The Milagro detector has seen cosmic-ray hot-spots.Milagro / U. Maryland / LANLPosted on 11/29/2008 1:24:32 PM PST by neverdem
Proton discovery may cast doubt on dark-matter theories.
The Milagro detector has seen cosmic-ray hot-spots.Milagro / U. Maryland / LANLHot on the heels of speculation that cosmic rays may have revealed the signature of elusive dark matter in space, new observations could challenge that idea and reinforce an alternative explanation.
A seven-year-long experiment at the Milagro cosmic-ray detector near Los Alamos, New Mexico, has revealed 'bright patches' of high-energy cosmic rays in the sky1 – something incompatible with a dark-matter source.
Cosmic rays are charged particles, mostly protons and electrons, that are produced in space and generally have a characteristic energy spectrum — the higher their energy, the rarer they are.
But last week, researchers working on the Advanced Thin Ionization Calorimeter (ATIC) experiment, which uses detectors borne by a high-altitude balloon to measure cosmic-ray electrons above the Antarctic, reported an unexpected bump in this energy spectrum, corresponding to a surfeit of electrons with energies between 300 and 800 gigaelectronvolts2.
Hints at such an anomaly have been seen before. A satellite observatory — Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) — detected an excess of cosmic-ray positrons, the anti-particles of electrons, at similar energies3. And a Japanese detector called the Balloon-borne Electron Telescope with Scintillating fibers (BETS) also found a small excess of cosmic-ray electrons at high energy4.
These cosmic rays may be the decay products of hypothetical particles of dark matter, thought to make up about 85% of all matter in the Universe. Astronomers have invoked dark matter's gravitational effects to explain why rotating galaxies don't fall apart as they whirl through space. But as the name implies, dark matter can't be seen directly and its identity remains obscure.
A common assumption is that dark matter consists of a hitherto unknown particle that interacts weakly with other forms of matter. In some theories, two dark-matter particles are predicted to annihilate when they collide, producing a high-energy electron–positron pair. These could account for the ATIC cosmic-ray bump and the hints of it in the PAMELA data. But if that's so, the anomalous cosmic rays should be distributed more or less evenly across the sky.
In contrast, the Milagro team, led by Jordan Goodman at the University of Maryland, College Park, found cosmic-ray protons bunched up in two 'hot spots': one between the Orion and Taurus constellations, the other near Gemini. They think that the excess cosmic rays may be coming from exotic sources such as the rapidly rotating neutron stars known as pulsars, rather than dark-matter annihilations.
Goodman stresses that it's not yet clear if the ATIC and Milagro results are related, because the former measure cosmic-ray electrons whereas the latter detect protons. But he says the sources of the protons they have seen could also plausibly generate the electrons and positrons found in the earlier studies. "If it's the same phenomenon making them all, then it's not dark matter," he says.
But the dark-mater explanation still cannot be ruled out. "I've been totally perplexed by the hot spots but I don't see any reason to connect them with the ATIC findings," says Dan Hooper, a theoretical physicist at Fermi National Accelerator Laboratory in Batavia, Illinois.
The Milagro detector isn't aimed primarily at investigating cosmic rays, but is instead used for gamma-ray astronomy. When high-energy gamma rays hit our atmosphere they trigger a shower of exotic particles. These particles annihilate when they collide with water in Milagro's giant tank, producing a flash of light that can be recorded by sensors.
But 99.9% of the flashes seen by Milagro originate from collisions of cosmic-ray protons, explains Goodman. That creates a background signal that has to be subtracted in order to identify gamma rays from energetic astrophysical sources. Goodman says that finding localized sources of cosmic-ray protons in this background came as a surprise to them.
An earlier cosmic-ray experiment called the Tibet Air Shower Array, run by a team of researchers in Japan and China, saw broad differences in the cosmic-ray intensity between the two hemispheres5, but no one had previously seen such smaller-scale concentrations.
The Milagro team suggests that the protons, with energies of around 10,000 gigaelectronvolts, may be generated in the extreme astrophysical environment of a super-dense neutron star or pulsar. At least some high-energy cosmic rays have previously been shown to come from super-massive black holes in nearby galaxies6.
