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Thread: Apparent diameter of quasars?

  1. #1

    Apparent diameter of quasars?

    I know that quasar stands for quasi-stellar objects so that they have a small apparent diameters, but cannot find a source giving typical apparent diameters. Can someone please tell me either a good source for this or perhaps a few typical cases such as some low redshift ones like 3C273 (I managed to find a photo but without a scale) and some higher redshift ones also if they can be resolved.

    Thanks
    Ray

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    Quasar means Quasi stellar. Or sort of star like. To speak in terms of apparent diameter is not correct for stars. We speak in terms of apparent magnitude or brightness. We do this because we cannot reslove the diameter of stars only their magnitude or brightness. We have to question whether the brightness as it appears is due to it's actual brightness, its nearness to us or its size.

    Our sun is about 4 light seconds across. Our galaxy is a hundred thousand light years across. At the distance of quasars we can resolve galaxies well enough to see that they are galaxies. A quasar emits as much energy as an entire qalaxy. But we cannot resolve quasars like we cannot resolve stars at that distance.

    So, it emits as much energy as a qalaxy but cannot be resolved like a star at that distance cannot.

    So like a star in that it cannot be resolved but like a galaxy in that it emits a lot.

    So it's somthing like a star, a quasi star, a quasar.

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    astrotech,

    Your reply seems to dismiss the importance of the apparent diameters
    of quasars, but knowing the apparent diameter is absolutely vital to
    understanding what they are. I am as interested in knowing the apparent
    diameter as Ray, because shortly after they were discovered, I thought
    quasars might be the cores of very early galaxies in which supernovae
    were occurring at an enormous rate -- several a day. I was told that
    quasars are too small for that to be possible, but I've never seen actual
    measurements of their sizes.

    -- Jeff, in Minneapolis

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    Thank You

    Quote Originally Posted by Ari Jokimaki View Post

    Here's NED page for one SDSS quasar
    Excellent reference.

    Armchair astronomer folks (like me), note how much work has gone into the sites referenced by Jokomaki. This is not a casual enterprise.

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    Why is their apparent size so small? If space were static, then I would understand them appearing small, but since space is modeled as expanding, wouldn't their apparent size be the size we would have seen them at the time the light we are now recieving actually left their galaxy?
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by rtomes View Post
    I know that quasar stands for quasi-stellar objects so that they have a small apparent diameters, but cannot find a source giving typical apparent diameters. ...
    The optical light from quasars is not coming from a small central point.
    I think the best measurement of the size and shape of a particular quasar did NOT come from a nearby one like 3c273, but came from study of the Einstein Cross. The study of the microlensing events in the five paths through the intervening galaxy has given information that can be seen as a map of the light source.

    I don't have a pointer to this, but you should be able to find it.
    Forming opinions as we speak

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    Most of the visible light from a quasar is emitted by gas in an accretion disk around the central black hole. There are several ways to estimate the sizes of these accretion disks -- simple blackbody emission calculations, more detailed radiative transfer models, gravitational microlensing, spectral modeling. You can find papers describing details by going to the ADS

    http://adsabs.harvard.edu/abstract_service.html

    and typing into the "Abstract Words" box terms such as

    quasar accretion disk radius

    and pressing the "Send Query" button. You'll receive a list of many papers; read through the abstracts and pick the ones you find most promising.

    For example,

    http://adsabs.harvard.edu/abs/2005AJ....129.1225S
    http://adsabs.harvard.edu/abs/2002MNRAS.331.1041W
    http://adsabs.harvard.edu/abs/2008ApJ...673...34P

    These papers provide evidence for accretion disks which range from 10^15 to 10^17 cm in radius -- or, rather, for gas at those radii which emits visible and near-IR radiation.

    The apparent angular size of a "quasar" will depend on both the physical size of the accretion disk and on its distance from us, of course.

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    A lot of confusion here (above George's post)

    First, many hundreds of stars other than our Sun ARE spatially resolved - through interferometry, in eclipsing binary systems, and via other methods.

    Second, the diameters (in units of arc seconds) quoted for that quasar must be of that of the host galaxy, as defined by some surface brightness criterion. At the cosmological redshift of this particular quasar, the scale is something like 40,000 pc (130,000 light years) per arc second.

