PDA

View Full Version : Supermassive Black holes



PeeDee
03-16-2007, 02:19 AM
So. I watched a fascinating show on the National Geographic channel the other night, and then based on the notes I took during that show (because I'm a dweeb) I've been reading up on "supermassive black holes"

This is fascinating, and alarming. Up until my recent love affair with science, the last thing I'd read about them was Einstein theorizing their existence.

The show was interesting, in that they studied a galaxy (I forget the designation) where there should have been a supermassive black hole at the center, and then studied our nearby Andromeda galaxy as a "normal" galaxy to compare the two. What they found out was that the galaxy whic SHOULD HAVE had a black hole didn't....and Andromeda did.

But the black hole at the center of Andromeda was a dormant supermassive black hole. That fascinates me, as do the whole concept of black holes. My current interest is DORMANT black holes. I didn't know such a thing could occur. To me, it seems its like having a whirlpool in water that doesn't cause currents or suck anything down.

The alarming bit came from learning that apparently, we have a dormant supermassive black hole at the heart of our own Milky Way Galaxy.

I wonder what makes them go dormant, and what makes them go active. And I wish we could send probes into them and expect to retrieve data from them once they're past the event horizon.

Pthom
03-16-2007, 02:38 AM
Could it be that, like planets that clear out entire circular regions of a solar system from stuff like dust and asteroids, a black hole ultimately gobbles up all the stuff that, because it isn't orbiting fast enough, gets drawn in?

I'm thinking along the lines of binary stars--or even planets (Earth and Luna being nearly a binary planet)--that because of their relatively similar masses, continue to orbit one another but never collide.

And somewhere recently, I heard that information about a thing is not lost when it passes the event horizon of a black hole. (Something on NOVA or the Discovery channel, I think. These things come, I watch, say "wow!" and they go, and I forget when and where.)

Meerkat
03-16-2007, 02:39 AM
I wish we could send probes into them and expect to retrieve data from them once they're past the event horizon.

I think according to both Stephen Hawking and Ray Kurzweil, this is indeed possible, and it is probably the case that information is coming out of them....elsewhere or elsewhen. Grist for your fiction mill, no?

PeeDee
03-16-2007, 02:53 AM
I don't think it's lost, because I tend to think of black holes in the same sense as hurricanes and tornados. If you get inside, you're safer than on the outside edges of it. I realize this is probably wildly inaccurate, but that's where my mind goes.

I just wonder what happens to things inside. I mean, its not just SPACE tha curves toward black holes, it's TIME (how do they know this? That's something that fascinates me. How does time curve? How does a blakc hole curve time?)

benbradley
03-16-2007, 02:53 AM
I've never heard of "dormant" vs. "active" black holes. They're not like volcanoes which may randomly (as far as we see on the surface) erupt. Black holes are like, well, holes in space, and nothing happens until and unless matter gets too near them. Then the matter gets accelerated big time, gas particles hit each other at high rates of speed, heating up and making light, x-rays and other electromagnetic radiation that we would see around a black hole (or we would see this "as" the black hole). It's all the bits of matter rushing in, approaching the speed of light and running into each other, that makes all the excitement of stuff around a black hole.

There's Hawking radiation, but it's insignificant except for very small (microscopic) black holes. These may have been created in the Big Bang, but would have evaporated away by now.

But that's mainly for "small" black holes, a few solar masses (that would be created in the collapse of a star just a few times larger than the Sun) or smaller (which would have been created in the Big Bang, or in more speculative ways). The huge black holes at galactic centers are so big that it may not look like much is going on. Sure, the stars are orbiting around the core at a pretty fast clip, but other than that... the gravitational tide is much, much lower, so you and your spaceship could be near or even into the event horizon and not even notice. Except it will take a long time to get back out, and you may eventually figure out that you're not ever gonna get out. Is that more comforting than the thought of approaching a smaller black hole, and getting literally torn apart by gravity that increases by thousands of G's for every foot closer you get?

My guess is that a black hole that is "dormant" means there's not a lot of matter in its vicinity that's falling into it, and "active" means there IS a lot of matter falling in.

Thump
03-16-2007, 02:54 AM
Oh gosh! I used to be such a black hole geek :D! I still love the space documentaries passionately, especially those with topics most people can't get their heads around X-D Quantum physics anyone? I might not get the maths but I can picture what's going on.

Who said science-fiction didn't teach you anything?

Oh yeah, that was my dad :D

Anyway, this is the first time I hear about dormant black holes. I must know proceed to torture the information out of google.

PeeDee
03-16-2007, 02:58 AM
http://www.lsw.uni-heidelberg.de/users/mcamenzi/SMBlackHoles.html

Dormant black holes, as near as I can tell from articles such as this, are not actively pulling things in or excreting energy. They're just a well of gravity that isn't receiving any fuel. They are at the hearts of most galaxies, it's theorized, especially galaxies where stars are spinning too fast to be held together without the black hole at the center. Without it, they would just spin off into space.

Tachyon
03-16-2007, 03:03 AM
I think according to both Stephen Hawking and Ray Kurzweil, this is indeed possible, and it is probably the case that information is coming out of them....elsewhere or elsewhen. Grist for your fiction mill, no?
Information that enters a black hole is indeed recoverable, perhaps in the form of Hawking radiation (http://en.wikipedia.org/wiki/Hawking_radiation). Of course, such information is garbled beyond recognition.

I'm not quite sure what is meant by a "dormant" black hole. But as a black hole gets larger, the event horizon itself gets further from the "centre" of the black hole, so the gravitation forces become more diffuse. Or perhaps dormant black holes are such that they are evaporating (from the emission of Hawking radiation) faster than they are consuming more matter? I don't know. :D


Dormant black holes, as near as I can tell from articles such as this, are not actively pulling things in or excreting energy. They're just a well of gravity that isn't receiving any fuel. They are at the hearts of most galaxies, it's theorized, especially galaxies where stars are spinning too fast to be held together without the black hole at the center. Without it, they would just spin off into space.
Ah, that makes sense.

PeeDee
03-16-2007, 03:14 AM
I have only found references to dormancy when reading about supermassive black holes which may change things altogether.

My big question rihgt now is the bending of space-time around black holes, and what that means.

In the process of reading about it, I found this fascinating article. (http://www.channel4.com/science/microsites/S/science/space/timemachine.html)

Meerkat
03-16-2007, 03:15 AM
Information that enters a black hole is indeed recoverable, perhaps in the form of Hawking radiation (http://en.wikipedia.org/wiki/Hawking_radiation). Of course, such information is garbled beyond recognition.


