A question?

reply to post by Bedlam


Radius of a Black Hole

Any thoughts?

reply to post by Bedlam


Your point is that repeated "Any thoughts?" is annoying?

Mary Rose
reply to post by Bedlam

 

Your point is that repeated "Any thoughts?" is annoying?

Well, at first long ago, but now I try to just respond with whatever I'm actually thinking about at the moment I read it. As long as it's PG rated or better.

Kashai
reply to post by Bedlam

 

Radius of a Black Hole

They've actually measured the diameter of a black hole.

The radius may be undefined. At any rate, if the radius IS defined, then no, it doesn't have infinite density.

Any thoughts?

It's about time to hit the sack if I'm going to have enough time to read the day report before assuming charge of the night crew. The MIC sucks at times. I don't really feel like working tomorrow. I go away for three weeks to clean air, and invariably, when I get back to the San Joaquin Valley area where work lies, the funky air makes me sick as a dog for two weeks. I swear, I could tell you when we get close because I start coughing on the plane somewhere over NTC on the way in.

Bedlam
The MIC sucks at times.

Military Industrial Complex?

Bedlam
I swear, I could tell you when we get close because I start coughing on the plane somewhere over NTC on the way in.

Fort Irwin & the National Training Center?

Bedlam
They've actually measured the diameter of a black hole.

The radius may be undefined. At any rate, if the radius IS defined, then no, it doesn't have infinite density.

I'm not sure how accurate black hole theory is (I think at best it's probably incomplete since we lack a theory of quantum gravity), but to the extent we think we understand them, we need to define the different types of radii. I'm not going to discuss them all because that will just unnecessarily confuse the issue.

That article is about an event horizon, which is known also as a Schwarzchild radius. That type of radius is not relevant to the rotating matter question, as there is no matter rotating at that diameter in the absence of an accretion disk, according to black hole theory.

Black Holes

The horizon is not a physical surface, merely a conceptual one, and although it marks the point of no return for material plummeting toward the singularity, relativity says that nothing special happens there

In fact the theory states it's only apparent to an external observer (like us measuring it in that article) but if you flew into that black hole in a space ship, you'd fly right past the event horizon without even realizing anything was there, because nothing is there; there's no matter to rotate (The radius measurement article references a supermassive black hole, which can have quite large event horizons). Our own supermassive black hole at the center of the Milky Way has had nothing at the event horizon for decades, though recently we observed a gas cloud approaching it and we are looking forward to observing what happens when it "feeds" upon the gas cloud, such as whether we will see Synchrotron radiation or whatever. I'm hoping we can measure or at least estimate the speed of the matter falling in, but the point is, previously, there hasn't been any matter falling in since we've been observing it.

The other relevant radius is of the collapsed matter inside the black hole. If it's a non rotating black hole, it's a point with no volume (you could call it a radius of zero), or if it's a rotating black hole, it's a 2-dimensional disc with no volume which would have a radius far smaller than that of the event horizon.

Black Hole Singularity

At the center of a black hole as described by general relativity lies a gravitational singularity, a region where the spacetime curvature becomes infinite. For a non-rotating black hole, this region takes the shape of a single point and for a rotating black hole, it is smeared out to form a ring singularity lying in the plane of rotation. In both cases, the singular region has zero volume. It can also be shown that the singular region contains all the mass of the black hole solution. The singular region can thus be thought of as having infinite density.

The problem is, our theories "break down" inside the event horizon, meaning what we define as "space-time" doesn't exist inside the event horizon, so, if there's no time, so how can you calculate a velocity? Even at the event horizon, time appears to crawl to a standstill to outside observers leading to the term "frozen stars" but that gets into the other radii not really relevant to the rotating matter question in this thread.

The appearance of singularities in general relativity is commonly perceived as signaling the breakdown of the theory.[63] This breakdown, however, is expected; it occurs in a situation where quantum effects should describe these actions, due to the extremely high density and therefore particle interactions. To date, it has not been possible to combine quantum and gravitational effects into a single theory, although there exist attempts to formulate such a theory of quantum gravity. It is generally expected that such a theory will not feature any singularities.