    Excepting the (infrequent) presence of the powerful radio jets that can be as large as 100s or 1000s of kiloparsecs, the regions that generate the luminous power of quasars (which lie at the centers of massive galaxies) are tiny, tiny, tiny compared to galactic size scales. The region that generates the continuum light from the UV to the visible in luminous quasars is no more than a ~ few tenths of a light year across (and most of that light comes from a region maybe 10x smaller), the main X-ray emitting region is likely even smaller still, while that of the emission line region is typically no more than a few light years across. Thus at the distance of this object, these light emitting regions of the quasar range from something like ~ 0.05-50 micro-arcseconds.

    These size estimates come from variability arguments: the X-rays, UV and visible light continuum emission all vary in intensity, and the broad emission lines (that are powered by the UV-X-ray light) also vary but delayed in time due to the finite speed of light. As mentioned above we occasionally get spatial information of the light emitting regions from gravitational microlensing observations. We also have basic working models for these light emitting mechanisms, and although the details still elude us (keeps me and others busy in research), the observations and model predictions are in reasonable agreement.

    There are plans to begin using interferometric methods to resolve the broad emission line regions (the gas responsible for the strong, very broad emission lines) in some nearby sources.

    George is correct in that for the standard cosmological parameters, the angular diameter distance (aka the emission distance) reaches a peak near a redshift of 1.6 and then declines thereafter, but that's not a big effect for this redshift 2 quasar.
    Last edited by Spaceman Spiff; 2008-Mar-18 at 03:50 PM. Reason: minor additions

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    One more source of confusion: Type 2 quasars (or Type II quasars).

    For these AGN galaxies, the central accretion disk is obscured, by the dust torus (or whatever), but the scattered light of the disk is still enough to dominate that from the host galaxy ... the size of these types of 'quasars', on the sky, may be much greater than the angle subtended by the accretion disk.

    Oh how important it is to be sure you have a clear, consistent definition of a term like 'quasar'!

  11. #11
    Quote Originally Posted by Ari Jokimaki View Post
    This gives four measurements of the one object as having a radius of 1.80, 0.57, 0.04 and 0.06 seconds of arc. Not exactly great consistency!!

    If there are photos of 3C273 showing great details:

    then it must be easy enough to measure, but that photo does not come with a scale. My science teacher in school would take off a lot of marks if you didn't show the scale. :-)

    Anyway, an interesting photo.

    Quote Originally Posted by Nereid View Post
    One more source of confusion: Type 2 quasars (or Type II quasars).

    For these AGN galaxies, the central accretion disk is obscured, by the dust torus (or whatever), but the scattered light of the disk is still enough to dominate that from the host galaxy ... the size of these types of 'quasars', on the sky, may be much greater than the angle subtended by the accretion disk.

    Oh how important it is to be sure you have a clear, consistent definition of a term like 'quasar'!
    Well if there are differences for different types of quasars, I would like to know about that. But what I am really after is the typical optical diameter of quasars, perhaps as a function of redshift. If they often have a black spot on them like 3C273 then it would be good to know about the typical size of that too (as a function of redshift).

    Quote Originally Posted by StupendousMan View Post
    Most of the visible light from a quasar is emitted by gas in an accretion disk around the central black hole. There are several ways to estimate the sizes of these accretion disks -- simple blackbody emission calculations, more detailed radiative transfer models, gravitational microlensing, spectral modeling. You can find papers describing details by going to the ADS

    http://adsabs.harvard.edu/abstract_service.html

    and typing into the "Abstract Words" box terms such as

    quasar accretion disk radius

    and pressing the "Send Query" button. You'll receive a list of many papers; read through the abstracts and pick the ones you find most promising.

    For example,

    http://adsabs.harvard.edu/abs/2005AJ....129.1225S
    http://adsabs.harvard.edu/abs/2002MNRAS.331.1041W
    http://adsabs.harvard.edu/abs/2008ApJ...673...34P

    These papers provide evidence for accretion disks which range from 10^15 to 10^17 cm in radius -- or, rather, for gas at those radii which emits visible and near-IR radiation.

    The apparent angular size of a "quasar" will depend on both the physical size of the accretion disk and on its distance from us, of course.
    Not only useful information but also "how to do it" for future reference, thanks StupendousMan.

    However the first one of these papers abstract starts:
    Because quasars are unresolved in optical imaging, their structures must currently be inferred.
    Why would they say that when there are photos of quasars that show details, and various reports about movements in parts of quasars (some that appear faster than c) and other such stuff published regularly?

    Thanks to all those that supplied information.

