neutrinos

[ihwip]

OK. I find myself perplexed by neutrinos and have some questions.

1) If quantum partle/anti-particles are constantly forming and annihilating each other in space, do they still produce neutrinos? That doesn't seem to make sense to me.

2) Since we cannot reliably detect neutrinos and they don't emit photons (that I know of) is it possible that the collective mass of neutrinos are responsible for what we call Dark Matter?

3) Are neutrinos generated when matter falls into a black hole?

I'll start with these ones

 

[origin]

OK. I find myself perplexed by neutrinos and have some questions.

Since no one has answered your questions I will attempt to and then someone can correct my errors.

1) If quantum partle/anti-particles are constantly forming and annihilating each other in space, do they still produce neutrinos? That doesn't seem to make sense to me.

Virtual particles are kinda weird (already with the technical jargon). They 'pop' into exsistence because of the uncertainty principle - that is, there is uncertainty as to the energy level in a region in space. The virtual pair 'borrow' energy from space and pop into existence and then immediately annihilte each other with no resultant photons produced. At first glance this seems to violate the conservation of energy but remember they essentially came from nothing and return to nothing (on a plank time scale), therefore there is no net loss or gain of energy. So no real particles are produced from a virtual particle pair annihilation (no neutrinos).

2) Since we cannot reliably detect neutrinos and they don't emit photons (that I know of) is it possible that the collective mass of neutrinos are responsible for what we call Dark Matter?

We can detect neutrinos, it is just very difficult to directly detect them because they only very weakly interact with matter. Neutrinos are not a candidate for the 'missing mass' in the universe. Energy/mass balances of atomic reactions indicate that if neutrinos have mass it is very very small. Besides the dark matter appears to be concentrated around galaxies and neutrions are zipping around at very close to the speed of light so would not concentrate around galaxies.

3) Are neutrinos generated when matter falls into a black hole?

Kind of. Neutrinos are produced by radiactive decay, fission, fusion and collisions. In the accrection disc around a black hole there are all sorts of collisions and fusion reactions going on so that there certainly could be a sizable production of neutrinos going on. I do not believe an atom falling into a black hole in and of itself would result in the formation of a neutrino. Of course even though neutrinos do not typically interact with matter they are still affected by gravity and so can end up be absorbed into a black hole.

 

[ihwip]

Thanks, very helpful. I just read an article on ScienceDaily about electrostatic stars that theoretically convert quarks into leptons (and neutrinos) so perhaps black holes are rarer than initially thought and most supernovas spew out massive amounts of neutrinos instead. Perhaps that would explain dark matter neutrinos being localized in galaxies? Probably not

 

[weeman]

I shall do my best...

1) This is a bit out of my league. Neutrinos are more commonly formed in nuclear fusion, and other high-energy events in the universe.

2) I would say, no. They are extremely elusive particles - they do not interact much with other matter. It may even take a slab of lead that's one lightyear thick to stop a single neutrino! Hence, as humans/scientists, we are very lucky when we can even catch one.

3) Like question one, the most common place we would find neutrinos nearby is the sun. When the sun's intense heat fuses lighter hydrogen into heavier helium, the fusion creates "excess" particles. Quite often, these excess particles are neutrinos. Therefore, with each fusion reaction, neutrinos are hurtled away at near-lightspeed velocities. In fact, as you read this, it's likely that billions if not trillions of neutrinos are passing through the floor, through your body, into the atmosphere, and back into deep space!

 

[Jerromy]

Some things puzzle me as to the nature of neutrinos as well... it seems quite an energy drain of the solar energy system involved in a star which expels these particles at such high velocities. In a supernova event I could understand particles being ejected at such a high frequency as well as velocity but in a normal solar environment I would think the amount of energy expelled as neutrinos would be excessive compared to the amount of matter they constitute. The only other reference of neutrinos I know of involve annihilation reactions between matter and antimatter where supposedly all of the mass of the reacting opposites is converted to energy and the inefficient part of the reaction seems to be the production of neutrinos, which are NOT completely energy and are beyond our techniques of harnessing let alone understanding.

They seem to be very elusive particles in a manner of speaking and I am also curious to see if anyone here can shed some light on the state of scientific understanding.