Scientists May Have Detected Neutrinos From Another Galaxy 151
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."
Re:in joules. please (Score:5, Informative)
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
Re:Stargate (Score:4, Informative)
It was obviously the explosion created from the enormous energy from a supergate in the galaxy Atlantis lives in.
That would be our galaxy. It moved here in the final episode (San Francisco I think).
Re:in joules. please (Score:4, Informative)
160 uJ, give or take.
Re:Finally, (Score:4, Informative)
Re:not so good with numbers... (Score:5, Informative)
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.
Re:in joules. please (Score:5, Informative)
The comment modding system exists precisely so you can register your admiration without the rest of us having to hear about your nostriladamus incident.
Re:Please explain : aren't neutrinos, ah...'neutra (Score:3, Informative)
One of the properties that IceCube takes advantage of is that at higher energies, neutrinos are much more likely to interact with matter and produce particles that it can detect. There's actually a specific energy close to the observed energy of these particles for an electron anti-neutrino where there is a spike in the probability to interact with electrons (6.3 PeV, the Glashow resonance).
Re:in joules. please (Score:2, Informative)
I'm 40 and live in the UK so I watched Sanford and Son when it was called Steptoe and Son.
Re:Could dark matter be super low-energy neutrinos (Score:5, Informative)
Same thing happened to the neutrinos as happened to the photons. They cooled down. Currently, the neutrino background is ~1.7K, I believe (they're a bit cooler than photons as photons decoupled from matter much later in the early universe than neutrinos did). Neutrinos are, on cosmological scales, treated mostly the same way photons are (they behave in a similar fashion). In any case, the current energy in neutrinos is about ~60% of that in photons, and photons are about 4 orders of magnitude below the energy in dark matter.
We can also predict how the universe would evolve if neutrinos made up the bulk of dark matter. Since it didn't evolve that way, dark matter has to be something else.
Re:in joules. please (Score:4, Informative)
Yup. If you want a number, 3 x 10^8 m/s (i.e. the speed of light in a vacuum) works pretty well. A neutrino with that much energy must be going at 99.many-nines % of the speed of light. The actual number of nines depends on the mass.
Even regular solar neutrinos go at essentially the speed of light, as far as the m/s scale goes, and they have energies that are far lower.
Re:in joules. please (Score:4, Informative)
We've got poor direct limits on muon neutrino mass from muon neutrino experiments; however, there are other sources of much stronger constraints on neutrino masses. See the "summed mass" limits a few pages down in your reference.
From a Borexino neutrino experiment page at Princeton [princeton.edu]:
The current limits from cosmological considerations are less than about 0.5 eV (one millionth of the electron mass!) for the sum of the masses of all three neutrino types. The known values of the mass-squared differences imply that the heaviest neutrino type cannot be less massive than about 0.05 eV.
Not your "everyday" Neutrino (Score:5, Informative)
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.
Re:Could dark matter be super low-energy neutrinos (Score:4, Informative)
Nope.
Or at least, they could still only account for a small fraction of observed dark-matter.
http://www.astro.princeton.edu/~dns/MAP/Bahcall/node6.html [princeton.edu]
Re:Finally, (Score:5, Informative)
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 [wikipedia.org], neutrino detectors saw neutrinos about three hours before light reached earth's telescopes.
Re:Direction (Score:4, Informative)
When a neutrino impacts a particle in the detector, it creates a cascade of new particles. Since the momentum of the neutrino is conserved in the cascade of particles that can be more easily detected, the direction that the neutrino came from can be determined.