Great "Cosmic Nothingness" found

[Pluto]

Hello Hilton

 

Well put.

 

Hello Tomod

 

Not all black holes affect there surrounding, particularly this great void. There has to be something there for the black hole to affect. Space itself cannot be strectched or compacted.

[Tormod]

Not all black holes affect there surrounding, particularly this great void. There has to be something there for the black hole to affect. Space itself cannot be strectched or compacted.

 

I don't understand your point but you seem to be trying to refute something (although I'm not sure what).

 

Black holes are basically easy to spot, although not everyone agrees that black holes do exist (which simply means that what we observe as black holes could be something else, but that is another discussion).

 

Black holes evaporate radiation (hawking radiation) when matter fall within the horizon. That the "void" that has been found is *completely* empty is not something I would suggest. Hilton pointed out that there would be radiation and particles.

 

Black holes would indeed warp space. This is basically what black holes are - concentrated areas in space where gravity is so strong that it warps spacetime around it. This means that black holes are easily spotted because they bend light that passes close to it.

 

In fact, one of the basics of general relativity is that all matter influences space by warping it.

 

General Relativity & Black Holes

 

I am not sure why black holes are so important to you in this case, maybe you can elaborate on that?

[Tormod]

The Cosmological Principle states that at some or other "large scale" the Universe is homogeneous and isotropic, in other words, that it does not have large scale structure. It should be smooth and featureless in all directions.

 

Thanks.

 

However, I was of the impression that the anisotropy was best observed in the CMBR and particularly in the early universe. On large scales it would be more different due to small variations in the early universe.

 

That's how I interpret the COBE/WMAP results, anyway.

 

What's your take on the "void"?

[Hilton Ratcliffe]

Hi Tormod,

 

I was of the impression that the anisotropy was best observed in the CMBR and particularly in the early universe. On large scales it would be more different due to small variations in the early universe.

 

There are two important aspects of cosmology that require the imposition of the Cosmological Principle: The GRT/Friedmann/Hubble expanding Universe; and the CMBR. When one looks at the former scenario, it is crucial (for Hubble expansion to work properly) that the Cosmological Principle should apply. The Hubble constant is a measure of isotropic expansion, that is, it gives us a value by which all objects at the same distance apart recede from one another, no matter where they might be located and irrespective of what their neighbours are, if indeed they are "small" enough to have neighbours. If H0 (H-nought) is say 80 km/sec/Mpc, then for Earth and three galaxies A, B, and C, each 1 Mpc apart and radially aligned with Earth, A moves away from Earth at 80 km/sec, B from Earth at 160 km/sec, C from Earth at 240 km/sec, and C from B at 80 km/sec. This holds true at some still-to-be-determined "large scale". However, and this is crucially important, it is only at that "large scale" that the maths works. The Friedmann solutions of GR field equations do not allow large scale structure. For that reason also we cannot test "expanding space" physics on Earth, because here (in our Solar System, in our galaxy) space does not expand. Tormod, you are a practical person involved in space science, and you have a clear mind. Draw your own conclusions.

 

As far as CMBR analysis is concerned, your guess is as good as anyone's. If we look at it without an a priori model in mind, it looks to be short wave radio noise with a preferred direction towards Virgo, and vague shadow alignments of local astrophysical structures. Do an interesting but somewhat pointless statistical review of published WMAP papers. Choose 100 at random and print the abstracts. Count how many use the word "anomaly" or "anomalous" (or equivalent which means "did not meet expectations"). I got >60%.

 

What's your take on the "void"?

 

I find it fascinating. Quite frankly, I'm not at all surprised at the discovery of this so-called void (I guess it's ok to call it a void if we get no signal from it at all). In fact, I would be greatly surprised if we did not come across voids like this one. I see yin and yang everywhere I look in the cosmos, and to me it is reasonable to expect vast volumes of low density to counterbalance the great big lumps of relative high density that our deep space surveys are uncovering. Bear in mind though, that our picture of far way things is blurred by time and space. I think it's time to coin Ratcliffe's Remoteness Principle: In astronomy, uncertainty increases as the 4th power of distance. :shrug:

 

Regards

Hilton

[Pluto]

Hello Tomod

 

You said

 

Black holes would indeed warp space. This is basically what black holes are - concentrated areas in space where gravity is so strong that it warps spacetime around it. This means that black holes are easily spotted because they bend light that passes close to it.

 

I agree with you.

 

The point that I'm making is this.

 

If by chance a black hole existed and that nothing was around it. Than how can we see it.

 

Even if it warps space we could not see it unless something was in it to be effected.

 

As for spacetime thats another issue.

 

Time in communication is affected not actual time.

[Tormod]

Even if it warps space we could not see it unless something was in it to be effected.

 

...

 

As for spacetime thats another issue.

 

No, it's the same issue. If no matter falls into the hole, we could see it simply *because* a black hole warps spacetime. Since light is passing through the void, light would bend around the black hole in a very visible manner. If there were multiple very small black holes I think we might miss them completely, but if the void holds supermassive black holes they should be easy to spot.

 

If we find such holes, then we need an explanation for how they can clean out an area like the void. That's not a likely scenario for me.

[Tormod]

I read an article in New Scientist online which said that this void would also be empty of dark matter, since dark matter tends to clump around matter (so to speak). The dark matter distribution was charted for the first time last year, and shows the "scaffolding of the universe" as a colleague of mine called it.

 

Article:

Biggest void in space is 1 billion light years across - space - 24 August 2007 - New Scientist Space

 

Hubble discovery:

HubbleSite - NewsCenter - Hubble Maps the Cosmic Web of "Clumpy" Dark Matter in 3-D (01/07/2007) - Release Images

 

A colleague of mine mentioned that this implies that dark energy may be at work here - but I didn't quite understand why (something to follow up).