Right, but if I remember right, each of the guys I mentioned had thought of a way that it was not necessarily garbled beyond recovery...similar to the way you can have an ink spot in a vial of very thick, transparent fluid. You carefully stir the fluid clockwise three times, and the spot disappears. But when you stir three times counterclockwise, the spot is restored to its original appearance. Their ways probably included the creation of polarized comparison particles though, not untangling the original, tortured mess.

scarletpeaches
03-16-2007, 03:16 AM
I thought this thread was about the song. Remarkably, as this forum is for writers, the group which sings it is called Muse. :D

PeeDee
03-16-2007, 03:19 AM
Right, but if I remember right, each of the guys I mentioned had thought of a way that it was not necessarily garbled beyond recovery...similar to the way you can have an ink spot in a vial of very thick, transparent fluid. You carefully stir the fluid clockwise three times, and the spot disappears. But when you stir three times counterclockwise, the spot is restored to its original appearance. Their ways probably included the creation of polarized comparison particles though, not untangling the original, tortured mess.

I don't suppose you have a link where I can read about this ink spot business, which ALSO sounds fascinating.

(I'm in science-sponge mode. :) )

benbradley
03-16-2007, 03:26 AM
I don't think it's lost, because I tend to think of black holes in the same sense as hurricanes and tornados. If you get inside, you're safer than on the outside edges of it. I realize this is probably wildly inaccurate, but that's where my mind goes.

I just wonder what happens to things inside. I mean, its not just SPACE tha curves toward black holes, it's TIME (how do they know this? That's something that fascinates me. How does time curve? How does a blakc hole curve time?)

As a followup, I'm reading "Ripples on a Cosmic Sea: The Search for Gravitational Waves" (1998)- I'm skimming much of it because I've read so many other science and physics books (by John Gribbin, Roger Penrose, many others I forget at the moment, and even a "more recent" Brian Greene Superstring book) that a lot of it is already familiar to me, but he does give, among other things, a history of the developent of ideas of black holes, neutron stars, neutron binaries, supernovas and other fun astronomical things that almost surely generate (very weak and hard to detect) gravitational waves.

But to answer your question, I don't know that there's an explanation of "how", but the fact is "it happens." Any mass creates gravity, and gravity causes time to go slower, much like increasing speed toward the speed of light causes time to go slower for that thing whizzing by. Precise atomic clocks, one at sea level and one on a mountaintop, will run at measurably different rates because the Earth's gravitational force is less at the top of the mountain. The GPS sattelites in space have such clocks and they are being continuously compensated for the effects of how far they are from Earth and the speed at which they're orbiting.

The effect of time slowing down is much more pronounced near a black hole because the gravity (no pun intended, but glad I thought of it...) is so much greater.

The thing about black holes "preserving information" is a quite recent revelation. The idea is from the 1970's, but was settled (at least to SOME physicists' satisfaction) only a few years ago. It was easy for me to Google because I recall that Hawking lost a bet on this issue, and gave the winner a baseball encyclopedia. Here are a couple articles on it:
http://www.theory.caltech.edu/~preskill/globe-and-mail.html (http://www.theory.caltech.edu/%7Epreskill/globe-and-mail.html)
http://en.wikipedia.org/wiki/Black_hole_information_paradox

Meerkat
03-16-2007, 03:31 AM
I don't suppose you have a link where I can read about this ink spot business, which ALSO sounds fascinating.

(I'm in science-sponge mode. :) )

Sorry PeeDee....I just tried to google various combinations. Nothing. But the good news is I now know how to remove a variety of stains from the carpet, and a few formulae for disappearing ink!

PeeDee
03-16-2007, 03:32 AM
I'm wandering afield of blac holes now, except that it's all sort-of-related, but...

WHY does gravity affect time? I mean, I realize that the concept of "days, weeks, years," are just humans quantifying time into something usable, but I don't understand how gravity, something present in the first three dimensions, can affect the fourth dimension as well. I just don't get that.

And I thought this was fascinting, quoted from the article above.



The notion of time travel is rooted in the early 20th century physics of Albert Einstein (http://www.channel4.com/science/microsites/S/science/life/biog_einstein.html). Einstein knew that for 20 years scientists had been puzzled by a discovery that suggested there was something decidedly odd about the speed of light. In the 1880s, two American scientists, Albert Michelson and Edward Morley set out to measure how the speed of light was affected by Earth's motion through space. They discovered, to their amazement, that the speed of Earth made no difference to the passage of light through space (which they called the ether). No matter how fast you travel, the speed of light remained the same.

How could this be? Surely if you were travelling at half the speed of light and the beam from a torch passed you, the speed of the light from the torch would be seen as travelling slower than if you were stationary. The answer is definitely no! The speed of light is always 300 million metres per second.

benbradley
03-16-2007, 03:57 AM
Here's a third page on the information coming out of a black hole by John Preskill, the winner of the bet and lucky recipient of the Baseball Encyclopedia:
http://www.theory.caltech.edu/~preskill/jp_24jul04.html

benbradley
03-16-2007, 04:02 AM
I don't suppose you have a link where I can read about this ink spot business, which ALSO sounds fascinating.
Me too.

(I'm in science-sponge mode. :) )
I've ALWAYS been in science-sponge mode, since perhaps age 5. I shudda been a scientist.

Thump
03-16-2007, 04:10 AM
I love this thread :D

I loved the post about the speed of light. That is indeed fascinating.

Teach me more of the secrets and mysteries of the universe oh great masters!

PeeDee
03-16-2007, 04:13 AM
I've ALWAYS been in science-sponge mode, since perhaps age 5. I shudda been a scientist.

See, this is a recent thing for me. I had some Very Silly Ideas when I was young, in that if I didn't actively need it for writing, I wasn't interested in it. this is because I was an idiot.

In science classes, I mostly just worked on short stories. Like I said, Pete = Idiot.

So now, I'm making up for it. I'm eating this and history stuff that I also missed out on like nothing else. Threads like this make me hyper and excited.

blacbird
03-24-2007, 08:40 AM
Could it be that, like planets that clear out entire circular regions of a solar system from stuff like dust and asteroids, a black hole ultimately gobbles up all the stuff that, because it isn't orbiting fast enough, gets drawn in?

It appears that you are exactly correct here. Black holes go "dormant" once they've cleared out the neighborhood of stuff they can swallow. Which is not much different from the formation of stars, which essentially stop growing in their birth nebula once they've done the same thing. The sun isn't gobbling up appreciable amounts of material anymore because everything orbiting it is far enough away to be in stable, balanced orbital relationships. Same with black holes.

caw

PeeDee
03-25-2007, 12:50 AM
Interesting. So in theory, a black hole could work as the center of an orbital system of planets, provided they were far enough and moving fast enough.

