WMAP cold spot and void in the universe

[cmantzioros]

I'm doing a research paper on the supervoid found in the constellation Eridanus and it was discovered by WMAP which recorded a cold spot where the hole is ... I just don't know why a drop in temperature of the CMB radiation indicates a hole... can anyone explain please?

 

[Garth]

I'm doing a research paper on the supervoid found in the constellation Eridanus and it was discovered by WMAP which recorded a cold spot where the hole is ... I just don't know why a drop in temperature of the CMB radiation indicates a hole... can anyone explain please?

The drop in temperature itself does not indicate a hole.

There are two separate observations: firstly a cold spot in the WMAP data, and secondly a drop in the number of radio sources.

These two observations are aligned in the same part of the sky in Eridanus, the drop in radio sources indicates a 'hole' or void in the 'foreground' while the WMAP cold spot is in the 'background'.

The void could itself cause the cold spot through the "Integrated Sachs-Wolfe Effect" or "Rees-Sciama effect which are enhanced by the effect of dark energy stretching the void as photons pass through it.

It seems reasonable to assume that the cold spot and void are connected so that a large under-dense of the sky at the Surface of Last Scattering, at a red-shift of z ~1100, subsequently gave rise to an under-dense region or void later on, which we now observe at a smaller red-shift of z ~ 1.

The observations are described in this paper: Extragalactic Radio Sources and the WMAP Cold Spot. If the void is as large as it appears then this would cause a problem for the standard model:

This is far outside the current expectations of the concordance cosmology, and adds to the anomalies seen in the CMB.

Garth