View Full Version here: : How reliable are astronomical measurements?
03-05-2011, 05:21 PM
I am currently reading a great book called "Measuring The Universe,The historical quest to quantify space" by Kitty Ferguson.
I have just read about how red shifts are used to measure distances to far galaxies or quasars.
Here is the excerpt:
Quote - "Halton C.Arp,who has spent many years at Mount Wilson Observatory studying galaxies,has cast a minority vote on the question of how much red shift should be trusted as a way of measuring distance to far-off galaxies and quasars.With Geoffrey Burbidge of the University of California,Arp has studied the brightest quasar,3C273.Its red shift indicates that it should be about 2 billion light years away.Arp has found,However,that 3C273 appears to be intercating with a giant elliptical cloud of hydrogen gas no more than 65 million light years away in the constellation of Virgo.There are other mysterious cases where objects at dramatically different red shifts appear to be linked.Arp believes that quasars are not as remote as astronomers have been measuring them,but much closer to home.Most of Arp's colleagues pass off his evidence as coincidence."
My question is are these 2 objects linked between space at these great distances from each other or is 3C273 much closer to home than thought before.
I was wondering this as I was looking at trying to observe this quasar through my 12'' Dob and wanted to have the satisfaction of knowing that I am indeed looking at an object so far away.
Thanks in advance
03-05-2011, 08:53 PM
I am interested to see what unfolds from your question!
All I vaguely know of this issue comes from reading the book "Arp Atlas of Peculiar Galaxies". My understanding is that Halton Arp reported a high correlation between the location of quasars and the galaxies that he classified as peculiar. How could this be as the red shift of the quasars puts them at great distance beyond the galaxies? His argument is that the red shift of quasars is not due only to the expansion of the universe, but also to some intrinsic property of the quasar. Basically that the peculiar galaxies created the quasars and ejected them as a result. His idea of intrinsic red shift is not widely regarded as compatible with mainstream physics.
I suspect that you will get replies by people far more educated, eloquent and committed in this regard than me.
I think the argument against Arp is in part based on doubt about the statistics of his claimed correlation between peculiar galaxies and quasars.
03-05-2011, 11:44 PM
Whatever you two are reading is more than a tad out of date.
Google is your friend. First hit: http://en.wikipedia.org/wiki/3C_273
04-05-2011, 12:27 AM
To answer the threads title, depends on the method of measurement.
But getting on to the body of the text, I got interested in this as any case of Quasars interacting with gas such as Hanny’s Voorwerp is worth understanding. Pity with much searching the argument doesn't seem to be raised or concerned by any other scientist.
The quote "However,that 3C273 appears to be interacting with a giant elliptical cloud of hydrogen gas no more than 65 million light years away in the constellation of Virgo." stood out personally, as it makes a claim of direct interaction between an object 2.4 billion light years away and another 65 million light years away. That's a big gap between them.
The only case of "interacting" I can find documented to any volume is the Lyman Alpha forests where gas between the quasar and us is causing absorption lines in the resultant light. This is to be expected, and it's been a method of finding these clouds of hydrogen gas between galaxies.
As far as any direct interaction between the quasar and the gas, only Arp has made the claim.
Then you start reading more and find that Arp is getting quoted on places like Answers in Genesis. While it doesn't seem that Arp himself is a creationist, it's more likely his arguments are going to be broken down by someone who knows better.
Follow the link for a brief run down on someone else's opinion on his claims, included supporting sources. http://homepage.mac.com/cygnusx1/anomalies/discordantz.html
It seems that Arp makes the argument that if they appear connected, they are connected. It doesn't take a professional astronomer to tell you that a chance arrangement in the sky has nothing to do with physical proximity. Personally I think Arp's work is flawed, and if there is any inaccuracy with the distance it will be due to something such as a new understanding of light in the early universe etc.
Now recently I got the audio book "13 things that don't make sense" by Michael Brooks. It was an entertaining book, but with a lot of science in the media, be it reporting or literature, you need to take it with a grain of salt. In the book he provides a chapter on Homoeopathy, which decidedly has no real value but those facts are twisted in artistic licence.
So while enjoying science based literature should be recommended, approach it with a level head and a healthy dose of scepticisms.
So where does that get us? Right now you can safely trust yourself that the light you are seeing probably spent a bloody long time getting here from something insanely bright. At 10 parsecs its as bright as the sun... sheesh.
04-05-2011, 08:47 AM
I imagine literal creationists like Arp's arguments as it can make the universe look smaller and help them with the problem of an observable ob universe that is held to be 6000 years old and 13 billion light years across.
