# What's in a Black Hole - Can't We Find Out?

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Very simple question. Why can't NASA or other space agencies around the world send a Voyager-type space craft straight into a Black Hole to broadcast information right up to the point it is obliterated? Or are there problems associated with this question because it is an experiment that does not seem to have been performed yet?

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You can't pass information out of a black hole. But there is noting to stop you going to take a look personally, if you are really curious (other than the fact that you would be pulled apart by the gravity of course).

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The main problem with the experiment is that nothing ever launched from earth by humans has even remotely come close to going far enough to arrive at any known black hole. Even the fastest spacecraft launchable in the near future would take decades (maybe even centuries) to arrive at the nearest one.

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Good responses above. As already suggested, the answer to the OP has two main points:

1) The nearest BH is too far away to reach with our current technology in anything less than hundreds/thousands of years.

2) Once you cross the event horizon, no signal or information you try to send back to earth can overcome the gravity exerted by the BH. So, your probe would not even be into the blackhole yet and already you'll have stopped receiving information from it. We'd stop receiving information well before we saw anything interesting inside of the hole.

The second one is really the deeper reason this won't work. The first reason is more specific to your "why won't NASA send something" question. It's just that even if NASA could send something, it wouldn't be able to relay any information once it got there and had crossed the EH.

Remember, this "information" being sent is in the form of electromagnetic radiation... the light spectrum basically. Since not even light can escape the BH gravity, your information or "signal" can't either.

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The nearest BH, is thought to be *V4641 Sgr.* about 1600 light years from earth. The fastest space craft is the *New Horizon* launched January 2006, to explore Pluto/Charon, in 2015, traveling 150k m/p/h. By comparison the *Pioneer's* traveled 40k m/p/h.

A light hour, or the time light travels in one hour is 671 Million miles. There are 14 million light hours in 1600 l/y. For that space craft traveling 150k m/p/h it would take 4474 earth hours (186.4 days) to cover ONE light hour of space. In short your talking about one earth year to cover 2 light hours of miles or 14 million earth years to reach the THOUGHT closest BH. There are many other variables (gravity Resistance/attraction, acceleration, fuels ect. to say nothing of equipment failure for such a period) but the reality is we have no technology to even plan such a trip...

There would be no reason IMO to purposely direct a probe into the object being explored, whether the sun, Pluto or some comet/asteroid or if possible a BH. We do have the technology to explore radiation and/or effects of objects by a number of means. We have two probes near the sun, beaming back 3D pictures of the sun, which alone has changed/confirmed some theory.

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Black holes are out of our current reach. Maybe in the future we will discover some closer to earth and we could perhaps send a probe to orbit the black hole while it tosses pebbles at it and watch what happens.

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No. Once the pebble is tossed beyond the event horizon, you can no longer watch what happens to it if you are beyond the event horizon's edge. The light you need to "watch" cannot escapte the gravity of the hole.

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Thanks for the answer guys. That is, assuming that Black Holes really exist? I remember reading something confusing suggesting that they don't exist but cannot find the reference.

This, and the fact that I was reading about the Voyager Missions, prompted me to think why send Voyagers out on either side of the ecliptic but neglect to look at the Black Holes which are apparently at the centre of each galaxy to help galaxies to form in the first place.

http://news.bbc.co.uk/2/hi/science/nature/7774287.stm

You can't pass information out of a black hole. But there is noting to stop you going to take a look personally, if you are really curious (other than the fact that you would be pulled apart by the gravity of course).

Thanks for the offer. I 'll give it a miss. My wife would not forgive me if I went into suspended animation for a thousand years - she would find a way to get at me somehow - regardless of the time or place

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Thanks for the answer guys. That is, assuming that Black Holes really exist? I remember reading something confusing suggesting that they don't exist but cannot find the reference.

That's a non-issue. They do exist, and, in fact, have been found to be at the center or pretty much every single galaxy out there, including at the center of our own galaxy, the Milky Way.

More here on work observing them:

http://chandra.harvard.edu/xray_sources/blackholes.html

There's a short video here that may address some of the more basic questions in your mind:

http://videos.howstuffworks.com/discovery/31008-black-holes-the-heart-of-every-galaxy-video.htm

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No. Once the pebble is tossed beyond the event horizon, you can no longer watch what happens to it if you are beyond the event horizon's edge. The light you need to "watch" cannot escapte the gravity of the hole.

Yes, but you can certainly watch an object approach the event horizon and see what happens before it passes the EH. You may see some crazy fireworks. Quasars are the result of matter before it crosses the EH.

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Since gravity waves can exit black holes (otherwise they wouldn't exhibit gravity); would it be possible to make observations based upon the gravity waves? The internal structure of the earth has been similarly mapped using sound waves for example. A pebble tossed into the black hole might make all kinds of interesting gravity wave sounds...

Or does it not work this way?