They would get no heat or light from it, since it's a black hole, but if thi were a science fiction novel, you coul dhave a race of creatures that live and see on radiation spectrums, the way we do on light spectrums.

Pthom
03-25-2007, 03:45 AM
The light we see is a radiation spectrum. It's a very narrow band approximately in the center of the electomagnetic spectrum, which extends from gamma radiation on one end, to radio waves on the other:

http://praxis.pha.jhu.edu/pictures/emspec.gif

As I understand it, a black hole doesn't suck up only visible light, but electromagnetic radiation spectrum wide. I also understand that black holes emit (or eject) x-ray radiation in gigantic jets, but these are oriented along the axis of rotation, not in the plane where any orbiting planets might exist.

And that, folks, is about the extent of my understanding of black holes...except that they are, and no doubt will be for some time to come, great fodder for SF stories.

Sage
03-25-2007, 03:53 AM
Black holes scare me.

Ali B
03-25-2007, 04:15 AM
Hyperspace by Michio Kaku is facinating. He covers things like time warps, the 10th dimension, parallel universes, etc. Kinda mind blowing if you can actually understand it. Half of the time I can't. lol

Summonere
03-25-2007, 06:09 AM
PeeDee:
I mean, its not just SPACE tha curves toward black holes, it's TIME (how do they know this? That's something that fascinates me. How does time curve? How does a blakc hole curve time?)


Space and time are the same thing. Some smart guys figured this out using math and a calculator. If you warp one, you warp the other, but warping one that we can readily observe -- space -- requires lots and lots of "energy." In this case, that energy is mass. (By the way, they "know" this merely in a theoretical sense. Right now, the math of the theory's component parts seems to hold up, suggesting it's true. Might find out otherwise later.)



PeeDee:
WHY does gravity affect time?


Here's an analogy. Maybe a useful one, maybe not. (Though it should work in multiple ways, some of which may even be clearer than what I'll present here.) The analogy involves this diagram:

)--------)-------)------)-----) O)))))

Imagine that O above is an object speeding through air. Maybe a supersonic jet. It's moving from left to right. As it approaches supersonic speed, it compresses air in front of it. That's what these ))))) things are, compressed air. The farther-spaced things behind the O are normal air, uncompressed.

Imagine, now, that this thing is not a supersonic jet hurling through air, but is a supermassive body, say a black hole. And now imagine that everything on the right of it in the diagram above represents everything within its gravitational influence, and everything on the left remains outside that influence. It's the sheer crushing weight of the thing that squishes space around it just like a speeding jet squishes air ahead of it. Since space and time are the same, compressed space = compressed time. When we consider the left side of the graphic above, we see normal space, uncompressed space.

Also, note that the wee diagram above can be used to illustrate, in its own bad way, at least three of the Lorentz transformations: (1) space shrinks in the direction of motion (Lorentz contraction); (2) time slows down (time dilation); (3) clocks desynchronize (relativity of simultaneity or "sync shift"); (4) mass increases in the moving frame. (I forgot to add that these are how things appear to an observer in a fixed frame of reference when observing the moving frame of reference, as represented in the diagram).

I'd write more, but since I've been up since four this morning, this is all I can squeeze out of my brain. Heck, some of it may be remotely right. (Or it might embarrass me in daylight.)

Mom'sWrite
03-25-2007, 06:29 AM
I wonder what makes them go dormant, and what makes them go active.


The hours of activity and dormancy are set by the union. Sheesh, you didn't know that?

Ali B
03-25-2007, 06:31 AM
This, however confusing, is the difference between reg. black holes and supermassive:
Supermassive black holes have some interesting properties which distinguish them from relatively low-mass cousins:
The average density of a supermassive black hole can be very low, and may actually be lower than the density of water. This is because the Schwarzschild radius is directly proportional to mass, such that density is inversely proportional to the square of the mass.
The tidal forces in the vicinity of the event horizon are significantly weaker. Since the central singularity is so far away from the horizon, a hypothetical astronaut travelling towards the black hole center would not experience significant tidal force until very deep into the black hole.
Found at: http://en.wikipedia.org/wiki/Supermassive_black_hole

TsukiRyoko
03-25-2007, 06:43 AM
I believe they're considered dormant because the black hole itself has vanished, leaving a "scar"/Hawking radiation behind it. It's still considered a black hole because they're still massive in weight and affect the fabric of space, but they don't actually produce a strong gravitation field capable of sucking in planets and the like. They can mess with orbits, though.

I may be wrong, though.

I also find the concepts of black holes absolutely amazing. I have a good bit of books on them, but I've never seen one that really thoroughly explains what a dormant black hole is.

Science is wonderful thing.

benbradley
03-25-2007, 07:13 AM
Interesting. So in theory, a black hole could work as the center of an orbital system of planets, provided they were far enough and moving fast enough.

They would get no heat or light from it, since it's a black hole, but if thi were a science fiction novel, you coul dhave a race of creatures that live and see on radiation spectrums, the way we do on light spectrums.

As far as the "far enough and moving fast enough," the main determinate is the mass of the black hole. The main difference between a black hole and the same mass of "ordinary" matter is the size. Black holes are much, much smaller. A black hole with the mass of the Earth would have a diameter of about 1/3 inch (outside the USA, that would be about one centimeter). If you orbit that black hole 4,100 miles away, you'll go around it in 90 minutes, just like the Space Shuttle does when orbiting 100 miles above the Earth's surface (and being 4,100 miles from the Earth's center).

If you replace the Sun with a black hole of the same mass as the Sun, then nothing will change as far as the orbits of the planets. From the quote below (and converting km radius to diameter in miles) such a black hole would be a sphere just under 4 miles diameter, so it would be a really tiny thing from Earth's distance of 93 million miles. Yes, it probably would be visible in a telescope as random atoms fall toward it and run into one another at near lightspeed, giving of heat, light, UV, x-rays and gamma rays, just about everything in that spectrum in Pthom's post, but probably most of the output would be in the x-ray and gamma ray range (this stiuff is mostly filtered out by Earth's atmosphere, which is a Good Thing). The black hole might give off enough light to be be visible to the naked eye when a comet or other 'large' chunk of matter (perhaps as large as a grain of sand) falls in and gets too close, heating up and causing a flash. One thing that would be visible around the black hole is how the images of the stars near it are pushed around because of its gravity bending the light rays that go near it like a lens (this is actually called a gravitational lens). But that might only be noticable very close to it, I think you would at least need binoculars to see the effect.
Quoting from:
http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html


If the Sun was replaced with a black hole that had the same mass as the Sun, the Schwarzschild radius would be 3 km (compared to the Sun's radius of nearly 700,000 km). Hence the Earth would have to get very close to get sucked into a black hole at the center of our solar system.