04-05-2011, 11:54 AM
I doubt they even need it to go that far. For a lot of creationists, simply saying Science is not always 100% accurate is enough for their needs.
But it is a case of if they can scrounge together enough evidence to make their case seem reasonable to the less educated in society, they can spin their young universe ideas and pretend to back it up.
05-05-2011, 07:15 AM
Thanks for the input Paddy and arcanemagik.
Unfortunatly this is somehow true.
I will pursue trying to find this quasi-steller object.I'll let you guys know how i go.
05-05-2011, 09:04 AM
3C273 is a magnitude of 12.9 so you are going to need some very dark sky to visualise it well. Suburbia may or may not resolve it as a Pulsar.
Funny I am doing an assignment, just started on 3C273 calculation of luminosity and distances for my Uni course :)
05-05-2011, 04:00 PM
The QUASAR 3C273 Is quite easily seen as a a star in a 10"scope from a dark site as a STAR LIKE OBJECT.
It was observed from Cambroon in a 10" scope by Wes (Zubenel) about a year ago and I confirmed it
05-05-2011, 06:08 PM
I found the main issue with observing 3C273 is knowing which "star" it actually is, so a good detailed print out of the stars close to it is very helpful. My recollection is that there is a fairly distinctive little asterism that it sits with. I found it readily observable with a 12" scope under dark sky. I reckon you'll nail it.
10-05-2011, 09:47 AM
Ha....good ol' Halton Arp. He just can't seem to let go of his idea when just about every observation ever made has shown him to be at fault. The problems with Arp's hypothesis are quite well known. For a start, his sample size is only rather small when compared to to the numbers of galaxies and quasars that have been observed....a couple of hundred or less compared to several million (for quasars) and billions (for galaxies). Statistically, his sample size is meaningless and can be easily explained as just random alignments of objects at different distances. Secondly, in order to explain any connection between a quasar of high redshift and galaxy of low redshift, you have to come up with a satisfactory explanation for why there are the disparate redshifts. No satisfactory explanation has been proposed, or even observed for that matter. Various "throw away ideas, have been proposed by Arp and his disciples but none of them make either logical (scientific) or observational sense. Things like the old ideas about "tired light" and such. Some of his latest observations, like quasars that appear to lie "in front" of galactic nuclei and have been "ejected" are nothing more than misinterpretations of the observations being made....optical illusions. Quasars are bright enough to appear as "foreground" stars through the bodies of galaxies. You only have to look at piccies of galaxies where background objects can be clearly seen through their structures to understand why it's easy to make the mistake of thinking the quasar is lying in front of the galaxy. Then, the selection effect of seeing a connection because you believe one will be there starts to kick in. Thirdly, you also have to come up with a satisfactory explanation as to what mechanism could actually eject a quasar from the centre of a galaxy. especially at the high velocities that the redshifts say they're being ejected at. You also have to explain why just redshifts...if the objects are being ejected, then why aren't there also blueshifted quasars. Why would there be a preferential direction of ejection??. There's no known mechanism that can satisfactorily explain why an object should be ejected in one particular direction in preference to another. Statistically, the direction of ejection should be the same for any quasar/galaxy combination...they should be ejected in any random direction. This is also why such a small sample size, like the one that Arp has used, is meaningless. There is no correlation between between redshift and the supposed ejection of quasars from a host galaxy. Nor is there any correlation between the direction of ejection and the mechanism of ejection. They simply don't exist. Now, despite all that I've said, there is a possibility of finding an actual quasar/galaxy connection where a quasar has been ejected from that galaxy. It could happen, given the right conditions, but so far we haven't observed anything like that. If we did, it would be news and magazines like Astronomy and Sky and Telescope would be writing it up. The journals would be full of papers on the subject. They're not.
Halton Arp came up with his idea in the late 50's early 60's when they didn't know what quasars actually were, and were just beginning to make observations of these objects. They didn't know what mechanisms were behind the nature of these objects and had no concept of the physics that explain them. Arp's ideas were speculation then...they're tired, misguided and outdated ideas now. Like quite a few scientist, when they get old, they become controversial because they start to become potty. They want to go out with a bang, so they revive old ideas that are clearly nonsense, or they push ideas they once had which have been proven wrong in order to justify their continuing tenures. Invariably, they get some old colleagues come along for the ride (like Geoffrey Burbidge), especially when they've been a bit maverick themselves, in the past, and also some younger ones who want to make a name for themselves with some new ideas or standout observations...which is just a case of hero worship. Understandable, simply because these old scientists were very good in their day and are excellent teachers. However, just because you come up with an idea (brilliant or otherwise) doesn't make it correct, even if you still believe that it is, despite everything else to the contrary.
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