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The nature of black holes from the evidence


ukgazzer
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If you were given no knowledge of modern theories what would you guess black holes would be like from observations?

-They seem to emit no light.

-Massive amounts of material seem to be being shot out from areas in the vicinity of black holes- Do spiral bars come from there?

Is that all we know?If so,what would be a best guess for the nature of black holes and how much does it agree with theory?

What other observations agree with the conventional wisdom that they are singularities?

(Sorry,another speculative BH topic)

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well, we'd come to the same conclusions.

 

we have never directly observed a blackhole, we only know they emit no light because of logical deduction.

 

we can however observe the accretion disk and get an estimate of its size, mass and temperature. from observations of these disks we would be able to deduce that they are orbiting a body of immense density. From this data we can deduce the amount of force necessary to hold a body from collapsing under its own weight and find that nothing even comes close. from this we can deduce that unless there is an unknown force never before encountered it has collapsed to a singularity or at least a point where the rest of our physical theories breakdown.

 

we could also find that the escape velocity as its surface exceeds the speed of light. due to knowledge of gravitational redshifting (which can be observed even on earth) we would be able to deduce that it would appear black as no light is escaping from it.

 

astonishingly, this is us already 99% of the way there to modern blackhole science. the rest is details. details that have been deduced by the observations you say we have access to and applying physical models (models from other areas of physics such as relativity and quantum mechanics).

 

As our modernday theories are direct products of observation, any new investigation tabula rasa is going to end up either in exactly the same place or one very close to it.

 

The only time where it could have ended up vastly different is when blackholes were still a prediction and not a fact. One of the awesome things about science, sometimes you can predict things before you've seen them. When you do find them, it is huge evidence that your theories are on the right track. If you don't find them then it hints that there is new and interesting physics to be found.

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If you were given no knowledge of modern theories what would you guess black holes would be like from observations?

-They seem to emit no light.

-Massive amounts of material seem to be being shot out from areas in the vicinity of black holes- Do spiral bars come from there?

Is that all we know?If so,what would be a best guess for the nature of black holes and how much does it agree with theory?

What other observations agree with the conventional wisdom that they are singularities?

(Sorry,another speculative BH topic)

 

In the first place, a black hole is not a singularity; a black hole contains a singularity.

 

In the second place, they would not be named "black holes", because a black hole is a concept that arises from a given theory as general relativity. A possible name could be black compact object.

 

We would be able to measure the mass, charge and angular momentum of those objects. We would be able to measure gravitational lensing and X-ray emissions in binary systems.

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well, we'd come to the same conclusions.

 

we have never directly observed a blackhole, we only know they emit no light because of logical deduction.

Don't forget about the Hawking Radiation comming from the region around a black hole. Also in some cases there are accreation disks around black holes.

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That radiation is highly hypothetical and has never been observed up to now.

 

It is plausible though. It also explains why small blackholes don't seem to exist. of course, until we can isolate a black hole to see what radiation it gives off this will likely remain theoretical.

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It is plausible though. It also explains why small blackholes don't seem to exist. of course, until we can isolate a black hole to see what radiation it gives off this will likely remain theoretical.

Hawking radiation will remain theoretical for a stellar blackhole or larger. For a solar mass non-rotating blackhole, Hawking radiation has a temperature of 62 nanokelvin, a peak frequency of 3.6 kHz, and a power of 9.0×10-29 watts sent over 4 pi steradians. Utterly undetectable.

Edited by D H
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It is plausible though. It also explains why small blackholes don't seem to exist. of course, until we can isolate a black hole to see what radiation it gives off this will likely remain theoretical.

 

I do not think so. Apart from the observational difficulties, the Hawking radiation model assumes that one can freely mix quantum field theory with the event horizon associated to general relativity. The problem is that GR+QFT is not a consistent theory. For instance, when we consistently take into account gravitons, the event horizon associated to the classical theory disappears. The so-named black hole thermodynamics (which is used to define the temperature of that radiation) is open to objections as well.

Edited by juanrga
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If you were given no knowledge of modern theories what would you guess black holes would be like from observations?

-They seem to emit no light.

-Massive amounts of material seem to be being shot out from areas in the vicinity of black holes- Do spiral bars come from there?

Is that all we know?If so,what would be a best guess for the nature of black holes and how much does it agree with theory?

What other observations agree with the conventional wisdom that they are singularities?

(Sorry,another speculative BH topic)

They still would appear to be very massive based upon their gravitational influences, so I would guess them to be highly condensed burned-out stars absent the BB theory and present stellar evolution theory.