blacbird
03-25-2007, 08:25 AM
The real sexy thing right now would be "dark matter" creatures. The term "dark matter", like the term "big bang", sucks, but we're stuck with it. Whatever it is, it isn't really "dark". It's invisible. It doesn't respond to the electromagnetic energy spectrum in any way. The only relationship it appears to have with forces we "normal matter" creatures recognize is gravity. Gravity just happens to be the most mysterious and uncontrollable of the major physical forces we know. Some evidence exists to indicate that most, perhaps all, dark matter was expelled from what we now recognize as galaxies in their earliest formational period, perhaps by quasars (???). Anyhow, most, perhaps all, of it seems to hang out as halos around galaxies which exert control over galactic rotation (which is the only way we can detect it). Light and other electromagnetic radiation passes through it as if it's not there, but the gravitational effects can produce Einsteinian lensing of distant light sources, like quasars. There's no evidence I know of, other than the gravitational effects, that this stuff interacts with "normal" matter in any way. But the gravitational effects are huge, and indicate that the "mass" of this dark matter (if we can ascribe "mass" to it) is much greater than the observable mass of regular matter.

It could be all around us. Some of it could be passing through your body even as you read this, and you'd never know. Sort of like Homeland Security, you know?

My head hurts. I need a drink.

caw

Histry Nerd
03-25-2007, 08:31 AM
If you replace the Sun with a black hole of the same mass as the Sun, then nothing will change as far as the orbits of the planets. From the quote below (and converting km radius to diameter in miles) such a black hole would be a sphere just under 4 miles diameter, so it would be a really tiny thing from Earth's distance of 93 million miles. Yes, it probably would be visible in a telescope as random atoms fall toward it and run into one another at near lightspeed, giving of heat, light, UV, x-rays and gamma rays, just about everything in that spectrum in Pthom's post, but probably most of the output would be in the x-ray and gamma ray range (this stiuff is mostly filtered out by Earth's atmosphere, which is a Good Thing). The black hole might give off enough light to be be visible to the naked eye when a comet or other 'large' chunk of matter (perhaps as large as a grain of sand) falls in and gets too close, heating up and causing a flash. One thing that would be visible around the black hole is how the images of the stars near it are pushed around because of its gravity bending the light rays that go near it like a lens (this is actually called a gravitational lens). But that might only be noticable very close to it, I think you would at least need binoculars to see the effect.

I'm loving this thread.

One thing to remember about your planetary system, PeeDee: black holes do not emit radiation of their own. They "shine" only because matter falling into them reaches an extremely energetic state at the event horizon; it is this matter that emits the x and gamma rays by which we can "see" black holes. So in order for life to evolve in such a system, the black hole at its center would have to be extremely well fed, and more importantly, it would have to be consistently well fed; the radiation emitted by the infalling matter would have to remain constant over the millions of years it would take for such life to evolve. And whatever was feeding the black hole would have to be able to do so without disrupting the orbit of the planet on which life was evolving. Like, say, a brown dwarf/black hole binary system, in which matter from the brown dwarf falls off and forms an accretion disk (http://antwrp.gsfc.nasa.gov/apod/ap991219.html)around the black hole.

Of course, if life somehow evolved in a system with highly variable conditions, it could just end up producing the toughest, most resilient MFers in the galaxy--in which case they might be enslaved and used as soldiers by a more advanced civilization who used them to conquer said galaxy, whereupon they might just realize they no longer needed their masters and take the lot for themselves. Gotta be a story in there for somebody....

On the subject of gravitational lensing: one easy-to-see example is called the Einstein Cross (http://antwrp.gsfc.nasa.gov/apod/ap001010.html). It is actually a quasar lensed through a galaxy, but the effect is very similar, I think, to what you might see if a star were lensed behind a black hole:

http://antwrp.gsfc.nasa.gov/apod/image/0010/qso2237_wiyn.jpg (http://antwrp.gsfc.nasa.gov/apod/image/0010/qso2237_wiyn.jpg)

Of course, if you live on a planet orbiting a black hole, and the black hole lenses background stars in this way, you could tell what time of year it was by which star was being lensed on a particular day. So a hypothetical civilization that developed on such a world might track the progression of their year not by the position of the sunrise or sunset, or by the positions of the constellations, but by which star was multiplied in that season.

Sorry. Hope that's not too much nerd. This is as close as I come to writing SF.

HN

PeeDee
03-25-2007, 08:42 AM
I'm not going to reply to most of this stuff because...er...I have nothing to reply with. This stuff is all far and away for bigger brains than mine, and I'm really, really enjoying reading it. Absolutely fascinating.

I just wanted to point out, if I wasn't clear, that I didn't expect the black hole to give off any "light," and thus serve as an effective replacement for a star in a solar system. Just that it could have planets orbiting it. In a similar manner.

I confess, I do understand in principle how extreme gravity, such as a black hole possesses can affect both space, light, and solid matter. I don't know if I'm being deliberately dense (har har) but I just don't get how it affects time at all. I don't understand how time and space are the same thing.

People move through time. Yes. We move through space. Yes. We are four-dimensional creatures, in that we are moving through four dimensions.

But I don't follow how time can be a physicality which can be compressed or expanded by a black hole, or by anything else.

blacbird
03-25-2007, 08:47 AM
But I don't follow how time can be a physicality which can be compressed or expanded by a black hole, or by anything else.

Trust your feelings, Luke.

caw

PeeDee
03-25-2007, 08:48 AM
That's probably how science works in the Star Wars universe, too...

Anya Smith
03-25-2007, 09:01 AM
I find black holes absolutely fascinating.

As for bending time, the way I understand it is black holes don't really bend time, but rather they bend our perception of time. We are traveling in a linear fashion, but in the four dimensional space all aspects of time, past, present, future happen simultaneously. It's because we travel from present to future, IMO, time seems bent near a black hole.

I came late to this post, so I just want to mention that recently, about 50 years ago, our black hole consumed a chunk of matter about the size of the sun. Of course, it wasn't so recent in cosmic times, because we're located roughly 27,000 light years from the center of our galaxy, so it means it had happened 27,000 years + 50.

Here's a poem I scribbled. Sometimes these cosmic objects won't leave me alone. The meter is off, but I'm not a poet.

SCHWARTZCHILD (GRAVITY)

That awesome Creator, the Supreme of All,
Giving Its children chores upon chores.
Schwartzchild is hungry, hes ravenous by nature,
Avoid getting near him, for he gobbled up his neighbor.

Schwartzchild is mighty in his domain.
He is a big bully who worked out a way
To shepherd the strong and lure the unwary
Beyond his horizon, his reign is unfailing.

