Lensed Quasar Pair: Retaining Point-like Appearance

[turbo]

"lensed" quasar pair

Here is a paper about a purportedly lensed quasar.

http://xxx.lanl.gov/abs/astro-ph/0505248

Has anybody notice how "lensed" quasars, like those comprising the Einstein cross, seem to manage to retain their point-like appearance instead of exhibiting arc-like distortion around the center of mass of the "lensing" mass? Why is this? Can light from quasars blithely ignore the laws of classical optics? As a board-certified optician, I would find it difficult to build you any lens (short of combinations of basic prisms) that would give you multiple images of a point object and retain their point-like appearance with no smearing. How do these "lensing" clusters and galaxies manage to accomplish this preferentially along the line of sight to US?

 

[Chronos]

Concerning the referenced paper, it is not clear this is a lensing event. From the abstract:

we revisit the long-standing question of whether this quasar pair is a binary quasar or a wide-separation lens.
and
Unless the mass-to-light ratio of the galaxy is at least 80 times larger than usual, the lensing hypothesis requires that the galaxy group or cluster plays a uniquely important role in producing the observed deflections.

Image distortion in lensing events is largely a matter of alignment
http://hubblesite.org/newscenter/newsdesk/archive/releases/1995/43/text/
A gravitational lens is produced by the enormous gravitational field of a massive object which bends light to magnify, brighten and distort the image of a more distant object. Depending on the alignment between the objects and the mass distribution of the foreground lens, the more distant object can be smeared into arcs or split into pairs, triples, or even quadruple images.

http://www.mira.org/newsletr/nlsum97/gravlens.htm
The best known type of lens occurs when light from a distant quasar (source) is deflected by close passage to a single galaxy (lens). In this case, the result appears to be several identical quasars located very close together; these usually occur as double, triple, and quadruple images of the same source. In addition to these multiply imaged objects, gravitational lenses can also appear as arcs and sometimes even complete rings of light! Arcs and rings are generally made when light from very distant galaxies passes through massive clusters of galaxies (arcs), or when a quasar is precisely aligned with the center of a single galaxy (rings).

 

[SpaceTiger]

Has anybody notice how "lensed" quasars, like those comprising the Einstein cross, seem to manage to retain their point-like appearance instead of exhibiting arc-like distortion around the center of mass of the "lensing" mass? Why is this? Can light from quasars blithely ignore the laws of classical optics?

Do you mind being more specific about which laws you think are being violated? I don't see any reason why a light beam couldn't be split into multiple images (without distortion) in the laws of GR.

 

[turbo]

Do you mind being more specific about which laws you think are being violated? I don't see any reason why a light beam couldn't be split into multiple images (without distortion) in the laws of GR.

In classical optics, it is easy to produce point-like multiple images of a point source. The solutions to these problems involve prism-like refractive media with relatively planar density transitions (think of a faceted gem). Trying to produce point-like images with refractive media like the lenticular or spheroidal fields surrounding galaxies or the more complex fields of clusters is impossible. The field densities and the shapes of the fields cannot possibly conspire to produce perfect point-like images preferentially along the line of sight to us. The images of the "point-like source" (quasar) will be smeared radially, axially, or both and will not appear point-like.

GR is valuable and predictive on a variety of scales, but it cannot trump optical principles that were proven centuries ago and are used to validate GR today. Some GR adherents say that the Einstein cross is a perfect case of gravitational lensing (with no explanation of how GR accomplishes this amazing feat), but in the next breath they say that if a galactic core is on the line of sight to a quasar, the quasar will appear as a ring (which is FAR more likely in classical optics). The members of the Einstein Cross are point-like, with no real axial or radial distortions, AND the light curves of the four elements have diverged in significant ways over the years. They are most likely four individual objects that have been ejected from the core of the "lensing" galaxy. The fact that the objects have excess redshift with respect to the galaxy prohibits GR believers from believing that they can be physically associated with it. This is puzzling to me, since we have known for decades that very dense objects exhibit intrinsic redshifts. If black holes accrete in galactic cores and are perturbed out of the core, their accretion zones should exhibit extreme redshifts, especially if the accretion zones are very close to the event horizons.

 

[SpaceTiger]

None of what you've just said actually shows which part of the math is wrong. I've seen the solutions of these equations actually derived for multiple quasars, so if you're going to dispute that, you'll have to show the problems with the derivation.

You have to remember that quasars are VERY point-like. The majority of the emission comes from a region less than a tenth of a parsec in size, while the quasars are gigaparsecs away. This means that, in the absence of perfect alignment, the actual "smearing" will be difficult to detect (though it does occur). This is why people have been thinking about using microlensing to study the properties of the quasar emission region. The magnifications in microlensing are so large that the quasar might actually become resolvable. See http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1988ApJ...335..593N&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf paper, for example.

 

[Chronos]

GR is valuable and predictive on a variety of scales, but it cannot trump optical principles that were proven centuries ago and are used to validate GR today. Some GR adherents say that the Einstein cross is a perfect case of gravitational lensing (with no explanation of how GR accomplishes this amazing feat), but in the next breath they say that if a galactic core is on the line of sight to a quasar, the quasar will appear as a ring (which is FAR more likely in classical optics). The members of the Einstein Cross are point-like, with no real axial or radial distortions...

