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Scientists May Have Detected Neutrinos From Another Galaxy
The Bad Astronomer writes "A experiment called IceCube — consisting of sensitive light detectors buried deep in the Antarctic ice — has detected two ultra-high-energy neutrinos, each with over a peta-electronVolt of energy (a quadrillion times the energy of a visible light photon), the highest energy neutrinos ever seen. The two events, nicknamed Bert and Ernie, have a 99% chance of originating outside our galaxy, likely created either by a supermassive black hole or an exploding gamma-ray burst."
FTA:
Out of the countless detections it’s seen, two of them—nicknamed, seriously, Bert and Ernie—were phenomenally, unbelievably energetic: Each had an energy over one thousand trillion times the energy of a visible light photon. That’s huge, far larger energies than even the Large Hadron Collider can create. It’s very roughly equivalent to the energy of a raindrop hitting you on the head which may not sound like much, but remember we’re taking about a single subatomic particle with that much energy
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are you not familiar with the upside the head measurement of force? measured in FredSanfords
Neutrinos, as matter, have plenty of characteristics that could be used to identify them. And saying that it comes from a specific place is not really that difficult since things coming in from space don't take U-turns or pit stops. They come at us in a straight line only perturbed by gravity or other objects that we can observe and compensate for. So if a particle has a certain energy level and direction that does not match anything inside the galaxy, you can do a pretty reasonable job of figuring out where it came from.
As for black holes, yes, nothing is coming out of a black hole's singularity, but the black hole does affect matter outside its event horizon and it is expected that certain black holes will cause matter to be accelerated in such a way that it attains highly energetic characteristics. This is what they mean, or they mean that the neutrino was created in the initial supernova/hypernova that generated the black hole to begin with. Probably the former, as most large black holes are probably generated by accretion over time, and not sudden stellar compression.
Troyusrex: I'm familiar with this use of probability, so allow me to clarify:
There's no need for quantum anything. Probability is simply how one quantifies uncertainty. Here's an example: suppose I flip a coin and you do not see it. I might see it come up heads, and so I would assign a 100% probability that it came up heads. You would assign a probability of 50% to each possible outcome. Who's right? We both are: we're both describing our personal states of awareness about what happened, and they are different.
In this case, the scientists who conducted the experiment are 99% sure that they originated outside our galaxy, presumably because they were able to reject most in-galaxy source explanations. But they cannot be 100% sure.
If you want to learn more, read about Bayesian probability theory.
While the angular resolution of IceCube is not GREAT it DOES detect the direction from which the particles it detects came. This happens because, as others pointed out, the neutrino has a momentum. When it slams into a nucleus in the dectector the resulting collision debris carries away that momentum, thus the velocities of those particles, which are easily determined allows an estimate of the velocity of the original neutrino and thus its point of origin in the sky.
Of course the distance it came from is not readily determined, but if there's nothing terribly energetic nearby, then presumably you're looking at something from further away, and when we're talking about PeV neutrinos it has to be VERY energetic, not something we'd likely miss if it was nearby. Remember, we detected 2 neutrinos, that means there were literally trillions more (well, far more than that probably) that simply passed on through the detector with the same energies.
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The comment modding system exists precisely so you can register your admiration without the rest of us having to hear about your nostriladamus incident.
Back when it was thought that neutrinos were massless, it was impossible to believe that there were huge masses of neutrinos surrounding galaxies, as they would have to travel at the speed of light. But now that we know that neutrinos have mass, maybe they could travel a lot more slowly, slow enough to be captured by a galaxy.
Think about it; there are a huge amount of neutrinos created every microsecond in every star in every galaxy, and they hardly interact with anything. They've been accumulating since the big bang.
What happened to the early photons? Those created as the universe first became transparent initially were very high energy indeed, but as the universe has expanded they've lost energy, to the point that they correspond to a temperature of just 3 degrees kelvin. What happens to neutrinos of a similar vintage?
I love Mondays. On a Monday, anything is possible.
Yeah, Fuck the Pole-Ice!
The neutrino is going to go straight through you with a 99.99999% probability.
Actually that is probably not quite true. For the vast majority of neutrinos you encounter on a daily basis (from radioactive decay, relic Big Bang neutrinos, solar etc.) you are completely correct. Indeed for these, as the article states, they will pass through the earth without blinking.
However PeV neutrinos are NOT your everyday neutrino. These guys have such an incredible energy (over 100 times the proton energy in the LHC) that the earth is actually opaque to them. In fact if you look at the IceCube analysis they look for down going neutrino i.e. ones coming in from above despite the problems with the back grounds from cosmic rays. This is because they cannot look for neutrinos which have passed through the earth because, at these energies, there will be none!
The reason for this is that neutrinos interact with matter through W and Z bosons. These have a mass ~80 to 90 times the mass of a proton. The reason that normally neutrinos do not interact is that there is insufficient energy to make a "real" W or Z in the interaction and this heavily suppresses the chance of it happening (due to quantum mechanics it can till occur though). Above a PeV the energy becomes high enough that this energy suppression effect gets a lot smaller and so the chance of interacting becomes a lot higher - eventually becoming slightly stronger than electromagnetism at really high energy when real W's and Z's can be created.
So the upshot of this is that a really high energy neutrino might actually have a reasonable chance of interacting in your body and the article is completely wrong when it describes the earth as basically transparent to these neutrinos...although it is an understandable mistake given that it is transparent to most neutrinos.
Actually, neutrinos do arrive slightly faster than light from supernovae. Space isn't completely empty --- tiny amounts of interstellar gas give it a refractive index slightly higher than "perfect" vacuum, which ever-so-slightly slows down light. Neutrinos interact far less than light with matter; so, a supernova neutrino going at very nearly the speed of light can outrun a photon through space. In Supernova 1987A, neutrino detectors saw neutrinos about three hours before light reached earth's telescopes.