He lurks in a black pit, deep and compressing
His feelers are dark-lit, mean and oppressing.
Anything he captures, subjoin with his might,
Adding to his power, theyre trapped for all time.

In wisdom hes lacking, and hes not a genius,
But he managed to create the Schwartzchild radius,
Behind which he hoards his ill-gained plunder.
His Sire is watching and waiting for his blunder

PeeDee
03-25-2007, 09:03 AM
That just begs for a Dave McKean illustration. That's really cool.

And I think...that I actually follow your explanation of time-bending. Or at least, I grasp it more than I've previously managed, and that's a start.

benbradley
03-25-2007, 09:47 AM
Trust your feelings, Luke.

caw
Use the product of mass and accelleration, Luke.

For an SF example of using huge black holes to "extend" time, there's the Gateway series, aka "the Heechee Saga" by Fredrick Pohl. I think it's in the second book that things get interesting (mega-super-massive black-hole wise). It doesn't explain "why" any more than anything else, but (IMHO) it puts the effect to good use in the story.

TsukiRyoko
03-25-2007, 10:00 AM
One thing to remember about your planetary system, PeeDee: black holes do not emit radiation of their own.
Actually, Histry, they DO emit radiation. Look up Hawking radiation. By this radiation, we can determine what went into the black hole. Also, while the radiation scarcely produces light, it IS possible.

Histry Nerd
03-25-2007, 03:47 PM
Actually, Histry, they DO emit radiation. Look up Hawking radiation. By this radiation, we can determine what went into the black hole. Also, while the radiation scarcely produces light, it IS possible.

Thanks for the correction, Tsuki. I had never heard of Hawking radiation. But it seems the amount emitted by any but a very small black hole would be unusable by the inhabitants of PeeDee's planetary system. The Wikipedia article (http://en.wikipedia.org/wiki/Hawking_radiation) contained this example:


A black hole (http://en.wikipedia.org/wiki/Black_hole) of one solar mass (http://en.wikipedia.org/wiki/Solar_mass) has a temperature of only 60 nanokelvins; in fact, such a black hole would absorb far more cosmic microwave background radiation (http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation) than it emits. A black hole of 4.5 10 kg (about the mass of the Moon (http://en.wikipedia.org/wiki/Moon)) would be in equilibrium at 2.7 kelvins, absorbing as much radiation as it emits. Yet smaller primordial black holes (http://en.wikipedia.org/wiki/Primordial_black_hole) would emit more than they absorb, and thereby lose mass.

Water freezes at just over 273 Kelvins. So at 60 nanokelvins, our hypothetical sun-sized black hole is very cold indeed. If life were to evolve there, it would need a lot more radiation than it could get from the Hawking photons.

But your point was that black holes do emit radiation of their own, and on that you are correct. Thanks for helping me learn something new today!

HN

PeeDee
03-25-2007, 06:47 PM
Thanks for the correction, Tsuki. I had never heard of Hawking radiation. But it seems the amount emitted by any but a very small black hole would be unusable by the inhabitants of PeeDee's planetary system. The Wikipedia article (http://en.wikipedia.org/wiki/Hawking_radiation) contained this example:

Well, I was hardly trying to prove a point. It was just spinning hypotheticals. I don't expect there are plentary systems with a black hole at the center, supermassive or otherwise, and I also don't think there's going to be any life there.

Jamesaritchie
03-25-2007, 07:01 PM
It's the math that gives me a headache. But gravity certainly does slow time, even here on earth. A watch placed on a mountain peak runs measurable faster than one placed at the base of the mountain.

If humans lived long enough, one twin could spend a million years or so on top of the mountain, while the other spent a million years at the base of the mountain, and the twin at the top would then be an actual year older than the twin at the base.

The things I do know.

1. Most of what we believe about black holes, large or small, is still theory, and the theory changes regularly.

2. A dormant black holes is nothing more than a black hole that has nothing to eat. Should any material come within eating distance, the black hole then becomes active.

3. Hawking radiation certainly exists, but the exact cause, and the exact effect, are unknown. The radiation may not shrink the black hole at all, since it may be produced by the creation of two equal particles, one of which escapes the gravitational pull of the black hole, and the other of which maintains the conservation of matter and energy by falling into the black hole.

4. We think we know what causes gravity, but we don't even know if gravity is an actual force, an actual object, or simply an effect of something else entirely. No one has even seen gravity, no one has ever found gravity, etc. All we have managed to do is measure the effect of gravity. Gravity, as an actual, physical thing, may not even exist.

One theory, hugely simplified, states that gravity may work more like a vacuum cleaner than anything else. Mass warping space and time may simply create what can be considered a quantum vacuum cleaner that tries to pull everything within sucking distance into the "hole." Which would mean we haven't been able so see gravity, can't measure anything except the effect of gravity, because there isn't anything to see or measure. There are no "vacuum waves" to be found, only the effects of the vacuum cleaner itself. The vacuum cleaner is the vacuum, and warped time and space IS gravity.

More mass does not create more gravity, but simply a stronger quantum vacuum cleaner. In other words, gravity may be passive, rather than active.

This would also explain why gravity seems to be a force that pushes down, as well as a force that pulls down.

5. Time is a physical dimension, and as such, a "physical" object, or at least as much so as the first three dimensions.

6. Many still believe that every galaxy has a massive black hole at its core, but that only a tiny percent are active. We still have great trouble detecting dormant black holes, and it may well be impossible to do so in many cases, at least from earth.

7. Quantum mechanics causes my brain to leak out my ears, but it is fun to study. For anyone interested, I think this is a decent place to start because it begins with classical mechanics, and uses these as an introduction to quantum mechanics. The math made my eyes bleed at first, but it isn't quite as difficult as it first appears. Just have plenty of whiskey on hand.

TsukiRyoko
03-25-2007, 07:23 PM
Well, I was hardly trying to prove a point. It was just spinning hypotheticals. I don't expect there are plentary systems with a black hole at the center, supermassive or otherwise, and I also don't think there's going to be any life there.
In addition to the millions of stars we can and can't see (all solar systems of their own), there are other systems with black holes as their central points. They are still called solar systems, I think, because while there's nothing solar about them right now, their central point was once a massive super blue star. After the star's death, the black holes and the suns act much in the same way and keep the planets/masses in an orbit. Granted, I don't think these systems last long in atronomical terms (most black holes grow the more they "eat", unless they're very small, like Histry said, and emit more than they absorb. Eventually, I'd imagine most systems with black holes at their centers would be lunch), but they do exist.

