Missing matter found by squinting through gravitational lens Some of the universe's “missing matter” might have been found in an unexpected place: exactly where it ought to be, sitting in galaxies. The missing matter question arose when the ESA's Planck mission team published this paper on Arxiv, in which they pointed out an apparent discrepancy between the “wrinkles” in the cosmic …
I have not read the paper yet, but given that it is about Sunyaev-Zeldovich effect and gravitational lensing in galaxy *clusters* I suppose what is "weighed" here is the clusters - the largest structures in the Universe - and not the constituent galaxies. There is more intergalactic matter (luminous or dark) in clusters than is "sitting in galaxies" as the article says.
I assume that the (surprisingly) inaccurate title in Nature influenced the Reg - the contents of the Nature piece clearly talk about "weighing clusters".
Nope.
Despite El Reg claiming the "lots of uncertainty" is a characteristic of this branch of cosmology, the truth is there's lots more uncertainty about most of astro than scientists will freely admit. In fact one of the things that's the most amazing about astro is how accurately we can describe stuff given the uncertainties.
While the emphasis on this study is on the Sunyaev-Zeldovich discrepancy, the problem is bigger than that. You can also estimate the speed at which galaxies rotate based on difference in the red shift between edges of the galaxy. Based on those results and the masses we estimated galaxies shouldn't hold together even a little. And spiral arms? That's serious black box voodo magic. Add bars to those arms and there's grey matter all over the place following the exploding heads. If we didn't have the observational data we'd swear it was impossible.
i'd heard that the rotation of galaxies more resembled a solid object than a collection of gravitationally bound stars, dust and gas. then they said it is an effect of dark matter.
now you're telling me that there's grey matter all over the place?
[does anything matter anymore?]
Not at all. Only that there may not be a need for some fancy invisible, high mass particle that is hanging about.
The solar system itself is lousy with dark matter, it's called dust, asteroids, kuiper belt objects and all things oort.
The galaxy (actually, all galaxies and intergalactic space) is also lousy with the same stuff.
Add in energy transfer, relativistic mass increase, etc and you get a whole new set of numbers that, while miniscule in each number, adds up when one is looking at galactic clusters.
No, willi0000000 nailed the funamental problem: They move like solid objects.
No matter how much more stuff you add to the gravitational matrix, they shouldn't move like dots drawn on the surface of a balloon. It should look more like the rings around Saturn. Fine detail, but a complete jumble. It doesn't jump out with the globular galaxies, it's the spirals where you first notice the problem. And the bars, at least according to our theoretical basis for gravity, simply shouldn't exist. It's a bit like a helicopter or bee flying.
What I find interesting is that there are now two ways to measure galactic cluster mass. The boosted photon method and the grav lens method, and they disagree with each other, by a substantial amount.
These two tests can't both be accurate at the same time, so at least one must be way off. That means the theory behind one or both has flaws that need to be worked out. Any talk of "finding mass' should wait 'till the descrepancies are resolved.
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