Your insistence the images cannot be pointlike remains unfounded. You would think a few scientists are sufficiently competent to have recognized and written a paper detailing any violations of optical physics commited by these images.

They are most likely four individual objects that have been ejected from the core of the "lensing" galaxy. The fact that the objects have excess redshift with respect to the galaxy prohibits GR believers from believing that they can be physically associated with it. This is puzzling to me, since we have known for decades that very dense objects exhibit intrinsic redshifts. If black holes accrete in galactic cores and are perturbed out of the core, their accretion zones should exhibit extreme redshifts, especially if the accretion zones are very close to the event horizons.

Interesting. What evidence of physical association between the 'ejected' quasars and the 'mother' galaxy do you have in mind? Why would radiation only be emitted near the event horizon? Accretion discs must be continuously replenished by infalling matter. Would you not think this infalling matter would become highly luminous long before it got anywhere near enough the event horizon to attain the huge redshifts you are suggesting? Would you expect this radiation to be blindingly bright compared to the pitiful squawk of photons emitted near the event horizon?

...AND the light curves of the four elements have diverged in significant ways over the years.

Indeed, they have. In fact, this data can be used to calculate the distance of the lensed quasar independent of its redshift. You may find this interesting:
http://www.mira.org/museum/lens.htm

 

[turbo]

None of what you've just said actually shows which part of the math is wrong. I've seen the solutions of these equations actually derived for multiple quasars, so if you're going to dispute that, you'll have to show the problems with the derivation.

You have to remember that quasars are VERY point-like. The majority of the emission comes from a region less than a tenth of a parsec in size, while the quasars are gigaparsecs away. This means that, in the absence of perfect alignment, the actual "smearing" will be difficult to detect (though it does occur). This is why people have been thinking about using microlensing to study the properties of the quasar emission region. The magnifications in microlensing are so large that the quasar might actually become resolvable. See http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1988ApJ...335..593N&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf paper, for example.

Hi, ST. Let me first say that that with objects that are VERY point-like (your words) we should expect some optical effects that will shed some light on the nature of the "lensing" involved. The more point-like the source objects, the more critically we can examine the image(s).

The next thing that we have to look at is whether the distortion of the shapes of the observed objects can be significantly changed by the geometry of the source-lensing object-observing frame relationship. This is a tough one. How can a "distant" object end up being "multiply imaged" by a lensing entity instead of being smeared? There is no critical break-point in any models that I have found that can can suddenly result in multiple point-like images of a quasar when a quasar is lensed by a galaxy.

It is incumbent on the GR folks to explain how GR "optics" demonstrates how the Einstein Cross can be an example of optical lensing. If, (as I believe) it is an example of a four high-redshift bodies embedded in a low-redshift galaxy, somebody is going to shake the hand of the king of Sweden over this one. It would be a real shame if it happened only after all of us were pushing daisies.

 

[SpaceTiger]

The next thing that we have to look at is whether the distortion of the shapes of the observed objects can be significantly changed by the geometry of the source-lensing object-observing frame relationship. This is a tough one. How can a "distant" object end up being "multiply imaged" by a lensing entity instead of being smeared?

http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1994A%26A...284..285K&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf

Section 3.4

 

[Chronos]

Hi, ST. Let me first say that that with objects that are VERY point-like (your words) we should expect some optical effects that will shed some light on the nature of the "lensing" involved. The more point-like the source objects, the more critically we can examine the image(s).

The next thing that we have to look at is whether the distortion of the shapes of the observed objects can be significantly changed by the geometry of the source-lensing object-observing frame relationship. This is a tough one. How can a "distant" object end up being "multiply imaged" by a lensing entity instead of being smeared? There is no critical break-point in any models that I have found that can can suddenly result in multiple point-like images of a quasar when a quasar is lensed by a galaxy.

It is incumbent on the GR folks to explain how GR "optics" demonstrates how the Einstein Cross can be an example of optical lensing. If, (as I believe) it is an example of a four high-redshift bodies embedded in a low-redshift galaxy, somebody is going to shake the hand of the king of Sweden over this one. It would be a real shame if it happened only after all of us were pushing daisies.

Did you read the links ST and I have offered? Does it not appear you resort to vague generalizations when confronted with hard questions?

 

[turbo]

http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1994A%26A...284..285K&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf

Section 3.4

The approach of the paper is interesting, but it fails to explain how four images of a distant point-like source can be accurately reproduced as point-like images symmetrically spaced around the core of a lensing galaxy. The multiple-image effect might be a wonderful explanation for the production of mirror arclets (seen in real examples of galactic or cluster lensing), but it does not address the question of how the lensing galaxy can provide perfectly-focused multiple images of the lensed body. This raises the questions of "why are we at the correct focal length to see these wonderful images focused so nicely?" and "why are we on the correct line of sight to see these images at all?".