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Yes, but you can certainly watch an object approach the event horizon and see what happens before it passes the EH. You may see some crazy fireworks.

Actually, it would just appear to freeze... to be forever static right there at the edge of the event horizon... from the perspective of an outside observer, that is. Intersting to note, (I think it was) the Russians used to call blackholes "Frozen Stars."

The light from the object is infinitely red-shifted, so appears to be frozen in time from an outside observers perspective.

Also, you should read up on quasars. Your description is close, but way oversimplified.

http://en.wikipedia.org/wiki/Quasar

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Deleted

Edited by Snail
too much study, makes Snail an idiot

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Actually, it would just appear to freeze... to be forever static right there at the edge of the event horizon... from the perspective of an outside observer, that is...

Like a big magnet collecting matter? Could you elaborate on that? Or a link.

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The wiki covers it briefly:

http://en.wikipedia.org/wiki/Event_horizon

Also here:

http://www.phys.vt.edu/~jhs/faq/blackholes.html

The normal presentation of these gravitational time dilation effects can lead one to a mistaken conclusion. It is true that if an observer (A) is stationary near the event horizon of a black hole, and a second observer (B) is stationary at great distance from the event horizon, then B will see A's clock to be ticking slow, and A will see B's clock to be ticking fast. But if A falls down toward the event horizon (eventually crossing it) while B remains stationary, then what each sees is not as straight forward as the above situation suggests.

As B sees things: A falls toward the event horizon, photons from A take longer and longer to climb out of the "gravtiational well" leading to the apparent slowing down of A's clock as seen by B, and when A is at the horizon, any photon emitted by A's clock takes (formally) an infinite time to get out to B. Imagine that each person's clock emits one photon for each tick of the clock, to make it easy to think about. Thus, A appears to freeze, as seen by B, just as you say. However, A has crossed the event horizon! It is only an illusion (literally an "optical" illusion) that makes B think A never crosses the horizon.

As A sees things: A falls, and crosses the horizon (in perhaps a very short time). A sees B's clock emitting photons, but A is rushing away from B, and so never gets to collect more than a finite number of those photons before crossing the event horizon. (If you wish, you can think of this as due to a cancellation of the gravitational time dilation by a doppler effect --- due to the motion of A away from B). After crossing the event horizon, the photons coming in from above are not easily sorted out by origin, so A cannot figure out how B's clock continued to tick.

A finite number of photons were emitted by A before A crossed the horizon, and a finite number of photons were emitted by B (and collected by A) before A crossed the horizon.

You might ask What if A were to be lowered ever so slowly toward the event horizon? Yes, then the doppler effect would not come into play, UNTIL, at some practical limit, A got too close to the horizon and would not be able to keep from falling in. Then A would only see a finite total of photons form B (but now a larger number --- covering more of B's time). Of course, if A "hung on" long enough before actually falling in, then A might see the future course of the universe.

Bottom line: simply falling into a black hole won't give you a view of the entire future of the universe. Black holes can exist without being part of the final big crunch, and matter can fall into black holes.

For a very nice discussion of black holes for non-scientists, see Kip Thorne's book: Black Holes and Time Warps.

For the record, reading that book referenced by Kip Thorne is how I came to understand these concepts.

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Actually, it would just appear to freeze... to be forever static right there at the edge of the event horizon... from the perspective of an outside observer, that is. Intersting to note, (I think it was) the Russians used to call blackholes "Frozen Stars."

The light from the object is infinitely red-shifted, so appears to be frozen in time from an outside observers perspective.

Also, you should read up on quasars. Your description is close, but way oversimplified.

http://en.wikipedia.org/wiki/Quasar

I do not believe that an object falling into a black hole would appear to freeze. You would see it being accelerated and as it was compressed it would be heated to Billions of degrees and you would see some fireworks, depending upon the mass. If what you said was true, quasars and relativistic jets would not exist.

What is so oversimplified? Quasars are the result of matter falling into supermassive black holes.

Can we get a third party to mediate on this one?

Edited by Airbrush

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Since gravity waves can exit black holes (otherwise they wouldn't exhibit gravity); would it be possible to make observations based upon the gravity waves? The internal structure of the earth has been similarly mapped using sound waves for example. A pebble tossed into the black hole might make all kinds of interesting gravity wave sounds...

Or does it not work this way?

That is a cool idea. Since you haven't gotten a response, it might be either no one knows or hasn't encountered/considered this possibility.

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I thought that gravity is more like a warping of space than a particle that leaves the massive object and travels outward. Have they even proven that gravitons exist? Gravitons are supposed to be without mass. I don't know, maybe you are on to something.

http://en.wikipedia.org/wiki/Gravitons

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I do not believe that an object falling into a black hole would appear to freeze.

I shared a link explaining exactly why this DOES happen. Can you share a link supporting your claims, as reality (and me also) doesn't really give a darn what you "believe," especially since your belief is in opposition to the facts.