TsukiRyoko
03-25-2007, 07:28 PM
If humans lived long enough, one twin could spend a million years or so on top of the mountain, while the other spent a million years at the base of the mountain, and the twin at the top would then be an actual year older than the twin at the base.
Wanna hear something cool? Say we have a set of identical twins, or hell, even clones. If we could hypothetically send a twin into space, accelerating their speed until they just reached lightspeed, then immediately sent them back, the twin that we left on Earth would be 50-100 years olders, and the twin we sent up in space would have barely had the time to read a book.

PeeDee
03-25-2007, 08:14 PM
Christ, my brain's hurting already.

I think the concept of time as a quantifiable fourth dimension, as able to be affected by gravity as the others, is just beyond my brain. I absolutely Do Not Get It. Nor do I get how time can run faster on a mountain peak. So hypothetically, if I put one twin on a mountain peak and one twin at the very deepest part of the ocean, wuld the one at the bottom have a shorter lifespan*? I don't get why, but thats' where I follow the logic to.

If, with Hawking radiation, we cannot spot the cause, and we cannot measure the effect, then how do we have any idea it exists? Is it purely mathematical theory, just like black holes were back when Einstein was still scribbling numbers?



* "shorter lifespan," obviously not including the bit where he's crushed to a few molecules width and drowned because he's at the bottom of the ocean, mind you.

TsukiRyoko
03-25-2007, 10:11 PM
Christ, my brain's hurting already.

I think the concept of time as a quantifiable fourth dimension, as able to be affected by gravity as the others, is just beyond my brain. I absolutely Do Not Get It. Nor do I get how time can run faster on a mountain peak. So hypothetically, if I put one twin on a mountain peak and one twin at the very deepest part of the ocean, wuld the one at the bottom have a shorter lifespan*? I don't get why, but thats' where I follow the logic to.

If, with Hawking radiation, we cannot spot the cause, and we cannot measure the effect, then how do we have any idea it exists? Is it purely mathematical theory, just like black holes were back when Einstein was still scribbling numbers?



* "shorter lifespan," obviously not including the bit where he's crushed to a few molecules width and drowned because he's at the bottom of the ocean, mind you.
It's actually very simple. It all has to do with relativity. Time, theoretically our fourth dimension, can be manipulated and moved about, just like the other dimensions. Time can easily be swayed using speed, gravity, and perspective. Fascinating, isn't it?

Actually the theory of black holes and radiation (still at the quantum physics stage) first came to be when we began to estime the measure of the universe. First, the measurements would come our straight. Then, they would show the universe being curved. Put a black hole into the equation, and voila! It fits!

PeeDee
03-25-2007, 10:15 PM
1)It's actually very simple. It all has to do with relativity. Time, theoretically our fourth dimension, can be manipulated and moved about, just like the other dimensions. Time can easily be swayed using speed, gravity, and perspective. Fascinating, isn't it?

2)Actually the theory of black holes and radiation (still at the quantum physics stage) first came to be when we began to estime the measure of the universe. First, the measurements would come our straight. Then, they would show the universe being curved. Put a black hole into the equation, and voila! It fits!

I get paragraph two. Makes sense to me.

Paragraph one, I'm just mentally blockd against it. I dont' get HOW time can be swayed by anything. I've been reading all sorts of articles on time all morning, trying to fiure it out, and they've all explained it as lucidly you folks have. So it must just be me...

Ali B
03-25-2007, 11:02 PM
* "shorter lifespan," obviously not including the bit where he's crushed to a few molecules width and drowned because he's at the bottom of the ocean, mind you.
LOL, there's always those little annoying extras that ruin a good idea.

TsukiRyoko
03-25-2007, 11:34 PM
I get paragraph two. Makes sense to me.

Paragraph one, I'm just mentally blockd against it. I dont' get HOW time can be swayed by anything. I've been reading all sorts of articles on time all morning, trying to fiure it out, and they've all explained it as lucidly you folks have. So it must just be me...
Some people understand stuff, and some just don't. You don't understand swaying time, I don't understand how things get rusty. I mean, really, how does it happen? Oxidation this, chemical reaction that- I still don't get how it really happens, and I've had it explained very well to me.

Michael Dracon
03-26-2007, 01:06 AM
I get paragraph two. Makes sense to me.

Paragraph one, I'm just mentally blockd against it. I dont' get HOW time can be swayed by anything. I've been reading all sorts of articles on time all morning, trying to fiure it out, and they've all explained it as lucidly you folks have. So it must just be me...


That's because it cannot be swayed. It's completely impossible. Time is a measurement of a sequence of things that happen one after the other. You cannot alter time. You can only alter the sequence that it measures.

The perception of time can be swayed though. You can see things that actually do not happen a that time. You do it daily, just by looking at the any celestial object.

Example: NASA finds a planet 10 lightyears away. Their telescope is powerful enough to actually see aliens walking around on the planet. And since it's 10 lightyears away you'll see things as they are 10 years ago, because it takes that long for light coming from that planet to reach Earth.

Now lets say that NASA has a device that managed to get you there in 5 minutes. You didn't travel through time there. It took you 5 whole minutes.

But now let's look though that telescope. It will take 10 years and 5 minutes for that image to catch up with you arriving. But, as said above, the journey took you 5 minutes. Despite you traveling a million times the speed of light you didn't travel trough time 10 years, it just appears that way. The speed of light is just insufficient to show the actual real result of you taking 5 minutes to get there.

And there you have it. Traveling faster than light does not constitute traveling through time.


Now to apply this to black holes: Black holes actually manage to trap light and bend it into the hole. This will most certainly distort what you see. But it still doesn't mean that you are traveling through time.



-----
Now I know someone is going to use this example, so let me shoot that one out of the sky before you do so:

NASA has done with atomic clocks in orbit and found that time seems to flow differently when moving faster. The actual problem there is that atomic clocks count a repeating movement inside the atoms to accurately measure time. But they do not take into account the movement of the ship along with the the movement of the particle inside the atomic clock.

Example: You have two walls that are fixed to eachother at say 5 meters from eachother. The ground is not attached to these walls. Just walk back and forth at a regular speed between two walls while they are standing still. Now do the same at the same speed while this contraption of two walls is moving around. You'll move around more than when they were standing still.

Now try to do this in within a fixed timespan. If you manage to go back and forth 60 times while they are standing still. You will not manage to get to 60 times if they are moving around, provided that you move at the same speed.

Lets sat you managed to get to 50 while they were moving. Now lets go back to the atomic clock. The one standing still says 60 units have gone by, while the one moving stats 50 units. If these units are used to measure time in minutes then 60 minutes went by in one situation while in the other only 50 went by. But we did this thing in a fixed timespan, so they couldn't both be right.

And there you go. Time was not swayed, since it all happened within a fixed timespan. However the perception of time did get swayed because the device that measured time was affected.

