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

The falloff of light is 1/r^2

[BadAnalogyGuy]

As light fans out, it does so at the rate of 1/r^2. Double the distance, and you've quadrupled the surface area of the light beam. You've also reduced the luminosity at any point in the beam's surface by a quarter.

But why do we just assume that gravity needs to fall off at the same rate as light?

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

[Jarjarthejedi]

Precisely. I know you've gotten a lot of poor responses but I've always thought this was a good theory (from when I first heard of the idea in MOND Modified Newtonian Gravity). Science has made a lot of assumptions about the universe, and this is one of them. Whether gravity falls off at a slightly slower rate or there is a large volume of unknown matter in the universe the end result will be the same, so why do people so quickly call others idiots when they suggest an alternate explanation?

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

[jay-be-em]

It's remarkable to me that you knew that and didn't know Newton's Law of Universal Gravitation,
and the amount of evidence that it's a very close approximation in most situations.

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

[Ambitwistor]

All MOND states (last time I checked) is that gravities falloff rate is slower at long distances. MOND is weirder than that. Instead of modifying gravity at some length scale as you suggest, MOND makes the gravitational force dependent on a body's acceleration instead of just its position.

MOND's main problems are that (1) it can't account for as many phenomena as can dark matter (it does great on galactic rotation curves but not so great at, say, cosmology), (2) it's hard to make consistent with relativity (Bekenstein has a proposal but it has a number of free parameters that appear to require fine tuning to match observations), (3) there is fairly direct evidence for dark matter (e.g., the Bullet Cluster) so even if MOND is true, it doesn't really achieve its original goal of replacing dark matter.

Do the math.

[644bd346996]

Please. It really isn't hard to show that the dependency on r can only take on a few values and still yield a universe that comes at all close to what we observe. For example, the only halfway-plausible power of r that allows closed orbits (such as planets around stars) in classical mechanics is exactly 2. All other values either don't allow closed orbits in general, or are trivially shown by experiment to be absurdly wrong. Now, we have observed that orbits aren't exactly closed (the most famous example being the precession of the perihelion of Mercury), but these were explained astoundingly well by relativity.

Astrophysics is way beyond getting the growth rate of a fundamental force wrong.

Re:Bias in Physics?

[tjstork]

The Einstein fanatics and the Big Bang proponents refuse to consider it as a possibility (a lot of careers depend on Big Bang and Esintein being right). Einstein is a demigod in some circles and his wisdom must not be questioned. As a result little funding is allocated for research in this area. That's too bad. We are probably missing some very exciting physics in the process.


Boy, this is spoken like someone who is completely disconnected from the academic process. There is no bigger fantasy a 20-something working on a phd physicist than to write THE paper that shows Einstein failed to account for some cosmological phenomon, that gravity is clearly explained by some new thing, the universe is really some other age, and by the way, faster than light travel is easily arranged, as demonstrated by this new machine that he or she invented.

Scientists don't work to prop-up theories, they are a bunch of jackasses that learn to understand the old because they have to, but, they would love to put their own stuff in its place. These people aren't stodgy old guardians of the scrolls of doom nearly as much as they are a bunch of sharks circling information, just waiting for that first bit of blood that suggests a hole in some established theory.