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    rtomes -

    That image is the image of the host galaxy of 3C 273. It is enormous in size (like Milky Way), in comparison to the quasar (whose light was blotted out in the image you posted). The "inconsistencies" in sizes noted are not such, but the different results using different measures of different size scales.

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    Quote Originally Posted by Nereid View Post
    One more source of confusion: Type 2 quasars (or Type II quasars).

    For these AGN galaxies, the central accretion disk is obscured, by the dust torus (or whatever), but the scattered light of the disk is still enough to dominate that from the host galaxy ... the size of these types of 'quasars', on the sky, may be much greater than the angle subtended by the accretion disk.

    Oh how important it is to be sure you have a clear, consistent definition of a term like 'quasar'!
    Yeah, but even then the obscuring 'torus' isn't really considered part of the quasar, or if one were to include it (as the most immediate supply of gas to the inner accretion disk surrounding the supermassive black hole), then it's also present in all/most quasars (and it only gets in the way when we view the system edge-on).

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    And I think that's part of the problem ... if the term is used to mean just the accretion disk (more or less), then indeed it will be tiny (in arcseconds).

    However, I think you'll find that the word* is used with a range of different meanings, not only in different contexts, by different authors, and so on, but also it's changed in the last four decades or so.

    I think rtomes, in the OP, was referring to an observational definition, as used by astronomers working in the visual waveband, and (likely) before the unified AGN model was much more than a topic of morning tea time speculation.

    If that's so, then 'quasar' could mean the host galaxy (+torus+jets+...) and, IIRC, even some 40 years ago there were papers discussing the ~2" or so 'fuzz' that seemed to surround some of the newly discovered quasars.

    * Along with QSO, AGN, and, no doubt, many others

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    Of course we are seeing quasars as the looked billions of years ago. Likely they are much dimmer now, and perhaps even smaller, as the reduced photon and ion pressure would allow the orbits to contract. Generally galaxtic groups and smaller things do not universe expand with the space between the galaxtic groups. There should be a former quasar within a few million light years of Earth, perhaps much closer. Any other ideas what to look for? Do typical quasars send us light that was red shifted mostly from gamma when it left the quasar? Neil

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    Re post#11:

    That's an image of 3C 273, taken by the Hubble Space Telescope's Advanced Camera for Surveys, using the camera's coronograph*, and part of News Release Number: STScI-2003-03 (note that the scale is given).

    You need to read the details of how the relevant SDSS data reduction pipeline(s) makes estimates of 'diameters' to understand what the differences are in the r band major axis estimates of SDSS J002814.79+150605.1, though the "Detailed Information for Each Entry" gives you some clues.

    * That's what produces the 'black spot'!

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    Quote Originally Posted by John Mendenhall View Post
    Excellent reference.

    Armchair astronomer folks (like me), note how much work has gone into the sites referenced by Jokomaki. This is not a casual enterprise.
    You're absolutely right. It's getting deep into the heart of astrophysics.

    So, I third your opinion.

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    Quote Originally Posted by rtomes View Post
    Why would they say that when there are photos of quasars that show details, and various reports about movements in parts of quasars (some that appear faster than c) and other such stuff published regularly?

    Thanks to all those that supplied information.
    I believe you're absolutely right in requiring some sort of a published scale.

    How about (and I'm only a very amateur astronomer) ((so please feel freel to add)):

    All Internet-posted astronomical objects are required to include means of telemetry (details on specific devices used during the observation), observation data (inclination, degrees, date/time of observation, nomenclature of object being observed (if applicable)).

    Cut to the chase, gentleman, just putting out "ooh/aah" shots of glorious clusters is no longer acceptable.

    Give us the specific information along with the shots.

    Is that such a difficult task, paticularly given the fact that my 7th grade astronomy teacher has most of that programmed into his computer-controlled telescope, but can't access the details (like where it is in space?) when he reads it online if what I consider the most prominent Astronomy forum available, today?

    Uh, duh, we're a bit brighter than that these days (I would think), and if you're having a database problem, please bring it on.

    I can fix it.

    I've solved more than a few, and have, over thirty years, discovered that most such problems are because most people don't understand data.

    I do. That's what I do.