You will note that the authors repeatedly state that modeling the gravitational lensing effects of bodies with elliptical mass distributions is problematic.

Here is a physicist (Matthias Bartelmann) with a proper understanding of optics and lensing.

http://www.mpa-garching.mpg.de/mpa/publications/preprints/pp2003/MPA1552.pdf

Lensing is rich in spectacular misnomers. The term “gravitational lens” itself is misleading because gravitational lenses are highly astigmatic, poor optical systems without a well-defined focal length. “Straight” and “radial arcs” are further examples for memorable oxymorons.

Lensing magnifies and distorts images, but the principal problem with image magnifications is that the size of the sources is generally unknown. A possible way to measure magnifications is through the magnification bias. Magnification due to lensing is caused by increasing the solid angle under which a source is seen, thus focussing a larger fraction of the source’s flux on the observer. In addition, the patch of sky around the source is stretched, thus reducing the number density of sources. Thus, fewer sources are seen per solid angle, but they appear brighter.

Here is a quick-time movie of a gavitational lens by the same author.

http://spiff.rit.edu/classes/phys240/lectures/grav_lens/GL_4.qt

 

[turbo]

Your insistence the images cannot be pointlike remains unfounded. You would think a few scientists are sufficiently competent to have recognized and written a paper detailing any violations of optical physics commited by these images.

Unfounded? Are you aware that the "lensing" galaxy of the Einstein Cross is a barred spiral and not a homogeneous lenticular body? Do you know how little asymmetry in the shape or density of refractive media to produce severe distortion? I do, having supplied thousands of people with lenses designed to compensate for the astigmatism caused by the distortion of their eyes' lenses. I do not need a peer-reviewed paper from an astronomer to teach me basic optics. Finally, it should not surprise you that there are not a raft of peer-reviewd papers questioning the nature of the Einstein Cross. Such papers would land the authors in the same dog house that Arp is in, IF they got past the referees.

Interesting. What evidence of physical association between the 'ejected' quasars and the 'mother' galaxy do you have in mind?

Well, the most obvious sign of physical association is the location of the quasars around the nucleus of the host galaxy. If you search Google Scholar on "radiation recoil" you will find any number of papers modeling the ejection of black holes from galactic nuclei.

Why would radiation only be emitted near the event horizon? Accretion discs must be continuously replenished by infalling matter. Would you not think this infalling matter would become highly luminous long before it got anywhere near enough the event horizon to attain the huge redshifts you are suggesting? Would you expect this radiation to be blindingly bright compared to the pitiful squawk of photons emitted near the event horizon?

If a black hole is hurtling through a galaxy, I expect that it will be stripping materials along the way. This is not equivalent to the behaviour of a BH that condensed in place and has had millions of years to develop a large stable accretion disk.

Indeed, they have. In fact, this data can be used to calculate the distance of the lensed quasar independent of its redshift. You may find this interesting:
http://www.mira.org/museum/lens.htm

Can you explain the light curves of the four components in your lensing model? You will note that objects B and C have been trending in opposite directions (in luminosity) for a number of years. Not shown on that MIRA page are the color differences between the four objects and their changes over time.

http://vela.astro.ulg.ac.be/themes/dataproc/deconv/articles/q2237/q2237.html#len

We found a colour excess of B with respect to A of E(V-I) = -0.08 ± 0.02, magnitudes. This is in agreement with Vakulik et al. (1997) who found E(V-I) = -0.12 ± 0.05 magnitudes, also from observations taken in 1995. However, Yee et al. (1988) found that B was reddened relative to A, E(g-i) = +0.08 ± 0.03.

A possible change in the relative colours over time might be explained by colour dependent microlensing or, less likely, by dust extinction that varies over time (e.g., Rix et al. 1992). The reason for a colour change in the Einstein Cross will remain unclear unless long term multicolour photometric monitoring or preferably spectrophotometry is carried out on a dedicated telescope.

Here is another paper that examines the infrared hump surrounding the four objects. Their conclusion is that the quasar's light is being absorbed and reradiated by dust. This is easy to believe if the quasars are actually embedded in the host galaxy.

http://www.atnf.csiro.au/pasa/18_2/agol/paper/node4.html

Even stronger evidence for extended infrared emission comes from the Y2K data. Between the 1999 and 2000 observations, image C decreased by a factor of two (from 1.49 to 0.76 mJy) in V band (as monitored by OGLE, http://bulge.princeton.edu/~ ogle/ogle2/huchra.html, Wozniak et al. 2000). The other three optical images remained unchanged between the two observations; however, image A underwent a 30% amplification in between. The story is much different in the infrared: the infrared data taken in 2000 show no significant variation over a one-year timescale. Microlensing simulations convolved with sources of various sizes have been used to compute the probability that the infrared source could remain constant in flux within 10% while the optical flux decreased by a factor of 2 within 0.2 RE (the approximate distance traversed by the QSO over 1.2 years). This probability is nearly independent of the lens model, since it simply depends on the flux of a single image. Figure 1 shows the probability as a function of infrared source size assuming the SWL model 2. The largest source shown was limited by the size of the microlensing simulation (100 RE). This plot indicates that R < RE is ruled out at about 90% confidence, thus ruling out the synchrotron emission model.

