Intergalactic Missing Mass Missing Again

Ponca City, We Love You writes "Researchers at the University Of Alabama In Huntsville have discovered that some x-rays thought to come from intergalactic clouds of 'warm' gas are instead probably caused by lightweight electrons — leaving the mass of the universe as much as ten to 20 percent lighter (in terms of its ordinary matter) than previously calculated. In 2002 the same team reported finding large amounts of extra 'soft' (relatively low-energy) x-rays coming from the vast spaces in the middle of galaxy clusters. Their cumulative mass was thought to account for as much as ten percent of the mass and gravity needed to hold together galaxies, galaxy clusters, and perhaps the universe itself. When the team looked at data from a galaxy cluster in the southern sky, however, they found that energy from those additional soft x-rays doesn't look like it should. 'The best, most logical explanation seems to be that a large fraction of the energy comes from electrons smashing into photons instead of from warm atoms and ions, which would have recognizable spectral emission lines,' said Dr. Max Bonamente. The work was published Oct. 20 in the Astrophysical Journal."

Comments

Re:The falloff of light is 1/r^2

[Aesir1984]

It's because the surface area of a sphere increases as r^2 so anything that expands into a volume will fall off in intensity at this rate without outside influence. The only reason this would change is if space-time is curved which we have run experiments to test and if there is a curvature it is so slight as to be negligible for experiments like TFA talks about.

As for the person above who mentioned that light might not expand as 1/r^2 outside of a gravity well, the fact is that it doesn't expand at exactly 1/r^2 inside a gravity well. But we 1/r^2 is a good approximation for any gravitational fields near us.

Re:Bias in Physics?

[tm2b]

I never advocated tossing GR out the window, it's way too successful and I have way too much investment in the math to reject it (as they say, nature abhors a second order differential equation, right?).

Don't be silly. MOND doesn't cover the regime of gravitational time dilation- and is in fact not at odds with GR. MOND and GR cover different regimes, MOND concerns itself with gravitational/inertial interactions at very small accelerations (of less than about 10^-10 m/s^2, ignoring the Hubble constant correction term).

The point is that we have a fundamental choice between believing that there's more mass that we can't detect by EM in the Universe than that which we can detect, or that we're missing a big piece of how gravity (or, if you prefer, inertia) works, or (of course) "something else." And the jury is absolutely still out.

While the physics community certainly favors the dark matter model right now, most will say that the door isn't shut on MOND yet. Dismissing anybody who mentions it as a crank is not reasonable and it's dishonest to try to put a Mr. Physics Authority Figure face on doing so - MOND papers are still published in indiscriminate rags like the Journal of Cosmology and Astroparticle Physics and tenure-holding proponents are seen in polite company that would shun cold fusion researchers.

I have no idea how many physics undergrads "really" know GR and QM - I suspect that most probably haven't gotten past the wave equation formulation or even heard of quantum field theory, and might or might not have had to sling a few tensors around in an elective - most probably don't do graduate computational cosmology work, either (even if it was back when having time on a Cray meant something). There's more money in commercial software, though.