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ToSeek
2005-Feb-24, 05:38 PM
Matter Nears Light Speed Entering a Black Hole (http://www.universetoday.com/am/publish/matter_nears_light_speed.html?2322005)


Just before matter is gobbled up by a hungry black hole, it's hurtling around the monster at nearly the speed of light. This heats up the material and it can release a tremendous amount of energy as X-rays. Different elements release energy with a specific fingerprint that astronomers can detect. Researchers from Europe have measured iron as it hurtles around black holes and found a relativistic effect because it's moving so quickly. The team averaged out the X-ray light from 100 distant black holes to show the telltale signature of material about to be consumed by a black hole.

Grey
2005-Feb-24, 05:47 PM
Matter Nears Light Speed Entering a Black Hole (http://www.universetoday.com/am/publish/matter_nears_light_speed.html?2322005)
Thinking about it, this makes a certain amount of sense. If something begins falling toward any object from very far away (starting at negligible velocity), its speed is always equal to the escape velocity from the object at that distance. The escape velocity at the event horizon is light speed, so...

Evan
2005-Feb-24, 06:10 PM
That of course implies that at the event horizon matter is traveling at the speed of light and therefore has infinite mass.

What's wrong with this picture?

Grey
2005-Feb-24, 06:18 PM
That of course implies that at the event horizon matter is traveling at the speed of light and therefore has infinite mass.

What's wrong with this picture?
Of course, from far away, we never actually see it hit the event horizon due to time dilation effects. :) But I expect that what's really wrong with this picture is that I was using a classical approximation as a very rough estimate for what is clearly a relativistic situation.

Wally
2005-Feb-24, 06:56 PM
That of course implies that at the event horizon matter is traveling at the speed of light and therefore has infinite mass.

What's wrong with this picture?

Never thought about this, but how the heck would the singularity survive the impact of something with infinite kinetic mass??? Or is it continuously being bashed to bits, only to instantaneously pull itself back together again. . . :-?

Evan
2005-Feb-24, 07:47 PM
This brings up another question. How "thick" is the event horizon? Is possible for an atomic particle such as a proton to be partially within the event horizon and partially out resulting in the momentary generation of free quarks? What sort of radiation would result?

Argos
2005-Feb-24, 07:49 PM
Matter Nears Light Speed Entering a Black Hole

They should have shown the exact figures, since speed is the extraordinary claim, as far as this article is concerned. They don´t say anything about what particular relativistic effect they´ve found that hasn´t been reported in other studies. It seems that a typical (and more realistic) speed for an accretion disc would be 30,000 km/s, like this one (http://www.atlasaerospace.net/eng/newsi-r.htm?id=1882).

Taibak
2005-Feb-24, 08:36 PM
That of course implies that at the event horizon matter is traveling at the speed of light and therefore has infinite mass.

What's wrong with this picture?

Never thought about this, but how the heck would the singularity survive the impact of something with infinite kinetic mass??? Or is it continuously being bashed to bits, only to instantaneously pull itself back together again. . . :-?

It's a question of reference frame. As far as I'm aware, the only time you'll see an object pass an event horizon with v = c is if you're at rest on the event horizon. However, that's an impossible reference frame - you can't be at rest on an event horizon because of the hole's gravity.

Argos
2005-Feb-24, 08:39 PM
An interesting applet on Orbits in Strongly Curved Spacetime (http://www.fourmilab.to/gravitation/orbits/)

Ilya
2005-Feb-24, 08:43 PM
It's a question of reference frame. As far as I'm aware, the only time you'll see an object pass an event horizon with v = c is if you're at rest on the event horizon. However, that's an impossible reference frame - you can't be at rest on an event horizon because of the hole's gravity.

Which means that from our point of view no singularity actually had formed yet. As far as we are concerned, the entire mass of every collapsed star is still hanging just outside its event horizon, whether it collapsed yesterday, a million years ago, or a ten billions.

Bob Berman (http://www.astronomy.com/asy/default.aspx?c=ss&id=110) is a strong proponent of this portrayal of black holes. He says they should be regarded not as "vacuums" which suck all matter into an infinitely small point, but as "cosmic trash compactors" which compress all matter into very (NOT infinitely) thin spherical shells.

W.F. Tomba
2005-Feb-24, 08:59 PM
Which means that from our point of view no singularity actually had formed yet. As far as we are concerned, the entire mass of every collapsed star is still hanging just outside its event horizon, whether it collapsed yesterday, a million years ago, or a ten billions.
The entire mass? Wouldn't some of it have been inside the event horizon to begin with?

Swift
2005-Feb-24, 09:30 PM
An interesting applet on Orbits in Strongly Curved Spacetime (http://www.fourmilab.to/gravitation/orbits/)
8) that was fun to play with

sidmel
2005-Feb-24, 09:45 PM
That of course implies that at the event horizon matter is traveling at the speed of light and therefore has infinite mass.

What's wrong with this picture?

The article does state that matter 'nears' light speed, implying that it never reaches light speed and infinite mass. Still wouldn’t want to be hit by it. :o

Doodler
2005-Feb-24, 10:19 PM
I have a little question for the wiser minds here. Just because the escape velocity at the event horizon equals the speed of light, does it necessarily follow that objects inside the event horizon must necessarily be moving at the speed of light?