 

[turbo]

Did you read the links ST and I have offered? Does it not appear you resort to vague generalizations when confronted with hard questions?

When people respond with links, I read them. In the case of papers, I try to follow relevant citations as well, which takes time. I explain my reasoning as clearly as possible and I try to find applicable reasearch to illuminate my answers. If these answers are "vague generalizations" to you, then maybe you are not understanding the relevance of the answers, or are simply dismissing them out of hand as "crackpot", "cowpie", without even thinking about them.

 

[turbo]

http://citebase.eprints.org/cgi-bin/fulltext?format=application/pdf&identifier=oai%3AarXiv.org%3Aastro-ph%2F0301592

Here is a paper documenting Chandra observations of the Einstein cross. Interestingly, Object D may actually be 2 separate objects.

Most interesting, they observed a broad Iron/Potassium alpha emission line (99.99% confidence level) ONLY in object A, not in B,C,D₁,D₂. The authors suggest that microlensing could account for the appearance of the emission line, although not very entusiastically or convincingly.

 

[Chronos]

Unfounded? Are you aware that the "lensing" galaxy of the Einstein Cross is a barred spiral and not a homogeneous lenticular body? Do you know how little asymmetry in the shape or density of refractive media to produce severe distortion? I do, having supplied thousands of people with lenses designed to compensate for the astigmatism caused by the distortion of their eyes' lenses. I do not need a peer-reviewed paper from an astronomer to teach me basic optics.

Irrelevant.

Finally, it should not surprise you that there are not a raft of peer-reviewd papers questioning the nature of the Einstein Cross. Such papers would land the authors in the same dog house that Arp is in, IF they got past the referees.

Writing unsound papers tends to have that effect. Suppose we assume the lensing galaxy has a central black hole that does most of the lensing. Would that tend to make the images a bit more focused? Furthermore, the images are not undistorted when sufficiently magnified. Take another look at the images in the paper you cited. You can try these as well:
http://articles.adsabs.harvard.edu//full/seri/AJ.../0095//0999999P096.html
http://www.journals.uchicago.edu/ApJ/journal/issues/ApJL/v503n1/985373/985373.web.pdf?erFrom=-4166844869564147657Guest
The associated papers are also worth reading.

Well, the most obvious sign of physical association is the location of the quasars around the nucleus of the host galaxy. If you search Google Scholar on "radiation recoil" you will find any number of papers modeling the ejection of black holes from galactic nuclei.

Line of sight is irrelevant. More importantly, how does an ejected black hole manage to drag an accretion source along with it?

If a black hole is hurtling through a galaxy, I expect that it will be stripping materials along the way. This is not equivalent to the behaviour of a BH that condensed in place and has had millions of years to develop a large stable accretion disk.

Good point. So where are the pictures of quasars still within the ejecting galaxy?

Can you explain the light curves of the four components in your lensing model?

I don't have a model, unless agreeing with the preponderance of evidence constitutes a model.

You will note that objects B and C have been trending in opposite directions (in luminosity) for a number of years. Not shown on that MIRA page are the color differences between the four objects and their changes over time.
http://vela.astro.ulg.ac.be/themes/dataproc/deconv/articles/q2237/q2237.html#len

I fail to see where, or how this suggests the images are separate objects.

Here is another paper that examines the infrared hump surrounding the four objects. Their conclusion is that the quasar's light is being absorbed and reradiated by dust. This is easy to believe if the quasars are actually embedded in the host galaxy.

It is also easy to believe if the quasars are behind the lensing galaxy. How would the dust know how far away the light source was?

 

[turbo]

Irrelevant.

If you think that the asymmetry of the lensing media is irrelevant to the images produced, you might want to do a little reading about optics.

Line of sight is irrelevant.

Line of sight is absolutely critical, as you would know if you will spend a little time reading about lensing. You might want to download this free program. You will see that alignment offsets of as little as .01 arcsecond produce noticeable changes in the appearance of the lensed image.

http://www.kwakkelflap.com/gravlens.html

More importantly, how does an ejected black hole manage to drag an accretion source along with it?

Now, you're starting to catch on. A BH slinging through a galactic disk cannot develop and drag along a stable accretion disk. Its relationship with the material that it accretes will be predominantly collisional.

Good point. So where are the pictures of quasars still within the ejecting galaxy?

When you look at the Einstein Cross, you will see the best example known to us.

 

[Chronos]

A lively and fun exchange! Let's just cut our losses and agree to disagree. I am the dour mainstreamer and you are the rebel. We will never convince the other to convert. It's still fun to clash.

 

[SpaceTiger]

The approach of the paper is interesting, but it fails to explain how four images of a distant point-like source can be accurately reproduced as point-like images symmetrically spaced around the core of a lensing galaxy.

Actually it does, do you understand the equations presented there?

