cosmic background radiation - alternative proposal

**zforgetaboutit** · Mar14-04, 01:39 AM

I've had this idea for years but never had a forum.

How do we know we aren't merely measuring the energy emitted by our sun's Heliosphere ?

**russ_watters** · Mar14-04, 02:31 AM

We see the background radiation in every direction - not just in the direction of the sun.

**zforgetaboutit** · Mar14-04, 08:49 AM

The solar wind contents (heliosphere diagram) are also in every direction, relative to where we've been making CBR measurements.

The solar wind consists of particles, ionized atoms from the solar corona, and fields, in particular magnetic fields. (see web link for details - zforgetaboutit)

**russ_watters** · Mar14-04, 10:54 AM

Solar wind and cosmological background radiation are completely unrelated concepts.

**Janus** · Mar14-04, 11:48 AM

Originally posted by zforgetaboutit
The solar wind contents (heliosphere diagram) are also in every direction, relative to where we've been making CBR measurements.

But, the Solar wind becomes more concentrated as you near the Sun, so if it were the source of the CBR, then the radiation we measure would become stronger as we started pointing our detectors near the Sun. This doesn't happen.

**zforgetaboutit** · Mar14-04, 11:52 AM

Originally posted by russ_watters
Solar wind and cosmological background radiation are completely unrelated concepts.

They are related inasmuch as they may both contribute to the perceived temperature of the night time sky.

If the dust of nebulas is illuminated by solar radiation, then the particles of the solar wind could also be lit up by radiation from our Sun. If the nebulas emit IR radiation then so could the solar wind, also consisting of particles, for the same reason.

**zforgetaboutit** · Mar14-04, 12:11 PM

Originally posted by Janus
But, the Solar wind becomes more concentrated as you near the Sun, so if it were the source of the CBR, then the radiation we measure would become stronger as we started pointing our detectors near the Sun. This doesn't happen.

Fair enough. Do you happen to have a web link which mentions this lack of change when the detector is pointed closer to the Sun in a non-trivial way?

**Hurkyl** · Mar14-04, 12:18 PM

Solar wind would also, I imagine, be much warmer than the CBR.

**UltraPi1** · Mar14-04, 12:27 PM

The CBR could be the result of an ongoing process. I.E The universe is incomplete and new material is still being created.

**Nereid** · Mar14-04, 07:53 PM

Originally posted by zforgetaboutit
*SNIP
If the dust of nebulas is illuminated by solar radiation, then the particles of the solar wind could also be lit up by radiation from our Sun. If the nebulas emit IR radiation then so could the solar wind, also consisting of particles, for the same reason.

Before the COBE, WMAP, ACBAR, BOOMERANG, etc teams present results of their observations of the CMB, they must remove 'foreground' contributions to the microwave signal. For satellite observatories, there are two primary sources of such contributions (after purely instrumental effects are accounted for), the IR from solar system dust (which is also responsible for the 'zodiacal light'), and dust in the Milky Way.

Here's how the WMAP team dealt with the Milky Way sources.

Among the difficulties that zforgetaboutit's idea would have to deal with are:
- the CMB has a near-perfect black-body spectrum; as Hurkyl said, it's very difficult to see why 'solar wind particles' should be so cold (~2.73K)
- whatever solar wind particles are, they would have an emission spectrum that differed from a black-body; for example, silicate, carbon-compound, etc bands
- AFAIK, the 'solar wind particles' are ions, mostly atomic ions; how could they give rise to microwave radiation?
- quite a few other stars have 'solar winds' much stronger than the Sun's, yet AFAIK none have a spectrum resembling the CMB
- ditto zodiacal dust

**zforgetaboutit** · Mar14-04, 10:04 PM

Originally posted by Nereid
- AFAIK, the 'solar wind particles' are ions, mostly atomic ions; how could they give rise to microwave radiation?

I didn't read about solar wind ions as a microwave source but I haven't finished the paper yet (~40 pages).

Reasonable replies, so far. The link is a good read (from what little I can grasp). I quote from it:

In addition to the thermal emission from dust, above, there are various other ways in which dust can radiate at microwave wavelengths. These include electric dipole emission from spinning dust grains and magnetic dipole emission from thermally fluctuating dust grains (Erickson 1957; Draine & Lazarian 1999, 1998a,b). Emission from spinning dust can produce -2 from 20-40 GHz. The high-frequency cut-off of spinning dust emission is due to the limited speed at which a dust grain can spin.

