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Previous Next Up Topic Cosmology / Alternative Cosmology / Dark Gulping - I Kid You Not (3128 hits)
By Mike Petersen Date 2009-04-23 03:29
Here we go again, fellas.

Dark Gulping

Sigh...when will it ever end?
By David Russell Date 2009-04-23 14:18
And some of you thought I was crazy when I suggested that we propose "dark redshift" to explain the discordant redshifts!  

Regarding all this dark stuff that isn't actual stuff, I once suggested to Halton Arp that "An epicycle can never be disproven, it can only be proven."  :)
By Jade Annand Date 2009-04-23 18:32
*laugh* Mike, you hurt my head, albeit in a good way, finding these gloriously exhausting mainstream forays into minor madness. Sorry, I think I meant "Dark Madness" :)

David said:

And some of you thought I was crazy when I suggested that we propose "dark redshift" to explain the discordant redshifts!


If I ever did suggest such a thing, then I deserve a bop on the noggin. So many things can be smuggled in under the auspices of a popular prefix - witness the "e-" prefix to everything for quite a while, the "i" prefix currently, and slapping "Green" into a product or service. "Dark Redshift" might very well work by the same premise; you're right.

The preprint for the paper that the article is based on is here. Penetrate the abstract, if you dare:

arXiv Abstract said:

We analyse the radial structure of self-gravitating spheres consisting of multiple interpenetrating fluids, such as the X-ray emitting gas and the dark halo of a galaxy cluster. In these dipolytropic models, adiabatic dark matter sits in equilibrium, while the gas develops a gradual, smooth, quasi-stationary cooling flow. Both affect and respond to the collective gravitational field. We find that all subsonic, radially continuous, steady solutions require a non-zero minimum central point mass. For Mpc-sized halos with 7 to 10 effective degrees of freedom (F2), the minimum central mass is compatible with observations of supermassive black holes. Smaller gas mass influxes enable smaller central masses for wider ranges of F2. The halo comprises a sharp spike around the central mass, embedded within a core of nearly constant density (at 10-10^2.5kpc scales), with outskirts that attenuate and naturally truncate at finite radius (several Mpc). The gas density resembles a broken power law in radius, but the temperature dips and peaks within the dark core. A finite minimum temperature occurs due to gravitational self-warming, without cold mass dropout nor needing regulatory heating. X-ray emission from the intracluster medium mimics a beta-model plus bright compact nucleus. Near-sonic points in the gas flow are bottlenecks to allowed steady solutions; the outermost are at kpc scales. These sites may preferentially develop cold mass dropout during strong perturbations off equilibrium. Within the sonic point, the profile of gas specific entropy is flatter than s r^{1/2}, but this is a shallow ramp and not an isentropic core. When F2 is large, the inner halo spike is only marginally Jeans stable in the central pc, suggesting that a large non-linear disturbance could trigger local dark collapse onto the central object.


Inside the paper, you can learn about dark cusps, too!

(Though I think they can be forgiven somewhat, given what it looks like they're taking on)

I think that is referring to the "cusp/core crisis" in this page talking about the HI Nearby Galaxy Survey:

THINGS page said:

Considerable debates about the description of universe on the galaxy scales predicted by Λ Cold Dark Matter (ΛCDM) have been continued and the central density problem (so-called "cusp/core") lies at the very centre of them with other two crisis such as the missing satellite galaxies and the angular momentum catastrophe. The dark matter N-body simulations based on the CDM paradigm consistently predict the divergent density profiles towards the galaxy centre, which gives a "cusp" feature near the centre. According to the ΛCDM predition, this high concentration of dark matter in the galaxy centre is universal and should be found in every galaxy (from tiny to big galaxies). In contrast to the simulations, the followed observations have mostly shown that the dark matter particles in the galaxy centres are not such highly concentrated as predicted by ΛCDM but even cored.


I liked one of the quotes that popped up in the comment sections. I hadn't heard this one of Nikola Tesla's before:

Nikola Tesla said:

Today's scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality.


Certainly applicable to string theorists, a little less so to Big Bang Theorists - at least they see some of the oddities in the data and change accordingly... it just happens to be in an ever-widening spiral away from a clean explanation.

DGR said:

Regarding all this dark stuff that isn't actual stuff, I once suggested to Halton Arp that "An epicycle can never be disproven, it can only be proven."  :)


I would perhaps perform a minor substitution here and say "An epicycle can never be disproven, only embellished" :)
By Ari Jokimäki Date 2009-04-24 08:44
So it's back to dark ages then?

I tried to find the thread where we discussed these dark x's last time but I didn't find it. I know there was an e-mail discussion involving Dave where we discussed them, but I think there was a thread in here as well but I can't remember the title.
Previous Next Up Topic Cosmology / Alternative Cosmology / Dark Gulping - I Kid You Not (3128 hits)

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