The multiple-image effect might be a wonderful explanation for the production of mirror arclets (seen in real examples of galactic or cluster lensing), but it does not address the question of how the lensing galaxy can provide perfectly-focused multiple images of the lensed body.

I already addressed this. A perfect point source will not be distorted at all because it will only satisfy their equation (equation 35) at specific points. A nearly perfect point source will experience a distortion that depends on its actual angular size. Since the physical size of the emission region is so small, there's no reason we should expect to be able to resolve this distortion for quasars. The images will look like point sources.

This raises the questions of "why are we at the correct focal length to see these wonderful images focused so nicely?" and "why are we on the correct line of sight to see these images at all?".

A point source cannot be said to be "focused" at all because it's not resolved. If we had infinite resolution, we would see a distorted image of the broad-line region smeared over milli- or micro-arcseconds (probably in arc shapes), but we don't have those capabilities. We do see such arcs in lensing of galaxies because galaxies aren't even nearly point sources on arcsecond scales. For quasars, as far as our instruments can tell, the sources are points.

You will note that the authors repeatedly state that modeling the gravitational lensing effects of bodies with elliptical mass distributions is problematic.

They state that the models are unphysical only for high axis ratios, and this has nothing to do with the lensing, just gravitational stability. If you put a small value of f into equation 35, you'll get a result that's perfectly physical.

 

[turbo]

Actually it does, do you understand the equations presented there?

I follow how they calculate the positions of the critical images. What I don't see is how perfectly-focused point-like images result at these locations.

I already addressed this. A perfect point source will not be distorted at all because it will only satisfy their equation (equation 35) at specific points. A nearly perfect point source will experience a distortion that depends on its actual angular size. Since the physical size of the emission region is so small, there's no reason we should expect to be able to resolve this distortion for quasars. The images will look like point sources.

A point source cannot be said to be "focused" at all because it's not resolved. If we had infinite resolution, we would see a distorted image of the broad-line region smeared over milli- or micro-arcseconds (probably in arc shapes), but we don't have those capabilities. We do see such arcs in lensing of galaxies because galaxies aren't even nearly point sources on arcsecond scales. For quasars, as far as our instruments can tell, the sources are points.

Can you explain this effect? The vast majority of the stars in our sky are point-like in ANY instrument that we can image them in. If the optics of the instrument are not perfect, these point-like images will be distorted. We might expect to see shear (arcing) coma (radial flaring off-axis) astigmatism (induced by cylindrical aberration in some preferential direction) or any number of distortions in the image, depending on the asymmetry of the lensing media. Perhaps I am just really obtuse, but I cannot for the life of me understand how galactic lenses can violate these rules when clusters obey them implicitly.

 

[Chronos]

They can't be explained, turbo-1, when you refuse to accept any reasonable explanation. Pardon me for being blunt, but your argument appears to be a wind chime.

 

[turbo]

They can't be explained, turbo-1, when you refuse to accept any reasonable explanation. Pardon me for being blunt, but your argument appears to be a wind chime.

Just give me a reasonable explanation, then, and we'll be done with it. You quote sources that touch on the subject tangentially, then claim that I refuse to see the truth (do I see a pattern here?), but you seem to have trouble producing an explanation of how a lensing galaxy can produce four point-like images of a background object. I fully expect (given your combative nature) that you have searched for just such a citation, and have come up short. Why is that?

Earlier, you told me essentially that I must be wrong because there haven't been papers published supporting my view. This is a bit silly, don't you think? It's like saying that everything that can be known is already known and accepted by people smarter than me, so I should stop asking questions and trust that "other people" are taking care of real science. The fact that other people have uncritically accepted the "lensing" explanation of the Einstein Cross is not proof that it is an example of lensing. Acceptance of this kind of "proof" is simple herd behavior - it has no bearing on the validity of an idea. Scientists have uncritically accepted things for decades, even centuries, that we now believe to be wrong. Are we at a perfect age, in which all the mysteries are solved? When did this happen? I must have missed the press release.

To get back to the subject: should we believe that somehow, there are four nearly-perfect preferential paths that light from a quasar gigaparsecs away can follow around this lensing galaxy on its way to our eyes? I do not believe that, and cannot find a way to reconcile that with what I know about optics. If you can supply a relevant citation (addressing the focused discrete images), I would be grateful. If the paper also explains how only object A has a broad emission line in the Fe/K alpha while objects B,C,D (and perhaps D₂, if the Chandra observations are to be believed) do not, you will get a gold star.

I will cheerfully ignore simple naysaying, carpet-bombing with irrelevant citations, and insults regarding my mental abilities (as always) - just give me a relevant citation. You are dead-certain that I am wrong and have said so in enough ways - now prove it.

 

[SpaceTiger]

Can you explain this effect? The vast majority of the stars in our sky are point-like in ANY instrument that we can image them in. If the optics of the instrument are not perfect, these point-like images will be distorted.