 

Black holes as a Singularity is mathematical theory absent any possible observational confirmation at full scale, therefore conceivably just one possibility concerning black holes in general. Black hole models as a more condensed form of matter is the alternative theoretical idea.

 

Black holes are even more condensed than neutron stars. For example, a 1-solar-mass black hole would have a radius of about 2 mi (3 km).

(quote from top link, shown below)

 

http://www.answers.c...tional-collapse

http://www.answers.com/topic/gravitational-collapse#ixzz1sKMjRIbh

 

There are black hole hypothesis proposing such ideas as quark stars, compressed fundamental particles or strings of some kind, and a number of other proposals and ideas.

//

Edited by pantheory
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Fine opinions above. If only we knew just what's inside that event horizon. Maybe some day we/they will.

 

However, one thing that frustrates me is how some geniuses have the audacity to claim that the singularity (condensed matter) inside the black hole is infinitely small -- or atomic -- in size. I'm not a rocket scientist, but that seems ridiculous! Something the size of an atom can affect an entire galaxy with it's gravity hole??? Right.

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If you were given no knowledge of modern theories what would you guess black holes would be like from observations?

-They seem to emit no light.

-Massive amounts of material seem to be being shot out from areas in the vicinity of black holes- Do spiral bars come from there?

Is that all we know?If so,what would be a best guess for the nature of black holes and how much does it agree with theory?

What other observations agree with the conventional wisdom that they are singularities?

(Sorry,another speculative BH topic)

 

Any time we see a star orbiting something invisible, we can calculate the mass of the invisible object and if it is small in size, the only explanation is a very massive, small object. Only a black hole explains this.

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Any time we see a star orbiting something invisible, we can calculate the mass of the invisible object and if it is small in size, the only explanation is a very massive, small object. Only a black hole explains this.

 

No. The specialized literature is full of alternative explanations.

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Fine opinions above. If only we knew just what's inside that event horizon. Maybe some day we/they will.

 

However, one thing that frustrates me is how some geniuses have the audacity to claim that the singularity (condensed matter) inside the black hole is infinitely small -- or atomic -- in size. I'm not a rocket scientist, but that seems ridiculous! Something the size of an atom can affect an entire galaxy with it's gravity hole??? Right.

 

 

When a star like our Sun runs out of nuclear fuel, its core collapses to a white dwarf. The gravitational collapse is stopped by electron Fermi pressure.

 

For a star I think 4 to 8 times larger, the core collapse overcomes electron Fermi pressure to become a super-dense neutron star. The collapse is stopped by neutron Fermi pressure.

 

For even bigger stars, we know of nothing which can stop the collapse. So a black hole is formed.

 

For an idealized non-rotating black hole, all the mass of the black hole star's core is crushed into an infinitessimally small point. It may seem ridiculous to you, but this is our current best understanding. This "singularity" is a place-holder until a new theory combining general relativity and quantum mechanics gives us a better explanation.

Edited by IM Egdall
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How about this for rotating stars?

Kerr showed with GR that a rotating star collapses into a spinning 2-D ring (to preserve angular momentum) with the Planck length that would vibrate due to quantum effects. Observations support the spinning singularity proposal.

It is an interesting duality that if all of the closed strings in such a star were crushed together due to gravity, then the end result would be the same. The strings might stack onto each other (remaining for all intents one 2-D string) and their individual vibrations would amplify from harmonics. Thus one closed string vibrating at a very high pitch to represent a massive particle (the singularity) and Kerr’s description of a singularity would be the same.

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Black holes are black because mathematics is deemed useless in defining their properties.

 

Black holes, i would submit, are the 'top of the hierachy' in the orbital tree ( star family ) .

Black holes also orbit ' a master black hole' - this is a cosmic nature law. A hierachy of orbit.

 

I would also submit, black holes are dark bue to energy acceleration - exceeding the speed of light

is why we dont see anything - its too fast to be visible electromagnetic radiation.

Magnetism and gravity work hand in hand in the centre of galaxies.

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No. The specialized literature is full of alternative explanations.

 

Then please summarize a few of the alternative explanations of black holes. I've never heard of any.

Edited by Airbrush
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Then please summarize a few of the alternative explanations of black holes. I've never heard of any.

 

There are lots of alternatives: Q-stars, gravastars...

 

A recent paper on gravastars is Francisco S N Lobo and Aarón V B Arellano 2007 Class. Quantum Grav. 24 1069.