"We don't know what is causing it," Goodman admits. He suggests that the localization may be partly caused by magnetic fields focusing the protons' trajectories.
But in general, magnetic fields in interstellar space should exert a randomizing influence, destroying any bright spots, says Hooper. "I can't imagine how they're created, and I don't know if anyone has any great ideas," he says.
bump
ET left the porch light on.
NO, ET is nuking a burrito in a poorly shielded Chinese Microwave.
Should not the mathematics and the “cosmological theories” tell why WHAT we see is WHAT we see?
Rather than assume that 90% of what is in the universe can never be seen and must be invisible? (Personally, rather than believe in “dark matter” - I've seen much more evidence for a Designer or a “God” than I've seen of dark matter and dark energy.
Then again.... Speaking of “dark energy” ...
I lived one mile (in a straight line, not by road) from that scientific site. Then I retired, and the wife wanted to move back to Oklahoma.
I miss northern New Mexico.
Take an educated guess and call it science?
Let's wait for the reviews from the Hollywood critics. They make educated guesses too! (s/)
thanks aruanan (got these from his links page).
NASA Researchers Put New Spin On Einstein’s Relativity Theory
Science Daily | NASA’s Jet Propulsion Laboratory | 10 April 2003
Posted on 04/10/2003 11:37:49 AM PDT by sourcery
http://www.freerepublic.com/focus/f-news/890123/posts
Astronomers Deal Blow To Quantum Theories Of Time, Space, Gravity
Space Daily | Huntsville - Mar 28, 2003 | Editorial Staff
Posted on 03/28/2003 5:49:29 PM PST by vannrox
http://www.freerepublic.com/focus/f-news/878827/posts
An Introduction to Zero-Point Energy
CalPhysics.org
Posted on 02/28/2003 2:59:02 PM PST by sourcery
http://www.freerepublic.com/focus/news/854135/posts
Will Spacecraft ever Go Faster than the speed of Light?
Various - See Text | 16 FEB 2003 | Various
Posted on 02/16/2003 2:16:44 PM PST by vannrox
http://www.freerepublic.com/focus/news/844807/posts
Harvard M.D.Challenges Big Bang Theory
[try “reload” if it doesn’t load]
Source: SPACE.com
Author: Erik Baard
Posted on 06/07/2000 08:34:53 PDT by USA2000
http://www.FreeRepublic.com/forum/a393e6b9d1ff6.htm
:’) You’re welcome.
That's what they are trying to do. We "see" that the galaxies appear not to have enough mass to cause the orbits of their stars to be as "tight" as they are, so just as with the aether, it is postulated that there must be some mass there, that we cannot "see" directly. Then the challenge is to explore the implications of that assumption. That is, are there other observations that can be explained via "dark matter". Any way, independent of galactic gravity, to detect if it's there or not. In the case of the "aether", those experiments, by Michelson and Morley in 1887, attempting to detect the relative motion of the earth through the aether, failed to find any such motion, even though they knew that the earth was indeed moving. That failure eventually lead to Einstein postulating that maybe the speed of light in a vacuum is constant, regardless of the motion of the source and the receiver. That in turn lead to E=MC^2.
Astronomers have invoked dark matter's gravitational effects to explain why rotating galaxies don't fall apart as they whirl through space.--- from the article
So if this experiment suggests there is no dark matter, and if it turns out that, indeed, there is no dark matter, then what's preventing the galaxies from falling apart as they whirl through space.
It seems like getting rid of dark matter as a possibility introduces as many problems as it solves.
That's the way it goes. That is that's the way our theories are honed to more closely match reality. Once they no longer fit the observed reality, we need new theories.
For example Newtonian mechanics are just for every day use, (where every day is any events with relative velocities well below the speed of light), but at high speeds/energies, they no longer "work", and are replaced by Einstein's special relativity. (But only for constant motions, add acceleration, and even that no longer fits)
So you’re suggesting there’s some completely as-yet-undiscovered, as-yet-unconceived-of, mechanism holding each galaxy in tight rotation around it’s center, despite the lack of mass to account for that rotation...
Interesting.
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