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    Quote Originally Posted by rtomes View Post
    This gives four measurements of the one object as having a radius of 1.80, 0.57, 0.04 and 0.06 seconds of arc. Not exactly great consistency!!
    Those different sizes are all consistent with the object being a point source. They are also very different "sizes:" deVaucouleurs and Exponential are galaxy fits (and the radius is the half-light radius), a description of the Petrosian magnitude is on the SDSS website, and the isophotal radius is the semi-major axis of an elliptical gaussian fit. Only the isophotal radius really means anything in this case, since the Sloan PSF is ~1.4, so sizes smaller than that are meaningless (and in this case, they mean that those models aren't good fits). The SDSS pipeline fits all models to every source, which is why they are all reported on NED.

    Quote Originally Posted by rtomes View Post
    If there are photos of 3C273 showing great details:
    then it must be easy enough to measure, but that photo does not come with a scale. My science teacher in school would take off a lot of marks if you didn't show the scale. :-)
    It's not at all easy to measure. The quasar is much brighter than the host galaxy, so you either need a very solid understanding of the PSF (as a group did using adaptive optics on the gemini telescope) or some way to block out the central point source, as was done for the Hubble ACS image.

    But where the heck did you find just the picture? Nereid's link to the press release has all the details, including a scale, so I don't know how you would have missed them. Here's the paper describing the research that went into that image. Took me about 30 seconds to find (google search for 3c273 hubble ACS)...

    Quote Originally Posted by rtomes View Post
    Well if there are differences for different types of quasars, I would like to know about that.
    I've given you plenty of links in other threads about this. There are also some relevant links in my What's a quasar thread, including a history of AGN.

    Quote Originally Posted by rtomes View Post
    But what I am really after is the typical optical diameter of quasars, perhaps as a function of redshift. If they often have a black spot on them like 3C273 then it would be good to know about the typical size of that too (as a function of redshift).
    Though StupendousMan and Spaceman Spiff have all pretty much said this above, I'll just reiterate:
    All quasars are point sources to all current optical detectors (though, I think a few of the nearest bright AGN might have their broad-line region resolvable whenever the VLT interferometer is working at maximum spec). The "black spot" is the coronograph on ACS, which blocked out the quasar's light to show the host galaxy. Even the so-called "narrow line region" is of order a hundred light years across, which is too small to image. The broad line region is maybe a couple light years and the accretion disk a few hundred AU, at most. That's pretty small.

    If you really want more information, why don't you read some of the links that I've posted in other threads of yours (like the one you have going in ATM right now), hmmm?

    Quote Originally Posted by neilzero
    There should be a former quasar within a few million light years of Earth, perhaps much closer. Any other ideas what to look for?
    Neil: we've got a ~4 million solar mass black hole in our own galaxy: SgrA*. There are two main groups that study it; UCLA, headed by Prof. Andrea Ghez and Max-Planck headed by Prof. Reinhard Genzel. However, SgrA* was probably never a quasar: it isn't big enough, and our galaxy hasn't had enough big interactions. M87 is probably the best candidate for a nearby former quasar, though M84 (described at the same link) is another good one.

    And I'll have to respectfully disagree with Spaceman Spiff in this case: the term quasar often refers to the whole package, including the accretion disk, disk winds and corona, broad line region, narrow line region, dusty/clumpy/bumpy torus, etc. But typically not the host galaxy (which is called exactly that), and usually not the jet (unless the jet is point right at us, in which case we have a Blazar...). That's not to say that it should refer to all of that, instead of just the accretion disk, but those features are all fairly common to accreting supermassive black holes.

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    I Think Mug Has a Good Point

    Quote Originally Posted by mugaliens View Post

    Cut to the chase, gentleman, just putting out "ooh/aah" shots of glorious clusters is no longer acceptable.
    My favorites are the pictures of starfields with no coordinates, no arrows, no distiguishing marks, no references, and a caption that reads something like "Notice the interesting red dwarf" (or brown dwarf, or faint object, or whatever). Maddening.
    Last edited by John Mendenhall; 2008-Mar-19 at 07:13 PM. Reason: clarity

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    Quote Originally Posted by John Mendenhall View Post
    My favorites are the pictures of starfields with no coordinates, no arrows, no distiguishing marks, no references, and a caption that reads something like "Notice the interesting red dwarf" (or brown dwarf, or faint object, or whatever). Maddening.
    But how do you enforce penalties on the myriad sites that just repost images? (Although I do admit to knowing of cases where this was done to keep competitors off the trail before publication, and at least once to help enforce a journal's prepublication press embargo - something increasingly anachronistic these days)