PeeDee
03-26-2007, 01:42 AM
I get what you mean, Michael, and I think it's starting to shuffle into some sort of sese. I can understand the perception of time being affected, sure, makes sense. It was the actual physical warping of the fourth dimension that I didn't follow. (and perhaps still don't)

TsukiRyoko
03-26-2007, 03:33 AM
I get what you mean, Michael, and I think it's starting to shuffle into some sort of sese. I can understand the perception of time being affected, sure, makes sense. It was the actual physical warping of the fourth dimension that I didn't follow. (and perhaps still don't)
Someone once said to me that time is a figment of our imaginations. True, to an extent. Time as we see it on clocks, calendar, and days of the week, if just a figment of our minds- something we made for convenience. But the passage of time is very real.

...I started to make a point, but I forgot what it was. Shit.

blacbird
03-26-2007, 07:10 AM
Time is a fig newton of our imaginations.

I need yet another drink.

caw

PeeDee
03-26-2007, 07:10 AM
I could really go for some fig newtons...

Michael Dracon
03-28-2007, 08:16 PM
I get what you mean, Michael, and I think it's starting to shuffle into some sort of sese. I can understand the perception of time being affected, sure, makes sense. It was the actual physical warping of the fourth dimension that I didn't follow. (and perhaps still don't)


Okay, an easy way (I hope) to visualize 4D warping, provided that you see the 4th dimension as another physical dimension rather than time:

Take a piece of paper. This is effectively 2D, just length and width, but no (well, almost anyway) no heigth. Now grab the two opposing short sides and fold the paper until they touch. You now made a 3D object out of a 2D object. You didn't change the shape of the paper (as in: no cutting or glueing involved) just the way it curves. If an ant was on one side short end it could now take a shortcut to get to the other short end. If a person who can only see 2 dimensions sees this happening it would appear as if the ant would teleport from one end to the other, because this person cannot see the curvature and thus also cannot see the two sides touching eachother.


Now imagine the same with a 3D object where you pick a random part and bend it to touch another part. This way you're making it a 4D object. Keep in mind that in reality you would not actually see the object change, but the curvature is there nonetheless. To you an ant walking on the object and using this curvature as a bridge would suddenly pop up on the other end without you seeing what happened in between.


This is an example of 4D warping. The word Wormhole is a common term to describe it. This came from an example very similar to mine, but with a worm 'digging' through using the 4th dimension, rather then bending the object.

Actually, you could use it as a propulsion, if applied properly (in fact, I think Star Trek Warp speed oes exactly that). You just squeese the 3rd dimension tight behind you and push that forward, just like you would move a liquid in a straw by squising that tight and moving the fingers that squeese along the straw.

a tree of night
03-29-2007, 07:59 PM
If, with Hawking radiation, we cannot spot the cause, and we cannot measure the effect, then how do we have any idea it exists? Is it purely mathematical theory, just like black holes were back when Einstein was still scribbling numbers?

Hawking radiation is purely theory. It's a theory based on theory (Bekenstein's postulation that black holes are likely to exhibit thermal properties). That's not to say there isn't a whole lot of heavy thinking behind it, but to say it's proven or widely accepted would be a stretch. And let's not forget Hawking himself changes his mind from time to time on the subject.

PeeDee
03-29-2007, 08:06 PM
Michael, thanks for the explanation. I think I actually followed it and it sunk in. I'm not left with the sense of "Yeah, but, yes, but, no, but, yes, but, what!?" that I was previously stuck with. Very well done.

Tree, thanks, I was just reading stuff about Hawking radiation. It seems iffy to me to be making a theory which is based on a theory. I find it dangerous to stack What Ifs, you never know if they'll stand. But this is perhaps why I am not a scientist.

a tree of night
03-29-2007, 08:11 PM
I think the thing to remember about time is that it is, in fact, truly constant. Nothing we do changes time in any way. When we "see" time dilation, warping, or other "effects", we're only changing our frame of reference relative to constant time. So if I travel around the speed of light for a while and you remain at a relativistically low velocity, I will have "aged" less when I return, but not because I've altered time. All I've done is step outside the frame of reference that you remained in. If I never return to that frame of reference, neither of us is the wiser.

PeeDee
03-29-2007, 08:14 PM
*blink*

Okay, so...er... Erk.

Unless time actually slowed down, wouldn't your molecular structure have continued to decay at the same speed as everyone else's, regardless of the speed that your body as a whole is traveling?

a tree of night
03-30-2007, 12:50 AM
*blink*

Okay, so...er... Erk.

Unless time actually slowed down, wouldn't your molecular structure have continued to decay at the same speed as everyone else's, regardless of the speed that your body as a whole is traveling?

It is at the same rate, but in my frame of reference, not as much time has passed. From my perspective, time is constant. From your perspective, time is constant. The difference only occurs when you compare the two.

PeeDee
03-30-2007, 01:00 AM
It is at the same rate, but in my frame of reference, not as much time has passed. From my perspective, time is constant. From your perspective, time is constant. The difference only occurs when you compare the two.

But if we treated time as an objective flow, irrelevant to our own perceptions within it, then...then time is constant, no matter what, correct? You've merely accelerated your own personal time frame, and mine has remained within sync to the constant objective time. right?

a tree of night
03-30-2007, 07:33 PM
There isn't a "correct" time. There's just the time that you're experiencing and the time that I'm experiencing. If anything were a "standard" time, it'd be a completely stationary particle in the absence of any gravitational fields. For most purposes, time is simply an abstraction of our experiences.

Disclaimer : this is just my personal take on things. I'm not making any authoritative statements here, just trying to clarify how I understand things to work.

PeeDee
03-30-2007, 08:01 PM
That doesn't make sense to me either. If time were just an abstraction of how we view things, a method by which to measure the decay of our molecular structure the aging of the world around us, then how could time be the fourth dimension?

Lycius
03-30-2007, 09:38 PM
Oh My Gawd!

Dork fest!

I love this forum now. Thanks for the links!

TsukiRyoko
03-31-2007, 02:46 AM
But if we treated time as an objective flow, irrelevant to our own perceptions within it, then...then time is constant, no matter what, correct? You've merely accelerated your own personal time frame, and mine has remained within sync to the constant objective time. right?
Time is only objective in an individual's perception of it. I know what time is, you know what time is. I can tell you when an hour has passed, just the same as you can tell me when an hour has passed. But, whenever you compare one person's perception to another person's, that's when it becomes subjective. We can all relate to the passage of time and the flow of time moving forward, but no two people experience the flow of time the same way. Much like color, time is different for everyone. Grass is green, everyone agrees, but the green n my reality isn't the same green as in your reality.

a tree of night
04-02-2007, 07:47 PM
When I said "time is an abstraction", I meant for practical purposes in that particular instance in that it's only relevant to describe an event (or sequence of events) in your particular frame of reference. Time is fundamental, scientifically speaking, in that you can only define it through measurement. Space, which is very closely related to time, especially if you're speaking dimensionally, is also fundamental. And they both dilate at relativistic speeds, which is a good thing, because if only one did, you'd have some serious problems.