[Hilton Ratcliffe]

Hi everyone,

 

Thanks, Tormod, for the New Scientist link. Several things are curious about Rudnick's study. Firstly, if the void is not radiating anything, I wonder how they obtain distance to it? I will look at the ApJ paper to see if they explain that. Secondly, it is surprising that they admit to significant anisotropy in CMBR (the cold spot is arguably the biggest) being directly aligned with astrophysical structure in the intervening universe. See what I mean? The CMBR supposedly came from very nearly the time of the Big Bang, and anisotropies in the radiation picture are supposed to be reflections of uneveness existing at that time. The void at 6 to 10 GY old is considerably younger than that, so are they saying that spots on the CMBR images are shadows of things closer to home? If so, they are opening a can of worms. The third thing that puzzled me is by what physics they attribute a gain in energy for photons passing through a gravitational well. As I understand it, the photons would lose energy (redshift) and the effect of expansion would mean that they might be less redshifted than would be the case if the universe had not expanded, but nevertheless, there would be a net loss in energy. Unless they are saying that dark energy blueshifts light?? If that's the case then I will simply keep quiet and continue to look at the stars in the foolish belief that they are real objects obeying real laws of nature.:surprise:

 

Regards

Hilton

[Hilton Ratcliffe]

Hi everyone,

 

Further to my previous post, I have subsequently taken a look at the paper on which the New Scientist article was based (Rudnick, Shea, and Brown, "Extragalactic radio sources and the WMAP Cold spot", arXiv:astro-ph/0704.0908 v2), and quote selectively from it as follows (emphasis with italics added by me):

 

If the cold spot does originate from structures at modest redshifts, as we suggest, then there is no remaining need for non-Gaussian processes at the last scattering surface of the CMB to explain the cold spot. The late integrated Sachs-Wolfe effect, already seen statistically for NVSS source counts, can now be seen to operate on a single region. To create the magnitude and angular size of the WMAP cold spot requires a ~140 Mpc radius completely empty void at z=<1 along this line of sight. This is far outside the current expectations of the concordance cosmology, and adds to the anomalies seen in the CMB.

 

The non-gaussianity of this extreme region has been scrutinized, concluding that it cannot be explained by either foreground correction problems or the normal Gaussian fluctuations of the CMB. Thus, the cold spot seems to require a distinct origin – either primordial or local.

 

The WMAP cold spot could have three origins: a) at the last scattering surface (z ~ 1000), :surprise: cosmologically local (z < 1), or c) galactic. Because the spot corresponds to a significant deficit of flux (and source number counts) in the NVSS, we have argued here that the spot is cosmologically local and hence, a localized manifestation of the late ISW effect.

 

How likely is such a large underdense region in a concordance cosmology? Suppose there is only one such large underdense region in the whole volume up to z=1. The corresponding void frequency is then the ratio of the comoving volume of the void to the comoving volume of the Universe to z=1, which is roughly 3 × 10^−5. Is this consistent with Lambda-CDM? Void statistics have been done for a number of optical galaxy surveys, as well as numerical structure formation simulations. Taking the most optimistic void statistics which can be approximated by log P = −(r/Mpc)/15, a 140 Mpc void would occur with a probability of 5 × 10^−10, considerably more rare than our estimate for our Universe (3×10^−5) based on the existence of the cold spot.

 

With this caveat, we conclude that the cold spot arises from effects along the line of sight, and not at the last scattering surface itself. Any non-gaussianity of the WMAP cold spot therefore would then have a local origin.

A 140 Mpc radius, completely empty void at z=<1 is sufficient to create the magnitude and angular size of the cold spot through the late integrated Sachs-Wolfe effect. Voids this large currently seem improbable in the concordance cosmology, adding to the anomalies associated with the CMB.

 

I wish to emphasise that I had not yet seen this paper when I made my last two posts.

 

Regarding the Hubblesite article on clumping of dark matter, there is a contradiction between the posited torus-like distribution of dark matter (externally, like Einstein rings) and the suggestion that dark matter caused the primordial gravitational collapse that seeded the formation of structure. If that were the case, dark matter would be concentrated around the centre of gravity of objects thus formed (eg the cores of galaxies). If it is, though, there emerges a concomitant problem with galaxy rotation. They can't have it both ways.

 

Regards

Hilton

[Pluto]

Hello Tomod

 

you said

 

I read an article in New Scientist online which said that this void would also be empty of dark matter, since dark matter tends to clump around matter (so to speak). The dark matter distribution was charted for the first time last year, and shows the "scaffolding of the universe" as a colleague of mine called it.

 

I agree, but I do not agree with your logic about black holes, its sounds like you think its a cyclone matrix going into a hole. This is not the case matter enters at about 90 Deg to the jet stream.

 

==========================================

 

 

Hello Hilton

 

You are so logical, you hit the nail on the head.

[Tormod]

I found an interesting post in the New Scientist space blog:

 

New Scientist Space Blog: Colossal void may spell trouble for cosmology

[kmarinas86]

I doubt that the largest cold spot in the WMAP is in the Eridanus constellation. There are larger ones. Perhaps we will find bigger voids.

[Michaelangelica]

I am getting a bit lost here.

 

This discovery seems to have nothing to do with black holes

 

It is just a very, very, very, big bit of nothingness

 

Astronomers find largest hole in universe

Reuters

Friday, 24 August 2007

The newly found hole is nearly a billion light-years across and no one knows why it's there (Image: iStockphoto)

A giant hole in the universe is devoid of galaxies, stars and even lacks dark matter, astronomers say.

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