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2002-Feb-20, 07:22 AM
Particles similar to neutrinos emitted from the center of galaxies may be gravatationaly/rotationaly trapped in the outer reaches of a spiralling galaxy.

As they exhibit energitic properties similar to neutrinos, they may be impossible to be directly detected witout being there.

Flaming comentary mandatory?!

Chip
2002-Feb-20, 09:01 AM
RPN wrote:
"Particles similar to neutrinos emitted from the center of galaxies may be gravatationaly/rotationaly trapped in the outer reaches of a spiraling galaxy.

As they exhibit energetic properties similar to neutrinos, they may be impossible to be directly detected without being there."

Flaming commentary mandatory?!
=============================================
Chip:
No "flaming commentary" from me, but I have some questions.

1. What are "particles similar to neutrinos"? Same zero mass characteristics but not neutrinos? Dark matter?

2. If such particles are coming from the centers of spiral galaxies (like ours) and are "gravitationally rotationally trapped in the outer reaches" would they not pass through our neighborhood? How would we tell them from regular neutrinos whose paths are also detected in tanks of Clorox deep within mineshafts?

3. What force is trapping them "in the outer reaches of a spiraling galaxy"? Since they have no mass, how would gravity affect them?

Interesting stuff, but not sure what the main idea is. /phpBB/images/smiles/icon_wink.gif

lpetrich
2002-Feb-20, 05:25 PM
Neutrinos almost certainly have rest masses, but these masses are very small compared to the kinetic energies that they usually have. Thus, they are effectively massless.

Also, they interact only very weakly with ordinary matter, with the exception of their gravitational interactions. This makes them difficult to trap.

However, neutrinos left over from the Big Bang are a possible "dark matter" particle; such neutrinos would now be relatively slow-moving if their rest mass is greater than the total mass-energy of cosmic-microwave-background photons. They would have similar momentum values, which allows us to estimate their velocities.

A CMB photon has an average energy of 3*10^-4 eV, and therefore a momentum of 3*10^-4 eV/c. A neutrino with 1 eV of rest mass will have an average CMB-relative velocity of about 100 km/s. However, the Sun's orbital velocity around the center of the Milky Way is about 200 km/s, meaning that such neutrinos could be trapped if they got deflected by some massive object. However, they would not get trapped very efficiently, and for that reason, it's thought that most "dark matter" originally had much less velocity dispersion ("cold dark matter" vs. "hot dark matter"), implying a much greater mass of particle.

There are several candidates for such a particle that arise from various particle-physics theories; however, none of them has ever been convincingly found, though they may simply be out of reach of our particle accelerators.

ljbrs
2002-Feb-21, 12:00 AM
lpetrich:

You beat me to it (and did it better than I possibly could have done). It is good to have some members here who understand particle physics.

Sorry, I am like a troll. I tend to flit in and out, paying most of my attention to interesting posts for which I have absolutely no scientific complaints.

ljbrs /phpBB/images/smiles/icon_biggrin.gif /phpBB/images/smiles/icon_smile.gif

_________________
*Nothing is more damaging to a new truth than an old error.* Goethe

<font size=-1>[ This Message was edited by: ljbrs on 2002-02-20 19:02 ]</font>

Koilon
2009-Mar-25, 03:47 AM
Also, they interact only very weakly with ordinary matter, with the exception of their gravitational interactions. This makes them difficult to trap.

I think they can also interact via their magnetic dipole moment with the magnetic field of a galaxy. However, I have been unable to find any theoretical discussion of this possibility. Do you know of any or have any thoughts on it?