Let's take a look at what's going on in an imaging system, like a telescope or a human eye, and see how it differs from a gravitational lens.

http://qonos.princeton.edu/nbond/vision-refractive1.gif

Above is a picture showing how the lensing system of the human eye works. Basically, our eye contains a lens that attempts to focus all light coming from a given direction to a single location on the retina. Can this be achieved easily with any refractive material in any shape? No, evolution has carefully molded the shape of the eye to achieve this effect. It's a very tricky thing to do, actually, and it should be no surprise that it isn't always done exactly right. Sometimes light coming in at the top of the lens will be focused to a different location on the retina than light coming in at the middle or bottom. Such imperfections will mean that light from an object in a given direction (point source or otherwise) will be spread out across the retina and "distorted". This is the kind of effect that I assume you are talking about.

How does this compare to gravitational lensing? Well, we ought to be able to scale up the same picture, replacing the refractive material with a gravitational lens (say a cluster of galaxies), and everything will be the same, right? No! There are two things you should notice:

1. We are not sampling the entire image plane. The light that's being bent by the lens is only collected if it falls on our telescope. This corresponds, effectively, to a point on the image plane (or, analogously, a point on the retina).
2. Gravitational lenses are nowhere near perfect lenses. In fact, they don't focus parallel rays to anything even approaching a single point -- this requires a very specially designed lens. If they did, that would be an awfully strange coincidence of nature.

What if they were perfect lenses? Imagine light coming in from the single direction shown in the picture (a point source). Then imagine you're a person living on the point on the retina where the light rays are converging. You see light coming at you from everywhere on the lens! If you're anywhere else on the retina, however, you'll see nothing from that source. Perhaps fortunately, however, clusters are not perfect lenses, so what we see is quite different from this. Instead, the light coming from the point source that hits the top of the lens will be sent in a different direction than light from the same source hitting the bottom. The gravitational lenses are so imperfect, in fact, that at most a few points on the lens will focus incoming light to the same point. When a few points on the lens focus to the same point at the location of earth, we see multiple images of the object.

For the most part, gravitational lensing amounts only to redirection of the light, so it won't smear point sources. Extended sources, however, will be distorted because their light is coming in from multiple directions (think of it as a combination of point sources), each of which will be bent in a way that depends on the structure of the lens.

 

[Chronos]

Just give me a reasonable explanation, then, and we'll be done with it. You quote sources that touch on the subject tangentially, then claim that I refuse to see the truth (do I see a pattern here?), but you seem to have trouble producing an explanation of how a lensing galaxy can produce four point-like images of a background object. I fully expect (given your combative nature) that you have searched for just such a citation, and have come up short. Why is that?

I quote sources that are widely cited and considered credible. You quote sources [Arp] that seem to have trouble getting published in any respectable journal. Why is that? I see no problem how a lensing galaxy can produce pointlike images of a pointlike source. Is this combative, or merely factual?

Earlier, you told me essentially that I must be wrong because there haven't been papers published supporting my view. This is a bit silly, don't you think? It's like saying that everything that can be known is already known and accepted by people smarter than me, so I should stop asking questions and trust that "other people" are taking care of real science.

If there is a dearth of published papers supporting any given view, it might not enjoy much popular support.

The fact that other people have uncritically accepted the "lensing" explanation of the Einstein Cross is not proof that it is an example of lensing. Acceptance of this kind of "proof" is simple herd behavior - it has no bearing on the validity of an idea. Scientists have uncritically accepted things for decades, even centuries, that we now believe to be wrong. Are we at a perfect age, in which all the mysteries are solved? When did this happen? I must have missed the press release. To get back to the subject: should we believe that somehow, there are four nearly-perfect preferential paths that light from a quasar gigaparsecs away can follow around this lensing galaxy on its way to our eyes? I do not believe that, and cannot find a way to reconcile that with what I know about optics.

Real scientists do not uncritically accept anything. In this particular case, I would say you are ignoring a great deal of good observational evidence.

If you can supply a relevant citation (addressing the focused discrete images), I would be grateful. If the paper also explains how only object A has a broad emission line in the Fe/K alpha while objects B,C,D (and perhaps D₂, if the Chandra observations are to be believed) do not, you will get a gold star.

ST already did that. In fact, he went to great lengths to explain how a point source can remain a point source after being lensed.

I will cheerfully ignore simple naysaying, carpet-bombing with irrelevant citations, and insults regarding my mental abilities (as always) - just give me a relevant citation. You are dead-certain that I am wrong and have said so in enough ways - now prove it.

The citations are not wrong, IMO, and I have never questioned your character or mental abilities, to my knowledge. Disagreeing with your theories... yes, I have done that. If I thought your ideas were without merit, we wouldn't even be having this conversation. If you prefer, I will refrain from posting in any thread you start.

 

[turbo]

I quote sources that are widely cited and considered credible.

None of the citations explained how gravitational lensing by galaxies can cause point-like images. ST offered a citation that explained how images might form at four discrete angles around the galactic center, but again, there is no explanation of how the images can be undistorted point-like images. I have been searching for just such papers off and on all week with no success. Apart from simple assertions that galaxies can produce multiple point-like images (like you linked to above) I have not found a single logical proof of this concept in the literature. Certainly, there must be a proof of such an important concept.