 

Moreover recent studies give doubts about the ordinary computation that leads to the concept of black holes in general relativity. Check No More Black Holes?

 

Personally I am more familiarized with the compact objects that arise in the field theory of gravity when the energy of gravitons is taken into account. The consideration of gravitons shows that an event horizon is a crude geometrical idealisation and thus that black holes are not real. There is some dispute on the specialised literature on if the black hole model has been already observationally disproved or not.

Edited by juanrga
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When Airbrush asks for alternative explanations he is referring to methods for stopping the gravitational collapse. For example as has been mentioned electron degeneracy resistance stops the further collapse of white dwarf stars, and neutron degeneracy resists further collapse of neutron stars.

What is the mechanism for stopping the gravitational collapse of these Q-stars and gravastars ?

And if Q-stars are quark stars their degeneracy resistance is equivalent to that of a neutron star I would think, but not being too familiar with QCD, the quarks that comprise neutrons may have energy levels and could sink to 'lower' energy leves. Even so, they would just be one more step on the way to black holes because eventually a star massive enough to overcome quark degeneracy resistance would gravitationally collapse ( such as the galactic centre sized black holes ).

 

So like I said, don't give us fancy names, propose mechanisms that would stop gravitational collapse for ANY ( no matter how big ) star. Its like Chandrashekar vs. Eddington all over again.

Edited by MigL
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I have a question. How can a blackhole have more energy kenetic/potential than the star itself, at or after the time of supernova? Did it gain energy from a source other than the star? Or am I misunderstanding what types or amounts of energies that are envolved?

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When Airbrush asks for alternative explanations he is referring to methods for stopping the gravitational collapse. For example as has been mentioned electron degeneracy resistance stops the further collapse of white dwarf stars, and neutron degeneracy resists further collapse of neutron stars.

What is the mechanism for stopping the gravitational collapse of these Q-stars and gravastars ?

And if Q-stars are quark stars their degeneracy resistance is equivalent to that of a neutron star I would think, but not being too familiar with QCD, the quarks that comprise neutrons may have energy levels and could sink to 'lower' energy leves. Even so, they would just be one more step on the way to black holes because eventually a star massive enough to overcome quark degeneracy resistance would gravitationally collapse ( such as the galactic centre sized black holes ).

 

So like I said, don't give us fancy names, propose mechanisms that would stop gravitational collapse for ANY ( no matter how big ) star. Its like Chandrashekar vs. Eddington all over again.

 

Mechanisms that stop gravitational collapse are given in the literature associated to those objects. Regarding the one that I am familiar (see my previous post), gravitational collapse is stopped by the pressure exerted by the own graviton field associated to ANY star.

Edited by juanrga
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I have a question. How can a blackhole have more energy kenetic/potential than the star itself, at or after the time of supernova? Did it gain energy from a source other than the star? Or am I misunderstanding what types or amounts of energies that are envolved?

 

A tiny amount a matter contains a huge amount of energy (E=mc^2) and that is constant whether it is a star or black hole. When a star supernovas most of the matter is blasted off into space and much is converted into pure energy which also radiates away at the speed of light. What is left is enough matter to squash itself into a black hole. It never gains energy in the process.

Edited by Airbrush
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Well the gravastar paper is even more far-fetched than black holes ever were.

Self gravitating magnetic monopoles with charge g ???

Monopoles are the unicorns of particle physics, and if inflationary big bang theory is correct, then only few would have been created on the boundaries of broken symmetry areas. Or are these different monopoles ( how many can you have ??) ? And would g then be the elementary quantum of gravitation ??

 

As for your second link, I haven't heard that explanation for black holes since Landau and Zel'dovich used to call them 'frozen stars' in the 50s before John Archibald Wheeler coined the term 'black holes' which has nasty connotations in Russian. It is easily explained by the proper choice of reference frame. In effect, an external observer sees time slow down and stop as an astronaut approaches the event horizon, but the astronaut himself notices no such slow down and stoppage, he continues through the event horizon to the possible singularity at regular time.

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  • 2 weeks later...

Stupidly I can answer this question by telling you what I thought they were before I got into astronomy, when all I had was a GCSE in science, I thought a black hole was like a rip in space, like a tear where time and space itself just didn't exist because the supernova had destroyed anything that existed there before, we still don't know what a black hole actually is, we know how it's created and how it interacts with the universe, we know that they help shape galaxies, some scientist don't believe they should exist and some even don't believe that they do, I've heard intelligent men even refer to them add dark energy stars

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