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Another Case For Intrinsic Redshifts

02/19/06

  01:06:56 am, by Nimble   , 676 words  
Categories: Thoughts, Science

Another Case For Intrinsic Redshifts

Another pre-print from our very own Morley Bell of the Herzberg Institute with another interesting case for intrinsic redshifts in a paper bestowed with the enormous name, "Evidence that Quasars and Related Active Galaxies are Good Radio Standard Candles and that they are Likely to be a Lot Closer than their Redshifts Imply".

As you look further out into the universe, spectral lines caused by heated gases shift towards the red part of the spectrum. The further out you look, generally, the redder it gets. Conventional wisdom has it that this red-shift corresponds very closely with distance. This is "cosmological redshift". Conventional wisdom also holds that this is due to velocity away from us. A while back, this was believed to be an actual speed, but now it is believed to be due to "space expanding".

The existence of intrinsic redshift throws some caveats into this picture. An "intrinsic" redshift is a redshift not caused by distance or velocity. It can cause things to be more red-shifted than they "should" be, meaning that the objects are nearer or moving more slowly than conventional theory would indicate.

However, it would also solve a number of problems. There would no longer need to be a special explanation of superluminal, that is to say, apparently faster-than-light, ejections in space. If the objects are actually much nearer, then the ejections don't require strange workarounds to explain them.

To quote from the paper:

In simple ejection models, if source distances are known, changes in the angular positions of blobs associated with their jets can be converted into linear ejection velocity components perpendicular to the line-of-sight.

However, it has been known since the 1970s that this simple in terpretation leads, in many cases, to apparent velocities v-app = beta-app*c, where beta-app is greater than 1 and c is the speed of light.

The velocity thus appears to exceed the speed of light and has been referred to as superluminal. Although this apparent anomaly can be readily explained if the objects are really much closer than their redshifts imply, models involving relativistic expansion were developed to explain the rapid variabilty (Woltjer 1966; Rees 1966, 1967), so astronomers did not have to give up their belief that redshifts are reliable distance indicators.

Relativistic beaming models also nicely explained the apparent superluminal ejection velocities. However, although relativistic motions in the ejected blobs can explain the apparent anomaly, even after forty years there is little convincing observational evidence that this

is the correct interpretation.

Also Bell, like D. G. Russell, takes one of Arp's ideas without the theoretical underpinning that has many people in a twist. This idea is "DIR" - Decreasing Intrinsic Redshift, and the idea is simply that younger objects have a high intrinsic redshift, and that it decreases over time. Quasars are implied as being young by many DIR proponents, and DIR would imply that they are a lot closer than cosmological redshift would imply. The paper talks about quasars actually being good standard candles at their DIR distances, without faster-than-light jets coming out of them.

The paper itself is pretty interesting, though you will need plenty of background astronomical knowledge and jargon to make sense ot it. Its implications are pretty interesting, and it's a direction I have been hoping cosmology and astronomy takes at some point - that is, not to tie everything to one assumption (redshift=distance) and do incredible contortions to explain away the empirical observations. It's just one paper of a few, though, and it's a pre-print. We will see what the peer review process brings.

There are some potential signs of warming up to instrinic redshift ideas, however. It was in the program at the 2003 Americal Physical Society meeting, and I've even seen some signs of a few folks warming to intrinsic redshift over at the Bad Astronomy Forum. (My personal thanks to Phil Plait for his Against the Mainstream sections, though you know there are plenty of cranks as well :) )

Intrinsic redshifts, if proven out, will be a great tool to cosmologists.

Here's to hoping cosmology gets out of its current rut :)

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