You quote sources [Arp] that seem to have trouble getting published in any respectable journal. Why is that?

I do this not because I agree with everything he says, but to illustrate that observations can lead us to interpret things in radical ways, if our assumptions are different. For instance, if quasars are at the distances redshifts suggested by their redshifts (in the standard model), at least some of them have 10s of billions of mSol and reside in galaxies with trillions of mSol that formed only a few hundred million years after the BB. Unfortunately, the short-term variability of the luminosities of many quasars also leads us to believe that they are no larger than our solar system, and perhaps much smaller. These characteristics are all quite extreme, and they can all be ameliorated if the redshift of quasars is intrinsic, and is not cosmological. Is it possible that quasars can have intrinsic redshift? Why not? White dwarf stars do. Black holes (as we understand them) do.

In this particular case, I would say you are ignoring a great deal of good observational evidence.

I am not ignoring the evidence. I am trying to understand the interpretation of the observations. This is a very different thing.

ST already did that. In fact, he went to great lengths to explain how a point source can remain a point source after being lensed.

Yes, he explained it in a way that makes sense superficially, but the explanation does not fit well with my understanding of optics. The thought that gravitation can bend perfectly-focused images without distortion is impossible for me to conceptualize, and as I said, I have been searching diligently for papers that might explain this concept, to no avail. I find popular accounts (and some papers) that assume the effect is real, but have found no explanation of how occurs.

If you prefer, I will refrain from posting in any thread you start.

That is not necessary. It might be nice if you toned down the cowpie/crackpot comments though. :uhh:

 

[SpaceTiger]

Yes, he explained it in a way that makes sense superficially, but the explanation does not fit well with my understanding of optics.

So you won't accept mathematical explanations and you won't accept conceptual ones. Give us one good reason why we shouldn't think of you as a crackpot? It's one thing to simply be confused about something, it's something else entirely to insist that an entire community of astronomers is confused. I don't blame Chronos for not wanting to refute your arguments in great detail and I'm getting sort of mad at myself for wasting time on it. Even Arp himself wouldn't put forward arguments that show such a blatant misunderstanding of astrophysical mechanisms.

 

[turbo]

So you won't accept mathematical explanations and you won't accept conceptual ones. Give us one good reason why we shouldn't think of you as a crackpot? It's one thing to simply be confused about something, it's something else entirely to insist that an entire community of astronomers is confused. I don't blame Chronos for not wanting to refute your arguments in great detail and I'm getting sort of mad at myself for wasting time on it. Even Arp himself wouldn't put forward arguments that show such a blatant misunderstanding of astrophysical mechanisms.

I am searching quite diligently for papers that can explain how these images can be point-like. Please understand that I am not rejecting out-of-hand the question of whether or not the images can be point-like, but I have trouble reconciling this with classical optics. I have not yet found a single paper that explains how the images can be point-like and undistorted, although certainly there must be one somewhere, if so many people believe the effect is real. I have found many papers discribing how arcs and radial smearing occurs and even (in a perfect or near-perfect orientation) Einstein rings. Not a single one (to date) has explained how perfectly focused undistorted images of a lensed object can occur. I have spent many hours on Google Scholar and Citebase looking for such an explanation, and have not found one yet.

 

[SpaceTiger]

I have spent many hours on Google Scholar and Citebase looking for such an explanation, and have not found one yet.

I just gave you an explanation. Which parts are confusing you?

 

[turbo]

I just gave you an explanation. Which parts are confusing you?

It's this part:

For the most part, gravitational lensing amounts only to redirection of the light, so it won't smear point sources. Extended sources, however, will be distorted because their light is coming in from multiple directions (think of it as a combination of point sources), each of which will be bent in a way that depends on the structure of the lens.

Light from a very distant quasar impinges equally on all parts of a not-so-distant galaxy. The mass-distribution of the galaxy somehow conspires to focus this bath of light to produce four (or five, if the Chandra observation of D₂ is real) perfectly formed images of the lensed object at our location. I have a hard time understanding how that barred spiral can distort space-time in such a way as to produce 4 (or 5) perfect images of a background object without distorting the images, and I have not yet found a single paper that provides an explanation of the effect.

I am absolutely willing to accept the reality of the effect if it can be explained in terms of classical optics. Clusters behave in perfectly understandable ways in classical optics (if we accept the mass shortfall necessitating the invocation of DM), producing radial smears, arcs, etc. I believe that the explanation that point sources lensed by galaxies cannot be smeared is flawed - point sources are smeared just like extended objects are smeared, they are just difficult to detect after they are smeared when they are already faint to begin with.

Please forget anything you know, think, or assume about my motivation in this regard, and let's talk about point-like lensed images. I am still searching for citations, papers, anything that will lead to a reasonable explanation of this effect, and will spend many more hours this weekend doing so, if the (rainy) forecast comes true.

Thanks

 

[SpaceTiger]

Light from a very distant quasar impinges equally on all parts of a not-so-distant galaxy. The mass-distribution of the galaxy somehow conspires to focus this bath of light to produce four (or five, if the Chandra observation of D₂ is real) perfectly formed images of the lensed object at our location.