So thermal emission from dust can emit microwaves. We already agree on a possible heat source (the Sun). As a source of dust, how about whatever ablates from comets as they are heated by the Sun? Comet dust may be spread about quite a bit from their orbital plane, due to eons of buffeting by the solar wind and may inhabit a spherical shell by now. We may be looking through this shell when making our measurements

**russ_watters** · Mar14-04, 11:22 PM

Originally posted by zforgetaboutit
Fair enough. Do you happen to have a web link which mentions this lack of change when the detector is pointed closer to the Sun in a non-trivial way?

[?] [?] Thats basic - its the reason we care about the cmb. Any single paragraph description of the cmb mentions its homogeneity. HERE is a good description which includes a map of the sky.

A map of the sky at microwave frequencies, showing that the CMB is almost completely the same in all directions.

**Nereid** · Mar14-04, 11:28 PM

There's no doubt that comets 'shed' dust! That's what meteor showers are, the dust streams in the orbits of comets, intersecting the Earth. There's also no doubt that this - and other - dust can be detected; IRAS may have given us the first 'all-sky' observation of this dust. As they journeyed out of the solar system, the Voyager (1 and 2) and Pioneer (10 and 11) spacecraft also measured dust.

IIRC, the IRAS etc results are all pretty clear - there's far too little dust in the outer reaches of the solar system to generate an 'undetected' zodiacal signal. Further, if there was enough dust to generate non-thermal microwaves at frequencies where the CMB is strong, a) it wouldn't have such a perfect black-body spectrum, b) the thermal signal from the dust - at considerably higher temperature than ~3K - would be very obvious, and c) there'd be significant anisotropy, near the shock-front of the heliosphere (and no, the CMB dipole is in quite a different direction from where the Sun is going).

**Loren Booda** · Mar15-04, 12:21 AM

The CMB includes small changes in temperature: 2.735 [+/-] .0001 K across the sky. These fluctuations are thus some 20,000,000-fold less than the Sun's blackbody temperature at ~5800 K. The magnitude and variation of the Sun's radiation easily masks the CMB patterns; I believe this is the reason that COBE and similar explorers have been purposely hidden by the Earth from the Sun. The measured CMB has been used to calculate the age of the universe at 13.7 billion years, no solar artifact.

**zforgetaboutit** · Mar15-04, 01:31 AM

As a lay person not trained in thermodynamics nor radio, my overall understanding of the paper's details is poor.

They performed an awful lot of statistical analysis and necessary (they claim) data smoothing to arrive at their results. Unfortunately I'm not qualified enough to referee this but am naturally wary of too much fudging.

However, you know how you can view some "microwave pictures" of this subject, and they purport to show the relative uniformity of the CMB?

Well I'm taken aback at the recent long exposure deep field Hubble pics that show a high number of galaxies having a non-trivial angular size inhabiting the picture. It's like increase the sensor exposure time enough and the entire frame would be occupied by pictorially visible galaxies.

What "background" would there then be ... the emissions from all these galaxies in our line of sight, barely leaving room for "empty black" space? By the time you removed all the pixels containing radiation from galaxies (the foreground anomalies) there might not be any pixels left!

I'm suggesting, without being educated in the subject, the temperature would not reasonably be ~3K. This is what I expect if COBE was to zoom in on, say, the Andromeda Galaxy as opposed to an empty piece of sky. I don't expect them to roughly be the same.

I'm thinking if COBE et al also had a much longer exposure time available, there might be no uniformity to its measurements.

Can anybody yet say COBE's uniformity results would not drastically change because its exposure times are already long enough to make final conclusions?

**Nereid** · Mar15-04, 09:54 AM

Indeed, the WMAP team found ~200 point sources in their results, and they corresponded very closely with the ~200 that they expected to find, based on the known spectrum of (radio) galaxies, observed in different wavelength regions. Do other galaxies also emit microwaves? Certainly. Can at least some of these other galaxies also be detected in the wavelength bands at which WMAP (and later Planck) observes? Almost certainly. Is the combined contribution of all galaxies' microwave emission going to be detected any time soon? No; it's far, far too faint.

Interestingly there are other signatures which can be investigated, e.g. Sunyaev-Zel'dovich effect, Sachs-Wolfe effect.

Bottom line: COBE, WMAP, ACBAR, BOOMERANG, DASI, ... have observed the CMB. While there will always be fine tuning to be done, there's no evidence of 'local' contributions to the observed microwave sky, other than those already detected and analysed.