to differ. Also, if what you write were true, how would black holes ever gain mass? Does it accumulate at the event horizon, contributing to the mass that way? Call me ... skeptical.

Also, I'm pretty sure time does not stop at the event horizon at all, by anyone's clock. The passage of time on an infalling test object (e.g. a clock) as measured by a faraway observer will appear to stop at the event horizon because the light emitted by the object takes ever longer and loses ever more energy in climbing away from the black hole, and past the EH, all of the light's possible paths lead to the singularity, so we don't see the clok fall in. The light gets 'infinitely' red-shifted, too, so we would end up seeing a lingering far-infrared image of the object hovering at the event horizon. IANAP, but I'm under the impression that the observed freezing of time is just an optical illusion.

If a tree falls in a forest and no-one is around to actually hear it fall, does it make a noise?

[Dr. Skeptic]

Here is a question I don't understand at all. Hopefully all you smart university grads can break it down for me.

Why when falling into a smaller black hole would you get ripped apart by the tidal forces before crossing the event horizon yet in a larger one you wont get torn apart until after you have crossed the event horizon?

There would be no difference, atoms cannot cross an EH. The accretion disk directly outside the EH is composed of high energy particles only. Also, time moves inversely proportional to the proximity of the EH to the point some theories predict that ∆ time is reduced to 0 so it would take "forever" to cross the EH.

No difference? Most online sources (including Chef StiX's link in his post above) would beg to differ. Also, if what you write were true, how would black holes ever gain mass? Does it accumulate at the event horizon, contributing to the mass that way? Call me ... skeptical.

Also, I'm pretty sure time does not stop at the event horizon at all, by anyone's clock. The passage of time on an infalling test object (e.g. a clock) as measured by a faraway observer will appear to stop at the event horizon because the light emitted by the object takes ever longer and loses ever more energy in climbing away from the black hole, and past the EH, all of the light's possible paths lead to the singularity, so we don't see the clok fall in. The light gets 'infinitely' red-shifted, too, so we would end up seeing a lingering far-infrared image of the object hovering at the event horizon. IANAP, but I'm under the impression that the observed freezing of time is just an optical illusion.

From the infalling object's reference frame, nothing remarkable will happen as it crosses the event horizon. As it falls into the black hole, it will observe outside time to speed up, possibly infinitely only at the singularity...That last bit is speculation on my part, so flame me, don't quote me

To attempt to answer Chef StiX's question: while gravity follows the inverse square law (10x distance = 1/100 of original gravitational pull), tidal force approximates an inverse cube law (10x distance = 1/1000 of original gravitational pull), and drops off much more compared to gravity with increasing distance from the gravitating object.

I guess you can obtain any answer you like if you keep inserting improbable hypothetical qualifiers.

The particle speeds at the EH is near C - figure it out.

[Pete]

If a tree falls in a forest and no-one is around to actually hear it fall, does it make a noise?

If a tree falls on Schrödinger's cat and nobody is around, is the cat alive or dead?

I guess you can obtain any answer you like if you keep inserting improbable hypothetical qualifiers.

To avoid coming off as some arrogant, self-aggrandizing skeptical guy, I provide either speculation disclaimers or information sources in my posts. That way, readers know whether they're reading about actual published ideas (and how sure I am of what I'm writing) or just my own nonsensical interpretations thrown out there to spark discussion. Hey look, it's working!

The particle speeds at the EH is near C - figure it out.

Figure what out? Do you mean the statements:

atoms cannot cross an EH

time moves inversely proportional to the proximity of the EH to the point some theories predict that ∆ time is reduced to 0 so it would take "forever" to cross the EH.

Can you elaborate?

nitpick: it's "c" unless you meant 6.24 x 10^18 elementary charges

[Qev]

ACTUAL TIME NEVER CHANGES

No such beastie!

RELATIVE TIME CHANGES

That's true enough, though.

If we travel twice the speed of light from earth, we could look at the past radio signals. The time recorded will be from those signals.

Big if though. We can't travel at twice the speed of light. It's kind of a fundamental limit.

As for small and big black holes the event horison distance, is relative distance to its mass.

Quick rule of thumb for black holes, the event horizon radius increases by roughly 3km per solar mass (or the diameter by 6km per solar mass, if you prefer).

[BMAONE23]

If we COULD travel faster than light we probably wouldn't be able to pick up the older signals as they would be moving too slow. We might pick up some slow reverse moving signal that would appear garbled. When we slowed below C or stopped, the older signals would be there to be heard again.

[harry]

Hello All

Hello Qev and MBAONE23

Travelling at the speed of light is not possibble unless you propogate at the speed of gravity.

Anyway that was just an example of an "IF" thing and a bit of salt.