No, it doesn't, that was the whole point of my post. Only a few of the light rays that strike the galaxy will bend such that they reach earth. If the galaxy weren't bending the light, only the rays passing directly from the source to the Earth would reach our telescopes. With the galaxy there, we see instead one or more diverted rays, making it seem as if the source is in one or more different locations on the sky. The rays still come in very nearly parallel to one another, however, so the source still appears like a point. The image is formed by the optics of our telescopes, not the galaxy. The term "gravitational lens" should not be taken too literally, since it doesn't have anything approaching a single focal length.

 

[turbo]

No, it doesn't, that was the whole point of my post. Only a few of the light rays that strike the galaxy will bend such that they reach earth. If the galaxy weren't bending the light, only the rays passing directly from the source to the Earth would reach our telescopes. With the galaxy there, we see instead one or more diverted rays, making it seem as if the source is in one or more different locations on the sky. The rays still come in very nearly parallel to one another, however, so the source still appears like a point. The image is formed by the optics of our telescopes, not the galaxy. The term "gravitational lens" should not be taken too literally, since it doesn't have anything approaching a single focal length.

In cluster lensing, we are often told that the cluster magnifies the images so that we can see faint (albeit distorted) images that we would not be able to see if the cluster were not there to lens the source. Why does the galaxy select only a few light rays and show them to us and reject the rest? This would imply that the lensed source is FAR brighter than we could infer from the luminosity of the lensed images, in opposition to the cluster-lensing models.

 

[SpaceTiger]

In cluster lensing, we are often told that the cluster magnifies the images so that we can see faint (albeit distorted) images that we would not be able to see if the cluster were not there to lens the source.

Yes, there are magnification and distortion effects, but they're of order unity, so a "distorted" point source will still not be resolvable. Lensing preserves surface brightness, so the magnification and "distortion" effects are proportional.

Why does the galaxy select only a few light rays and show them to us and reject the rest?

It's no different from the source "selecting" those light rays to strike us which lie on a straight line between us and the source (in the absence of lensing). If there's a gravitational lens in the way, then instead of getting direct rays from the source, you get bent rays from the source (direct ones are sent off in a different direction). Depending on the geometry of the lens, you will sometimes get bent rays coming from multiple directions. That's when you get multiple images.

 

[Chronos]

Nothing wrong with questions, turbo, and they are interesting. We should, however, remain focused on observational evidence. In the case of the Einstein cross, there is a great deal of good evidence it is a gravitational lensing event - emission and absorption lines, microlensing, time delay in brightness fluctuations, and redshift correlations. Physicists are not disturbed by the absence of any apparent distortion in lensed, point-like sources - like a distant quasar. You can recreate this effect with a pinhole camera. I hand polished a short focus Newtonian mirrer once. Pits in the reflective surface can produce these kind of images when viewed off axis. Try some ray traces and see if you can find a configuration that gives multiple, point-like images from a point source. Anyways, I think your point is sufficiently interesting to do some digging... so I spent the evening mining. This is all I came up with so far:

http://nedwww.ipac.caltech.edu/level5/Mellier/Mellier2_1.html
Note that for a point-like object like a QSO, the total amplification of light and the image position will be the only observable parameters.

http://astro.ic.ac.uk/Research/Extragal/
A gravitational lens can form multiple images of the source. These are point images for a point source such as a quasar, but a galaxy, being extended, is lensed into arcs or a ring.

http://www.jb.man.ac.uk/research/gravlens/intro/intro.html
If the line of sight to the quasar passes exactly through the galaxy, the symmetry of the system results in the formation of an ``Einstein ring''. If the line of sight is slightly off-centre, this produces multiple point images

http://folk.uio.no/kjetikj/science/master/description.html
Illustrated in above is a typical case of gravitational macrolensing, a galaxy is situated between us and a remote quasar, and we observe several images. In fact, it can be proved that there will be an odd number of images, but also that we will almost always see just an even number of images because one image will be heavily demagnified.

 

[turbo]

Nothing wrong with questions, turbo, and they are interesting. We should, however, remain focused on observational evidence. In the case of the Einstein cross, there is a great deal of good evidence it is a gravitational lensing event - emission and absorption lines...

Please see the paper I linked above regarding Chandra observations. Object A exhibits broad Fe/Kalpha emission lines and the remaining objects do not. It would be easy to explain how object A might have absorption lines that the other objects do not (using the light-path explanation), but if these are all images of one lensed object, they should all have the same emission spectra, even if the absorption lines differ.

I helped a friend build a deck today - now mining for papers (with heating pads on my old achey knees). :grumpy:

 

[Chronos]

Will review. I ran across some stuff the other day related to that, but really didn't digest it. No doubt there are lots of ideas lurking about. Physics as usual keeps plenty of escape pods handy - I hope jumping out of your chair did not aggravate your knee issues. Old age is not for the faint of heart. I lugged around a bunch of pool sand bags around yesterday and I'm still breathing hard.