Duplicatting the Sun

... and they are! That's one of my doubts about the value of projects like WMAP and the like: To get the background, they suppress the contributions of stars and galaxies, for as far as they can be resolved. But given the gradual fading of detail with increasing distance, how does one decide what is object and what is background? It seems rather arbitrary.

I should work out one day if a receding black body radiator can be distinguished from a stationary cooler one under circumstances where we can't appreciate the increase in distance of the former.

Jeroen Belleman

there

That would imply that the background radiation were "white". AFAIK, it's a "blackbody" of 3K, which should be distinguishable from a BBR of 10K. No?

there

The "red shift" is primarily determined by the shift in spectral lines, this cannot be explained by objects simply being cooler.

there

Yes, for resolved objects. But for the background, there are no resolved spectral lines. My question is: Can an infinitely deep background of randomly distributed red-shifted stars at sufficient distances to remain utterly unresolved result in a 3K black body radiation spectrum? I guess the answer is "yes". Would an improvement of the spatial resolution of measurements lower the background temperature? I'd guess that it would, but I don't trust my intuition there and I think I'm not enough of a physicist to work it out.

I imagine that for the most distant objects for which red-shift has been measured, the results aren't as clear-cut as suggested. I suppose the red-shift is measured by correlating the measured spectrum of an object with a red-shifted version of the hydrogen spectrum, with the amount of red-shift as the independent variable. The spectrum of the most distant measured objects is by necessity very noisy, and therefore, so will be the correlation.

Jeroen Belleman

It would come unstuck principally because stars evolve and have significantly different temperatures and luminosities as they age (ranging from 2700K to 10000K). To get a 3K *black body* curve you would have to shift the stars away from us at different speeds as they aged. The steady state guys like Hoyle fought a vitriolic rearguard action against the Big Bang cosmologies in the 1960's and lost the battle. Hoyle coined the term Big Bang as a pejorative term - it stuck.

They were completely stuffed by the new science of radio astronomy that showed that the early universe (at greater distances than optical can really see) was very different to our local neighbourhood.

One of the brightest objects in the radio sky Cygnus A which is in a puny looking faint galaxy. Most of the other early catalogued radio objects objects are too faint to see at all optically and exceedingly numerous as you go to ever fainter flux limits.

These days they can do rather better optically with much more sensitive CCD detectors and bigger telescopes. For instance:

Actually they are very clear cut out to some considerable distance. And some of the other predictions of the Big Bang cosmological model also follow from that - the look back time to great distances shows us clearly that the early universe was a much more violent place.

It isn't that noisy except when they are trying to break distance and redshift limits and with big groundbased scopes, modern satellites and incredibly sensitive detectors it is possible to get good spectra on extremely faint and incredibly distant objects. This is also helped by the distant objects in many cases being obligingly bright.

And you can see the so called Lyman forest of neutral hydrogen clouds along the line of sight between us and the very distant objects.

Regards, Martin Brown

there

A cooler object would have a peak radiation with a longer wavelength, as would a red-shifted "hotter" object.

The title is "Duplicating the Sun" Obviously the son was a typo error. You already gave a positive input. Why ruin your reputation?

John Taylor

there

But my point was that in general these can be distinguished by the shift (or not) in their spectral *lines* (not simply the peak of the black body curve).

there

I thought we were talking about the source of the 3K background (red-shifted or cooled, edge of the universe).

All you had to do is cry out "mah ribs are all already cracked..."

It was a joke, ya little wuss. So much for your reputation.