The only absolute measure of time is that light can only go forward, so if you see light, it was "sent" from the past. And if someone else sees light from you "sent", they are in the future from when your "sending" occurred. Other measures of time are only applicable to the perspective of the observer and the phenomenon being measured.

Angelinity
04-02-2007, 10:54 PM
here's another take on space/time/motion and the unified theory.


http://www.spaceandmotion.com/Physics-Time.htm

Inkdaub
04-06-2007, 02:29 PM
This thread reminds me of Hyperion.

Most of this stuff I can grasp but have no frame of reference to explain why. The fact that gravity can affect time makes sense but if you asked me why I thought so I couldn't answer. It just sounds right. It's like when you know the answer but it's just around the corner in your brain and you can't quite catch it.

Then again, the telephone mystifies me and I can't figure out why digital code is all ones and zeros. It seems like you could shorten things up quite a bit if you used some other numbers as well.

laurel29
04-07-2007, 08:48 PM
This thread inspired me to go out and buy some books on physics. Today I was reading about light (I really started out trying to learn more about the way sound waves react) and I thought these links were interesting.

http://www.eurekalert.org/pub_releases/2005-08/epfd-ltt081905.php
http://actualites.epfl.ch/presseinfo-com?id=288
And then there is this-
http://www.abc.net.au/science/news/stories/s154610.htm
I thought this discussion was pretty interesting today as well –
http://forum.physorg.com/index.php?showtopic=9840
There was this that I thought was interesting as well –
http://www.physorg.com/news12084.html
and a discussion about it here-
http://astronomer.proboards23.com/index.cgi?board=astrophysics&action=display&thread=1143174426&page=1

I hope my links work, but if not you can copy and paste. I hope that isn't too many to post at once (the first two are a bit redundant,)but they were all related.
Okay so I couldn't resist adding these two -
http://www.world-science.net/othernews/060811_quasar.htm
and a short discussion of it here
http://astronomer.proboards23.com/index.cgi?board=astrophysics&action=display&thread=1155392509

Science is so much fun even if I don't understand half of it :).

I found this article that mentions dormant black holes -
http://web.phys.cmu.edu/~tiziana/BHGrow/
and you can find a lot of other interesting things here -
http://hubblesite.org/newscenter/archive/releases/2006/04/related/

I picked up a special edition of Scientific American that was about black holes. There were a couple of neat articles in it, but they aren't available online. One had to do with black holes humming and another was about trying to model how hawkings radiation works. One of the models they were doing used sound waves in water. It was really neat :D.

MargueriteMing
11-11-2007, 03:14 PM
But to answer your question, I don't know that there's an explanation of "how", but the fact is "it happens." Any mass creates gravity, and gravity causes time to go slower, much like increasing speed toward the speed of light causes time to go slower for that thing whizzing by. Precise atomic clocks, one at sea level and one on a mountaintop, will run at measurably different rates because the Earth's gravitational force is less at the top of the mountain. The GPS sattelites in space have such clocks and they are being continuously compensated for the effects of how far they are from Earth and the speed at which they're orbiting.

The effect of time slowing down is much more pronounced near a black hole because the gravity (no pun intended, but glad I thought of it...) is so much greater.



Umm, no. Time "runs" slower on a mountaintop because the earth is spinning. This means that the farther an object is from the earth's center, the faster its absolute velocity. The higher the velocity, the greater the effects of time dilation.

Mac H.
11-11-2007, 04:47 PM
>".. Gravity causes time to go slower, much like increasing speed toward the speed of light causes time to go slower for that thing whizzing by. Precise atomic clocks, one at sea level and one on a mountaintop, will run at measurably different rates because the Earth's gravitational force is less at the top of the mountain."


Umm, no. Time "runs" slower on a mountaintop because the earth is spinning. This means that the farther an object is from the earth's center, the faster its absolute velocity. The higher the velocity, the greater the effects of time dilation.

Both gravity & velocity make a difference. The affect due to gravity was predicted in general relativity, whereas the affect due to velocity was predicted due to special relativity.

See the results of the famous 'atomic clocks in planes' experiment here: http://en.wikipedia.org/wiki/Hafele-Keating_experiment

Basically the height of the aircraft contributed about 144 to 180 ns difference to the clocks, where as the direction contributed about -185 ns (eastword) to +96 ns (westward).

Mac

MargueriteMing
11-12-2007, 09:57 AM
This, however confusing, is the difference between reg. black holes and supermassive:
Supermassive black holes have some interesting properties which distinguish them from relatively low-mass cousins:
The average density of a supermassive black hole can be very low, and may actually be lower than the density of water. This is because the Schwarzschild radius is directly proportional to mass, such that density is inversely proportional to the square of the mass.
The tidal forces in the vicinity of the event horizon are significantly weaker. Since the central singularity is so far away from the horizon, a hypothetical astronaut travelling towards the black hole center would not experience significant tidal force until very deep into the black hole.
Found at: http://en.wikipedia.org/wiki/Supermassive_black_hole

I think most people think of the black hole as being the singularity object, which has been crushed down by gravity to incredible density. The event horizon, on the other hand, is the distance at which light can no longer escape from the gravity well. I wonder how much material is inside the event horizon but still in orbit about the singularity? It could be that inside the event horizon is a storm of stuff buzzing around.

If the topology of the universe is closed (ie there is enough mass that eventually the universe will shrink back together and collapse) then we are all actually within the universe's event horizon.

MargueriteMing
11-12-2007, 10:05 AM
Well, I was hardly trying to prove a point. It was just spinning hypotheticals. I don't expect there are plentary systems with a black hole at the center, supermassive or otherwise, and I also don't think there's going to be any life there.

Actually, there are about 10 known (or suspected) black holes in the milky way galaxy, remnants of collapsed stars. Most of them probably have planets, because planets generally form in stellar accretion discs.

blacbird
11-12-2007, 12:53 PM
Actually, there are about 10 known (or suspected) black holes in the milky way galaxy, remnants of collapsed stars. Most of them probably have planets, because planets generally form in stellar accretion discs.

Possible. Also possible that the supernoval event that generated the black hole might have been energetic enough to eject planetary bodies, severely scorched, out of orbit to drift as rogue objects into space. My feeling is that all imaginable permutations of star/planet relationships are feasible, and given the vast actuarial multitude of stars in the universe, almost certainly exist, somewhere.

caw