For all we know, matter pulled in could move at speeds well within relativity's grasp and become a part of the singularity within, we simply cannot observe this because of the horizon.

Grey
2005-Feb-24, 10:25 PM
For all we know, matter pulled in could move at speeds well within relativity's grasp and become a part of the singularity within, we simply cannot observe this because of the horizon.
From the frame of reference of an object falling in, it does proceed past the event horizon and reaches the singularity in a finite proper time. I'm not certain whether its local velocity is superluminal, and answering this is a bit complicated by the fact that the space and time coordinates switch roles inside the event horizon. So the singularity is suddenly not a place that you're heading, it's the future, which in one sense is why reaching the singularity has just become inevitable.

Evan
2005-Feb-24, 11:39 PM
...fact that the space and time coordinates switch roles inside the event horizon.

I was not aware that we are in a position to say anything about what is inside the event horizon.

Grey
2005-Feb-25, 12:46 AM
I was not aware that we are in a position to say anything about what is inside the event horizon.
Well, I admit that it would be tricky to test, but general relativity can describe what happens inside the event horizon just fine.

Sam5
2005-Feb-25, 04:08 AM
So the singularity is suddenly not a place that you're heading, it's the future, which in one sense is why reaching the singularity has just become inevitable.

Isn't any place we are heading the future?

Taibak
2005-Feb-25, 05:11 AM
I have a little question for the wiser minds here. Just because the escape velocity at the event horizon equals the speed of light, does it necessarily follow that objects inside the event horizon must necessarily be moving at the speed of light?

No no no. That's only true if you're sitting on the event horizon when you measure the object's speed. Like I said before, where it's impossible to sit on the event horizon, you NEVER observe the object travelling at the speed of light unless it was light to begin with.


For all we know, matter pulled in could move at speeds well within relativity's grasp and become a part of the singularity within, we simply cannot observe this because of the horizon.

That's what happens, actually. Depending on the reference frame you choose, you can plot the object's velocity at any point either before it crosses the horizon or after (assuming it actually crosses the horizon). For any possible frame of reference, a massive object will ALWAYS travel slower than the speed of light.

Tensor
2005-Feb-25, 05:33 AM
I was not aware that we are in a position to say anything about what is inside the event horizon.
Well, I admit that it would be tricky to test, but general relativity can describe what happens inside the event horizon just fine.

Well, until you get to the singularity.....

Maddad
2005-Feb-25, 08:00 AM
Just because the escape velocity at the event horizon equals the speed of light, does it necessarily follow that objects inside the event horizon must necessarily be moving at the speed of light?No, it necessarily follows that those objects are moving faster than the speed of light (assuming that they started falling from rest relative to the black hole and from an effective infinite distance.) Since they are carried along with contracting space, exceeding the speed of light does not violate special relativity.


That of course implies that at the event horizon matter is traveling at the speed of light and therefore has infinite mass. What's wrong with this picture?What's wrong is that you are mixing two different frames of reference. Time for the matter falling into the black hole is a different frame of reference from you watching it happen from a distance. From the matter's point of view, it's traveling 0 MPH and experiences no relativistic changes.

Argos
2005-Feb-25, 11:52 AM
One dollar for the one who shows me an accretion disc orbiting a black hole close (90% +) to the speed of light.

frogesque
2005-Feb-25, 12:17 PM
One dollar for the one who shows me an accretion disc orbiting a black hole close (90% +) to the speed of light.

Is that an Earth based $ or a relativisitic $ aproaching c with almost unlimited purchasing power :wink:

Argos
2005-Feb-25, 12:27 PM
One dollar for the one who shows me an accretion disc orbiting a black hole close (90% +) to the speed of light.

Is that an Earth based $ or a relativisitic $ aproaching c with almost unlimited purchasing power :wink:

Come to think of it, what about quantum dollars (you get it/you don´t get it)? :wink: 8)

Disinfo Agent
2005-Feb-25, 01:14 PM
In a Schroedinger's account. :D
You don't know whether you're rich or broke until you try to cash a cheque. :o

ngc3314
2005-Feb-25, 03:30 PM
In a Schroedinger's account. :D
You don't know whether you're rich or broke until you try to cash a cheque. :o

Wouldn't that happen if you try to cash it at the First Predestinarian Bank of Calvin? At least it would still be a Swiss account.

George
2005-Feb-25, 03:56 PM
In a Schroedinger's account. :D
You don't know whether you're rich or broke until you try to cash a cheque. :o

Wouldn't that happen if you try to cash it at the First Predestinarian Bank of Calvin?

No. Unlike FPB, at Schroedinger Security, all checks become valid (if you don't mind waiting). :)

Edit...

At least it would still be a Swiss account.
That might explain the holes in the FPB plan. :)

Grey
2005-Feb-25, 04:05 PM
Isn't any place we are heading the future?
I suppose in some sense, but it's not quite the same thing. For example, in an hour or so, I'm planning on going out to lunch, but I'm not exactly sure where I'm headed. So one could say that the place I decide to go is my "future", but my actions will affect where I end up, and I could decide to skip lunch and not go out at all. But no matter what I do, I'm going to reach noon, and there's nothing I can do about it because that's the way time works. So inside a black hole, I could decide to turn on my thrusters and move forward or backward in time, just like outside I can take actions which result in my going to different spatial destinations. But I'm going to reach the singularity in just the same way that outside the black hole I'm going to reach noon.