    Dave Hogg at NYU as been working on how to undo this problem - the goal of astrometry.net is to be able to find the coordinate system and orientation of any astronomical image (and if it has enough stars, the approximate epoch as well using proper motions).
    "We have built this astrometry service to create correct, standards-compliant astrometric meta-data for every useful astronomical image ever taken, past and future, in any state of archival disarray. We hope this will help organize, annotate and make searchable all the world's astronomical information." They asked early on, and I certainly contributed some sample data in what I thought was an impressive state of archival disarray. It's now in alpha test; there is a version of the code and databases available to download for those who want to experiment wholesale. I hope their definition of "standards-compliant" is less expansive than a lot of FITS coordinate systems I'e seen.

    And as much as I've been sitting on my hands for the rest of this thread - yes, as far as I am aware, no measurement at optical wavelengths has ever clearly distinguished the continuum spike (or broad-emission line region) of a quasar or type 1 Seyfert galaxy from the instrumental point-spread function. This applies to Hubble imaging, where the difficulty in subtracting the point source to see detail in host galaxies lies in how minute focus changes with spacecraft temperature ("breathing" ) change the details of the diffraction pattern between quasar and reference-star observations, and look indistinguishable from trying it on one star based on the diffraction pattern of another.

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    Quote Originally Posted by parejkoj View Post
    And I'll have to respectfully disagree with Spaceman Spiff in this case: the term quasar often refers to the whole package, including the accretion disk, disk winds and corona, broad line region, narrow line region, dusty/clumpy/bumpy torus, etc. But typically not the host galaxy (which is called exactly that), and usually not the jet (unless the jet is point right at us, in which case we have a Blazar...). That's not to say that it should refer to all of that, instead of just the accretion disk, but those features are all fairly common to accreting supermassive black holes.
    Thanks for all of your additional info.

    I'll have to respectfully disagree with your disagreement...but not entirely....

    We seem to be in agreement that that size scale of the quasar phenomenon is a fuzzy issue. The Narrow Line Region stretches out to scales that are normally considered "galactic" rather than "nuclear" environment, even in the lower luminosity "Seyfert" type of active galactic nuclei. Quasars also photoionize gas and produce Lyman alpha halos around their host galaxies on scales of ~100 kpc. The powerful relativistic particle jets (in a minority of quasars) extend even further beyond.

    So I will suggest that when the question of "resolving" a quasar comes up, one should be careful to frame the question around the specific phenomenon related to the quasar activity.

    Of course, the host galaxy itself would not be tagged as part of the quasar phenomenon.

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    Quote Originally Posted by Spaceman Spiff View Post
    I'll have to respectfully disagree with your disagreement...but not entirely....
    Are we agreeing that we disagree about our disagreement? Or are we disagreeing about that too?

    Quote Originally Posted by Spaceman Spiff View Post
    We seem to be in agreement that that size scale of the quasar phenomenon is a fuzzy issue. The Narrow Line Region stretches out to scales that are normally considered "galactic" rather than "nuclear" environment, even in the lower luminosity "Seyfert" type of active galactic nuclei.
    No disagreement there.

    Well, except in what you term (or not) the "nuclear" environment... I'd call within ~100pc or so, nuclear. But now I think we're just quibbling over details...

    Quote Originally Posted by Spaceman Spiff View Post
    So I will suggest that when the question of "resolving" a quasar comes up, one should be careful to frame the question around the specific phenomenon related to the quasar activity.
    Certainly.

    Oh, and which quasar is that in your profile image?

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    3c 273

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    Yep.

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    Quote Originally Posted by parejkoj View Post
    Are we agreeing that we disagree about our disagreement? Or are we disagreeing about that too?
    yes.

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    Quote Originally Posted by George View Post
    Why is their apparent size so small? If space were static, then I would understand them appearing small, but since space is modeled as expanding, wouldn't their apparent size be the size we would have seen them at the time the light we are now recieving actually left their galaxy?
    I'm thinking that since space is modelled as expanding, then it is not so much the relative speed between distant galaxies and an observer that causes a redshift, but that distant galaxies can be regarded as static in their own right, and it is space itself that expands, dragging them along with it somehow, but otherwise the galaxies remain stationary. This being the case, then in this sense it is the wavelength of the light itself, or the distance between wavecrests or individual photons, which would expand along with the expansion of the universe that causes a redshift over time, or over a distance travelled. But while the light is in transit, the expansion should also bring the observer further and further away from the wavefront of the light at the same time, I think, so the light ends up having further to travel. The lines of sight should also increase accordingly over the greater distance travelled, and by the time it reaches the observer, the angles for the lines of sight would probably just about match that for the current distance of the galaxy, not for the distance that it was when the light was originally emitted.