Actual time is the time through out the universe regardless of position, Cannot be changed or altered by a fantasy of multi dimensions.

If you want to use a different term thats fine.

[Dr. Skeptic]

To avoid coming off as some arrogant, self-aggrandizing skeptical guy, I provide either speculation disclaimers or information sources in my posts. That way, readers know whether they're reading about actual published ideas (and how sure I am of what I'm writing) or just my own nonsensical interpretations thrown out there to spark discussion. Hey look, it's working! Smile

Sorry, I get irritated when people don't use their own brains.

The initial question is hypothetical with a scientifically useless answer set as asked. Of course Chef StiX is confused, reading "scientifically immature" web pages with nonsensical extrapolations of legitimate data, is a sure way to dissolved any scientific coherency. The web page has the same merits as asking which X-Man is the most powerful.

Such is why I seldom post URLs, It takes an exorbitant amount of time to research their legitimacy and an equal amount to explain (mostly) where and why they're in error.

[harry]

Hello Dr Skeptic

Sorry, I get irritated when people don't use their own brains.

What type of a silly statement is that?

Think about it.

If you want perfection, do not ask for it, from people who just want to be part of this discussion.

[Chef StiX]

Qev thank you that explained a lot.

As for everyone else. I have no university degree and a college certificate for chef training and even I can understand one thing. Black holes are still technically theoritical and technically no point of view is wrong until it can be disprooven in a lab. Now lets all have a nice civilized discussion with some passive debate and make this a rewarding experience and not a bitch fest

A friend just recently told me about something he read called a "meeko" which would basically blow the theory of a black hole out of the water.
(now the spelling might be wrong because I just heard the name).

If anyone has the link for the article or other related material I would love to read it.

[Qev]

Ah, he's probably referring to a MECO, Magnetic Eternally-Collapsing Object, which is a recent competing theory describing objects that are usually considered possible black holes.

These objects would have physical surfaces instead of event horizons, and would have their own magnetic fields (black holes, I don't believe, can). From what I can tell, it's all pretty controversial right now.

[Dr. Skeptic]

Hello Dr Skeptic

Sorry, I get irritated when people don't use their own brains.

What type of a silly statement is that?

Think about it.

If you want perfection, do not ask for it, from people who just want to be part of this discussion.

It is wrong to perpetuate inaccurate and misleading data regardless how good the intentions, inadvertently or intentionally. If you would like to discuss the merits of web posting, great, but if you prefer to post web pages that lack credibility, those traits shall become yours.

[harry]

Hello Dr Skeptic

I agree, but! be respectful to the people around you.

I should also take that advice.

As for info, what concrete information have you added that is over and above and being correct with evidence.

[Dr. Skeptic]

Hello Dr Skeptic

I agree, but! be respectful to the people around you.

I should also take that advice.

As for info, what concrete information have you added that is over and above and being correct with evidence.

It is my job to "poke the holes" so the ignorance can drain out.

[linx]

It is my job to "poke the holes" so the ignorance can drain out

Hi Dr Skeptic,
i stand in wonder at the beauty of the Universe every day thanks to APOD
& scientists help laypeople like myself to understand & to think on the various possiblities & probablilites with regards to the formation of the Universe

i do not think your 'put-down' comments to other scientists have any place in this search for truth & or add to the wealth of wonders

+ it is not a good idea to poke holes just in case you find yourself leaking ..it is better just to have a decent discussion

Lin x

[Chef StiX]

I don't sapposed you would happen to know any good sites explaining them eh qev?

I could always google it but then you never know what you'll get.

[Dr. Skeptic]

It is my job to "poke the holes" so the ignorance can drain out

Hi Dr Skeptic,
i stand in wonder at the beauty of the Universe every day thanks to APOD
& scientists help laypeople like myself to understand & to think on the various possiblities & probablilites with regards to the formation of the Universe

i do not think your 'put-down' comments to other scientists have any place in this search for truth & or add to the wealth of wonders

+ it is not a good idea to poke holes just in case you find yourself leaking ..it is better just to have a decent discussion

Lin x

I don't put down scientist. I do what I can to promote good science and try to eradicate bad science. I love and have great respect for the APOD site, in turn do not want it to be overrun by those using bad science to promote there own philosophical agendas. It is imortant to add accountablity for what is posted.

PS If I leak, I will be less ignorant - and that is to my advantage.

[Qev]

I don't sapposed you would happen to know any good sites explaining them eh qev?

I could always google it but then you never know what you'll get.

Well, I don't know that I could recommend the Wikipedia article on them. While it goes into a fair bit of detail, the pro-MECO bias is so thick you can cut it with a knife. I suppose it's a place to start, though...

It's hard to find any neutral articles on it. I guess that's because it's still pretty new-ish.