Doubt cast over dark energy?

Boud Roukema boud w
Wto, 16 Gru 2003, 15:20:53 CET


So Burbidge/Hoyle/Narlikar "Reloaded" have got some media
coverage. Fine.

"Omega_matter = 1 (was Re: gas question)"

The article by Blanchard et al:

Look carefully at the figures. The triple-dotted-dashed line is the
model for an (Om_m=0.3, Om_Lambda=0.7). It's hard to find, but once you
find it, you'll see it matches the observations very, very nicely.

According to the authors, this triple-dotted-dashed line is for eq.~(6),
which replaces eq.~(2).  The difference between the dtwo eqns is a factor
of (1+z).

The authors' derivation of eq.~(2), in other papers, obtains this (1+z)
factor from the density of the Universe at the time that the cluster
virialises. So unless you throw out  rho = rho_0 (1+z)^3 , it's hard
to change the derivation.

However, if you just look at another derivation of the equivalent of
eq.~(2), i.e. a T-M relation, and look at the z evolution of,
e.g. equation (73) of

Niayesh Afshordi, Renyue Cen

then the (1+z) factor becomes essentially (1+ not much) over the
relevant redshift range.

In other words, Blanchard et al's figures, with Afshordi & Cen's
version of the T-M relation, give the concordance model.

Again in simpler words, Blanchard et al think that clusters form
in one way, Afshordi & Cen think they form in a somewhat different way,
leading to moderately different T-M relations and hence totally different
local curvature parameter inferences.

It's good to have dissidents around :). Sometimes they're right, sometimes
they're wrong.


On Tue, 16 Dec 2003, Andrzej Marecki wrote:

>              NEWSALERT: Saturday, December 13, 2003 @ 2327 GMT
>   ---------------------------------------------------------------------
>           The latest news from Astronomy Now and Spaceflight Now
> -------------------------------------------
> In a survey of distant clusters of galaxies, European Space Agency's
> XMM-Newton observatory has found puzzling differences between today's
> clusters of galaxies and those present in the Universe around seven
> thousand million years ago.
> Alain Blanchard of the Laboratoire d'Astrophysique de l'Observatoire
> Midi-Pyrenees and his team use the results to calculate how the abundance
> of galaxy clusters changes with time. Blanchard, knowing that this
> conclusion will be highly controversial, said: "To account for these
> results you have to have a lot of matter in the Universe and that leaves
> little room for dark energy."
> [...]
> ----- End of forwarded message from NewsAlert -----
> --
> Andrzej

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