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    Quote Originally Posted by grav View Post
    I'm thinking that since space is modelled as expanding, then it is not so much the relative speed between distant galaxies and an observer that causes a redshift, but that distant galaxies can be regarded as static in their own right, and it is space itself that expands, dragging them along with it somehow, but otherwise the galaxies remain stationary. This being the case, then in this sense it is the wavelength of the light itself, or the distance between wavecrests or individual photons, which would expand along with the expansion of the universe that causes a redshift over time, or over a distance travelled. But while the light is in transit, the expansion should also bring the observer further and further away from the wavefront of the light at the same time, I think, so the light ends up having further to travel.
    Isn't that how Doppler works, too? I have no problem with the view that galaxies have the gravitational strength necessary to easily overcome the expansion force that is acting on spacetime itself, and in agreement with the first part of your statement. But, as our galaxy expands away from the others, will it not gain relative velocity such that when the final photon packet arrives we will be traveling so much faster than when the photons were emitted that redshift must be observed? Don't take my view as carrying much weight, as this stuff is generally over my head.

    Yet, I don't think anyone has guessed the result of one of my little gedankenexperiments. Place a mirror on a long pole, say 1 billion light years long, then shine a monochromatic laser of your choice, I like green, at the mirror and wait to see what color it is when it returns. If it returns green, then space does not streetch the photons, otherwise, it probably does. I don't know if that even qualifies as a gedankenexperiment, but it illustrates a distinction that should exist, I think.

    The lines of sight should also increase accordingly over the greater distance travelled, and by the time it reaches the observer, the angles for the lines of sight would probably just about match that for the current distance of the galaxy, not for the distance that it was when the light was originally emitted.
    I suspect you are correct, and that Spaceman Spiff's earlier answer is right, too. I would bet the expansion rate determines the changes to apparent size, but has little effect for great distances, as you said.

    We know time flies, we just can't see its wings.

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    Quote Originally Posted by George View Post
    Isn't that how Doppler works, too?
    As far as the mathematics go, we can equally apply an expanding of space that increases wavelengths or a relative speed between galaxies that move apart with space due to the expansion, so it should probably work out the same using relativistic Doppler, yes.


    Yet, I don't think anyone has guessed the result of one of my little gedankenexperiments. Place a mirror on a long pole, say 1 billion light years long, then shine a monochromatic laser of your choice, I like green, at the mirror and wait to see what color it is when it returns. If it returns green, then space does not streetch the photons, otherwise, it probably does. I don't know if that even qualifies as a gedankenexperiment, but it illustrates a distinction that should exist, I think.
    Interesting experiment. On the one hand, the mirror remains stationary with the observer since expansion can't overcome the internal forces of the pole, so we should see no redshift. But on the other hand, the wavelengths are free to expand while the light is in transit, so should continue to redshift with the expansion of the universe. I think the redshift would still be observed in general, but the rate of expansion is so small that it is normally just neglected with relativistic Doppler. Tired light theory would also demonstrate this effect (as would "shrinking galaxies", which is synonymous with "expanding universe" in my opinion), so I think observing a redshift would be pretty much the case any way you go with it.

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    Quote Originally Posted by grav View Post
    Interesting experiment. On the one hand, the mirror remains stationary with the observer since expansion can't overcome the internal forces of the pole, so we should see no redshift. But on the other hand, the wavelengths are free to expand while the light is in transit, so should continue to redshift with the expansion of the universe. I think the redshift would still be observed in general, but the rate of expansion is so small that it is normally just neglected with relativistic Doppler. Tired light theory would also demonstrate this effect (as would "shrinking galaxies", which is synonymous with "expanding universe" in my opinion), so I think observing a redshift would be pretty much the case any way you go with it.
    It is one or the other. Maybe we should do a poll. [That's my lousy Friday pun, looks like you got it. ]

    I just can not imagine the expansion of space forcing its way into the strong region of the electromagnetic waves. We'll let the gravitational force subdue the expansion for galaxies, but the potent photon must yield? I say the laser leaves green, and green it stays. [where did the folding arm icon run off to? ]
    We know time flies, we just can't see its wings.

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