The object would accelerate as it approached the EH, it would then at some point near the EH appear to slow down and get redder as the light coming from it to us (the observers beyond the EH) would get more and more red shifted until the red-shift was infinite and it appeared frozen.

Quasars are different because they pertain to the accretion disk, not objects passing the EH.

EDIT: You seem to be missing the very basic fact that once an object has crossed the event horizon it's light can no longer escape, and we'd be left with a lingering and reddened image of it right before it crossed that final threshold.

Edited by iNow

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Since gravity waves can exit black holes (otherwise they wouldn't exhibit gravity); would it be possible to make observations based upon the gravity waves? The internal structure of the earth has been similarly mapped using sound waves for example. A pebble tossed into the black hole might make all kinds of interesting gravity wave sounds...

Or does it not work this way?

From the right distance away the black hole either follows classical gravity, or GR, we think so I suspect not, but maybe, it all depends on what is actually going on at the singularity, which we don't know so your question can't be given a definite answer atm...

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The object would accelerate as it approached the EH, it would then at some point near the EH appear to slow down and get redder as the light coming from it to us (the observers beyond the EH) would get more and more red shifted until the red-shift was infinite and it appeared frozen.

...and we'd be left with a lingering and reddened image of it right before it crossed that final threshold.

Then such frozen images should accumulate over time, and we would be able to see many accumulated frozen images of objects that HAD entered the black hole over Billions of years (or as long as it has existed). Because scientists do not report these frozen red-shifted images clustered around black holes is why I say I find that hard to believe. But you may be right, and we just have not identified these YET. Or have they seen such things?

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Because scientists do not report these frozen red-shifted images clustered around black holes is why I say I find that hard to believe.

I understand your difficulty. Relativity is very difficult for us mere humans to grasp on an intuitive level. It's not intuitive, and our senses are organized to perceive movement across plains and to evade predators going no faster than about 30-40mph. We evolved senses to deal with issues we face right here on earth, not objects falling into blackholes.

But you may be right, and we just have not identified these YET. Or have they seen such things?

I don't think you have an appreciation of just how powerful our telescope would need to be to actually see this. Also, it's not me who is right, but what I'm describing is a direct consequence of general relativity... and that's been proven right time and again.

http://www.astronomynotes.com/evolutn/s13.htm#A2.6.1

Within the event horizon space is so curved that any light emitted is bent back to the point mass. Karl Schwarzschild worked out the equations in General Relativity for a non-rotating black hole and found that the light rays within a certain distance of the point mass would be bent back to the point mass. The derived distance is the same as the event horizon value above. The event horizon is sometimes called the Schwarzschild radius in his honor.

Falling toward a black hole would not be a pleasant experience. If you fell in feet-first, your body would be scrunched sideways and stretched along the length of your body by the tidal forces of the black hole. Your body would look like a spaghetti noodle! The stretching happens because your feet would be pulled much more strongly than your head. The sideways scrunching happens because all points of your body would be pulled directly toward the center of the black hole. Therefore, your shoulders would be squeezed closer and closer together as you fell closer to the center of the black hole. The tidal stretching/squeezing of anything falling into a black hole is an effect conveniently forgotten by hollywood movie writers and directors.

Your friend watching you from a safe distance far from the black hole as you fell in would see your clock run slower and slower as you approached the event horizon. This is the effect of time dilation'' (see
). In fact, your friend would see you take an infinite amount of time to cross the event horizon---time would appear to stand still. However, in your reference frame your clock would run forward normally and you would reach the center very soon. If you beamed back the progress of your journey into a black hole, your friend would have to tune to progressivly longer wavelengths (lower frequencies) as you approached the event horizon. This is the effect of gravitational redshift'' (see
). Eventually, the photons would be stretched to infinitely long wavelengths.

Again, the issue here is gravitational redshift, which itself has been confirmed empiracally in experiments such as the Pound-Rebka experiment. One also needs to note gravitational time dilation.

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I don't mean to sound argumentative, and I do appreciate the efforts you have made to explain this point. It is still beyond me.

Then what you are saying is that suppose we launch a 100 kgm rocket towards a solar mass black hole. Suppose also that the rocket turns around and attempts to slow down its approach so we can get a better view of what happens. As it gets closer the BH gravity will overcome the rocket and drag it into oblivion very quickly. As the rocket is crushed and spaggetified the remaining flash will linger outside the EH forever? Then someday when we discover such a nearby BH and we can get a close enough view of it, we should see ghostly images all around it of matter that fell into it during its existence?

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Mr. Airbrush ; I would think the mass at the EH would be 2 Dimensional relative to an observer outside the BH. However I understand where you are comming from, because as we know some BH's are thought to spin, my question would be how can a BH spin if the relative time of an event occuring at the EH would be infinite to an observer outside the BH?

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That is great material iNow, thanks for that.

Primordial, the black hole can spin in its' own space-time, and what we see is only our impression.

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