There may be a way to do it using a theory of quantum gravity or some other theory like an unproven hypothetical string theory, but currently I don't know how to do it and even if I did, we don't know of any way to make observations inside the event horizon to determine if the math is right or not.

reply to post by Mary Rose


Yes to both. You fly over NTC on the way in, shortly afterwards the Joaquin Funk begins.

reply to post by Arbitrageur


For a point singularity there is no diameter or radius. For a ring, you know the diameter but the measured distance from center to edge may be undefined. It's non-Euclidean. That ring might have depth internally although it doesn't appear to from an outside observer.

Hold on guys I am taking about the original star keep in mind the original object had mass with a rotation, that rotation clearly accelerated in any such event.

A rotation then resulting in an implosion.

My bad on the article

reply to post by Mary Rose


My apologies if it bothered you it is something I have been doing on the internet since 1989.

Though the point is stars the size that can generate a black hole implode due to a rotation.

reply to post by Arbitrageur


Very informative post, thanks.

I wonder if things like 'point of no volume' and stuff like that are said because, the supermassive black hole is like (kinda at least) the exact center of a circle, but this is not just abstract immaterial geometry we are talking about when I can say a circle is a infinite points equal distance surrounding a common central point. Because when we think of the exact center of the galaxy its axis in a way, do we know what dimension of size that axial point must be? I know im not making sense but what im trying to get at is, what is the appropriate thickness of a point to use to insure it signifies the exact center, does that make a little more sense, the smallest point would be use most accurately to 'pin point' the exact center, and I think that may be why the idea of infinite and 0 volume and 0 dimensional comes up.

reply to post by ImaFungi

I tried to explain this in the last quote of my immediately previous post, and the comments that followed, that the "singularity" is an artifact of an incomplete theory of relativity, which is expected to disappear when a more complete theory of quantum gravity is developed (or something else like maybe string theory, if anybody can ever prove that). Since the singularity is not even a point when the black hole is rotating, and most black holes probably rotate, I don't see it as the point issue you mention.

Also remember the Milky Way and Andromeda galaxies are thought to be on a collision course, and it's likely that this collision will result in the black holes at the center of the two galaxies "dancing" around each other for a prolonged period of time as the new galaxy of the merger forms, in which case there will very likely be no singularity at the center of mass of the new merged galaxy for a long time.

Astronomers have found at least 33 "dancing" black hole pairs already and expect to find a lot more, which means the black holes are probably orbiting a common barycenter, which is probably just a relatively empty point in space, but we don't call that empty point a singularity because it's got no significant density (whereas a singularity in a black hole has infinite density according to relativity):

Dancing Black Holes Found In Distant Galaxies

Dr. Comerford and her colleagues discovered a total of 33 pairs of supermassive black holes in distant galaxies. These discoveries are significant because “they show that dual supermassive black hole systems are much more common than previously known from observations,” says Dr. Comerford, who is a postdoctoral researcher in astrophysics at the University of California, Berkeley. The dual supermassive black hole pairs can in turn be used to estimate how often galaxies merge, and the team concludes that red galaxies from between 4 and 7 billions years ago underwent 3 mergers every billion years.

reply to post by Arbitrageur


I more brought up the point in relation to the comments about infinite density, with what I said about that abstract idea of a mathematically non 3d point, it could relate to infinitesimal density because there is no exact quantity value to distinguish the exact central point...hm, I think its the difference between using pure math, and using quantized things like planck length, though because the point is not staying still, its hard to discuss quantity of planck lengths at that central focal point, so perhaps its expressing that with the influence of the dimension of time, it is infinite density, as in you can not pinpoint an exact density at any given time because it is always in flux. Anyway, with pure math there is no rule, I dont think that says the thickness of area your point can be defined as, unless you take away dimensions, but thats part of the problem, I dont know how you can talk about a 2d something existing in a 3d space, it seems impossible, so if I have a circle with an area of 5 lets say, couldnt I accurately represent the center of that circle with a dot with the area of 4? See what I mean, in abstract math to get more and more precise you would have to make the point smaller, and it couldnt be 0, so it would be infinitesimally approaching 0. This is just some things I thought may be related to the idea of infinite density and some other oddities slung around discussions of black holes.